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We report herein the synthesis of nine new molecularly engineered metal-free organic pyranylidene-based dyes as efficient photosensitizers for Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical, and photovoltaic properties were investigated, and their excited states have been modelled using Time-Dependent Density Functional Theory (TD-DFT). The investigation of the photovoltaic performances of this series of new dyes provided structure-property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer and the nature of the substituents on the upper (positions 2 and 6) and lower parts (substituents on the exocyclic carbon) of the pyranylidene electron donor moiety. While these dyes fulfilled the criteria of efficient sensitizers for TiO 2 -based DSSCs, their photovoltaic performances were found to depend on the dye packing arrangements controlled by substituents on the pyranylidene group. The highest Power Conversion Efficiency of 5.52% was reached with the 20a dye containing phenyl substituent groups in both upper and lower parts of the pyranylidene fragment and with one thienyl π-conjugated spacer. Image 1 • Structure-property relationships and photovoltaic performance of functionalized organic dyes have been investigated. • The most suitable dye packing controlling charge recombination processes has been identified. • The best PCE (5.52%) was achieved with dyes including phenyl-substituted pyranylidene and short thienyl π-conjugated spacer. [ABSTRACT FROM AUTHOR]

In this paper we describe the synthesis, the electrochemical behaviour as well as the linear and nonlinear optical (NLO) properties of two push-pull derivatives bearing pyranylidene electron donating fragment, pyrimidine/methyl pyrimidinium electron withdrawing moiety and a ferrocene part in the π-conjugated bridge. The properties of these two compounds were compared to their analogues without ferrocene or pyranylidene fragments. Experimental results were completed with DFT calculations to gain further insight into the intramolecular charge transfer (ICT). All the results indicate a significant charge transfer through the ferrocene unit. The ICT is however more limited than in all organic analogues. [ABSTRACT FROM AUTHOR]

The synthesis, thermal, electrochemical, and optical properties of a series of triphenylamine derivatives bearing pyridine fragments and their trifluoroacetate salts are described. A dramatic increase in the intramolecular charge transfer is observed upon protonation, as evidenced by a significant reduction in the HOMO-LUMO gap and a red shift of both the absorption and the emission band. White photoluminescence was obtained in solution by the controlled protonation of blue emitting pyridine derivatives, which resulted in the yellow-orange emissive acidified form. In the solid state the emission color of doped polystyrene thin films could be tuned from steel blue to lawn green when the ratio of the protonated form was increased. These compounds have potential applications in the fabrication of multi-color OLEDs based on only one material. [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]

Different D–π–A push–pull molecules in which dipicolylamine (DPA) is used as the donor group, different diazines as the acceptor groups, and styryl as the π-conjugated spacer have been synthesized in a straightforward manner by aldol condensation of 4-(di-2-picolylamino)benzaldehyde and the appropriate methyldiazine. All of the compounds showed π–π* transitions in the UV or visible region and the emission of yellow-green light upon irradiation. Significant red shifts were observed in the fluorescence emission maxima of these compounds on increasing the solvent polarity, a finding that suggests the formation of an intramolecular charge-separated emitting state that is also supported by semi-empirical calculations. In some cases, protonation led to marked color changes, thus showing the ability of these molecules to function as colorimetric pH sensors. The DPA and diazine units can act as coordination sites for metal cations such as Zn 2+ , Cd 2+ or Hg 2+ , leading to a blue or red shift in the fluorescence spectra due to the change in the intramolecular charge transfer properties. This phenomenon could become a powerful tool for the creation of multiple emission colors with a single molecule after suitable design. [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]

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]