Photochemical control of rheology

The main objective of the research work developed in the framework of this PhD thesis was the preparation and development of novel photorheological fluids. This was pursued following two distinct strategies. The first one focused on the synthesis of tripodal compounds functionalized with photodimerizable moieties of cinnamic acid, coumarin and anthracene. Two sets of compounds were prepared, varying the central unit as well as spacers resulting in molecules with different solubilities and molecular weight. All compounds were characterized towards their photochemical properties and all exhibited photoreactivity upon irradiation with ultra-violet light. In particular, both coumarin derivatives exhibited the greatest photopolymerization reactivity, resulting in the formation of dendrimeric nanoparticles or in the increase of viscosity of organic solutions. The second strategy was focused on the careful design of photosensitive ionic liquids, based on the results of several quantitative structure-property relationship studies. Thus, photosensitive ionic liquids were synthesized bearing cinnamic acid or coumarin moieties in the organic cation. Upon irradiation, all compounds exhibited reactivity, which resulted in changes in their physical properties, such as melting point or viscosity. In addition, novel coumarin chromophores with different photophysical and photochemical properties were developed. It is expected that these compounds may find application in the preparation of new photosensitive ionic liquids

Convenient Synthesis of 3-Vinyl and

A variety of 2-hydroxy aldehydes on reaction with 3-butenoic acid afford in a one-pot reaction the corresponding 3-vinylcoumarins. As expected, extension of the delocalized π-electron system accomplished by Heck coupling reactions with aryl halides results in an increased fluorescence of the compounds whose applicability is yet to be established

Síntese de sais de benzopirílio e aplicação como sensores fluorescentes e grupos protectores fotocliváveis

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Bioorgânica, especialidade em Química Fina.O trabalho de investigação elaborado no âmbito desta dissertação de Mestrado, teve como objectivo a síntese e aplicação de sais de flavílio funcionalizados na posição 4 como grupos protectores fotocliváveis ou sensores fluorescentes de concentração micelar crítica. Inicialmente, pretendia-se aplicar derivados do 4-hidroximetil-flavílio como grupos protectores para a libertação de fosfatos por aplicação de estímulos luminosos. Tendo-se verificado que tal não era possível, foram preparados derivados do 4- fenoximetil-flavílio e as suas propriedades fotoquímicas foram avaliadas. Foram igualmente sintetizados vários 4-alquil-flavílios que foram aplicados na medição de viscosidade de fluidos e determinação da concentração crítica micelar de surfactantes por espectrofluorimetria. Estes compostos mostraram ainda um acidocromismo reversível que pode ser controlado pela temperatura na presença de copolímeros do tipo Pluronic®, permitindo o desenvolvimento de sistemas termocrómicos. Todos os compostos aplicados em estudos espectroscópicos foram caracterizados por técnicas correntes como espectroscopia de RMN, análise elementar e absorção em UV/Vis

Aggregation induced emission of a new naphthyridine-ethynyl-gold(I) complex as a potential tool for sensing guanosine nucleotides in aqueous media

A new organometallic alkynyl-gold(I) complex, capable of exhibiting Aggregation Induced Emission was designed and synthesized. The linear complex structure possesses a central Au(I) atom, bearing two axial ligands: (1) 1,3,5-Triaza-7-phosphaadamantane; and (2) 2- acetamido-7-ethynyl-1,8-naphthyridine. While the former accounts for its partial solubility in aqueous environment, the latter acts as a receptor unit for binding guanosine nucleotides and derivatives via multiple hydrogen bonding. At high concentrations, aggregation of the complex was observed by the formation of new absorption (λmax ~ 400 nm) and emission bands (550-700 nm). Formation of aggregates of ca. 60 nm diameter was confirmed with Small Angle X-Ray Scattering (SAXS). Disruption of the aggregates in the presence of guanosine derivatives resulted in a ratiometric signal with apparent association constants in the order of 105 M-1 and high sensitivity (around 63% signal change) which are, to the best of our knowledge, in line with the highest recorded for nucleotide sensing based on hydrogen bonding that are capable of working in water. Computational studies indicate the presence of additional hydrogen bonding interactions that account for the strong binding of the Au(I) complex to phosphorylated Guanosine nucleotides

