Photophysics of platinum tetrayne oligomers: delocalization of triplet exciton.
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abstract
A series of platinum tetrayne oligomers, all-trans-Cl-Pt(P2)-[(CC)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 (3),* triplet state concentrated on the (CC)4 carbon chain and the vibronic progression originates from coupling of the excitation to the (CC) 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 -[(CC)4-Pt(P2)]- repeat units. Density functional theory calculations support the hypothesis that the triplet-triplet absorption arises from transitions that are delocalized over two repeat units.