Syntheses, spectroscopic properties, and polymerizations of 2,2 '-bitellurophene, 2,2 ': 5 ',2 ''-tertellurophene, and related hybrid terchalcogenophenes

2,2'-Bitellurophene, 2,2':5',2"-tertellurophene, and related hybrid terchal cogenophenes have been synthesized as a novel extended series of tellurophe ne homologues. The molecular and crystal structures of 2,2'-bitellurophene were elucidated by an X-Ray crystallographic analysis and compared with tho se of 2,2'-bithiophene and 2,2'-biselenophene. The molecular structure adop ts an almost completely planar transoid conformation, as seen for the other bichalcogenophenes, but the crystal structure is quite different, comprisi ng a unique herringbone-type of molecular packing with heteroatomic interac tions of tellurium. The electronic absorption spectra of the tellurophenes are characterized by strong pi-pi* transitions which appear in the longer w avelength region than those of thiophene and selenophene analogues and are systematically red-shifted with the increasing number of the conjugated tel lurophene units. On the other hand, the emission spectra suffer marked exti nction owing to a heavy atom effect of tellurium, and only the extended ter tellurophene shows weak fluorescence in the visible region. The elevation o f the HOMO levels of the tellurophenes is suggested by low oxidation potent ials in the cyclic voltammograms. Consequently, ready electrolytic and chem ical oxidative coupling reactions are liable to occur to give filmy or powd ered polytellurophenes, whose conductivities are wide-ranging with the orde r of 10(-3)-10(-9) S cm(-1), depending on the original tellurophene species and the polymerization conditions.