We report in this work the synthesis and the photophysical characterization of novel pyridazine derivatives, functionalized in position 3, with different (hetero)aromatic groups (indole, cyanophenyl, nitrophenyl). The diazines were synthesized by Suzuki coupling of 3-bromo-6-(thiophen-2-yl)pyridazine with commercially available (hetero)aryl-boronic acids. Due to their optical properties these push-pull π-conjugated systems can have application as versatile building blocks for the preparation of DSSCs, OLEDs, and nonlinear optical (SHG) materials.FCT, FEDER, QREN PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302

Fernandes, Sara S. M.

Raposo, M. Manuela M.

M. Raposo

Sara Fernandes

Crossref

&lt;strong&gt;Design, synthesis and characterization of novel thienylpyridazine derivatives for optical applications&lt;/strong&gt;

Universidade do Minho: RepositoriUM

1  Design, synthesis and characterization of novel thienylpyridazine derivatives for optical applications Sara S. M. Fernandes and M. Manuela M. Raposo* Centre of Chemistry, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal Email: mfox@quimica.uminho.pt   Abstract: We report in this work the synthesis and the photophysical characterization of novel pyridazine derivatives, functionalized in position 3, with different (hetero)aromatic groups (indole, cyanophenyl, nitrophenyl). The diazines were synthesized by Suzuki coupling of 3-bromo-6-(thiophen-2-yl)pyridazine with commercially available (hetero)aryl-boronic acids. Due to their optical properties these push-pull π-conjugated systems can have application as versatile building blocks for the preparation of DSSCs, OLEDs, and nonlinear optical (SHG) materials.  Keywords: push-pull –conjugated systems, thiophene, indole, pyridazine, Suzuki coupling, optical applications  1. Introduction In recent years, push-pull π-conjugated systems bearing electron rich (thiophene, pyrrole, furan) and electron deficient heterocycles ((benz)imidazole, (benzo)thiazole, pyridine, piridazine, phthalazine, etc.) have been widely used as NLO and photochromic materials, metal free organic sensitizers for DSSCs, OLEDs, etc. due to their easy synthesis and electronic arrangement that assures and efficient tuning of the photophysical properties through small structural modifications. The tuning of the optoelectronic properties of these push-pull systems can be achieved by modification of the electron donor, electron acceptor, and/or by modification of the electronic nature of the π-bridge. Concerning the π-spacer, several studies published in the past three decades have confirmed that substitution of the benzene ring of a chromophore bridge with easily delocalizable electro-rich and/or electron-poor heterocycles results in improved molecular optical (linear and nonlinear) properties of the corresponding push-pull systems. Due to their electronic nature and 2  low aromaticity, they can act efficiently as -bridges as well as auxiliary donors (electron-rich heterocycles) or as auxiliary acceptors (electron-poor heterocycles). Additionally, these heterocyclic systems are also thermally and photochemically stable. [1-13]   During the last decade our research group has published experimental and theoretical results concerning the auxiliary donor/acceptor effect of electron rich and electron deficient heterocycles on –conjugated systems for several optical applications. [5-13]  Based on our earlier work we were motivated to extend these studies in order to explore the potential application of a new series of donor-acceptor substituted thienylpyridazines in which the pyridazine heterocycle plays the dual role of -bridge and acceptor/auxiliary acceptor moiety. Therefore, the pyridazine ring was functionalized in position 3 with different (hetero)aryl-based groups (indole, benzonitrile and nitrophenyl) in order to study the effect of their electronic nature on the optical properties of the push-pull systems. We report in this work the synthesis and the photophysical characterization of novel thienylpyridazine derivatives which were synthesized through Suzuki coupling of 3-bromo-6-(thiophen-2-yl)pyridazine [14] with commercially available (hetero)aryl-boronic acids.  2. Experimental  2.1. Instruments NMR spectra were obtained on a Varian Unity Plus Spectrometer at an operating frequency of 300 MHz for 1H NMR and 75.4 MHz for 13C NMR, or a Brucker Avance III 400 at an operating frequency of 400 MHz for 1H NMR and 100.6 MHz for 13C NMR using the solvent peak as internal reference at 25 ºC (δ relative to TMS). All chemical shifts are given in Hz. Assignments were made by comparison of chemical shift, peak multiplicities and J values, and were supported by spin decoupling-double resonance and bidimensional heteronuclear HMBC and HMQC correlation techniques. IR spectra were determined on a BOMEM MB 104 spectrophotometer. UV-Visible absorption spectra (200-800 nm) were obtained using a Shimadzu UV/2501PC spectrophotometer. Fluorescence spectra were collected using a FluoroMax-4 spectrofluorometer. Luminescence quantum yields were measured in comparison with ethanol solution of 3  9,10-diphenylanthracene (ΦF = 0.95) [15]  as standard. All melting points were measured on a Gallenkamp melting point apparatus and are uncorrected. Mass spectrometry analysis were performed at the C.A.C.T.I. – Unidad de Espectrometria de Masas of University of Vigo, Spain.  2.2. Materials Boronic acids were purchased from Aldrich and used as received. TLC analysis were carried out on 0.25 mm thick precoated silica plates (Merck Fertigplatten Kieselgel 60F254) and the spots were visualized under UV light. Chromatography on silica gel was carried out on Merck Kieselgel (200-300 mesh).  2.3. Synthesis General procedure for the synthesis of thienyl-pyridazine derivatives 3 through Suzuki coupling: 3-bromo-6-(thiophen-2-yl)pyridazine 1 (0.5 mmol, 120 mg) was coupled with (hetero)arylboronic acids 2 (0.6 mmol) in a mixture of DME (8 mL), ethanol (2 mL), aqueous 2 M Na2CO3 (1 mL) and Pd(PPh3)4 (5 mol %) at 80 ºC under nitrogen. The reaction was monitored by TLC, which determined the reaction time (24-36 h). After cooling, the mixture was extracted with chloroform (3x20 mL), a saturated solution of NaCl was added (20 mL) and the phases were separated. The organic phase was washed with water (3x10 mL) and with aqueous solution NaOH 10% (10 mL). The organic phase obtained was dried (over MgSO4), filtered, and the solvent removed to give a crude mixture. The crude product was purified through a silica gel chromatography column using mixtures of chloroform and light petroleum of increasing polarity to afford the coupled products 3. Recrystallization from n-hexane / dichloromethane gave the pure compounds. 1-Methyl-5-(6’-(thiophen-2’’-yl)pyridazin-3’-yl)-1H-indole 3a. Beige solid (16%). Mp: 224-228 ºC (recrystallized from dichloromethane / n-hexane). UV (ethanol): max nm (, M-1cm-1) 326, (25,282). IR (liquid film)  3426, 2085, 1640, 1545, 1432, 1406, 1296, 1241, 1151, 807 cm-1. 1H NMR (Acetone-d6, 400 MHz)  3.94 (s, 3H, CH3), 6.61 (dd, 1H, H-3, J = 3.2 and 1.2 Hz), 7.26 (dd, 1H, H-4’’, J = 4.8 and 4.0 Hz), 7.35 (d, 1H, H-2, J = 3.2 Hz), 7.59 (d, 1H, H-7, J = 8.4 Hz), 7.69 (dd, 1H, H-5’’, J = 5.2 and 1.2 Hz), 7.90 (dd, 1H, H-3’’, J = 3.6 and 1.2 Hz), 8.15 (dd, 1H, H-6, J = 8.4 and 1.6 Hz), 8.16 (d, 1H, H-5’, J = 9.2 Hz), 8.22 (d, 1H, H-4’, J = 9.2 Hz), 8.46 (d, 1H, H-4, J = 1.2 Hz) ppm. 13C NMR (Acetone-d6, 400 MHz)  33.0 (CH3), 102.5 (C-3), 110.8 (C-7), 120.3 (C-4), 121.1 (C-6), 123.4 (C-5’), 124.5 (C-4’), 126.9 (C-3’’), 128.4 4  (C-5), 129.0 (C-4’’), 129.5 (C-5’’), 129.9 (C-7a), 131.3 (C-2), 138.8 (C-3a), 142.3 (C-2’’), 153.8 (C-6’), 159.5 (C-3’) ppm. MS (EI) m/z (%) = 292 ([M]+, 6), 291 (33), 155 (100), 154 (26). HRMS: m/z (EI) for C17H13N3S; calcd 291.0830; found 291.0831. 4-(6’-(Thiophen-2’’-yl)pyridazin-3’-yl)benzonitrile 3b. Yellow solid (28%). Mp: 249-252 ºC (recrystallized from dichloromethane / n-hexane).  UV (ethanol): max nm (, M-1cm-1) 323, (26,086). IR (liquid film)  3094, 2233, 1577, 1433, 1401, 1297, 1134, 852, 827, 720 cm-1. 1H NMR (Acetone-d6, 400 MHz)  7.29 (dd, 1H, H-4’’, J = 5.2 and 3.6 Hz), 7.76 (dd, 1H, H-5’’, J = 5.0 and 1.2 Hz), 7.98 (dd, 1H, H-3’’, J = 3.8 and 1.2 Hz), 8.00 (d, 2H, H-2 and H-6, J = 8.8 Hz), 8.29 (d, 1H, H-5’, J = 9.2 Hz), 8.34 (d, 1H, H-4’, J = 9.2 Hz), 8.46 (d, 2H, H-3 and H-5, J = 8.8 Hz) ppm. 13C NMR (Acetone-d6, 400 MHz)  114.1 (C-4), 119.1 (C-1), 123.7 (C-4’ or C-5’), 125.7 (C-4’ or C-5’), 128.2 (C-3’’), 128.3 (C-2 and C-6), 129.2 (C-4’’), 130.7 (C-5’’), 133.6 (C-3 and C-5), 141.5 (C-2’’), 155.3 (C-6’), 156.7 (C-3’), 206.1 (CN) ppm. MS (EI) m/z (%) = 264 ([M]+, 5), 263 (31), 127 (6), 109 (6), 108 (100). HRMS: m/z (EI) for C15H9N3S; calcd 263.0517; found 263.0516. 