Photophysics of platinum tetrayne oligomers: delocalization of triplet exciton.

A series of platinum tetrayne oligomers, all-trans-Cl–Pt(P2)–[(C≡C)4–Pt(P2)]n–Cl, where P = tri(p-tolyl)phosphine and n = 1–3, was subjected to a detailed photophysical investigation. The photoluminescence of each oligomer at low temperature (T < 140 K) in a 2-methyltetrahydrofuran (Me-THF) glass features an intense and narrow 0–0 phosphorescence band accompanied by a vibronic progression of sub-bands separated by ca. 2100 cm–1. The emission arises from a 3π,π* triplet state concentrated on the (C≡C)4 carbon chain and the vibronic progression originates from coupling of the excitation to the ν(C≡C) stretch. All of the experimental data including ambient temperature absorption, low-temperature photoluminescence, and ambient temperature transient absorption spectroscopy provide clear evidence that the triplet state is localized on a chromophore consisting of approximately two −[(C≡C)4–Pt(P2)]– repeat units. Density functional theory calculations support the hypothesis that the triplet–triplet absorption ari...