Double crossing conical intersections and anti-Vavilov fluorescence in tetraphenyl ethylene

Conical intersections (CIs) provide effective fast nonradiative decay pathways for electronic excitation, which can significantly influence molecular photoluminescence properties. However, in many cases, crossing a CI does not have direct observables, making studies of CIs experimentally challenging. Herein, the theoretically predicted double CIs by cis-trans twisting and cyclization in tetraphenyl ethylene, a well-known aggregation-induced emission molecule, are investigated with excitation dependent ultrafast UV/IR spectroscopy and fluorescence. Both the fluorescence quantum yield and the efficiency of cyclization are found to be smaller with a shorter excitation wavelength. An abrupt change occurs at about 300-310 nm. The results imply that crossing the twisting CI has a larger barrier than the cyclization CI, and the cis-trans twisting motion is probably involved with large solvation reorganization.& nbsp;& nbsp;Published under an exclusive license by AIP Publishing.

Automated summary

Conical intersections (CIs) play a crucial role in the nonradiative decay of electronically excited states. This study investigates double CIs in tetraphenyl ethylene using ultrafast spectroscopy and fluorescence. The results reveal the relationship between fluorescence quantum yield, cyclization efficiency, and excitation wavelength.