Triplett-Lebensdauern von Diphenylpolyenen und deuterierten Stilbenen in eingefrorener Lösung bei 77°K / Triplet Lifetime of Diphenylpolyenes and deuterated Stilbenes in frozen solution at 77°K

Abstract

The lowest triplet states of diphenylpolyenes and of deuterated stilbenes were observed by means of photoflash asportion spectroscopy. The diphenylpolyenes do not show phosphorescence. The triplet lifetime is strongly dependent on triplet energy. This is consistent with the known influence of Franck-Condon factors. The triplet lifetime of partially deuterated stilbenes depends on the number and the position of the deuterium atoms. The effect of olefinic monodeuteration on the non-radiative process is approximately 16 times larger than that of deuteration at an aromatic position. The observations can be explained in terms of isotope effects on vibronic spin-orbit coupling.

Temperature Dependence of the 1,6-Diphenyl-1,3,5-hexatriene Triplet Lifetime in Solution and Theoretical Evaluation of Triplet Conformer Interconversion

“…9 The lifetime increase to 400 µs in EPA (diethyl ether, isopentane, and ethanol in a 5:5:2 ratio) at 77 K corresponds to a triplet ttt-DPH decay rate constant of 2.5 × 10 3 s -1 . 15 Because no conformer interconversion can take place in such a rigid medium and no phosphorescence was detected, 15 that rate constant was assigned to the radiationless decay of 3 ttt*. 15 Accordingly, we had expected a very small DPH triplet lifetime T dependence, corresponding to an activation energy of no more than 0.4 kcal/ mol.…”

“…10 The nearly seven-fold attenuation in the decay rate constant upon changing the medium from fluid solution at room T to a glassy medium at 77 K does suggest that torsional motion plays a role in the decay process. 1,[15][16][17] This study tests (1) the DPH triplet decay mechanism experimentally through measurements of the T dependencies of triplet lifetimes and photostationary states and (2) the shape of the DPH triplet potential energy model computationally.…”

Cis-trans photoisomerization of 4-nitrostilbenes

“…<""!<: -7 tr 3 -> tr 0 (8) p3 -> Po (9) Po -> a.tr 0 + (1-a. )c 0 (10) Reaction 2 represents absorption of light by the trans ground state (tr 0 ).…”

“…tr 0 + (1 -a. )c 0 (9,10) Equation 12 represents absorption of light. The excited cis singlet state (c 1 ) converts to the twisted excited singlet state (p 1 , eq.…”

“…30). In the case of 4-nitro-4'-methoxystilbene the energy difference E(tr 3 ) -E(tr 0 ) is 46.5 kcal/mol whereas E(p 3 ) -E(p 0 ) is only [5][6][7][8][9][10]51). In other words the Franck-Condon factors strongly favour reaction 9 over reaction 8.…”