3-(3’-Nitrophenyl)-6-(thiophen-2’’-yl)pyridazine 3c. Yellow solid (25%). Mp: 249-252 ºC (recrystallized from dichloromethane / n-hexane).  UV (ethanol): max nm (, M-1cm-1) 314, (24,105). IR (liquid film)  3409, 2094, 1639, 1524, 1444, 1402, 1351, 1311, 1276, 1111, 1081, 1056, 838, 812, 727 cm-1. 1H NMR (Acetone-d6, 300 MHz)  7.29 (dd, 1H, H-4’’, J = 5.2 and 3.6 Hz), 7.78 (dd, 1H, H-5’’, J = 5.2 and 0.8 Hz), 7.92 (t, 1H, H-5’, J = 8.2), 8.00 (dd, 1H, H-3’’, J = 3.2 and 1.2 Hz), 8.33 (d, 1H, H-5, J = 9.2 Hz), 8.42 (dd, 1H, H-6’, J = 8.0 and 1.2 Hz), 8.43 (d, 1H, H-4, J = 9.2 Hz), 8.70 (dd, 1H, H-4’, J = 7.8 and 0.8 Hz), 9.10 (t, 1H, H-2’, J = 1.8 Hz) ppm. 13C NMR (Acetone-d6, 300 MHz)  122.1 (C-2’), 123.8 (C-5), 125.1 (C-4), 125.6 (C-6’), 128.2 (C-3’’), 129.2 (C-4’’), 130.7 (C-5’’), 131.3 (C-5’), 133.5 (C-4’), 139.0 (C-1’), 141.4 (C-2’’), 149.8 (C-3’), 155.4 (C-6), 156.2 (C-3) ppm. MS (EI) m/z (%) = 284 ([M]+, 4), 283 (47), 253 (27), 117 (70), 108 (100). HRMS: m/z (EI) for C14H9N3O2S; calcd 283.0415; found 283.0414.  3. Results and Discussion  3.1. Synthesis 5  The precursor bromo-thienylpyridazine 1 was synthesized by reaction of thienyl-pyridazinone with POBr3, which in turn, was previously prepared by condensation of methyl-4-oxo-4-(thiophen-2-yl)butanoate with hydrazine hydrate in ethanol.[14] Compounds 3a-c were prepared by Suzuki cross-coupling reaction of 3-bromo-6-(thiophen-2-yl)pyridazine 1 with commercially available (hetero)aryl-boronic acids 2a-c in fair yields (16-25 %) (Table 1, Scheme 1). The new thienyl-pyridazine derivatives 3 were characterized by the usual spectroscopic techniques.  Scheme 1. Synthesis of thienyl-pyridazine derivatives 3.  Table 1. Yields, UV-Visible absorption and emission data for thienyl-pyridazines 3. Cp Yield (%) λmax (nm) ε (M-1cm-1) λem (nm) ΦF Stokes Shift (nm) 3a 16 326 25,282 427 0.007 101 3b 28 323 26,086 404 0.006 81 3c 25 314 24,105 408 0.008 94  3.2. Optical properties  Electronic absorption spectra of pyridazines 3 in ethanol solutions (10-4 M) show intense lowest energy charge-transfer absorption bands in the UV-visible region between 314-326 nm. The position of these bands depends on the electronic nature of the (hetero)aromatic substituent linked in position 3 of the pyridazine heterocycle as well as the degree of the electronic delocalization (Table 1, Figure 1).  6  Therefore, the indole derivative 3a with the highest delocalizated π-conjugate system exhibit the highest max value (326 nm). On the other hand, compound 3b bearing the strong acceptor cyano group in position 4 of the phenyl ring (withdrawing mesomeric effect) exhibit a bathochromic shift of 9 nm when compared to compound  3c which is functionalized with a nitro group (inductive withdrawing effect) in position 3 of the phenyl ring. These results are in agreement with the higher electron-withdrawing ability of the acceptor groups, in the order 3-nitrophenyl < 4-cyanophenyl (Figure 1). Thienylpyridazines 3 were excited at the wavelength of maximum absorption, at room temperature, in order to study their fluorescence properties (Figure 1). The relative fluorescence quantum yields were determined using a 10-6 M solution of 9,10-diphenylanthracene in ethanol as fluorescence standard (ΦF = 0.95).[15] Compound 3a showed the longer wavelength of emission maxima (λem = 427 nm), compared to derivatives 3b-c (λem = 404-408 nm). All compounds showed weak emissive properties, with relative fluorescence quantum yields ranging from 0.006 to 0.008 and large Stokes’ shifts (the lowest being 81 nm and the highest 101 nm).   Figure 1. UV-Visible absorption and emission spectra of the novel thienyl-pyridazines 3 in ethanol solution.  4. Conclusions Three novel thienyl-pyridazines 3a-c were synthesized in fair yields through Suzuki coupling. The compounds exhibit absorption and emission bands in the UV-visible range which are influenced by the electronic nature of the (hetero)aromatic group linked in position 3 of the pyridazine heterocycle as well as the degree of the electronic delocalization of the π-conjugated system. 00.20.40.60.81300 350 400 450 500 550 600Normalized Absorption / EmissionWavelength (nm)3a EmissionAbsorption00.20.40.60.81300 350 400 450 500 550 600Wavelength (nm)3b EmissionAbsorption00.20.40.60.81300 350 400 450 500 550 600Wavelength (nm)3c EmissionAbsorption7  Due to their optical properties push-pull π-conjugated systems 3 can have application as versatile building blocks for the preparation of DSSCs, OLEDs, and nonlinear optical (SHG) materials.  Acknowledgements: The authors thank the Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química - Universidade do Minho, Project CQ/UM PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302) and a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. References: [1] L.R. Dalton, P.A. Sullivan, D.H. Bale, Electric Field Poled Organic Electro-optic Materials: State of the Art and Future Prospects. Chemical Reviews, 110 (2010) 25-55. [2] A. Mishra, M.K.R. Fischer, P. Bäuerle, Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules. Angewandte Chemie International Edition, 48 (2009) 2474-2499. [3] A. Mishra, C.-Q. Ma, P. Bäuerle, Functional Oligothiophenes: Molecular Design for Multidimensional Nanoarchitectures and Their Applications. Chemical Reviews, 109 (2009) 1141-1276. [4] Handbook of Thiophene-Based Materials: Applications in Organic electronics and Photonics, F. Perepichka, D.F. Perepishka, Wiley, New York, 2009. [5] S.S.M. Fernandes, M.C.R. Castro, I. Mesquita, L. Andrade, A. Mendes, M.M.M. Raposo, Synthesis and characterization of novel thieno[3,2-b]thiophene based metal-free organic dyes with different heteroaromatic donor moieties as sensitizers for dye-sensitized solar cells. Dyes and Pigments, 136 (2017) 46-53. [6] J. Garcia-Amorós, M.C. R. Castro, P. Coelho, M.M. M. Raposo, D. Velasco, Fastest non-ionic azo dyes and transfer of their thermal isomerisation kinetics into liquid-crystalline materials. Chemical Communications, 52 (2016) 5132-5135. 8  [7] M.C.R. Castro, M. Belsley, M.M.M. Raposo, Synthesis and characterization of push–pull bithienylpyrrole NLOphores with enhanced hyperpolarizabilities. Dyes and Pigments, 131 (2016) 333-339. [8] J. Pina, J.S. Seixas de Melo, R.M.F. Batista, S.P.G. Costa, M.M.M. Raposo, Triphenylamine–Benzimidazole Derivatives: Synthesis, Excited-State Characterization, and DFT Studies. The Journal of Organic Chemistry, 78 (2013) 11389-11395. [9] M.M.M. Raposo, A.M.R.C Sousa, G. Kirsch, F. Ferreira, M. Belsley, E. Matos Gomes, A.M.C. Fonseca, Synthesis and characterization of dicyanovinyl-substituted thienylpyrroles as new NLO-chromophores. Organic Letters, 8 (2006) 3681-3684.  [10] R.M.F. Batista, S.P.G. Costa, E.L. Malheiro, M. Belsley, M.M.M. Raposo, Synthesis and characterization of new thienylpyrrolyl-benzothiazoles as efficient and thermally stable nonlinear optical chromophores. Tetrahedron, 63 (2007) 4258-4265. [11] J. Pina, S. Seixas de Melo, R.M.F. Batista, S.P.G. Costa, M.M.M. Raposo, The influence of the relative position of the thiophene and pyrrole rings in donor-acceptor thienylpyrrolyl-benzothiazole derivatives: A photophysical and theoretical investigation. Physical Chemistry Chemical Physics, 12 (2010) 9719-9725. [12] M.M.M. Raposo, M.C.R. Castro, A.M.C. Fonseca, P. Schellenberg; M. Belsley, Design, synthesis and characterization of the electrochemical, nonlinear optical properties and theoretical studies of novel thienylpyrrole azo dyes bearing benzothiazole acceptor groups. Tetrahedron, 67 (2011) 5189-5198. [13] M.M.M. Raposo, A.M.C. Fonseca, M.C.R. Castro, M. Belsley, M.F.S. Cardoso, L. Carvalho, P. Coelho. Synthesis and characterization of novel diazenes bearing pyrrole, thiophene and thiazole heterocycles as efficient photochromic and nonlinear optical (NLO) materials. Dyes and Pigments, 91 (2011) 62-73. [14] M.M.M. Raposo, A.M.B.A. Sampaio, G. Kirsch. A Convenient access to thienyl-substituted phthalazines. Journal of  Heterocyclic Chemistry, 42 (2005) 1245-1251. [15] J.V. Morris, M.A. Mahaney, J.R. Huber. Fluorescence quantum yield determinations. 9,10-diphenylanthracene as a reference standard in different solvents. The Journal of Physical Chemistry, 80 (1976) 969-974.  

