Ring-opening reaction of a trifluorinated indolylfulgide: mode-specific photochemistry after pre-excitation

Abstract

SummaryThe ring-opening reaction of a trifluorinated indolylfulgide has been studied as a function of temperature and optical pre-excitation where it was found that reaction times decreased as temperature increased from 10.3 ps at 12 °C to 7.6 ps at 60 °C. Simultaneously, the quantum yields for the ring-opening reaction grew from 3.1% (12 °C) to 5.0% (60 °C). When the reaction was started from a nonequilibrium state generated by a directly preceding ring-closure process, the ring-opening reaction became faster and the quantum efficiency increased by more than a factor of three. Analysis of the experimental results points to mode-specific photochemistry in that the promoting, photochemically active modes of the photoreaction are efficiently excited by the directly preceding ring-closure reaction.

Stability and reaction dynamics of trifluorinated indolylfulgides

“…The further time constants observed in the transient absorption data can be assigned to cooling dynamics of the hot ground state of the reactant and product molecules. This result is in very good agreement with data on the ring-closure reaction of other indolylfulgides and indolylfulgimides, though the quantum efficiency η of fulgide 2 (about 8%) is lower and the reaction time is somewhat faster than in the previous investigated molecules [15,16,32-34]. It is observed that this reaction is not thermally activated, since reaction rates and efficiencies do not vary in the investigated temperature range between 287 and 333 K.…”

“…The essential features observed for fulgide 2 agree well with those found for other indolylfulgides and indolylfulgimides [15,17,30,33-37]. The experiments on the ring-opening reaction of fulgide 2 indicate that cycloreversion occurs on a time scale of about 4 ps (corresponding to the lifetime τ 2 of the excited state), whereas other signal components can be attributed to solvation and cooling dynamics.…”

“…One channel, the so-called nonreactive pathway, has a small barrier (375 cm −1 ) and leads exclusively back to the ground state of the C -form. The other, the reactive channel, which allows also access to the open Z -form, exhibits a higher barrier (1055 cm −1 ), see Table 1 [15]. …”

On the excitation wavelength dependence and Arrhenius behavior of stilbene isomerization rates in solution

“…Thus at 300 K, the gas-phase rate is about 1 ns À1 whereas in hexane it is more than 10 times faster [7][8][9][10][11][12][13][14]. Various explanations of this observation have been proposed [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], the restricted IVR mechanism [11][12][13][14][25][26][27] being now widely accepted. It suggests that stilbene torsion about the C@C bond is weakly coupled to other vibrational modes, resulting for isolated molecules in a slow energy transfer, and accordingly slow isomerization rates.…”

Controlling the Excited-State Reaction Dynamics of a Photochromic Molecular Switch with Sequential Two-Photon Excitation

“…27,38,43 However, this scenario is unlikely because the GSB does not recover to any extent on the ∼3 ps time scale, even though the hot ground state should at least partially recover the ground-state spectrum upon internal conversion. Furthermore, Shim et al 16 show that the timeresolved fluorescence of a very similar diarylethene derivative decays with two time scales (4 and 22 ps, in that compound), which can only be explained with two decay times in the excited state.…”