Synthesis and electronic properties of new photoluminescent platinum-containing polyynes with 9,9-dihexylfluorene and 9-butylcarbazole units

Soluble, thermally stable, and easily processable platinum(II) polyyne polymers trans[-Pt(PBu3)(2)C=CRC=C-](n) (R = 9,9-dihexylfluorene-2,7-diyl or 9-butylcarbazole-3,6-diyl) have been prepared in good yields by CuI-catalyzed polymerization involving the dehydrohalogenating coupling of trans-[PtCl2(PBu3)(2)] and HC=CRC=CH. We report their optical absorption and photoluminescence spectra and compare the results with the monomeric model complexes trans-[Pt(Ph)(PEt3)(2)C=CRC=CPt(Ph)-(PEt3)(2)] and other fluorene derivatives exhibiting different degrees of electronic conjugation. The regiochemical structure of the polymers has been ascertained by single-crystal X-ray analysis on the carbazole-linked model compound. With decreasing conjugation, the optical gap as well as intersystem crossing from the singlet excited state to the triplet excited state is increased. In both systems, our studies indicate that the S, singlet excited state extends over more than a repeat unit while the T, triplet state remains localized to less than one repeat unit. The photoconducting properties of these platinum polyynes are discussed.