Design, synthesis and characterization of novel thienylpyridazine derivatives for optical applications

In recent years, push-pull π-conjugated systems bearing electron rich (thiophene, pyrrole, furan) and electron deficient heterocycles (pyridine, pyridazine, benzothiazole, etc.) have been widely used as NLO and photochromic materials, metal free organic sensitizers for DSSCs, OLEDs, etc. due to their easy synthesis and efficient tuning of the photophysical properties through small structural modifications.1-2
During the last decade our research group has published experimental and theoretical results concerning the auxiliary donor/acceptor effect of electron rich and electron deficient heterocycles on –conjugated systems.2 Based on our earlier work we were motivated to extend these studies in order to explore the potential application of a new series of donor-acceptor substituted thienylpyridazines in which the pyridazine heterocycle plays the dual role of -bridge and acceptor/auxiliary acceptor moiety. Therefore, the pyridazine ring was functionalized in position 3 with different (hetero)aryl-based groups (indole, benzonitrile and nitrophenyl) in order to study the effect of their electronic nature on the optical properties of the push-pull systems.
We report in this work the synthesis and the photophysical characterization of novel thienylpyridazine derivatives which were synthesized through Suzuki coupling of 3-bromo-6-(thiophen-2-yl)pyridazine3 with commercially available (hetero)aryl-boronic acids.The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER.info:eu-repo/semantics/publishedVersio

Fernandes, S. S. M.

Design, synthesis and characterization of novel thienylpyridazine derivatives for optical applications  Sara S. M. Fernandes and M. Manuela M. Raposo* Centre of Chemistry, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal Email: mfox@quimica.uminho.pt  In recent years, push-pull π-conjugated systems bearing electron rich (thiophene, pyrrole, furan) and electron deficient heterocycles (pyridine, pyridazine, benzothiazole, etc.) have been widely used as NLO and photochromic materials, metal free organic sensitizers for DSSCs, OLEDs, etc. due to their easy synthesis and efficient tuning of the photophysical properties through small structural modifications.1-2 During the last decade our research group has published experimental and theoretical results concerning the auxiliary donor/acceptor effect of electron rich and electron deficient heterocycles on –conjugated systems.2 Based on our earlier work we were motivated to extend these studies in order to explore the potential application of a new series of donor-acceptor substituted thienylpyridazines in which the pyridazine heterocycle plays the dual role of -bridge and acceptor/auxiliary acceptor moiety. Therefore, the pyridazine ring was functionalized in position 3 with different (hetero)aryl-based groups (indole, benzonitrile and nitrophenyl) in order to study the effect of their electronic nature on the optical properties of the push-pull systems. We report in this work the synthesis and the photophysical characterization of novel thienylpyridazine derivatives which were synthesized through Suzuki coupling of 3-bromo-6-(thiophen-2-yl)pyridazine3 with commercially available (hetero)aryl-boronic acids.   Keywords: push-pull –conjugated systems, thiophene, pyridazine, Suzuki coupling, optical applications  Acknowledgements: Thank are due to Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716) and a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER.  References: 1. (a) Dalton, L. R.; Sullivan, P. A.; Bale, D. H.; Chem. Rev., 2010, 110, 25. (b) Misha, A.; Fischer, M. K. R.; Bauerle, P.; Angew. Chem. Int. Ed., 2009, 48, 2479. (c) Mishra, A.; Ma, C.-Q.; Baeuerle, P.; Chem. Rev., 2009, 109, 1141. (d) Handbook of Thiophene-Based Materials: Applications in Organic electronics and Photonics; Perepichka, F., Perepichka, D. F., Ed.; Wiley: New York, 2009. 2. For some recent examples see: (a) Fernandes, S. S. M.; Castro, M. C. R.; Mesquita, I.; Andrade, L.; Mendes, A.; Raposo, M. M. M.; Dyes Pigments 2017, 136, 46. (b) Garcia-Amorós, J.; Castro, M. C. R.; Coelho, P.; Raposo, M. M. M.; Velasco, D; Chem. Commun. 2016, 52, 5132. (c) Castro, M. C. R.; Belsley, M.; Raposo, M. M. M.; Dyes Pigments 2016, 131, 333. (d) Pina, J.; Seixas de Melo J. S.; Batista, R. M. F.; Costa, S. P. G.; Raposo, M. M. M.; J. Org. Chem. 2013, 78, 11389. 3. Raposo, M. M. M.; Sampaio, A. M. B. A; Kirsch, G.; J. Heterocyclic Chem. 2005, 42, 1245.  

English

Research on renewable energy sources have been expanding considerably in order to decrease the consumption of fossil fuels and therefore reduce global warming and environmental pollution. Solar cells based on organic dye sensitizers (DSSCs) is a photovoltaic device that have been extensively studied due to their high incident solar light-to-electricity conversion efficiency and low cost of production. In the interest of achieving chromophores with high performance for DSSCs, wide-ranging research has been conducted on structural modifications of the sensitizing dyes. One of the approaches is the tuning the pi-bridge with auxiliary electron donor/acceptor groups, such as electron-rich thiophene and furan heterocycles linked to the electron-deficient phthalazine ring substituted with appropriate acceptor groups, which are promising candidates among such push-pull systems.
As part of an on-going research to develop efficient donor – π-spacer – acceptor heterocyclic systems for several optoelectronic applications we report the synthesis and characterization of phthalazine derivatives functionalized with cyanoacetic or rhodanine-3-acetic acid as anchoring groups and (hetero)aryl groups as donor/π-spacers. The experimental results indicate that, these compounds could have potential application as NLO chromophores as well as sensitizers for DSSCs.Thanks are due to Fundacao para a Ciencia e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Quimica PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716) and a PhD grant to S.S.M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Brucker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT

