Radiationless Triplet—Singlet Transitions in Naphthalene

Abstract

The fluorescent intensity, phosphorescent intensity, and phosphorescent lifetime of naphthalene and naphthalene-ds, dissolved in durene, were measured as a function of temperature from 77° to 325°K. These measurements indicate that radiationless transitions from the first excited singlet state are temperature-independent but radiationless transitions from the lowest triplet are strongly temperature-dependent. Analysis of the data for the decay of the triplet state indicates that only one activated state is responsible for this temperature dependence. The activation energy and pre-exponential factor for decay from this state are 3559±79 cm—1 and (4.2±1.5)×107 sec—1 for naphthalene, and 3362±35 cm—1 and (1.30±0.24)×107 sec—1 for naphthalene-ds. These data can be interpreted as corresponding to the excitation of one of the intramolecular CC stretching modes to its second excited state or a combination of two CC fundamentals.

Photochemical transformations of small ring carbonyl compounds. XXIII. Photoinduced ring expansion of arylaroylazetidines. Mechanistic studies and characterization of the excited state

“…Substitution of hydrogen with deuterium in organic compounds may exert a marked effect on certain properties of their excited states. [30][31][32][33][34][35][36][37][38] Theory predicts that deuterium should decrease the rate of ' -* S°and S' -*-S°radiationless transitions.34 In addition, the usual isotope effect involved in the breaking of a C-D bond may cause a mod-ification in the photochemical behavior of an organic compound.35•36 Since information concerning radiationless decay paths of the benzoylazetidines under investigation is essential for a detailed understanding of the mechanism of these rearrangements, we were prompted to investigate the photochemical behavior of deuterated azetidines 9-12. Of specific concern was what effect deuterium substitution had on the quantum efficiency and distribution of photoproducts of the trans isomers 10 and 12.…”

Effects of impurity traps on exciton-guest, triplet-triplet annihilation in pyrene-d10 doped single crystal of fluorene

“…We restrict ourselves to observing reactions at times only after excitation cut-off which are long compared with (K~ +k~)-l. With this assumption we can apply the stationary state approximation in equation There could be another term in equation (7) representing the trap-trap triplet annihilation. At low impurity concentration we have neglected such a term from equation (11). Integration of equation-(7) yields the impurity phosphorescence…”

“…From here we conclude that the temperature-dependence of delayed fluorescence life times of pyrene-dl0 in the fluorene host is controlled by thermally stimulated intermolecular events, via the process Tli ~ T~ I followed by annihilation of T 1 p and. that temperature dependent intramolecular events are of no consequence [11]. Therefore the temperature-dependence of z is largely determined by the energy gap AE~ =(Tls -T,,)~_(T~ -TI~), and thus by the matrix.…”

Enhanced Intersystem Crossing due to Resonant Energy Transfer to a Remote Spin

“…An important consideration is the type of system in which this energy matching can occur. The energy difference between the sing-doublet and trip-doublet states is dominated by the singlet–triplet energy difference of the chromophore and is typically about 0.3–0.7 eV (2400–6800 cm –1 ) in porphyrins. , Higher values of ∼7500 cm –1 have been reported for some pentacene derivatives, and in naphthalene and anthracene, the gaps are 1.36 and 1.48 eV (11000 and 12000 cm –1 ). For the RSOC-ISC mechanism to be effective, excitation of the radical should overlap with these energies and the Franck–Condon factor for the excitation should not be small.…”