Phosphorescent platinum acetylide organogelators

Abstract

The series of platinum acetylide oligomers (PAOs) with the general structure trans,trans-[(RO)3Ph-C≡C-Pt(PMe3) 2-C≡C-(Ar)-C≡C-Pt(PMe3)2-C≡C- Ph(OR)3], where Ar = 1,4-phenylene, 2,5-thienylene, or bis-2,5-(S-2-methylbutoxy)-1,4-phenylene and R = n-C12H25 gel hydrocarbon solvents at concentrations above 1 mM. Gelation is thermally reversible (Tgel-sol ≈ 40-50deg;C), and it occurs due to aggregation of the PAOs resulting in the formation of a fibrous network that is observed for dried gels imaged by TEM. The influence of aggregation/gelation on the photophysical properties of the PAOs is explored in detail. Aggregation induces a significant blue shift in the oligomers' absorption spectra, and the shift is attributed to exciton interactions arising from H-aggregation of the chromophores. Strong circular dichroism (CD) is observed for gelled solutions of a PAO substituted with homochiral S-2-methylbutoxy side chains on the central phenylene unit. The CD is attributed to formation of a chiral supramolecular aggregate structure. The PAOs are phosphorescent at ambient temperature in solution and in the aggregate/ gel state. The phosphorescence band is blue-shifted ca. 20 nm in the aggregate/gel, and the shift is assigned to emission from an unrelaxed conformation of the triplet excited state. Phosphorescence spectroscopy of mixed aggregate/gels consisting of a triplet donor/host oligomer (Ar = 1,4-phenylene) doped with low concentrations of an acceptor/trap oligomer (Ar = 2,5-thienylene) indicates that energy transfer occurs efficiently in the aggregates. Triplet energy transfer involves exciton diffusion among the host chromophores followed by Dexter exchange energy transfer to the trap chromophore. © 2008 American Chemical Society.