1  Synthesis and characterization of novel phthalazine based push-pull heterocyclic systems for DSSCs Sara S. M. Fernandes, M. Manuela M. Raposo* Centre of Chemistry, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal Email: mfox@quimica.uminho.pt   Abstract: Research on renewable energy sources have been expanding considerably in order to decrease the consumption of fossil fuels and therefore reduce global warming and environmental pollution. Solar cells based on organic dye sensitizers (DSSCs) is a photovoltaic device that have been extensively studied due to their high incident solar light-to-electricity conversion efficiency and low cost of production. In the interest of achieving chromophores with high performance for DSSCs, wide-ranging research has been conducted on structural modifications of the sensitizing dyes. One of the approaches is the tuning the -bridge with auxiliary electron donor/acceptor groups, such as electron-rich thiophene and furan heterocycles linked to the electron-deficient phthalazine ring substituted with appropriate acceptor groups, which are promising candidates among such push-pull systems. As part of an on-going research to develop efficient donor – π-spacer – acceptor heterocyclic systems for several optoelectronic applications we report the synthesis and characterization of phthalazine derivatives functionalized with cyanoacetic or rhodanine-3-acetic acid as anchoring groups and (hetero)aryl groups as donor/π-spacers. The experimental results indicate that, these compounds could have potential application as NLO chromophores as well as sensitizers for DSSCs.            Keywords: Suzuki coupling, Knoevenagel condensation, Phthalazine, Cyanoacetic acid, Rhodanine-3-acetic acid, -Conjugated heterocyclic systems, Push-pull molecules, Dye-sensitized solar cells (DSSC)    2  1. Introduction  Research on renewable energy sources and sustainable development have been expanding considerably in order to decrease the consumption of fossil fuels and therefore reduce global warming and environmental pollution1. Solar energy is an excellent source due to its inexhaustibility and cleanness, and can be directly transformed into electric energy through photovoltaics, namely the most promising organic solar cells2. Solar cells based on organic dye sensitizers (DSSCs) adsorbed on nanocrystalline TiO2 electrodes have been extensively studied due to their high incident solar light-to-electricity conversion efficiency, colourful and decorative natures and low cost of production3. Wide-ranging research has been conducted on structural modifications of the sensitizing dyes in the interest of achieving chromophores with high performance for DSSCs2, 4. Dipolar chromophores, having an electron donor and electron acceptor groups linked through a -conjugated bridge electronic arrangement are currently of great interest because of their applicability to optical and photovoltaic devices such as nonlinear optics (NLO) and dye-sensitized solar cells (DSSCs), as it assures efficient intramolecular charge transfer and generates a dipolar push-pull system featuring low energy and intense charge transfer absorption. These systems can be improved by modification of the electron donor, electron acceptor, or/and the -bridge of the molecule. Recent approaches to the design of these compounds are based on the presence of a five-membered heterocyclic ring in a push-pull donor-acceptor chromophore. Another approach consists on adjusting the -bridge with electron rich and/or electron deficient aromatic rings that can an auxiliary electron donor/acceptor group performance2, 4a, 5. Electron-rich thiophene and furan heterocycles linked to the electron-deficient phthalazine ring substituted with appropriate acceptor groups are promising candidates among such push-pull systems. Having in mind these facts and also our recent work, in which we have used formyl heterocyclic systems, such as oligothiophenes, arylthiophenes, thienylpyrroles, arylfurans and thienylfurans6 as precursors for the synthesis of more complex molecules (e.g. dicyanovinyl- and thiobarbituric derivatives, benzothiazoles, (benz)imidazoles, benzoxazoles, BODIPYs, Schiff-bases, imidazo-crown ethers, thiosemicarbazones  etc.) for several optoelectronic applications (OLEDs, SHG, TPA, chemosensors)7, we decided to synthesize the new formyl-phthalazines 3a and 4a. Further derivatization of these precursors with cyanoacetic acid or rhodamine-3-acetic yield the final push-pull systems 3b-c and 4b-c. Compounds 3-4 were prepared in order to study the influence of the electronic nature of the (hetero)aryl group linked to the diazine moiety, as well as the influence of the strength of the acceptor group on the optical properties of the novel push-pull systems.    3  2. Experimental  2.1. Instruments  NMR spectra were obtained on a Varian Unity Plus Spectrometer at an operating frequency of 300 MHz for 1H NMR and 75.4 MHz for 13C NMR or a Brucker Avance III 400 at an operating frequency of 400 MHz for 1H NMR and 100.6 MHz for 13C NMR using the solvent peak as internal reference at 25 ºC ( relative to TMS). All chemical shifts are given in Hz. Assignments were made by comparison of chemical shifts, peak multiplicities  and J values and were supported by spin decoupling-double resonance and bidimensional heteronuclear HMBC and HMQC correlation techniques. UV-visible absorption spectra (200-800 nm) were obtained using a Shimadzu UV/2501PC spectrophotometer.  2.2. Materials  Phosphorous (V) oxybromide, boronic acids, cyanoacetic acid and rhodamine-3-acetic acid were purchased from Aldrich, Acros Organics and Fluka and used as received. All commercially available reagents and solvents were used as received. TLC analyses were carried out on 0.25 mm thick precoated silica plates (Merck Fertigplatten Kieselgel 60F254) and spots were visualized under UV light. Chromatography on silica gel was carried out on Merck Kieselgel (200-300 mesh).  2.3. Synthesis  Procedure for the synthesis of 1-bromo-4-(thiophen-2-yl)phthalazine8 2: A mixture of 4-(thiophen-2-yl)phthalazin-1(2H)-one 1 (2.2 mmol, 0.5 g) and POBr3 (5.5 mmol, 1.6g) was heated for 6 h at 110-120 ºC. This mixture was cooled till room temperature and then poured onto ice-water, basified with a solution of ammonia (2 M) and stirred for 30 min. to give a brown solid which was filtered and washed with water and light petroleum to give the pure thienylphthalazine 2 as brown solid (96%). 