Search

Donor–π–acceptor type pyridinium dyes that have been newly synthesized showed bathochromic shift of the absorption band with decreasing dielectric constant (r) of solvent (negative solvatochromism), and the bathochromic shifts in halogenated solvents were larger than those in non-halogenated solvents of similar rvalues. The influences of halogenated solvents on the large bathochromic shifts are studied on the basis of 1H NMR measurements, semi-empirical molecular calculations (AM1 and INDO/S using the SCRF Onsager model), and absorption spectral measurements of the dyes adsorbed on nanocrystalline TiO2film immersed in solvents. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports that mechanofluorochromism is found for a series of benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorophores (1a–5a) with different p-substituted phenyl groups as acceptor and dibutylamino groups as donor. Grinding of as-recrystallized dyes 1a–3a with strong electron-accepting group induces a fluorescent color change with an enhanced quantum yield and the fluorescent color is recovered by heating or exposure to solvent vapor. On the basis of experimental results and semi-empirical molecular orbital calculations (AM1 and INDO/S), we clarified that the mechanofluorochromism is attributed to a reversible switching between crystalline and amorphous states with changes of dipole–dipole interaction and intermolecular π–π interaction by changes of the densities of the solids before and after grinding. [ABSTRACT FROM AUTHOR]

Abstract: A series of new-type donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole fluorescent dyes with substituents such as various lengths of non-conjugated alkyl chains containing a carboxyl group at the end position, π-conjugated carboxyl, cyano and dibutylamino groups are designed and synthesized. Dye-sensitized solar cells were fabricated using these dyes. The influence of configuration of the dyes on TiO2 surface and chemical structures of the dyes on the photovoltaic performance are investigated and discussed on the basis of semi-empirical molecular orbital calculations (AM1 and INDO/S). It is concluded that a carboxyl group of donor–acceptor π-conjugated sensitizer is necessary not as the electron acceptor, but only as anchoring group for attachment on TiO2 surface. Therefore, it was proposed that the most important point for developing new and efficient donor–acceptor π-conjugated sensitizers for DSSCs is to design dye molecules capable of forming a strong interaction between the electron acceptor moiety of sensitizers and TiO2 surface. [Copyright &y& Elsevier]