Evidence of pure Lb1 fluorescence from redshifted indole-polar solvent complexes in a supersonic jet

Abstract

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 Lb1 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 Lb1 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 Lb1 emission. The ν26 vibration is the most intense nonorigin vibronic line, as expected for Lb1 emission. Finally, there is little or no intensity from the ν8, ν9, and ν10 vibrations, which would be strongly active with emission from the La1 state. These results show unequivocally that for these indole-polar solvent complexes the La1 state does not shift in energy below the Lb1 state—contrary to the interpretation of several recent papers. Further support is given to the assignment of Lb1 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.

Elongation method for calculating excited states of aromatic molecules embedded in polymers

“…The female natural sex hormone estradiol and amino acids tryptophan as part of protein chain are applicable in pharmaceutics and as fluorescent detectors in different biological objects. Fluorescent properties of tryptophan are controlled by the indole chromophore center and strongly depend on chemical and spatial structure of environment 30, 31. The tryptophan cage miniprotein is under consideration also as one of the realistic samples and appropriate for applying the hybrid technique of CIS and elongation methods.…”

Vibronic coupling in indole: II. Investigation of the 1La–1Lb interaction using rotationally resolved electronic spectroscopy

“…Whereas the 1 L b state behaves similarly to the ground electronic state, the 1 L a energy depends strongly on the solvent. These effects have been probed using microsolvation in van-der-Waals clusters using vibrationally 10,[18][19][20][21] and rotationally resolved spectroscopy. [22][23][24] From Stark effect measurements the dipole moment of indole-water in its ground and first excited electronic state was determined and a significant change of the water molecules' orientation upon excitation was observed.…”

Threshold photoionization in time‐of‐flight mass spectrometry

“…þ measured via the vibrationless intermediate state S 1 , 0 0 of the cluster at 35099 cm À1 (Hager et al, 1985;Tubergen & Levy, 1991;Braun, Grebner, & Neusser, 1998;Helm et al, 1998;Short & Callis, 1998) is shown in the middle trace of Figure 11. We identify intramolecular modes in the (indole Á H 2 O) þ spectrum by a comparison with the indole þ MATI spectrum.…”