ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Two-photon polarized fluorescence excitation and vibronically resolved one-photon dispersed fluorescence spectra of the long-wavelength absorbing van der Waals complexes of indole with water, methanol, and formamide were examined for the purpose of firmly assigning the nature of the lowest singlet excited electronic state. The two-photon spectra for all of these complexes have circular/linear polarization ratios of absorptivity (Ω-values) that show that excitation is to the 1Lb state. Analysis of the Franck–Condon (FC) patterns of the dispersed fluorescence for these indole-polar solvent complexes show that emission is also from the 1Lb state in each case. In the emission spectra, the intensity ratios of the origin and ν26 lines are about 2:1, which is the value expected for 1Lb emission. The ν26 vibration is the most intense nonorigin vibronic line, as expected for 1Lb emission. Finally, there is little or no intensity from the ν8, ν9, and ν10 vibrations, which would be strongly active with emission from the 1La state. These results show unequivocally that for these indole-polar solvent complexes the 1La state does not shift in energy below the 1Lb state—contrary to the interpretation of several recent papers. Further support is given to the assignment of 1Lb emission by spectral simulations. The jet-cooled complexes do not exhibit excited state complex (exciplex) characteristics, wherein the solvent is much more strongly bound in the excited state than in the ground state. © 1998 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.476478
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