Correlating ground and excited state properties: a quantum chemical study of the photodissociation of the C-N bond in N-substituted anilines
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Budyka, M. F.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
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Budyka, M. F.
(EN)
Structure and properties of the ground-state (S-0) and lowest excited singlet (S-1) and triplet states (T-1) of N-substituted anilines PhNH-R (R = CH3, CH2Ph, CHPh2, CPh3) were calculated using semiempirical PM3 method. Ab initio (HF, MP2) and DFT (B3LYP) methods for R = CH3, CH2Ph, and HF method for R = CHPh2 were used with 6-31G* and 6-31G** basis sets. All methods predict, in agreement with experiment, a pyramidal S-0 state, which flattens on excitation to S-1 and T-1 ones. The bond dissociation energy (BDE) values of the C-N bond were found to decrease upon insertion of phenyl groups at the benzylic carbon atom. PM3 calculations show, in full agreement with experimental data, that the lowest excited states of anilines studied are in fact the 'local' excited states of the anilino chromophore group. PM3 calculations of the minimal energy path for the C-N bond dissociation in the T-1 state predict a useful Evans-Polanyi linear relationship between activation energy E-a (excited-state property) and BDE (ground-state property). This enables one to estimate important reactivity parameters (activation energy and rate constant) of an excited state based on an easy accessible ground-state property such as the BDE. (C) 2002 Elsevier Science B.V. All rights reserved.
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