Rhodamine 3B+ ClO4− electronic transitions: reaction field and vibrational structure Original Research Article

The electronic absorption and emission in the visible region of the spectrum of a xanthene dye, Rhodamine 3B perchlorate, have been studied as a function of solvent and temperature. The spectral shifts correlate well with the function f(n2)=(n2−1)/(2n2+1) (Ooshika, Bayliss and McRae theory) and are essentially due to dispersion and induced electronic polarization. A further energy lowering occurs due to orientation polarization giving an estimation of μe−μg=1.7 D. The broadenings in absorption reveal the contribution from orbital expansion whilst in emission provide evidence for the opposite effect. The contribution of an electrostriction effect is inferred from the good correlation obtained between a vibronic function containing the elongation of molecular coordinates and the temperature. The double configuration coordinate model describes well the effect of temperature on both the S1↔S0 transitions Stokes shift and broadening at the vibronic 0↔0 bands.