Theoretical understanding of the increment of upon protonation of pyridine peripheral octupolar molecules: Toward nonlinear optical sensors

6 pages, 6 tables, 4 figures.In this article, we present a computational study of the nonlinear optical properties of pyridine-based octupolar molecules in their neutral and fully triprotonated states. The effect of the core substitution and the degree of conjugation with the periphery has been also established and confirms the possibility of fine-tuning the nonlinear optical response. Computations involving the time-dependent density-functional theory approach serve to further explore the existence of excited states with nonzero dipole moment. From these results, the origin of the high second-order nonlinear optical activity upon protonation is addressed.The present work was supported in part by the Dirección General de Enseñanza Superior DGES, MEC, Spain through research Project Nos. CTQ2006-14987-C02-01 and CTQ2005-01368. The authors are also indebted to Junta de Andalucía and Gobierno de Aragón Spain for funding their research groups FQM-0159 and E39. M.C.R.D. is grateful to the MEC/Fulbright for her Postdoctoral Fellowship at the Georgia Institute of Techology. J.C. is grateful to the MEC of Spain for an I3 professorship position of Chemistry at the University of Málaga and M.M.O. acknowledges the MEC for a personal grant.Peer reviewe

Tuning the Diradical Character of Indolocarbazoles: Impact of Structural Isomerism and Substitution Position

In this study, a set of 10 positional indolocarbazole (ICz) isomers substituted with dicyanomethylene groups connected via para or meta positions are computationally investigated with the aim of exploring the efficiency of structural isomerism and substitution position in controlling their optical and electronic properties. Unrestricted density functional theory (DFT), a spin-flip time-dependent DFT approach, and the multireference CASSCF/NEVPT2 method have been applied to correlate the diradical character with the energetic trends (i.e., singlet–triplet energy gaps). In addition, the nucleus-independent chemical shift together with ACID plots and Raman intensity calculations were used to strengthen the relationship between the diradical character and (anti)aromaticity. Our study reveals that the substitution pattern and structural isomerism represent a very effective way to tune the diradical properties in ICz-based systems with meta-substituted systems with a V-shaped structure displaying the largest diradical character. Thus, this work contributes to the elucidation of the challenging chemical reactivity and physical properties of diradicaloid systems, guiding experimental chemists to produce new molecules with desirable properties.Funding for open access charge: Univesidad de Málaga/CBUA. The work at the University of Málaga was funded by the MICINN (PID2019-110305GB-I00) and Junta de Andalucía (UMA18-FEDERJA-080, P09FQM-4708, and P18-FR-4559) projects. The authors thankfully acknowledge the computer resources, technical expertise, and assistance provided by the SCBI (Supercomputing and Bioinformatics) centre of the University of Málaga. The work at the University of Alicante was supported by the MICINN (PID2019-106114GB-I00). The work at the University of Bologna was supported by University of Bologna (RFO) funds

Enhanced functionality for donor-acceptor oligothiophenes via Inclusion of BODIPY : synthesis, electrochemistry, photophysics and model chemistry

We have synthesized several new push-pull oligothiophenes based on the BODIPY moiety as the electron acceptor and the well known oligothiophenes substituted with N,N-dialkylamino groups to enhance the electron donor ability. A complete characterization of the electronic properties has been done consisting of their photophysical, electrochemical and vibrational properties. The compounds have been studied after chemical treatment with acids and after oxidation. In this regard, they can be termed as NIR dyes and amphoteric redox electroactive molecules. We have described the presence of dual fluorescence in these molecules and fluorescence quenching either by energy transfer or, in the push-pull molecules, by the electron exchange. The combination of electrochemical and proton reversibility combined with the interesting optical properties of the new species offer an interesting platform for sensor and material applications.DGES, MEC (Spain) and Fundação para a Ciência e a Tecnologia (FCT

D-π-A compounds with tunable intramolecular charge transfer achieved by incorporation of butenolide nitriles as acceptor moieties

