Kinetic and radiative properties of the lowest triplet state of palladiumporphin

Abstract

A kinetic study, by means of zero field flash experiments and Zeeman experiments in fields up to 7·4 T, is reported of the phosphorescence of palladiumporphin in single crystals of n-octane between 1·2 and 4·2 K. From the intensities in the Zeeman multiplets the rates of decay from the spin sublevels to various vibronic bands of the ground state are found and from these the vibronic symmetries are partly deduced. Conspicuous in the spectrum is an e_g vibration the appearance of which is discussed in terms of intensity borrowing through spin-orbit and vibronic coupling. The observed intensity pattern in the e_g band appears compatible with a second order coupling path involving an intermediate charge transfer state. From the flash experiments values of ⩽ 0·1 ms^-1 and 1·40 ms^-1 for the relaxation rate of the transition τ _z →(τ _x , τ _y ) are found at 1·2 and 4·2 K respectively. Total decay rates for τ _z and (τ _x , τ _y ) are 1·33 ± 0·06 ms^-1 and 0·31 ± 0·02 ms^-1, respectively, relative populating rates are P _z(P _x +P _y ) = 2·1 ± 0·1 and relative steady state populations are N _z (N _x +N _y ) =0·47±0·03 at 1·2 K and 0·40±0·03 at 4·2 K.