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The effect of solvent polarity on the photophysical properties of 4-cyano-(4′-methylthio)diphenylacetylene: A prototypic donor-acceptor system

Lookup NU author(s): Professor Andrew Benniston, Emeritus Professor Anthony Harriman, James Rostron


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The photophysical properties of the target compound are extremely sensitive to changes in solvent polarity since the lowest-energy excited states possess considerable charge-transfer character. Excitation results in a greatly increased dipole moment, with the resultant excited singlet state retaining a lifetime of ca. 1 ns in all solvents. Radiative decay involves coupling between the lowest-energy excited singlet state and both the ground state and an upper excited singlet state. The level of coupling to the upper singlet decreases in non-polar solvents, presumably due to symmetry factors. The radiative rate constant decreases smoothly with increasing solvent polarity function as the molecule acquires an ever increasing dipolar character. Non-radiative decay includes both intersystem crossing and internal conversion, but the former process dominates in polar solvents. The excited singlet state lifetime is very weakly dependent upon temperature in the solid state. However, in polar solutions where the Stokes' shift decreases with decreasing temperature, there is clear evidence for an activated process. This is believed to involve coupling to the upper-lying singlet excited state. © The Owner Societies 2005.

Publication metadata

Author(s): Benniston AC, Harriman A, Rostron JP

Publication type: Article

Publication status: Published

Journal: Physical Chemistry Chemical Physics

Year: 2005

Volume: 7

Issue: 16

Pages: 3041-3047

ISSN (print): 1463-9076

ISSN (electronic): 1463-9084

Publisher: Royal Society of Chemistry


DOI: 10.1039/b506776f

PubMed id: 16186908


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