Pressure effects on the photophysical properties of the platinum(II) dimer Pt2(POP)44- (POP = .mu.-.eta.2-H2P2O52-) and related d8-d8 dinuclear complexes in solution

Abstract

The effect of hydrostatic pressure (0.1-300 MPa) upon phosphorescence lifetimes in fluid solution has been examined for four dinuclear d8-d8 transition-metal complexes: A, Pt2(POP)44- (POP = u-n2-H2P2O52-); B, Rh2(br)42+ (br = u-n2-1 ,3-diisocyanopropane); C, Ir2(pz)2(COD)2 (pz = u-n2-pyrazolate, COD = n4-1,4-cyclooctadiene); D, Rh2(TMB)42+ (TMB = u-n2-2,5-dimethyl-2,5-diisocyanohexane). In acetonitrile solutions, phosphorescence lifetimes of A and B proved to be relatively insensitive to pressure, and the rates for nonradiative deactivation displayed small, negative volumes of activation delta V*n. In contrast, triplet-state lifetimes for both C and D lengthened with increasing pressure, the result of substantial positive delta V*n values in these cases. These observations and the correlations between pressure and previously determined temperature effects on emission lifetimes are interpreted in terms of weak-coupling mechanisms dominating nonradiative deactivation from 3[A*] and 3[B*] and of strong-coupling mechanisms dominating the nonradiative deactivation from the triplet states of the less tightly bridged C and D.