Solvent and temperature dependence of absorption and phosphorescence of trans-diisothiocyanate (bis)ethylenediaminechromium(III) ion

Abstract

An unusual case of absorption and fluorescence bands shifting in the same direction as solvent varies is reported. Solvent shifts in the quartet absorption maximum and doublet or phosphorescence emission maximum of trans-Cren2(NCS)2+ ion are related to the Gutmann solvent donor number. The correlation is discussed in terms of solvent effects on the vibrations identified as responsible for the vibronic transitions and are in agreement with Hollebone's notion of "vibronic" intersystem crossing. The activation parameters for decay of phosphorescence in eight solvents correlate by a Barclay–Butler plot and are consistent with the possibility of a single common dominant mechanism for the T-dependent decay path. They do not, however, depend on solvent donor numbers as quantum yields for substitution do. Therefore, they offered no new support for the notion that the pathway is by chemical reaction. The activation parameters also fail to correlate with solvent fluidity.