EXCITED-STATE DYNAMICS OF P-CHLOROTOLUENE IN RIGID GLASS MATRICES

Excited state dynamics of dual phosphorescent p-chlorotoluene (PCT) wa s investigated in 3-methylpentane (3MP), methylcyclohexane (MCH), etha nol/methanol (EtOH/MeOH) and EPA rigid matrices in the temperature ran ge of 77-110 K. Dual phosphorescence was ascribed to two low-lying tri plet states, (3)pi pi and 3 pi sigma*. The rate of intersystem crossi ng (ISC) from S-1 to (3)pi pi and (3)pi sigma* states depends both on the temperature and solvent. Mutual conversion process between (3)pi pi and 3 pi sigma* states was observed above 87 K in 3MP, 92 K in MCH and 105 K in EtOH/MeOH matrices. Non-radiative decay rate constants s trongly depend on the viscosity of the solvent; in the more viscous so lvent, non-radiative decay rates become smaller. The activation energi es depend on the solvent viscosity and it was ascertained that the mut ual conversion process between (3)pi pi and (3)pi sigma* requires con formational change. (C) 1998 Elsevier Science S.A. All rights reserved .