Photophysics of 2-Phenyl-3-indolocarbocyanine Dyes

Article abstract of DOI:10.1021/j100278a041

In this paper the photophysics of the perchlorate and chloride salts of N-ethyl- and N-octadecyl-2-phenyl-3-indolocarbocyanine have been investigated.Stationary fluorescence spectra and quantum yields of these dyes were measured in various solvents.The quantum yields in the homologous series of linear aliphatic alcohols, with viscosities ranging from 0.6 to 14 cP, followed a linear Oster-Nishijima relationship.The quantum yields in nonalcohol solvents were higher than in alcohols of the same viscosity.Fluorescence decay times were obtained with a mode-locked, synchronously pumped R6G dye-laser system with time-correlated single photon counting detection.The fluorescence decays of the dyes could be adequately described by a dual-exponential decay law with a short decay time between 35 and 1040 ps and a long decay time varying from 103 to 3210 ps.In nonbranched alcohols, both decay times followed a linear Oster-Nishijima relationship.The double-exponential decays were interpreted in terms of a cis-trans isomerism rather than as an effect of excited-state relation or ion pairing.The cis-trans isomerism already exists in the ground state and was also observed for 9-alkyl-substituted oxa- and thiacarbocyanines and for 1,3'-diethyl-4,2'-quinolyloxacarbocyanine.