| Abstract |
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-alkyl rhodamines, espectively 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. |
