Temperature effect on the formation of the lowest excited triplet states of 9-bromoanthracene and 9,10-dibromoanthracene

Dibenzo[hi,st]ovalene as Highly Luminescent Nanographene: Efficient Synthesis via Photochemical Cyclodehydroiodination, Optoelectronic Properties, and Single-Molecule Spectroscopy

“…70 Studies of brominated anthracenes in 3-methylpentane over a comparable temperature range gave similar activation energies. 72 For pentacene/p-terphenyl mixed crystals, the temperature dependence of the pentacene ISC rate between 4.2 and 140 K was attributed to a vibronically induced process due to a lowfrequency (∼30 cm −1 ) out-of-plane vibrational mode of pentacene. 71 Although the details of the coupling mechanism between S 1 and T 1 can be quite involved and diverse, 66 owing to the varying contributions of, e.g., direct and vibronically induced spin−orbit coupling for different species, the common conclusion for the few systems studied appears to be that the thermal population of higher vibrational levels of S 1 lowers the energy gap to higher triplet states T n (n > 1), thereby increasing the ISC rate.…”

“…For anthracene crystals, it was found that in the range of 140–430 K, the temperature dependence of ISC follows a thermally activated process with an activation energy of 800 cm –1 . Studies of brominated anthracenes in 3-methylpentane over a comparable temperature range gave similar activation energies . For pentacene/ p -terphenyl mixed crystals, the temperature dependence of the pentacene ISC rate between 4.2 and 140 K was attributed to a vibronically induced process due to a low-frequency (∼30 cm –1 ) out-of-plane vibrational mode of pentacene .…”

“…The temperature dependence of S 1 –T 1 ISC has been studied for several PAHs, particularly linear polyacenes such as naphthalene and anthracene. ,− In general, ISC will be temperature dependent if higher vibrational levels v of S 1 (S 1, v ) have a different mechanism for the nonradiative transition to T 1 than the vibrationally relaxed S 1,0 level. In most cases, the temperature dependence of the ISC rate has been expressed as a thermally activated process, by which a higher triplet state T n ( n > 1) is populated at elevated temperatures.…”

Anisotropic Intersystem Crossing from the Upper Excited Triplet States of Anthracenes: Two-laser Time-Resolved EPR Study

“…Hamanoue et al pointed out that the direct S 1 → T 1 ISC is very important in BA and DBA at low temperatures, because the temperature independent rates of fluorescence and ISC are comparable. Since the direct S 1 → T 1 ISC process gives the preferential population into the middle and highest sublevels, the combination process involving the RISC followed by ISC diminishes the ESP generated by the IC process from the polarized T 2 state.…”

“…The relaxation processes from the excited states in anthracene and its derivatives have been under investigation more than three decades because of the large energy difference between the T 2 and T 1 states. Various experimental results, such as the buildup rates of the T−T absorption and the temperature dependence of the fluorescence yields as well as lifetimes, indicate the participation of the T n ( n = 2 or 3) states in the S 1 →T 1 ISC process. − It has been clarified, furthermore, that the rates of the RISC (T 2 →S 1 ) and T 2 → T 1 internal conversion (IC) are comparable. ,− The effects of temperature and heavy atoms on the quantum yield (Φ TS ) of the RISC were also studied by the stepwise two-photon excitation technique. The results were well interpreted in terms of the relative energy levels of the S 1 and T 2 levels and the spin−orbit coupling (SOC).…”