Chromophores where a polyenic spacer separates a 4H-pyranylidene or benzothiazolylidene donor and three different butenolide nitriles have been synthesized and characterized. The role of 2(5H)-furanones as acceptor units on the polarization and the second-order nonlinear (NLO) properties has been studied. Thus, their incorporation gives rise to moderately polarized structures with NLO responses that compare favorably to those of related compounds featuring more efficient electron-withdrawing moieties. Derivatives of the proaromatic butenolide PhFu show the best nonlinearities. Benzothiazolylidene-containing chromophores present less alternated structures than their pyranylidene analogues, and, unlike most merocyanines, the degree of charge transfer does not decrease on lengthening the π-bridge.Financial support from MICINN-FEDER (CTQ2011-22727 and MAT2011-27978- C02-02), MINECO (CTQ2014-52331R), and Gobierno de Aragon-Fondo Social Europeo (E39 and E04) is gratefully acknowledged. Research at the Universidad de Malaga was supported by MINECO (CTQ2012-33733) and Junta de Andalucıa (P09-4708).Peer Reviewe

Quantum chemical DFT and spectroscopic UV-Vis-NIR analysis of a series of push-pull oligothiophenes end capped by amino-cyanovinyl groups

A series of push-pull chromophores built around thiophene-based -conjugating spacers and bearing various types of amino-donors and cyanovinyl-acceptors have been analyzed by means of UV-Vis- NIR spectroscopic measurements. Density functional theory (DFT) calculations have also been performed to help the assignment of the most relevant electronic features and to derive useful information about the molecular structure of these NLO-phores. The effects of the donor/acceptor substitution in the electronic and molecular properties of the -conjugated spacer have been addressed. The effectiveness of the intramolecular charge transfer (ICT) has also been tested as a function of the nature of the end groups (i.e., electron-donating or electron-withdrawing capabilities).Research at the University of Málaga was supported by the Ministerio de Educación y Ciencia (MEC) of Spain through project CTQ2006-14987-C02-01, and by the Junta de Andalucía for funding our FQM- 0159 scientific group. J.C. is grateful to the Ministerio de Ciencia y Tecnología of Spain for a Ramón y Cajal position of Chemistry at the University of Málaga. M.C.R.D. is also grateful to the Ministerio de Educación y Ciencia of Spain for a personal grant. The group at the University of Minho acknowledges the Foundation for Science and Technology (Portugal) for financial support through Centro de Química (UM) and through POCTI, FEDER (ref. POCTI/QUI/37816/2001). M. Manuela M. Raposo and A. Maurício C. Fonseca are also grateful to Professor G. Kirsch from University of Metz (France) for his collaboration

Combined theoretical and spectroscopic Raman study of 3,4-ethylenedioxy and S,S-dioxide substituted terthiophenes and their parent polymers

Abstract This paper reports on the analysis of the Raman spectra, supported by DFT quantum chemical calculations, of a series of terthiophenes which present the novelty of being selectively functionalized with sulfone groups to increase their photoluminescence properties. The spectra have been carefully assigned on the basis of the theoretical vibrational eigenvectors. They suggest the occurrence of a segmentation of the electronic structure which can become a crucial feature for optimizing linear and non linear optical properties. Sulfonation fixes the two lone electron pairs of the sulfur atom, in particular that involved in the aromatization of the thiophene ring, thus coexisting two different kind of five member (aromatic and non aromatic) units in the same chain. This duality of the structure gives rise to the splitting of the characteristic Raman lines associated to the CaC/C-C stretching modes into components mainly located either on the external rings or on the internal one. The study also focuses on the electrosynthesized polymers obtained upon electropolymerization of the corresponding terthiophenes.

Optical Absorption and Emission Properties of End-capped Oligothienoacenes: A Joint Theoretical and Experimental Study

