Studies of the lowest excited triplet state of 3,3 '-biisoquinoline(dicyano)platinum(II) [Pt(CN)(2)(i-biq)] by means of time-resolved electron paramagnetic resonance and optical spectroscopy

The lowest excited triplet (T-1) state of 3,3'-biisoquinoline(dicyano)plati num(II) [Pt(CN)(2)(i-biq)] was examined by time-resolved electron paramagne tic resonance (TREPR) and optical techniques in comparison with that of a l igand 3,3'-biisoquinoline (i-biq). Trans and cis i-biqs were assigned from obtained and calculated zero-field splittings (zfs') in the T-1 state. The zfs parameter D increased with complex formation from 2.66 to 4.66 GHz in a rigid dimethylformamide solution; the polarization pattern of the spectrum was very different between the ligand and the complex. The triplet lifetim e (ca. 1 s) of i-biq is also remarkably shortened in the complex (ca. 2 ms) . These facts were analyzed in terms of the spin-orbit coupling (soc) betwe en T-1 (pi pi*) and (1,3)d pi*. From the analyses, the soc matrix element a nd the magnitude of delocalization of pi* electrons over the Pt atom are ob tained as 65 cm(-1) and 0.02, respectively. The solvent dependences of the D value and the tripler lifetime also support the importance of the (1,3)d pi* states for the T-1 (pi pi*) properties of the complex.