Journal of the Chemical Society - Faraday Transactions p. 733 - 740 (1996)
Update date:2022-08-11
Topics:
Eisenberger, Heike
Nickel, Bernhard
The rate constant kTO for the unimolecular decay of the lowest triplet state, T1, of 4-H-1-benzopyrane-4-thione (BPT) in perfluoro1,3-dimethylcyclohexane was determined between 230 and 300 K. By assuming a very fast and virtually complete thermal equilibration T1 ? S1 of the relative population of T1 and the lowest excited singlet state S1, three parameters can be calculated from the temperature dependence of kTO: the individual rate constants βS = (4.0 ± 0.2) × 106 s-1 for the decay of S1 to S0 and βTz = (8.2 ± 2) × 104 s-1 for the decay of the strongly phosphorescent triplet substate T1z to S0, and the energy difference ΔE(S1,T1z) = hc × (757 ± 13) cm-1l between T1z and S1. The value of ΔE(S1,T1z) is in agreement with the positions of T1,0 and S1,0 in the absorption spectrum. The spectrum of the S0 → S1 transition is estimated. The assignment of the hot-band range of the delayed luminescence above the energy hcν0,0 of T1,0 is facilitated by an inverse Boltzmann weighting (multiplication with exp[hc(ν - ν0,0)/kBT]). At the position of S1,0, a contribution of E-type delayed S1 → S0 fluorescence can be discerned. The contribution of diffusion-controlled concentration-quenching (rate constant kQ) to the triplet decay was eliminated by extrapolation to infinite dilution; kQ is proportional to the ratio T/η of temperature T and viscosity η. The temperature dependence of the viscosity and density of perfluoro-1,3-dimethylcyclohexane were measured.
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