Intersystem crossing rates of single perylene molecules in ortho-dichlorobenzene

Abstract

Triplet states can be interesting for optical switching of molecular fluorescence as well as quantum experiments relying on the manipulation of spin states. However, the ground state of molecules is usually a singlet state. It is therefore interesting to study the intersystem crossing (ISC) rates between singlet and triplet states. We have measured the autocorrelation function of the fluorescence from single perylene molecules in an ortho-dichlorobenzene host matrix at cryogenic temperatures (1.3 K). We observed two time scales in the autocorrelation function corresponding to intersystem crossing to two indistinguishable triplet states (TX and TY) and a third triplet state (TZ). By studying the power dependence of the correlation times and contrasts in the autocorrelation functions of single molecules, we determine the ISC rates of perylene for the first time.

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

“…The lifetimes of the two triplet states are longer than reported for perylene in o ‐DCB [2] (3.0 ms and 19 ms) and n ‐nonane [28] (1.1±0.5 ms), which might be related to the deuteration of the perylene [26] . In general the triplet lifetimes are reported to be longer for deuterated fluorophores compared to their non‐deuterated analogues [26] .…”

“…The autocorrelations were obtained at a broad range of excitation intensities, in order to observe if there was any saturation of the correlation time and of the correlation contrast at high intensities, as is common for regular ISC [2] . However, this was not the case.…”

“…Over the years, the spectroscopy of single perylene molecules has been studied in the polymer polyethylene, [27] the Shpol'skii matrix n ‐nonane [28] and organic crystalline hosts such as biphenyl [22] and ortho‐dichlorobenzene ( o ‐DCB) [2] . In almost all of the studied hosts, single‐molecule emission of perylene was accompanied with spectral diffusion, [22] broadened linewidths, [22] or low fluorescence rate due to long dark times [2] . One way to increase a molecule's fluorescence rate is by recovering an emitter from its dark triplet state by exciting it with visible light of sufficient energy back to its excited singlet state – a phenomenon that is known as reverse intersystem crossing (rISC).…”

“…As the single molecule enters the triplet state, its fluorescence is cut off for the time that it remains in this metastable dark state [1] . For some fluorophores, such as perylene, this time is relatively long – in the range of milliseconds [2] . The result is a relatively poor brightness of single perylene molecules and this is the main reason that their study in SMS has been mostly overtaken by bright and stable emitters such as dibenzoterrylene, known to have a very low triplet yield and a triplet lifetime on the order of tens of microseconds [3,4] .…”

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

“…This is a generalised statement, typically organic fluorescent compounds have k ISC in the region of 10 6 s À1 . [50][51][52] Assuming the rate constant for fluorescence is faster than k ISC , fluorescence is the only radiative decay process possible.…”