1H NMR (CDCl3, 400MHz)  7.26 (dd, 1 H, H-4’, J = 5.2 and 2.8 Hz), 7.63 (dd, 1 H, H-5’, J = 1.2 and 0.8 Hz), 7.68 (dd, 1 H, H-3', J = 3.6 and 1.2 Hz), 8.00 (m, 2 H, H-7 and H-8, J = 3.6 and 1.2 Hz), 8.33 (dd, 1 H, H-6, J = 6.2 and 1.6 Hz), 8.46 (d, 1 H, H-9, J = 7.0 and 2.4 Hz) ppm.  General procedure for the synthesis of aldehydes 3a and 4a through Suzuki coupling: 1-bromo-4-(thiophen-2-yl)phthalazine 2 (0.7 mmol) was coupled to boronic acids (0.9 mmol) in a mixture of DME (6 mL), aqueous 2 M Na2CO3 (1 mL) and Pd(PPh3)4 (5%) at 80°C under nitrogen. The reactions were monitored by TLC which determined the different reaction times (24-48 h). The mixture was cooled to room temperature, and neutralized with a saturated solution of sodium 4  acetate. The organic layer was extracted with chloroform, dried with anhydrous MgSO4 and the solvent was evaporated under reduced pressure. The product was purified by column chromatography on silica gel with increasing amounts of dichloromethane in light petroleum as solvent. The solvent was evaporated to give the coupled products as solids. Recrystallization from dichloromethane/hexane gave the pure compounds 3a and 4a.  4-(1’-(Thiophen-2’’-yl)phthalazin-4’-yl)benzaldehyde 3a. Yellow solid (56%). Pf. 161-163 ºC. UV (ethanol): max nm (, M-1cm-1) 331 (9167). 1H NMR (CDCl3, 300 MHz)  7.29 (dd, 1 H, H-4’’, J= 5.2 and 3.6 Hz), 7.65 (dd, 1 H, H-5’’, J= 5.2 and 1.2 Hz), 7.79 (dd, 1 H, H-3’’, J= 3.6 and 1.2 Hz), 7.93-8.03 (m, 4 H, H-7’, H-6’, H-3, H-5), 8.09-8.12 (m, 3H, H-2, H-6, H-8’), 8.62 (d, 1 H, H-5’, J= 8.0 Hz), 10.18 (s, 1 H, CHO) ppm.  5-(1’-Thiophen-2’’-yl)phthalazin-4’-yl)furan-2-carbaldehyde 4a. Yellow solid (21%). UV (ethanol): max nm (, M-1cm-1) 366, (12800). 1H NMR (CDCl3, 300 MHz)  7.30 (dd, 1 H, H-4’’, J= 5.0 and 3.6 Hz), 7.47 (dd, 1 H, H-5’’, J= 5.4 and 1.2 Hz), 7.67 (dd, 1H, H-3’’, J= 5.2 and 1.2 Hz), 7.83-7.98 (m, 2 H, H-7’, H-6’), 8.02-8.09 (m, 2 H, H-8’, H-5’), 8.61 (d, 1 H, H-4, J= 7.6 Hz), 9.09 (d, 1 H, H-3, J= 7.2 Hz), 9.84 (s, 1 H, CHO) ppm.  General procedure for the synthesis of cyanoacetic acids 3b and 4b through Knoevenagel condensation: To a solution of aldehyde (0.3 mmol) and 2-cyanoacetic acid (54 mg, 0.6 mmol) in ethanol was added 4 drops of N-triethylamine. The mixture was refluxed for 6 h then cooled down to room temperature. The crude product was concentrated and ethyl ether was added to induce precipitation. The precipitate was filtered and washed with ethyl ether to give the pure product.  2-Cyano-3-(4'-(1''-(thiophen-2'''-yl)phthalazin-4''-yl)phenyl)acrylic acid 3b. Yellow solid (70%). Pf. 170-172 ºC. UV (ethanol): max nm (, M-1cm-1) 345 (4500). 1H NMR (CDCl3, 300 MHz)  7.31 (d, 1 H, H-4’’, J= 3.9 Hz), 7.60 (d, 1 H, H-5'', J= 4.8 Hz), 7.76 (d, 1 H, H-3'', J= 3.9 Hz), 7.91-8,01 (m, 4 H, H-7’, H-6', H-3, H-5), 8.12 (d, 2 H, H-2, H-6, J= 7.5 Hz), 8.18 (d, 1 H, H-8’, J= 7.8 Hz), 8.36 (s, 1 H, =CH), 8.60 (d, 1 H, H-5', J= 8.4 Hz) ppm.  2-Cyano-3-(5'-(1''-(thiophen-2'''-yl)phthalazin-4''-yl)furan-2'-yl)acrylic acid 4b. Yellow solid (8%). UV (ethanol): max nm (, M-1cm-1) 392, (67500). 1H NMR (CDCl3, 400 MHz)  7.24 (dd, 1 H, H-4''', J= 5.0 and 4.0 Hz), 7.36 (d, 1 H, H-4', J= 4.0 Hz), 7.62 (dd, 1 H, H-5''', J= 5.0 and 1.2 Hz), 7.78 (dd, 1 H, H-3''', J= 3.6 Hz and 0.8 Hz), 7.83 (d, 1 H, H-3', J= 3.6 Hz), 7.96-8.08 (m, 3 H, =CH, H-7'', H-6''), 8.54 (d, 1 H, H-8'', J= 7.6 Hz), 9.30 (d, 1 H, H-5'', J= 8.8 Hz) ppm.  General procedure for the synthesis of rhodamine-3-acetic acids 3c and 4c through Knoevenagel condensation: To a solution of aldehyde (0.25 mmol) and rhodanine-3-acetic acid 5  (58 mg, 0.3 mmol) in ethanol was added 4 drops of N-triethylamine. The mixture was refluxed for 6 h then cooled down to room temperature. The crude product was concentrated and ethyl ether was added to induce precipitation. The precipitate was filtered and washed with ethyl ether to give the pure product.  2-(4'-Oxo-5'-((4''-(1'''-(thiophen-2''''-yl)phthalazin-4'''-yl)phenyl)methylene)-2'-thioxothiazolidin-3'-yl)acetic acid 3c. Yellow solid (76%). Pf. 189-191 ºC. UV (ethanol): max nm (, M-1cm-1) 382, (23750). 1H NMR (CDCl3, 300 MHz)  4.91 (s, 2 H, CH2), 7.31 (dd, 1 H, H-4'''', J= 5.4 and 3.6 Hz), 7.66 (dd, 1 H, H-5'''', J= 4.9 and 1.2 Hz), 7.73-7.78 (m, 3 H, =CH, H-6'', H-2''), 7.90-8.03 (m, 5 H, H-3'''', H-6''', H-7''', H-3'', H-5''), 8.16 (d, 1 H, H-8''', J= 7.5 Hz), 8.62 (d, 1 H, H-5''', J= 7.8 Hz) ppm.  2-(4'-Oxo-(5'-((5''-(1'''-(thiophen-2''''-yl)phthalazin-4'''-yl)furan-2''-yl)methylene)-2'-thioxothiazolidin-3'-yl)acetic acid 4c. Orange solid (41%). UV (ethanol): max nm (, M-1cm-1) 436, (21500). 1H NMR (CDCl3, 300 MHz)  4.63 (s, 2 H, CH2), 7.27 (dd, 1 H, H-4'''', J= 4.9 and 6.9 Hz), 7.33 (d, 1 H, H-4'', J= 3.6 Hz), 7.58 (d, 1 H, H-3'', J= 3.6 Hz), 7.72 (dd, 1 H, H-5'''', J= 4.9 and 1.2 Hz), 7.78 (dd, 1 H, H-3'''', J= 3.6 and 1.2 Hz), 7.97 (s, 1 H, =CH), 8.07-8.10 (m, 2 H, H-7''', H-6'''), 8.55-8.59 (m, 1 H, H-8'''), 8.80-8.83 (m, 1 H, H-5''') ppm.   3. Results and Discussion  3.1. Synthesis  The precursor phthalazinone 1 was prepared by condensation of ethyl-2-(thiophene-2-carbonyl)benzoate with hydrazine hydrate in ethanol. On the other hand the bromo-thienylphthalazine 2 was prepared by reaction of thienylphthalazinone 1 with POBr3. Formyl derivatives 3a and 4a were synthesized by Suzuki cross-coupling reaction of 3-bromo-6-(thiophen-2-yl)phthalazine 2 with commercially available (hetero)aryl-boronic acids in fair to good yields (21-56%) (Table 1, Scheme 1). Cyanoacetic acid derivatives 3b and 4b were obtained by Knoevenagel condensation of the formyl precursors with cyanoacetic acid in refluxing ethanol in fair to good yields (8-70%). On the other hand, rhodanine-acetic acid derivatives 3c and 4c were prepared by Knoevenagel condensation of the same formyl precursors with rhodanine-3-acetic acid in refluxing ethanol in moderate to good yields (41-76%). The new heterocyclic systems 3-4 were characterised by the usual spectroscopic techniques.   6    Scheme 1. Synthesis of compounds 2, 3 and 4.   