Reverse Intersystem Crossing of Single Deuterated Perylene Molecules in a Dibenzothiophene Matrix

Intersystem crossing to the long-lived metastable triplet state is often a strong limitation on fluorescence brightness of single molecules, particularly for perylene in various matrices. In this paper, we report on a strong excitation-induced reverse intersystem crossing (rISC), a process where single perylene molecules in a dibenzothiophene matrix recover faster from the triplet state, turning into bright emitters at saturated excitation powers. With a detailed study of single-molecule fluorescence autocorrelations, we quantify the effect of rISC. The intrinsic lifetimes found for the two effective triplet states (8.5 +/- 0.4 ms and 64 +/- 12 ms) become significantly shorter, into the sub-millisecond range, as the excitation power increases and fluorescence brightness is ultimately enhanced at least fourfold. Our results are relevant for the understanding of triplet state manipulation of single-molecule quantum emitters and for markedly improving their brightness.

Automated summary

In this study, a strong excitation-induced reverse intersystem crossing (rISC) phenomenon was discovered for single perylene molecules in a dibenzothiophene matrix, leading to faster recovery from the triplet state and significantly enhanced fluorescence brightness. The intrinsic lifetimes of the two effective triplet states were found to become shorter and fluorescence brightness ultimately increased at least fourfold as excitation power increased. These results are important for understanding triplet state manipulation of single-molecule quantum emitters and improving their brightness.