Influence of the N-alkyl chain length on the J-aggregation behavior of a cyanine dye.

A new series of benzimidocarbocyanine dyes having diffeerent N-alkyl chain lengths (C2-C12) but the same chromophoric system was synthesized to investigate the effect of the dye structure on the photophysical properties of J-aggregate-forming dyes. For these dyes, the number of J-absorption band depends on the chain length of the alkyl substiuents, whereas the fluorescence emission spectra exhibit only a single J-band. Furthermore, an increase in the N-alkyl-chain length leads to a strong decrease in the bandwidth of the J-absorption and emission bands.

Excition dynamics in the J-aggregates of a carbocyanine dye.

We report on the exciton dynamics in the J-aggregating dye 5,5', 6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine which is known readily to form J-aggregates, even at room temperature and at a low concentration. We performed a series of time-correlated singlephoton-counting experiments at different emission wavelengths and at different temperatures in the range between 1.5 and 125 K. Additionally, the temperature dependence of the relative fluorescence quantum yield was determined.