Table 1. Yields, UV-visible absorption data of thienylphthalazine dyes 3-4 in ethanol solutions. Cpd Yield (%) max (nm)   (M-1cm-1) CHCl3 EtOH DMSO 3a 56 - 331 - 9167 3b 70 338 345 339 4500 3c 76 388 382 387 23750 4a 21 - 366 - 12800 4a 8 388 392 397 67500 4b 41 450 436 445 21500   3.2. UV-Visible study  The electronic spectra of thienylphthalazine 3-4 were recorded in ethanol solutions (10-4 M) and exhibited an intense lowest energy charge-transfer absorption band in the UV-visible region (Table 1, Figure 1). The location of the aforementioned band depends not only on the electronic nature of the aryl or heterocycle group linked at position 4 of the phthalazine moiety, but also on the electronic nature of the acceptor moiety. Bathochromic shifts (35-54 nm) were detected upon substitution of the aryl group (3) with a furan heterocycle (4). This observation confirms previously obtained results6b, 6e, 6g showing that the incorporation of electron rich heterocycles such as thiophene, pyrrole or furan heterocycles in push-pull compounds enhances their 7  charge-transfer properties. Therefore, dyes 4a-c in which the phenyl ring was substituted by the furan ring exhibit improved optical properties compared to the corresponding aryl derivatives 3a-c, probably due to the auxiliary donor effect of the furan heterocycle. We also notice bathochromic shifts in the range of 14-70 nm upon substitution of the formyl group (a) by the cyanoacetic acid (b) or by the rhodanine-3-acetic acid moiety (c) due to the higher electronic delocalization as well as the stronger acceptor ability of the rhodanine-3-acetic acid group.    Figure 1. Normalized absorption spectra of thienylphthalazines 3-4 recorded in ethanol.  A preliminary solvatochromic study of the absorption spectra of compounds 3b-c and 4b-c in three selected solvents possessing different solvation character (ethanol, chloroform and DMSO) was performed (Table 1, Figure 2). For compounds 3c, 4b-c the highest-energy transitions are found in ethanol, more polar solvents such as DMSO result in lower energy transitions, thus indicating a positive solvatochromic response (Δνmax  = 1111-2000 cm-1), being compound 4c the most solvatochromic.  8   Figure 2. Normalized UV-Vis absorption spectra of thienylphthalazines 3b-c and 4b-c in chloroform, ethanol and dimethylsulfoxide.   4. Conclusions  Six novel thienyl-phthalazines 3a-c and 4a-c were synthesized in fair to good yields through several synthetic methodologies. Compounds 3-4 exhibit absorption bands in the UV-visible range influenced by the electronic nature of the (heteroaryl)aryl groups substituted on the thienyl-phthalazine conjugated bridge as well as by the different acceptor moieties. Due to their push-pull character and optical properties the synthesized thienylphthalazines 3b-c and 4b-c will be studied in the future for nonlinear optical applications as second-harmonic generation (SHG) chromophores. Additionally, and as a result of their functionalization with appropriate anchoring groups and their optical properties, compounds 3b-c and 4b-c could have also potential application as sensitizers for DSSCs, particularly dyes 4b and 4c. The studies concerning their application as NLO chromophores as well as sensitizers for DSSCs are currently underway.    5. Acknowledgments  Thanks are due to Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through the Centro de Química PEst-C/QUI/UI0686/2011 (F-COMP-01-9  0124-FEDER-022716) and a PhD grant to S.S.M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Brucker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT.   6. References 1. Ning, Z.; Fu, Y.; Tian, H., Improvement of dye-sensitized solar cells: what we know and what we need to know. Energy Environ. Sci. 2010, 3 (9), 1170-1181. 2. Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H., Dye-Sensitized Solar Cells. Chem. Rev. 2010, 110 (11), 6595-6663. 3. (a) Gratzel, M., Photoelectrochemical cells. Nature 2001, 414 (6861), 338-344; (b) Grätzel, M., Dye-sensitized solar cells. J. Photochem. Photobiol., C 2003, 4 (2), 145-153; (c) Grätzel, M., Solar Energy Conversion by Dye-Sensitized Photovoltaic Cells. Inorg. Chem. 2005, 44 (20), 6841-6851. 4. (a) Mishra, A.; Fischer, M. K. R.; Bäuerle, P., Metal-Free Organic Dyes for Dye-Sensitized Solar Cells: From Structure: Property Relationships to Design Rules. Angew. Chem. Int. Ed. 2009, 48 (14), 2474-2499; (b) Mishra, A.; Ma, C.-Q.; Bäuerle, P., Functional Oligothiophenes: Molecular Design for Multidimensional Nanoarchitectures and Their Applications†. Chem. Rev. 2009, 109 (3), 1141-1276; (c) Robertson, N., Optimizing Dyes for Dye-Sensitized Solar Cells. Angew. Chem. Int. Ed. 2006, 45 (15), 2338-2345; (d) Balasingam, S. K.; Lee, M.; Kang, M. G.; Jun, Y., Improvement of dye-sensitized solar cells toward the broader light harvesting of the solar spectrum. Chem. Commun. 2013, 49 (15), 1471-1487. 5. Dalton, L. R.; Sullivan, P. A.; Bale, D. H., Electric Field Poled Organic Electro-optic Materials: State of the Art and Future Prospects. Chem. Rev. 2010, 110 (1), 25-55. 6. (a) Raposo, M. M. M.; Kirsch, G., Formylation, dicyanovinylation and tricyanovinylation of 5-alkoxy- and 5-amino- substituted 2,2′-bithiophenes. Tetrahedron 2003, 59 (26), 4891-4899; (b) Raposo, M. M. M.; Sousa, A. M. R. C.; Fonseca, A. M. C.; Kirsch, G., Synthesis of formyl-thienylpyrroles: versatile building blocks for NLO materials. Tetrahedron 2006, 62 (15), 3493-3501. 7. (a) Batista, R. M. F.; Costa, S. P. G.; Belsley, M.; Raposo, M. M. M., Synthesis and second-order nonlinear optical properties of new chromophores containing benzimidazole, thiophene, and pyrrole heterocycles. Tetrahedron 2007, 63 (39), 9842-9849; (b) Genin, E.; Hugues, V.; Clermont, G.; Herbivo, C.; Castro, M. C. R.; Comel, A.; Raposo, M. M. M.; Blanchard-Desce, M., Fluorescence and two-photon absorption of push-pull aryl(bi)thiophenes: structure-property relationships. Photochem. Photobiol. Sci. 2012, 11 (11), 1756-1766; (c) Pina, J.; Seixas de Melo, J. S.; Batista, R. M. F.; Costa, S. P. G.; Raposo, M. M. M., Triphenylamine–Benzimidazole Derivatives: Synthesis, Excited-State Characterization, and DFT Studies. J. Org. Chem. 2013, 78 (22), 11389-11395. 8. Raposo, M. M. M.; Sampaio, A. M. B. A.; Kirsch, G., A Convenient access to thienyl-substituted phthalazines. J. Heterocycl. Chem. 2005, 42 (7), 1245-1251.  

