Intramolecular Electronic Interaction in Pyridinyl Diradicals Temperature Dependence and Electronic Structure

Abstract

Pyridiayl diradicals, Py(Ac)·(CH2)nPy(Ac), (in which Py (Ac)·is 4-CH3OCC5H4N·, and n=3 and 4) were obtained. Intramolecular electronic interaction between two 4-acetylpyridinyl moieties in the diradical n=3 was observed. Temperature dependence of absorption spectra suggests the conformational equilibrium between the open and closed forms in the, diradical n=3 (-ΔH=7.6 kcal and ΔS=-14 e.u.). Electronic absorption spectroscopy and SCF-CI molecular orbital calculation reveal that a strong visible absorption band in the closed form diradical (n=3) is ascribed to a charge-transfer band between two pyridinyl moieties.