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In this contribution, a series of seven new push–pull systems has been designed by combining a protonable diazine heterocycle (pyrimidine/pyrazine) with a deprotonable phenol unit through various π-conjugated linkers (phenylene, thienylene, thienylenevinylene, and phenylenevinylene). The (de)protonation in solution resulted in a systematic bathochromic shift both in the absorption and emission maxima compared to the neutral forms. Extensive Density Functional Theory (DFT) and its Time Dependent counterpart (TD-DFT) calculations were performed to rationalize this behavior and understand the impact of (de)protonation on the different optical transitions. These computations showed that (de)protonation affects both the energy and the nature of the vertical transitions, with a significant increase in the Intramolecular Charge Transfer (ICT) character of the (de)excitations. Some of the compounds remained moderately luminescent after (de)protonation, giving a mixture of complementary emitting species that were used to obtain white light emission. [ABSTRACT FROM AUTHOR]

A series of four V-shaped methylpyrimidinium salts bearing diphenylamino-electron-donating groups appended at various pyrimidine positions were designed. These chromophores were obtained by regioselective N(1) monomethylation by methyl methanesulfonate of the pyrimidine core. Linear optical properties were studied experimentally and electronic properties were further completed by (TD)-DFT calculations. The second-order nonlinear optical (NLO) properties were also studied using electric field induced second harmonic generation (EFISH) method in chloroform, and all pyrimidinium salts exhibited μβ0>1000×10-48 esu. The 2,4-disubstituted pyrimidinium core is preferred over 4,6-disubstitution as it enhances the NLO response and increases the dipole moment. (E,E)-2,4-Bis[4-(diphenylamino)styryl]-1-methylpyrimidin-1-ium methanesulfonate appears to be the best NLO-phore in chloroform in the series (μβ0=2500×10-48 esu) and a figure of merit μβ0/MW= 3.4 10-48 esumolg-1. [ABSTRACT FROM AUTHOR]

The photophysical properties of a series of conjugated push–pull (iso)quinolines were studied. The compounds were synthesized by well‐established and straightforward methodologies. The materials exhibited not only emission solvatochromism in a variety of nonpolar solvents, but also tunable halochromism. Some of the compounds remained moderately luminescent after protonation and had a red emissive form, which was used to obtain white‐light emission, both in solution and in thin films, by controlled protonation of the initially blue–green‐emitting materials. This methodology has potential applications in the fabrication of white organic light‐emitting diodes with two forms of a single emitter in equilibrium. [ABSTRACT FROM AUTHOR]

Conjugated push‐pull molecules that incorporate nitrogen heterocycles as electron‐withdrawing units are interesting materials because of their luminescence properties. These chromophores can be easily and reversibly protonated at the nitrogen atom of the heterocyclic ring and this can cause dramatic color changes. White and multi‐color photoluminescence both in solution and in the solid state can be obtained by an accurate control of the amount of acid. Thus, with a suitable design these compounds have potential applications in the development of colorimetric pH sensors and the fabrication of OLEDs based on only one material. We provide here a brief overview of our collaborative efforts made in this area. [ABSTRACT FROM AUTHOR]

Efficient synthetic routes that combine different palladium‐catalyzed cross‐coupling reactions have been developed for the preparation of a new family of push‐pull derivatives in which pyridine was used as the acceptor group and different para‐substituted diphenylamines as the donor groups. All compounds showed absorption in the UV/Vis region and blue‐green emission with high quantum yields. Significant red shifts were observed in the absorption and fluorescence emission maxima on increasing the electron‐donating ability of the substituents or on incorporating a π‐conjugated linker. This finding can be explained on the basis of enhanced intramolecular charge transfer (ICT). Strong emission solvatochromism confirmed the formation of an intramolecular charge‐separated emitting state. The HOMO‐LUMO energy gaps have been estimated by experimental electrochemical measurements and the results were interpreted with the aid of DFT calculations. The thermal behavior of all materials has also been studied by differential scanning calorimetry. A series of push‐pull chromophores with a pyridine electron‐withdrawing fragment and methoxy‐, 9H‐carbazol‐9‐yl‐, and 5‐methoxythiophen‐2‐yl‐substituted diphenylamino groups as electron‐donating units was designed. [ABSTRACT FROM AUTHOR]

This article presents the photophysical properties of a series of diazine chromophores. The influence of five parameters has been studied: the presence of a diazine/benzodiazine fragment, the nature of the diazine fragment (1,3-diazine/1,4-diazine), the presence or not of an vinyl linker between diazine ring and phenylene fragments of the π-conjugated bridge, the presence of a phenylene/biphenylene linker and the nature of electron donating group (dimethylamino/diphenylamino). Taguchi's design of experiment combined with analysis of variance methodologies have been employed to highlight the main structural parameters influencing the position of absorption and emission maxima of dichloromethane solution and the extend of emission solvatochromic range exhibited by this family of chromophores. [ABSTRACT FROM AUTHOR]

In this article, we describe the synthesis, redox characteristics, and linear and nonlinear optical (NLO) properties of seven new unsymmetrical push–pull diacetylide platinum-based complexes. These D–π-Pt–π-A complexes incorporate pyranylidene ligands as pro-aromatic donor groups (D), diazine rings as electron-withdrawing groups (A), and various aromatic fragments (styryl or thienylvinyl) as π-linkers separating the platinum diacetylide unit from the donor and the acceptor groups. This is one of the first examples of push–pull chromophores incorporating a platinum center in the π-conjugated core. The NLO properties of these complexes were compared with those of their purely organic analogues. All compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased upon methylation of the pyrimidine fragment. However, this increase was even more significant in the complexes due to the presence of platinum in the π-conjugated core. The effects of the linker on the redox and spectroscopic properties of the complexes are also discussed. In addition, DFT calculations were performed in order to gain further insight into the intramolecular charge transfer (ICT) occurring through the platinum center. [ABSTRACT FROM AUTHOR]

