Tuning Excited-State Electron Transfer from an Adiabatic to Nonadiabatic Type in Donor?Bridge?Acceptor Systems and the Associated Energy-Transfer Process
Resource
The Journal of Physical Chemistry A 110 (44): 12136-12144
Journal
The Journal of Physical Chemistry A
Journal Volume
110
Journal Issue
44
Pages
12136-12144
Date Issued
2006
Date
2006
Author(s)
Abstract
Through design and synthesis of a new series of dyads I-III composed of 2,3-dimethoxynaphthalene as an electron donor (D) and 2,3-dicyanonaphthalene as an acceptor (A) bridged by n-norbornadiene (n = 1 - 3) we demonstrate an excellent prototype to switch the excited-state electron-transfer dynamics from an adiabatic to a nonadiabatic process. I reveals a remarkable excitonic effect and undergoes an adiabatic type of electron transfer (ET), resulting in a unique charge-transfer emission, of which the peak wavelength exhibits strong solvatochromism. Conversely, upon exciting the donor moiety, a fast D → A energy transfer takes place for II (∼3 ps) and III (≤30 ps), followed by a nonadiabatic type, weak coupled electron transfer with a relatively slow ET rate, giving rise to dual emission in polar solvents. Further detailed temperature-dependent studies of the ET rate deduced reaction barriers of 2.7 kcal/mol (for II) and 1.3 kcal/mol (for III) in diethyl ether and CH 2Cl2, respectively. The results lead to a deduction of the reaction free energy and reorganization energy for both II (in diethyl ether) and III (in CH2Cl2). Theoretical (for I) and experimental (for II and III) approaches estimate the electronic coupling to be 860, 21.9, and 3.2 cm-1 for I, II, and III, respectively, supporting the adiabatic versus nonadiabatic switching mechanism. © 2006 American Chemical Society.
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