The electron–vibration coupling in a family of silyl end-capped oligothienoacenes is investigated on the basis of a joint experimental and theoretical study using UV–vis absorption and emission spectroscopies and density functional theory calculations. Well-resolved vibronic progressions are found in the low-temperature absorption and emission profiles of these silyl-functionalized organic molecules. As the size of the oligomer lengthens a bathochromic shift is observed in the near-UV–vis range, indicative of the extension of the effective π-conjugation. The absorption and emission bands are practically mirror-symmetric. The combination of two normal modes with frequencies of $\sim 1500 cm^{−1}$ and $\sim 500 cm^{−1}$ determines the main vibronic progression in absorption and emission for all the series, although for larger oligomers (n = 6, 7, and 8) the presence of low-frequency normal modes ($\sim100 cm^{−1}$) is also evident. The spacing of the vibrational features is slightly larger in absorption than in emission; this agrees with the predicted shifting of the C−C stretching modes of the inner-most ring toward the high-frequency region as a result of the reversal of the single–double C−C pattern in the electronic excited-state. Our calculations indicate that the contributions of the end-capping groups to the total relaxation energy of the $S_0 \rightarrow S_1$ and $S_1 \rightarrow S_0$ transitions are almost negligible. This result suggest that the vibronic structure and to a large extent the spectral profiles of the silyl end-capped oligothienoacenes are mainly determined by their respective oligothienyl core.Chemistry and Chemical Biolog

Carbazole and indolcarbazole-based systems: impact of the structural changes on the system properties

π-Conjugated diradical compounds, featuring unique unsaturated valences and radical centres in the ground state, are fundamentally important for understanding the nature of chemical bonds and have potential applications in material science [1] . During the last decade, there has been an increasing interest in the rationalization of how the structural changes stabilize (or destabilize) the diradical system. The tunability of the diradical character has been studied for different structural motifs such as the substitution pattern of lateral groups[2], the elongation of the conjugated core[3] or the molecular isomerism[4], among others. In this sense, we have recently reported an experimental/theoretical study of a family of carbazole-based diradicaloids with dicyanomethylene (DCM) groups incorporated via para (p-Cz and p-ICz) or meta positions (mCz and m-ICz) aiming to investigate how external stimuli impact on the molecular structure and supramolecular organization, and thus on the resulting optical and electronic properties. In addition, we theoretically investigate at the DFT level a set of ten indolocarbazole-based isomers substituted with DCM groups to disclose how their chemical reactivity and physical properties are affected by isomerism and different substitution pattern.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Plan Propio de Investigación de la UM

Reversible Dimerization/Polymerization of a Janus Diradical Producing Labile CC Bonds and Giant Chromism

En esta comunicación se presenta el estudio espectroscópico y téorico de la dimerización/oligomerización reversible de un birradical derivado de naftoditiofeno el cual en su forma monomérica presenta una intenso color azul mientras que al agregar se muestra incoloro, siendo éstas formas intercambiables gracias a la aplicación de estímulos débiles como presión o temperatura.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Amplified Spontaneous Emission in Pentathienoacene Dioxides by Direct Optical Pump and by Energy Transfer: Correlation with Photophysical Parameters

Amplified spontaneous emission (ASE) is observed, under optical pump, in polystyrene films doped with two pentathienoacene derivatives functionalised with thienyl-S,S-dioxide groups (compounds 2 and 3). The effect of the dioxide groups on the ASE properties is analysed by comparing the performance with that of its corresponding non-oxidized analogue (1). Films containing either 2 or 3 show ASE at 511 and 574 nm, respectively, when excited directly (at 435 nm) on their absorption bands, showing thresholds and linewidths larger than those obtained from films doped with 1, pumped at 355 nm. ASE is also observed under excitation at 355 nm, in samples containing 1 (host) and either 2 or 3 (guests), due to energy transfer from host to guest. For the blends with 3, the ASE threshold is lower than that obtained when the films are excited directly. Results are interpreted in terms of the photophysical parameters such as absorption capacity, fluorescence efficiency, singlet-to-triplet intersystem crossing leading to triplet-triplet re-absorptions, bimolecular energy-transfer efficiency, efficiency of internal conversion process, etc. State-of-the-art quantum chemical calculations are used in the interpretation of the experimental results.Authors from the University of Alicante acknowledge support from the Spanish Government (MINECO) and the European Community (FEDER) through grants MAT2008–06648-C02–01 and MAT2011–28167-C02–01. The work at the University of Málaga is supported by the MEC projects CTQ2012–33733 and by the PO9–4708 project by the Junta de Andalucía. Raquel Rondão acknowledges FCT for a PhD grant (SFRH/BD/38882/2007). D.A.S.F. gratefully acknowledges the financial support from the Brazilian Research Councils: CAPES, CNPq (grant 303084/2010–3) and FAP-DF (Fundação de Apoio à Pesquisa do Distrito Federal)