Photosensitized processes in dicarbocyanine dyes induced by energy transfer:: delayed fluorescence, trans → cis isomerization and electron transfer

The triplet-induced photoprocesses of 3,3'-diethylthiadicarbocyanine (1), 3,3'-diethyloxadicarbocyanine (2), its methyl (3), ethyl (4) and phenyl (5) derivatives as well as of 1,1',3,3,3',3'-hexamethylindodicarbocyanine (6) and its chlorine (7), bromine (8) and methyl (9) derivatives were studied in deoxygenated acetonitrile upon anthracene-sensitized excitation by conventional and ns-flash photolysis. The emission is attributed to the sensitized (mixed) type rather than E- or P-type delayed fluorescence. The triplet state of the dyes, radicals and a cis isomer with absorption maxima at 650-1000, 450-500 and 620-695 nm, respectively, were spectroscopically and kinetically distinguished. The trans --> cis photoisomerization can be initiated by both triplet (mostly) and singlet states of the dyes. (C) 2001 Elsevier Science B.V. All rights reserved.