Poly(silyleneethynylenephenylene) and Poly(silylenephenyleneethynylenephenylene)s: Synthesis and Photophysical Properties Related to Charge Transfer

Novel poly(dimethylsilyleneethynylenephenylene) [ 5 ] and poly(dimethyl (or diphenyl) silylenephenyleneethynylenephenylene)s [ 6 's] without diyne defects were synthesized by using the Pd/Cu-catalyzed AB-type coupling reaction. 6 's showed small but clear π-to-σ charge-transfer absorption bands at longer wavelengths (>340 nm) than those of π−π* absorption bands (<320 nm), whereas the charge-transfer absorption band was not found in 5 . When 6 's were excited at the π−π* absorption wavelengths, two type of emission were observed: One is the vibronically structured emission with a maximum around 325 nm due to the locally excited π* state, and the other is the intramolecular charge-transfer emission having a broad and structureless band (emission λ max ca. 370 nm) with a large Stokes shift. On the other hand, when excited at the charge-transfer absorption wavelengths, 6 's exhibited only the intramolecular charge-transfer emission with a maximum above 390 nm. This suggests that the indigo blue light emission of 6 's is due to the charge-transfer phenomenon and not to the locally excited π* state. The charge-transfer character of 6 's was clearly verified by the shift of emission in polar solvents.