Triplet excited states of some thiophene and triazole substituted platinum(II) acetylide chromophores.

The photophysical properties of a series of platinum(II) acetylide compounds (trans-Pt(PBu(3))(2)(C[triple bond]C-R)(2)) with the R group consisting of two or three aryl rings (phenyl, phenyl/thiophenyl, phenyl/triazolyl) linked together with ethynyl groups were systematically investigated. Four new structurally similar compounds are reported with: (i) a bithiophene unit in the ligands, (ii) methyl or (iii) methoxy substituents on the aryl ring ligands that promote a more twisted conformation along the long axis of the molecule, and (iv) with two different alkynylaryl ligands giving rise to an asymmetric substitution with respect to the photoactive metal ion center. The spectroscopic studies include optical absorption, spectrally and time-resolved luminescence, as well as transient absorption spectra. The ground-state UV absorption between 300 and 420 nm gave rise to fluorescence with quantum efficiencies in the range of 0.1-1% and efficient intersystem crossing to triplet states. Phosphorescence decay times were in the order of 10-500 micros in oxygen-evacuated samples. The triplet states also lead to strong broadband triplet-triplet absorption between 400 and 800 nm. The complex with asymmetric substitution was found to populate two triplet states of different structure and energy.