Group 14 Metalloles with Thienyl Groups on 2,5-Positions:  Effects of Group 14 Elements on Their π-Electronic Structures

A series of group 14 metalloles, from silole to stannole, together with cyclopentadiene, having two thienyl groups at the 2,5-positions, have been prepared. Their crystal structures, UV−vis absorption and fluorescence spectra, and cyclic voltammograms have been determined. Theoretical calculations on their electronic structures have also been carried out. On the basis of these experimental and theoretical results, we compared their properties and electronic structures. The group 14 metallole derivatives from silole to stannole have essentially the same electronic structures and, thereby, comparable photophysical properties to each other, while significant differences exist between the cyclopentadiene and silole derivatives. The central group 14 elements, silicon, germanium, and tin, of the metalloles affect the LUMO energy levels of the π-electronic systems to almost the same extent through σ*−π* conjugation.