Photoisomerization of stilbene in low viscosity solvents: Comparison of isolated and solvated molecules

Abstract

Viscosity and solvent dependence of lowbarrier processes: Photoisomerization of cisstilbene in compressed liquid solventsThe photoisom~rization .of stilbene has been studied in low viscosity liquid alkanes and in the gas ph~e. The bamer cross1Og process shows no evidence of a low-friction or energy controlled regton e~en at the lowest liquid visc~siti~s studied. We present evidence that the barrier crossing may be 10 the energy controlled regton 10 the thermal vapor. We discuss the influence of intramolecular.vibrati~nal energ! transfe~ on the observed dynamics and note that entropy effects should be conSIdered 10 companng expenmental data with theoretical models.

Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

“…First, the isomerization proceeds much faster in the former (∼2 ps) 7,8,11,14,16,18,24,25,27,32 than in the latter (10À200 ps). 9,10,24,25,36 The experiments illustrate that there is a relatively large barrier (∼3 kcal/mol) on the trans-to-cis isomerization path, 3,4,6,31 while the cis-to-trans reaction involves a negligible barrier or a barrierless process. 17,24,27,30,34 Second, in the cisstilbene isomerization reaction, a cyclization product, 4a,4b-dihydrophenanthrene (DHP), is observed along with the trans isomer product, although the experimental quantum yield is relatively small (0.10) compared to that of the trans isomer (0.35).…”

Communication: Optical cooling of trans-stilbene

“…On one hand, in solution, the isomerization rate is higher by an order of magnitude compared to the rate in low pressure gases. [12][13][14][15] On the other hand, transition-state or Rice-Ramsperger-Kassel-Marcus (RRKM) theories [21][22][23][24] predict similar rates. What is the mechanism which is responsible for speeding up the isomerization in a liquid environment?…”

“…Possible answers have been debatedwithout definite conclusion-since the 1980s. (i) Fleming and co-workers [14][15][16] conjectured that the reaction may be nonadiabatic in the isolated molecule but becomes adiabatic in liquids with increasing collision frequency. [3][4][5][6][7] (ii) A barrier E b to isomerization may become lower with increasing buffer density, due to clustering.…”

“…8,9,[13][14][15][16][17][18][19][20] Nevertheless a serious question remains unresolved. On one hand, in solution, the isomerization rate is higher by an order of magnitude compared to the rate in low pressure gases.…”

“…Photoinduced isomerization of trans-stilbene [1][2][3] has been studied for over 40 years under diverse conditions: in supersonic jets, [3][4][5][6][7] low and high pressure gases, 3,[10][11][12][13][14][15][16][17] and in liquids. 8,9,[13][14][15][16][17][18][19][20] Nevertheless a serious question remains unresolved.…”