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Ab initio MO investigations of molecular structures in the ground and first excited states of heterocyclic pyridinium betaine

✍ Scribed by Jiro Abe; Nobukatsu Nemoto; Yu Nagase; Yasuo Shirai

Publisher
Elsevier Science
Year
1996
Tongue
English
Weight
357 KB
Volume
261
Category
Article
ISSN
0009-2614

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✦ Synopsis

The molecular structure in the first excited state of the simplest heterocyclic pyridinium betaine, (l-pyridinio)benzimidazolate, was investigated through ab initio molecular orbital calculations. The central C-N bond shortens to a nearly double bond character in contrast to the case for the ground state, and the pyridinium ring takes a para-quinoid-like structure. The dipole moment direction in the excited state and the ground state are anti-parallel, and the benzimidazole ring acts as an electron-donating group and the pyridinium ring acts as an electron-withdrawing group, and the first excited state is characterized by an intramolecular charge transfer state. Based on these characteristic features of heterocyclic pyridinium betaines, a new concept for manipulating the molecular dipole moment and molecular first-order hyperpolarizability is proposed.

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