Computational Investigation into Photoswitching Efficiency of Diarylethene Derivatives: An Insight Based on the Decay Constant of Electron Tunneling

Abstract

The switching efficiency (SE) of the intramolecular exchange interaction <i>J</i> between the open- and the closed-ring isomers of diarylethenes (DAEs) was investigated using DFT calculations of DAE biradicals with different core structures: DAEs with 3-thienyl, thiophene-<i>S</i>,<i>S</i>-dioxide-3-yl, 2-thienyl, or thiophene-<i>S</i>,<i>S</i>-dioxide-2-yl rings. The SE of DAE with a 3-thienyl ring is calculated to be around 400-fold, which is the largest among the four calculated DAEs. The decay constant β of the exchange interaction <i>J</i> for the DAE molecular wires was evaluated by calculating <i>J</i> for biradicals with different lengths of wires. For the wires of the closed-ring isomers of DAE with 3-thienyl- and thiophene-<i>S</i>,<i>S</i>-dioxide-3-yl rings, which are supposed to take a quinoid structure, allyl nitronyl nitroxide radical was successfully employed. The calculated β values showed a significant difference between the open- and the closed-ring isomers, and this difference of β is considered to be the origin of photoswitching of <i>J</i>. The difference of β upon isomerization, Δβ, is in good agreement with SE, and the largest Δβ was obtained for the DAE with a 3-thienyl ring. We can understand the switching of <i>J</i> as the switching of electron tunneling efficiency β between the open- and the closed-ring isomers