Investigation of solvent isotope effects on Raman and fluorescence intensity of LDS750 in CH3OH and CD3OD

Citation
Fj. Knorr et al., Investigation of solvent isotope effects on Raman and fluorescence intensity of LDS750 in CH3OH and CD3OD, J PHYS CH A, 104(42), 2000, pp. 9494-9499
Citations number
35
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
10895639 → ACNP
Volume
104
Issue
42
Year of publication
2000
Pages
9494 - 9499
Database
ISI
SICI code
1089-5639(20001026)104:42<9494:IOSIEO>2.0.ZU;2-R
Abstract
The resonance Raman spectra of LDS750 in methanol-h(4) and methanol-d(4) ha ve been determined at excitation wavelengths on the blue side of the absorp tion maximum. In contrast to our previous studies of the solvatochromic mol ecule betaine-30, Raman intensities of LDS750 are observed to be independen t of solvent isotopomer. The fluorescence quantum yield, however, was signi ficantly larger in methanol-clr than in methanol-h(4) The results suggest t hat the dephasing dynamics that determine the resonance Raman intensities a re dominated by intramolecular relaxation rather than solvent motion. Excit ed-state population relaxation, on the other hand, is perturbed by solvent isotope and the more intense emission in deuterated solvent is a consequenc e of less favorable Franck-Condon factors for radiationless decay. The radi ative lifetime calculated from the quantum yield and fluorescence lifetime is considerably longer than that found using the Strickler-Berg equation, s uggesting that the transition moment in the relaxed geometry is reduced fro m that in the Franck-Condon geometry. Our conclusions concerning excited st ate dynamics in LDS750 are compared with those obtained from time-domain me asurements on this dye.