Femtosecond photoisomerization of cis-azobenzene

Femtosecond fluorescence up-conversion spectroscopy of a rotation-restricted azobenzene after excitation to the S1state

“…Both processes are assumed to take place through CIs between the S 1 and S 0 potential energy surfaces (PES) of the molecules near the mid-points of the transcis isomerization reaction coordinates. 11,[14][15][16][17][18][19][20][21]26,27 As has been shown, S 1 fluorescence and excited state (S n ' S 1 ) absorption decay on the same time scale and this decay is accompanied by the appearance of ''hot'' ground state absorption as signature of the S 1 -S 0 internal conversion. 11,12,15,28 Thus, nonradiative electronic relaxation and isomerization of AB are closely connected.…”

“…Considering the unsubstituted parent trans-or cis-AB, the ''inversion'' mechanism has received support from Na¨gele et al and Satzger et al, 11,15,27 who compared time-resolved absorption results on trans-and cis-AB after S 1 (np*) and after S 2 (pp*) excitation. Transient signals of trans-AB in ethanol or DMSO in the case of S 1 excitation were found to exhibit decay times of t 1 E 0.3 and t 2 E 2-3 ps; those of cis-AB could be described with decay times of t 1 E 0.1-0.17 and t 2 E 0.9-1.0 ps, in excellent agreement with the fluorescence up-conversion data on the S 1 state obtained in our laboratory 16 and by Lu et al 14 Apart from an additional very fast decay time (t0.1 ps) attributed to internal conversion from the S 2 to the S 1 state, virtually the same decay times were found following S 2 excitation, in agreement in this case with fluorescence up-conversion data by Fujino et al 37 These results were interpreted by Satzger et al in terms of a two step model, whereby an ultrafast radiationless transition (t0.1 ps) takes the molecules first from S 2 to S 1 .…”

“…[11][12][13][14][15][16] The corresponding reaction of cis-AB has been found to be even faster. 15,16 Most workers assumed the abovementioned semi-linear ''inversion'' pathway.…”

“…15,16 Most workers assumed the abovementioned semi-linear ''inversion'' pathway. [11][12][13]15 However, the ''rotational'' isomerization route has recently received substantial support from a number of quantum chemical calculations. In particular, calculations on the semi-linear inversion mechanism in the S 1 state predicted a potential energy barrier for that pathway.…”

Azobenzene-functionalized alkanethiols in self-assembled monolayers on gold

“…In solution optical excitation of the π−π * and n−π * transitions reversibly switches between these conformers. The (sub)picosecond time constant of the isomerization reaction in solution yields a quantum efficiency close to unity [1,2], and switching is possible even with a photodiode. In contrast, no successful reversible switching by optical excitation has been achieved to date when the bare azobenzene molecule is adsorbed at a metal surface.…”