Photo-induced spin alignment utilizing the excited molecular field between the excited triplet state of phenyl- or diphenylanthracene and the dangling nitroxide radicals: theoretical investigation of the mechanism for the intramolecular spin alignment

Abstract

In the previous paper [J. Am. Chem. Soc., 122 (2000) 984], we reported the first observation of the photo-excited quartet ( S=3/2) and quintet ( S=2) states arising from the radical-triplet pairs on the purely organic π-conjugated spin systems. 9-Anthracen(4-phenyliminonitroxide) ( 1) and 9,10-anthracen-bis(4-phenyliminonitroxide) ( 2) were designed and synthesized. The time-resolved ESR (TRESR) experiments were carried out in order to study the photo-induced spin alignments on the excited states. In this paper, we report the ab initio molecular orbital calculations based on the density functional theory for the photo-excited quartet ( S=3/2) state of 1 and the quintet ( S=2) state of 2 as well as the brief summary of our TRESR experiments. The mechanism of the photo-induced spin alignment has been clarified based on the spin distribution obtained by the MO calculations.