Strong, Nonresonant Radiation Enhances - Photoisomerization of Stilbene in Solution.

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 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 = 4.5 × 10 V/cm) enhances the → 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 stilbene molecules undergo isomerization to stilbene in the strong electric-field environment, indicating a significant increase relative to the 35% yield of stilbene under field-free conditions. This result correlates with a 1-3% enhancement in the 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 -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 -stilbene production.