ELECTRONIC RELAXATION IN A SERIES OF CYANINE DYES - EVIDENCE FOR ELECTRONIC AND STERIC CONTROL OF THE ROTATIONAL RATE

The photophysical properties of a series of substituted indocarbocyani ne dyes was examined by fluorescence and time-resolved absorption spec troscopy. The excited singlet-state lifetimes vary with the identity o f the substitutent. The lifetime is controlled primarily by rotation a bout a carbon-carbon bond. The substituents affect this process in sev eral ways.