Excited-state Solvation of Rhod a mines:Dielectric and Specific Contributions

摘要

Primary to tertiary amine based compounds of the form 9'-(2-ester-carbonyl)·phenyl-3',6'-bis-(amino)·xanthylium)are studied as models for this class of compounds as regards the S_1<-S_0 shifts in solution.The magnitude of the solvatochromic shift decreases from primary amine to tertiary amine rhodamine chromophore.Primary amino xanthylium spectral energy at maximum absorption decreases with the solvent electronic polarization whilst it increases with the orientational polarization function,suggesting extensive reorientation in the dipolar moment upon S_1<-S_0 excitation.By contrast,upon electronic excitation smaller dipolar moment variations are found in N-alky 1 rhodamines,respectively with secondary and tertiary amine groups.Primary and secondary amine rhodamines'NH groups establish strong interactions with electron rich atomic centers of solvent molecules increasing the electronic stabilization energy.