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Torsional Barriers in Aromatic Molecular Clusters as Probe of the Electronic Properties of the Chromophore
Author(s) -
Jacoby Christoph,
Schmitt Michael
Publication year - 2004
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400281
Subject(s) - chemistry , chromophore , excited state , moiety , phenol , photochemistry , cluster (spacecraft) , excitation , reaction rate constant , ammonia , hydrogen bond , molecule , stereochemistry , atomic physics , kinetics , organic chemistry , physics , quantum mechanics , computer science , electrical engineering , programming language , engineering
We present a computer program that is capable of fitting n ‐fold torsional barriers V n ( n =2–6) and torsional constants F simultaneously to high‐ and low‐resolution spectroscopic data of different isotopomeric internal rotors. The program has been utilized to fit independently barriers and torsional constants for both electronic states of several aromatic clusters. The constant F of the ammonia moiety in the phenol–ammonia cluster is shown to decrease upon electronic excitation, thus imaging the formation of a hydrogen‐bonded complex between the phenoxy radical and the NH 4 radical in the excited state. In contrast, for the naphthol–ammonia 1:1 clusters no change of F of ammonia could be found. For phenol–methanol cluster we found a decrease of F upon excitation which points to a stronger hydrogen bond between phenol and methanol in the excited state. A strong reduction of the torsional barrier upon excitation points to the formation of a methoxonium radical in a similar photoreaction as in phenol–ammonia cluster. For the phenol–water system we postulate the same mechanism, a photoreaction, which leads to a translocated hydrogen atom in the S 1 state what can be deduced from the change of the torsional constant upon electronic excitation.