TheT
1 state ofp-nitroaniline and related molecules: A CNDO/S study |
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Authors: | Richard W Bigelow Hans-Joachim Freund Bernhard Dick |
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Institution: | (1) Xerox Webster Research Center, 14580 Webster, New York, USA;(2) Lehrstuhl für Theoretische Chemie der Universität zu Köln, D-5000 Köln, Federal Republic of Germany |
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Abstract: | The nature of the lowest energy triplet state (T
1) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n( ) triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD
+ A
–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n( ) triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T
n
T
1 absorption measurements and relative photochemical behavior. |
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Keywords: | p-nitroaniline Nitrobenzene Triplet state Photo reductions Quantum Yield Solvent shifts |
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