Phosphorescence dynamic behavior of metalloporphyrins in methanol-dimethyl sulfoxide liquid mixtures

Metalloporphyrins with room-temperature phosphorescence (RTP) demonstrate great potential in information security and optoelectronic devices. However, the effects of different proportions of alcohols and binary mixtures on phosphorescence remain unclear, owing to varying nonradiative transition rate (k_nP) across different solvents. In this study, we investigated the phosphorescence behavior of Platinum(II) meso-tetraphenylporphyrin (Pt-TPP) in different proportions of methanol-dimethyl sulfoxide (DMSO) liquid mixtures. The changes in the phosphorescence characteristics of Pt-TPP in solvents with varying ratios of methanol and DMSO were assessed through photoluminescence and time-resolved spectroscopy, and the observed variation in phosphorescence was attributed exclusively to k_np. The increase of k_np is attributed to the gradual narrowing of the energy gap between the excited triplet state of Pt-TPP and the energy levels of the two-component mixed solvent, and k_np follows a mono-exponential trend with the energy gap. A linear relationship between the energy gap and the solvent composition was then established by analyzing the absorption spectra of mixtures with varying solvent proportions. Furthermore, a model was proposed to explain that k_np exhibits a nonlinear dependence on solvent concentration, as well as the solvent-induced variations in phosphorescence.