Determination of the population, depopulation and the anisotropic spin lattice relaxation rates in the photoexcited triplet state of phenazine. A light modulation-EPR study

Abstract

The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations ( p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants k p , the anisotropic spin lattice relaxation rate constants W p , and the ratios between the population constants A p are calculated: k x = (2.2 ± 0.3) × 10 2 s −1, k y = (0.21 ± 0.04) × 10 2 s −1, k z = (0.06 ± 0.03) × 10 2 s −1, W x = (8.6 ± 0.9) × 10 3 s −1, W y = (11.0 ± 1.0) × 10 3 s −1, W z = (14.0 ± 1.4) × 10 3 s −1, and A x : A y : A z ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τ x > is the active one.