Strong, Nonresonant Radiation Enhances Cis–Trans Photoisomerization of Stilbene in Solution

Abstract

Previously, it has been demonstrated that external electric fields may be used to exert control over chemical reactivity. In this study, the impact of a strong, nonresonant IR field (1064 nm) on the photoisomerization of cis-stilbene is investigated in cyclohexane solution. The design of a suitable reaction vessel for characterization of this effect is presented. The electric field supplied by the pulsed, near-IR radiation (ε l = 4.5 × 10 7 V/cm) enhances the cis → trans photoisomerization yield at the red edge of the absorption spectrum (wavelengths between 337 and 340 nm). Within the microliter focal volume, up to 75% of all cisstilbene molecules undergo isomerization to trans-stilbene in the strong electric-field environment, indicating a significant increase relative to the 35% yield of trans-stilbene under field-free conditions. This result correlates with a 1−3% enhancement in the trans-stilbene concentration throughout the bulk solution. Theoretical analysis suggests that the observed change is the result of dynamic Stark shifting of the ground and first excited states, leading to a significant redshift in cis-stilbene's absorption spectrum. The predicted increase in the absorption cross section in this range of excitation wavelengths is qualitatively consistent with the experimental increase in trans-stilbene production.

Spectral photokinetic conversion of the fluorescent probes BSB and K114 for improved detection of amyloid assemblies

“…As we have recently reported, the paradoxical intensity and spectral changes induced by repeated light exposure likely reflect complex photoreactions induced between the dye and surrounding residues of proteins making up the β-sheet assemblies [26]. It is possible that intensity and emission changes of the amyloid-bound dyes are driven by the trans-cis photoisomerization of the stilbene groups, catalyzed by high near-UV laser power [31,32]. Notably, in our previously published study, another Congo Red derivative, X-34, exhibited neither photoinduced fluorescence enhancement, nor the spectral blue-shifting, despite having a similar chemical structure to BSB and K114; the bromine atom on the central ring is one key difference and likely plays a key role in the observed photoreactions.…”

Non-Born–Oppenheimer effects in molecular photochemistry: an experimental perspective

“…But even under isolated molecule conditions, the PESs can be modified by external fields and we note recent interest in using intense non-resonant (typically near IR) laser fields and the dynamic Stark effect to shift and reshape the field-free BO PESs and the couplings between them. Notable demonstrations include intense IR-field induced changes in the relative yields of ground and spin-orbit excited Br atoms in the near UV photodissociation of IBr [102] and of ground and spin-orbit excited I atoms in the UV photolysis of CH 3 I [103], in the speed distributions of the H atoms resulting from UV photolysis of phenol (implying changes in the vibronic population distribution in the phenoxyl radical partner) [104] and even in the efficiency of the UV-driven isomerization of cis - to trans -stilbene in solution in cyclohexane [105].…”

Nanoscale Saturn Systems Based on C60/70 Bucky Ball and a Newly Designed [4]Cyclopara-1,2-diphenylethylene Hoop: A Strategy for Fullerene Encapsulation Release and Selective Recognition for C70

“…Azobenzene-containing molecules are widely used as photoresponsive compounds, − because they can perform reversible transformation between trans and cis forms with photoirradiation. Similarly, the 1,2-diphenylethylene unit is also an ideal photoresponsive group. − A large amount of experimental data − show that the quantum yields of 1,2-diphenylethylene from cis to trans and from trans to cis configuration are about 35 and 55%, respectively. The azobenzene group has been used for the design of the planar nanorings (which have no geometric matching with fullerenes), , whereas the 1,2-diphenylethylene unit is seldom applied to the design of nanoring molecules.…”