Synthesis and characterization of novel phthalazine based push-pull heterocyclic systems for DSSCs

Research on renewable energy sources and sustainable development have been expanding considerably in order to decrease the consumption of fossil fuels and therefore reduce global warming and environmental pollution. Solar energy is an excellent source due to its inexhaustibility and cleanness, and can be directly transformed into electric energy through photovoltaics, namely the most promising organic solar cells.
Solar cells based on organic dye sensitizers (DSSCs) adsorbed on monocrystalline TiO2 electrodes have been extensively studied due to their high incident solar light-to-electricity conversion efficiency, colourful and decorative natures and low cost of production. Wide-ranging research has been conducted on structural modifications of the sensitizing dyes in the interest of achieving chromophores with high performance for DSSCs1.
One approach for structural tuning consists on adjusting the -bridge with electron rich and/or electron deficient aromatic rings that can perform as an auxiliary electron donor/acceptor group. Electron-rich thiophene and furan heterocycles linked to the electron-deficient phthalazine ring substituted with appropriate acceptor groups are promising candidates among such push-pull systems1b, 2, 3.
As part of an on-going research to develop efficient donor – π-spacer – acceptor heterocyclic systems for several optoelectronic applications2 we report the synthesis and characterization of phthalazine derivatives functionalized with cyanoacetic or rhodanine-3-acetic acid as anchoring groups. The experimental results indicate that, these compounds could have potential application as sensitizers for DSSCs.Thanks are due to Fundação para a Ciência e Tecnologia (FCT-Portugal) and
FEDER-COMPETE for financial support through Centro de Química PEst-C/QUI/UI0686/2011 (FCOMP-01-0124-FEDER-022716),
a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The
NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within
the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005
with funds from POCI 2010 (FEDER) and FCT.info:eu-repo/semantics/publishedVersio

