Perylene in biphenyl and anthracene crystals: an example of the influence of the host on single-molecule signals Original Research Article

We studied mixed crystals of the strongly fluorescing guest perylene in two hosts with similar molecular size and crystal structure: biphenyl and anthracene. Although we found narrow spectral sites in sublimed samples of both crystals, we could detect single-molecule lines only in biphenyl. Using anthracene as a matrix, we measured for the first time the unsensitized, vibrationally resolved phosphorescence spectrum of perylene and its triplet lifetime. The triplet yield and the triplet lifetime are about 10 times larger than in biphenyl, which explains why we could not observe single perylene lines in anthracene. The single-molecule lines in biphenyl are at least 4 times broader than the lifetime-limited width. We attribute their broadening to dephasing by low-frequency excitations, which are known to occur in the incommensurate phase of biphenyl at low temperatures.