Conformer-specific vibronic spectroscopy and vibronic coupling in a flexible bichromophore: bis-(4-hydroxyphenyl)methane

Published

April 28, 2011

Author(s)

Chirantha P. Rodrigo, Christian Muller, Nathan Pillsbury, William H. James III, David F. Plusquellic, Timothy Zwier

Abstract

The vibronic spectroscopy of jet-cooled bis-(4-hydroxyphenyl)methane (b4HPM) has been explored using fluorescence excitation (FE), dispersed fluorescence (DFL), UV-UV holeburning (UVHB), UV depletion (UVD), and fluorescence-dip infrared (FDIR) spectroscopies. Calculations predict the presence of three nearly isoenergetic conformers that differ in the orientations of the two OH groups in the para positions on the two aromatic rings (labeled uu, dd, and ud). In practice, two conformers (labeled A and B) are observed, with S_0-Sd1 origins at 35184 cm^-u1 and 35209 cm^-u1, respectively. The two conformers have nearly identical vibronic spectra and hydride stretch infrared spectra. The low frequency vibronic structure is assigned to bands involving the phenyl torsions (T and T-bar), ring-flapping (R and R-bar) and butterfly (β) modes. Symmetry arguments lead to a tentative assignment of the two conformers as the C_{2 symmetric uu and dd conformers. The S}d0-S_{2 origins are assigned to bands located 132 cm}u-^{1 above the S_0-Sd1 origins of both conformers. DFL spectra from the S_{2 origin of the two conformers display extensive evidence for vibronic coupling between the two close-lying electronic states. Near-resonant coupling from the S}d2 origin occurs dominantly to S_{1 R-bar}u1 and S_{1 R-bar}u1 β}u1 levels, which are located -15 and +31 cm^-u1 from it. Unusual vibronic activity in the ring-breathing (Ņ_{1) and ring deformation (Ņ}d6_{a) modes is also attributed to vibronic coupling involving these Franck-Condon active modes. A multi-mode vibronic coupling model is developed based on earlier theoretical descriptions of molecular dimers [Fulton, R. L., Gouterman, M.; J. Chem. Phys. 1961, 35, 1059.] and applied here to flexible bichromophores. The model is able to account for the ring-mode activity under conditions in which the S}d2 origin is strongly mixed (60%/40%) with S^d1 and levels.

Citation

Journal of Chemical Physics

Volume

134

Issue

16

Pub Type

Journals

Download Paper

https://doi.org/10.1063/1.3580901

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Keywords

internal mixing, internal conversion, electronic energy transfer, vibronic coupling, bichromophore, vibronic coupling model

Citation

Rodrigo, C. , Muller, C. , Pillsbury, N. , James III, W. , Plusquellic, D. and Zwier, T. (2011), Conformer-specific vibronic spectroscopy and vibronic coupling in a flexible bichromophore: bis-(4-hydroxyphenyl)methane, Journal of Chemical Physics, [online], https://doi.org/10.1063/1.3580901, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=907736 (Accessed April 25, 2024)