Fernandes, Sara Sofia Marques

Synthesis and characterization of novel phthalazine based push-pull heterocyclic systems for DSSC

Synthesis and characterization of novel phthalazine based push-pull heterocyclic systems for DSSC  Sara S. M. Fernandes, M. Manuela M. Raposo* Centre of Chemistry, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal Email: mfox@quimica.uminho.pt  Abstract: Research on renewable energy sources and sustainable development have been expanding considerably in order to decrease the consumption of fossil fuels and therefore reduce global warming and environmental pollution. Solar energy is an excellent source due to its inexhaustibility and cleanness, and can be directly transformed into electric energy through photovoltaics, namely the most promising organic solar cells. Solar cells based on organic dye sensitizers (DSSCs) adsorbed on monocrystalline TiO2 electrodes have been extensively studied due to their high incident solar light-to-electricity conversion efficiency, colourful and decorative natures and low cost of production. Wide-ranging research has been conducted on structural modifications of the sensitizing dyes in the interest of achieving chromophores with high performance for DSSCs1. One approach for structural tuning consists on adjusting the -bridge with electron rich and/or electron deficient aromatic rings that can perform as an auxiliary electron donor/acceptor group. Electron-rich thiophene and furan heterocycles linked to the electron-deficient phthalazine ring substituted with appropriate acceptor groups are promising candidates among such push-pull systems1b, 2, 3. As part of an on-going research to develop efficient donor – π-spacer – acceptor heterocyclic systems for several optoelectronic applications2 we report the synthesis and characterization of phthalazine derivatives functionalized with cyanoacetic or rhodanine-3-acetic acid as anchoring groups. The experimental results indicate that, these compounds could have potential application as sensitizers for DSSCs.  Acknowledgements: Thanks are due to Fundação para a Ciência e Tecnologia (FCT-Portugal) and FEDER-COMPETE for financial support through Centro de Química PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716), a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT.  References 1- a) Ning, Z.; Fu, Y.; Tian, H., Improvement of dye-sensitized solar cells: what we know and what we need to know. Energy & Environmental Science 2010, 3 (9), 1170-1181. b) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H., Dye-Sensitized Solar Cells. Chemical Reviews 2010, 110 (11), 6595-6663. c) Gonçalves, L. M.; de Zea Bermudez, V.; Ribeiro, H. A.; Mendes, A. M., Dye-sensitized solar cells: A safe bet for the future. Energy & Environmental Science 2008, 1 (6), 655-667. 2- a) Castro, M. C. R.; Schellenberg, P.; Belsley, M.; Fonseca, A. M. C.; Fernandes, S. S. M.; Raposo, M. M. M. Design, synthesis and evaluation of redox, second order nonlinear optical properties and theoretical DFT studies of novel bithiophene azo dyes functionalized with dithiazole acceptor groups. Dyes Pigments 2012, 95(2): 392-399. b) Castro, M. C. R.; Belsley, M.; Fonseca, A. M. C.; Raposo, M. M. M. Synthesis and characterization of novel second-order NLO-chromophores bearing pyrrole as an electron donor group. Tetrahedron 2012, 68(39): 8147-8155. 3- Raposo, M. M. M., Sampaio; A. M. B. A.; Kirsch, G. A convenient access to thienyl-substituted phthalazines", J. Heterocyclic Chem. 2005, 42(7): 1245-1251. 

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Design, synthesis and characterization of novel thienylpyridazine derivatives for optical applications

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