Solvatochromism of novel donor–π–acceptor type pyridinium dyes in halogenated and non-halogenated solvents

Abstract

Donor–π–acceptor type pyridinium dyes that have been newly synthesized showed bathochromic shift of the absorption band with decreasing dielectric constant (ε_r) of solvent (negative solvatochromism), and the bathochromic shifts in halogenated solvents were larger than those in non-halogenated solvents of similar ε_r values. 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 TiO₂ film immersed in solvents.