“…Increasing the medium dipolarity-polarizability and, more importantly,t he mediumb asicity,h as the effect of increasing the effective charge on the phenolate oxygen, thus reducing the corresponding CT energy.T his is evident from a comparison of the effect of two solvents with similar average values of dipolarity-polarizability,t hat is, dichloromethane (SdP = 0.769, SP = 0.761) and acetone (SdP = 0.907, SP = 0.651), but that differ appreciably in terms of basicity (SB values = 0.178 and 0.475 for dichloromethane and acetone, respectively). [13e] The CT energiesa re consistently lower in acetone than in dichloromethane for all members of these "hybrid cyanine" dyes, [10,11] an observation that can be ascribed to the greater basicity of acetone. Increasing this basicity even further, by using DMF,D MA, or DMSO, leads in all cases to ac onsistent bathochromic shift of the solvatochromic band of these phenolate dyes.…”