Lanthanide-based complexes as efficient physiological temperature sensors

A new molecular thermometric sensor based on the terbium(III) complex [C2mim][Tb(fod)4] (C2mim – 1-methyl-3-ethylimidazolium, fod− - tetrakis-6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate), doped with 0.015% of its europium(III) analogue (1, [C2mim][Tb(fod)4]0.99985:[C2mim][Eu(fod)4]0.00015), was prepared and its thermochromic behaviour evaluated from ambient temperature up to 75 °C, including in the physiological range (35–45 °C). It was found that the intensity ratio of the 5D4→7F5 (TbIII) and 5D0→7F2 (EuIII) transitions is correlated with temperature having three different linear regimes. Visual colorimetry allowed the evaluation of the temperature in different ranges from green at ambient temperature, to yellow and finally red at higher temperatures. The TbIII complex emission intensity is extremely sensitive to small temperature variations, particularly between 25 and 35 °C, were it reaches only 40% of the initial intensity. Confinement of the dopped TbIII tetrakis-complex in the organic polymeric matrix poly(methylmethacrylate) (PMMA) induced higher thermal stability in 1, together with a strong temperature dependence of the most intense emissive transition of the TbIII complexes. The photoluminescence quantum yield of polymer-lanthanide hybrid materials increased significantly compared with that of 1. Under 366 nm irradiation, the hybrid material presents a green colour at 25 °C that evolves to yellow at 30 °C and to a white tone at 35 °C.publishe

Long-lived NIR emission in sulfur-doped zeolites due to the presence of [S3]2- clusters

Funding Information: The authors want to acknowledge the Portuguese Foundation for Science and Technology for funding through the grants SFRH/BD/145009/2019 and SFRH/BPD/120599/2016 , the individual contract 2020.00252. CEECIND and several projects PTDC/QUI-QFI/32007/2017, UIDB/04565/2020, UIDP/04565/2020, LA/P/0140/2020, LAQV-REQUIMTE (LA/P/0008/2020, UIDB/50006/2020 and UIDP/50006/2020), VICARTE (UIDP/00729/2020, UIDB/00729/2020) and C2TN (UIDB/04349/2020). MOSTMICRO-ITQB R&D Unit (UIDB/04612/2020, UIDP/04612/2020) and LS4FUTURE Associated Laboratory (LA/P/0087/2020) and by European Union's Horizon 2020 research and innovation program under grant agreement No. 810856. Funding Information: The authors want to acknowledge the Portuguese Foundation for Science and Technology for funding through the grants SFRH/BD/145009/2019 and SFRH/BPD/120599/2016, the individual contract 2020.00252. CEECIND and several projects PTDC/QUI-QFI/32007/2017, UIDB/04565/2020, UIDP/04565/2020, LA/P/0140/2020, LAQV-REQUIMTE (LA/P/0008/2020, UIDB/50006/2020 and UIDP/50006/2020), VICARTE (UIDP/00729/2020, UIDB/00729/2020) and C2TN (UIDB/04349/2020). MOSTMICRO-ITQB R&D Unit (UIDB/04612/2020, UIDP/04612/2020) and LS4FUTURE Associated Laboratory (LA/P/0087/2020) and by European Union's Horizon 2020 research and innovation program under grant agreement No. 810856. Publisher Copyright: © 2023 The Author(s)The exploration of novel long-lived near-infrared (NIR) luminescent materials has attracted significant attention due to their applications in optical communications, anticounterfeiting, and bioimaging. However, these materials usually present low photoluminescence quantum yields and low photo- and chemical stability. Novel emitters that overcome these limitations are in demand. In this study, NIR emission was achieved using widely available, sustainable, and non-toxic materials through the synthesis of sulfur-doped zeolites, with different S/Cl ratios. With a combination of computational calculations (TD-DFT) and spectroscopic data, this emission was assigned to the radiative decay of excited triplet states of [S3]2- clusters, which resulted in a remarkably high Stokes shift (1.97 eV, 440 nm) and an average decay time of 0.54 ms. These new materials present high stability, external quantum efficiency of up to 17%, and a long-lived NIR emission, placing these compounds in a unique position to be used in applications demanding NIR emitters.publishersversionpublishe

Multifunctionality of the [C2mim][Ln(fod)4] series (Ln = Nd-Tm except Pm):magnetic, luminescent and thermochemical studies

A series of nine tetrakis lanthanide β-diketonate complexes of the type [C2mim][Ln(fod)4] (C2mim = 1-ethyl-3-methylimidazolium, fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) were prepared, with yields above 80%, and their thermochemical, photophysical and magnetic susceptibilities were evaluated. Thermochemical studies presented a rare and reversible conversion between two solid phases (polymorphism), characteristic of the [Ln(fod)4]− anion. Photophysical and magnetic studies revealed that Dy and Er presented the multifunctionality of being simultaneously SMMs and visible (Dy) or near infra-red (Er) emitters. The Nd, Ho and Tm analogues present characteristic emission bands in the NIR region (800–1200 nm), while Sm, Eu, Tb and Dy present emissions in the visible range. Magnetic susceptibility of Tb, Dy, Ho, Er and Tm salts were measured in the temperature range of 2–300 K, showing paramagnetic behaviour, although with different regimes, with AC susceptibility measurements, at different frequencies in the range of 10–10 000 Hz, providing evidence of slow magnetic relaxation processes for Gd, Dy and Er analogues with SMM behavior.publishe

The contributions of molecular vibrations and higher triplet levels to the intersystem crossing mechanism in metal-free organic emitters.