BODIPY-based chromophores, in which an electron withdrawing difluoro-boraindacene fragment is connected via position 8 to different donor fragments, were synthesized. Their electrochemical and photophysical properties were studied. All compounds exhibit a quasi-reversible oxidation corresponding to the formation of a BODIPY π-radical cation at around 0.8 V vs. FeCp2+/FeCp2 that is slightly sensitive to the nature of the electron donating group. A reversible reduction is observed around−1.6 V vs. FeCp2 +/FeCp2 corresponding to the formation of the BODIPY π-radical anion. Cyclic voltammetry analysis of a γ-methylenepyran substituted BODIPY indicates the formation of redox bistable system with high bistability. In dichloromethane solution, the chromophores exhibit an intense absorption band around 502 nm and an emission in the 516-528 nm range. A significant emission quench is observed in case of amino and γ-methylenepyran substituents. [ABSTRACT FROM AUTHOR]

The synthesis of a series of push-pull arylvinyl (styryl), aryl, and arylethynyl quinazoline derivatives by means of different straightforward protocols is reported. The photophysical properties of the compounds are described. The preparation of arylvinylquinazolines was performed by aldol condensation of the appropriate methylquinazoline and functionalized benzaldehyde. Suzuki and Sonogashira cross-coupling reactions were used to prepare the aryl and arylethynyl compounds, respectively, starting from chloroquinazolines. Optical studies revealed that all of the compounds reported here behave in a way similar to that of their pyrimidine counterparts, with absorption bands in the UV or visible region and the emission of green light upon irradiation. Large red shifts were observed in the fluorescence emission maxima upon increasing the solvent polarity. This strong emission solvatochromism suggests the formation of an intramolecular charge-separated emitting state. The materials can be easily and reversibly protonated at the nitrogen atoms of the heterocyclic ring, and this causes dramatic color changes. This phenomenon opens up the possibility of developing colorimetric pH sensors that can be efficiently modified a posteriori for specific applications. [ABSTRACT FROM AUTHOR]

Fifteen new push-pull chromophores based on a proaromatic pyranylidene donor and its chalcogen analogues and various electron acceptor moieties were synthesized in a straightforward manner. These model molecules were designed and prepared to investigate the concept of proaromaticity as a tool to tune the fundamental properties of push-pull systems. All target chromophores with systematically varied structure were further investigated by electrochemistry, absorption spectra, and EFISH experiment in conjunction with DFT calculations. Employing structural variations such as chalcogen/acceptor replacement, extension of the π-system, and the position of substitution along the pyran ring, the HOMO-LUMO gap can be tuned within the range of 2.18 to 1.41 eV. A new and powerful electron withdrawing moiety, combining features of polarizable thiophene and successful indane-1,3-dione acceptor, cyclopenta[ c ]thiophen-4,6-dione (ThDione) has also been developed. [ABSTRACT FROM AUTHOR]

A series of five octupolar molecules with central triphenylamine donor and peripheral diazine electron-withdrawing groups has been prepared. These structures possess extended π-spacer comprising multiple bonds in a combination with 1,4-phenylene and 2,5-thienylene subunits. Starting from tris(4-ethynylphenyl)amine, the key step in the preparation of the chromophores involves triple Sonogashira cross-coupling reaction. The photophysical properties of the compounds are described. A strong positive emission solvatochromism, typical for dyes featuring Intramolecular Charge Transfer (ICT), is observed, two-photon absorption (2 PA) properties were also measured. Linear and nonlinear optical properties as well as electronic properties measured by cyclic voltametry and supported by DFT calculation were used to elucidate structure–property relationships. [ABSTRACT FROM AUTHOR]

This paper presents the photophysical properties of a series of pyrimidine chromophores. The influence of three parameters has been studied: the nature of the electron-donating group and of the π-conjugated linker as well as the substituted position of the pyrimidine core (2, 4 and 6 position). Taguchi design of experiment combined with analysis of variance methodologies have been employed. This approach has permitted to highlight the main factor affecting the absorption and emission wavelengths of the studied compounds. Absorption maxima of this family of compounds can be predicted with relatively good precision (±18 nm). The emission maxima can be also predicted, however the precision is lower (±39 nm). Taguchi methodology has been also employed with these families of compounds to optimize the intramolecular charge transfer estimated by emission solvatochromy. [ABSTRACT FROM AUTHOR]

Abstract: Thirteen novel dipolar and V-shaped chromophores with pyranylidene electron-donating part, diazine electron-withdrawing part and various π-linkers were synthesized. The extent of intramolecular charge transfer, structure-property relationships and optical properties were further investigated by UV/Vis absorption, electrochemistry, and DFT calculations. [Copyright &y& Elsevier]

The large library of nonlinear optical (NLO) chromophores based on pyrimidine scaffold is discussed in this review. Since the first examples described thirteen years ago, the interest in pyrimidine push-pull NLO chromophores has increased dramatically, especially for second harmonic generation and two photon absorption. More than 130 properly selected chromophores are presented to demonstrate fundamental structure-property relationships and to highlight key applications of pyrimidine-derived materials. • The large library of pyrimidine NLO chromophores has been reviewed. • Fundamental structure-property relationships were elucidated. • Methylpyrimidinium push-pull chromophores are superior second-order NLOphores. • 4,6-Distyrylpyrimidine derivatives proved to be well-established organic chromophores for two-photon absorption. [ABSTRACT FROM AUTHOR]