Energetics and Dynamics of the Low-Lying Electronic States of Constrained Polyenes: Implications for Infinite Polyenes
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Pentelute_Energetics and.pdf
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Author(s)
Christensen, Ronald L.
Enriquez, Miriam M.
Wagner, Nicole L.
Peacock-Villada, Alexandra Y.
Scriban, Corina
Polívka, Tomáš
Frank, Harry A.
Birge, Robert R.
Schrock, Richard Royce
Date Issued
January 2013
Journal
Journal of Physical Chemistry A
Publisher
American Chemical Society (ACS)
Citation
Christensen, Ronald L., Miriam M. Enriquez, Nicole L. Wagner, Alexandra Y. Peacock-Villada, Corina Scriban, Richard R. Schrock, Tomáš Polívka, Harry A. Frank, and Robert R. Birge. “Energetics and Dynamics of the Low-Lying Electronic States of Constrained Polyenes: Implications for Infinite Polyenes.” The Journal of Physical Chemistry A 117, no. 7 (February 21, 2013): 1449–1465.
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Author's final manuscript
Abstract
Steady-state and ultrafast transient absorption spectra were obtained for a series of conformationally constrained, isomerically pure polyenes with 5–23 conjugated double bonds (N). These data and fluorescence spectra of the shorter polyenes reveal the N dependence of the energies of six [superscript 1]B[subscript u] [superscript +] and two [superscript 1]A[subscript g] [superscript –] excited states. The [superscript 1]B[subscript u] [superscript +] states converge to a common infinite polyene limit of 15 900 ± 100 cm [superscript –1]. The two excited [superscript 1]A[subscript g] [superscript –] states, however, exhibit a large (∼9000 cm–1) energy difference in the infinite polyene limit, in contrast to the common value previously predicted by theory. EOM-CCSD ab initio and MNDO-PSDCI semiempirical MO theories account for the experimental transition energies and intensities. The complex, multistep dynamics of the 1[superscript 1]B[subscript u] [superscript +] → 2 [superscript 1]A[subscript g] [superscript –] → 1 [superscript 1]A[subscript g] [superscript –] excited state decay pathways as a function of N are compared with kinetic data from several natural and synthetic carotenoids. Distinctive transient absorption signals in the visible region, previously identified with S* states in carotenoids, also are observed for the longer polyenes. Analysis of the lifetimes of the 2 [superscript 1]A[subscript g] [superscript –] states, using the energy gap law for nonradiative decay, reveals remarkable similarities in the N dependence of the 2 [superscript 1]A[subscript g] [superscript –] decay kinetics of the carotenoid and polyene systems. These findings are important for understanding the mechanisms by which carotenoids carry out their roles as light-harvesting molecules and photoprotective agents in biological systems.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1021/jp310592s
