Energy transfer in bichromophoric molecules: The effect of symmetry and donor/acceptor energy gap

Journal Article · Thu Jan 07 04:00:00 EST 1999 · Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory

DOI:https://doi.org/10.1021/jp9831280· OSTI ID:320828

Yip, W T; Levy, D H ^[1]; Kobetic, R; Piotrowiak, P ^[2]

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1. Univ. of Chicago, IL (United States)
2. Rutgers Univ., Newark, NJ (United States). Dept. of Chemistry

The dependence of the rate of singlet excitation transfer on the donor-acceptor energy gap was investigated in bichromophoric spiranes with symmetry-forbidden zero-order electronic coupling. The fluorescence measurements were performed in a supersonic jet in order to avoid collisional and inhomogeneous line broadening. Fluorescence excitation spectra and single-vibronic-level emission spectra of the model chromophores cyclopentaphenanthrene and 1,8-dimethylnaphthalene and the bichromophores spirofluorenephenanthrene and spirofluorenanaphthalene are presented and analyzed. Although the transition moments of the linked chromophores are rigorously perpendicular and the exchange coupling between the {upsilon}{prime} = 0 states is computationally shown to be zero, all spiranes with energy gaps larger than {approximately}1000 cm{sup {minus}1} exhibited complete electronic energy transfer from all vibrational states of the electronically excited donor, including the undistorted {upsilon}{prime} = 0 state. This behavior is explained in terms of vibronic coupling between the sparse states of the donor and the dense manifold (pseudocontinuum) of the acceptor states. The electronic energy transfer was sufficiently fast to result in measurable lifetime broadening of the donor absorption lines, from which the k{sub EET} was estimated. The results demonstrate that the zero-order picture overestimates the degree of the molecular orbital symmetry control over electronic energy transfer and charge-transfer rates and that at sufficiently high driving forces the vibronically meditated symmetry-forbidden electronic energy transfer can be very rapid ({approximately}1 {times} 10{sup 12} s{sup {minus}1}).

• Sponsoring Organization: National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-97ER14756
• OSTI ID: 320828
• Journal Information: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 1 Vol. 103; ISSN 1089-5639; ISSN JPCAFH
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CONDENSED AROMATICS
COUPLING
ELECTRONIC STRUCTURE
EMISSION SPECTRA
ENERGY GAP
ENERGY TRANSFER
EXPERIMENTAL DATA
FLUORESCENCE