Intense, simultaneous, room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) is observed in a series of donor-acceptor-donor (D–A–D) molecules. This dual-luminescence is stronger in the “angular” isomers, compared to their “linear” regioisomers, which is consistent with an enhanced intersystem crossing (ISC) in the former. Herein, we demonstrate that the small energy gap between the triplet levels, T1-Tn, below the lowest singlet state, S1, in the “angular” regioisomers, enhances the coupling between S1 and T1 states and favors ISC and reverse ISC (rISC). This is consistent with a spin-vibronic mechanism. In the absence of this “triplet ladder”, due to the larger energy difference between T1 and Tn in the “linear” regioisomers, the ISC and rISC are not efficient. Remarkably the enhancement on the ISC rate in the “angular” regioisomers is accompanied by an increase on the rate of internal conversion (IC). These results highlight the contributions of higher triplet excited states and molecular vibronic coupling to harvest triplet states in organic compounds, and casts the TADF and RTP mechanisms into a common conceptual framework

Synthesis, Absortion and Emission Properties of a New Family of Styryl Coumarins. Potential Utility as Memory Media

SYNTHESIS, ABSORPTION AND EMISSION PROPERTIES OF A NEW FAMILY OF STYRYL COUMARINS. POTENTIAL UTILITY AS MEMORY MEDIA Sérgio Martins,[a] João Avó, [b] A. Jorge Parola, [b] João C. Lima, [b] Paula S. Branco[b] and António Pereira[a] [a] Centro de Química, Departamento de Química, Universidade de Évora, Évora, Portugal, [email protected] [b] REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Portugal Photochromism, the reversible transformation between two molecular forms that have different absorption spectra, resulting from photo-irradiation, has applicability in several fields including light modulation materials, optical recording materials, optical switches and photochromic ink.[1] The switching from one molecular state to another is dependent upon the efficiency of light absorption by the chromophore. Coumarins are an old class of compounds of natural occurrence in several plant families. On substitution with various functional groups at different positions the coumarin chromophores expand their interesting proprieties. In recent years we have devoted some interest to the study of coumarin chromophores, with special emphasis on their synthesis and photophysical properties.[2] We have been particularly interested in the extension of the -delocalized system of the coumarin chromophore at the 3-position which allowed us to obtain derivatives with promising fluorescent behavior. Here we present the synthesis of a new coumarin family, the 5-styryl coumarins 1 and the study of the effect of the extension of the -delocalized system of the coumarin chromophore at the 5-position (Fig.1). The synthesized compounds present E-Z isomerization around the carbon-carbon double bond which can potentially be envisaged to be used as a memory media. Figure1 Acknowledgments: Thanks are due to the Fundação para a Ciência e Tecnologia (Portugal), for partial financial support FCOMP-01-0124-FEDER-007448. [1] a) H. Bouas-Laurent, H. Durr, Pure Appl. Chem. 2001, 73, 639-665; b) V. I. Minkin, Chem. Rev. 2004, 104, 2751-2776; c) M. Irie, Chem. Rev. 2000, 100, 1685-1716. [2] a) J. Gordo, J. Avó, A. J. Parola, J. C. Lima, A. Pereira, P. S. Branco, 2011, 13, 5112–5115; b) S. M. A. Martins, P. S. Branco, A. M. D. R. L. Pereira, J. Braz. Chem. Soc. 2012; c) S. Martins, P. S. Branco, M. C. de la Torre, M. A. Sierra, A. Pereira, Synlett 2010, 2918-2922

Challenges in teaching organic chemistry remotely

The coronavirus disease (COVID-19) pandemic has changed not only people’s daily lives but also the education system. The rise of e-learning all across the world has challenged both students and teachers to adapt to digital technologies and a novel learning experience on both sides. As if COVID-19 was not enough, many students were facing the alien territory of organic chemistry for the first time. There is no denying that organic chemistry is a tough subject, and several students may also have preconceived misconceptions. In addition, organic chemistry can be challenging to teach remotely. It is very abstract in nature; it involves many concepts, and the teacher typically uses molecular models of one kind or another to depict molecules in three dimensions. Nonetheless, challenges provide an opportunity to implement new strategies to increase students’ interest, motivation, and understanding. However, most educators only had a few days to put everything they do in class onto an online platform. In this study, we evaluated the effect of these changes in the teaching and learning of organic chemistry at a first-year undergraduate level. Our results show that student success depends on the digital resources used for the different subjects. Students that received weekly quizzes performed better than those who did not, and a positive correlation exists between quiz scores and final exam marks. Based on the students’ feedback, the implementation of quizzes was a successful didactic tool that helped them review the topics. In addition, the incorporation of open-access web-based tools led to a dynamic online classroom experience.info:eu-repo/semantics/publishedVersio