Prediction of Thermal Stability of Photochromic Materials Used for Optical Switching and Data Storage Applications

Certain organic compounds posess the ability to change color under the influence of light, called photochromism. This change is often due to ultrafast chemical transition from open to closed ring isomers (photocyclization). Information thechnology applications of these photochromics require the reverse transformation to be very slow in the dark. We have applied Density Functional Theory (DFT) methods to predict kinetics of this cycloreversion. This cycloreversion occurs through symmetry forbidden conrotatory electrocyclic mechanism with transition state of strong diradical character, and requires the unrestricted broken-symmetry DFT formalism. Our results suggest that B3LYP functional describes the activation barrier for the cycloreversion process with about 1-2 kcal/mol error, while M052x functional gives an error of about 2-3 kcal/mol compared to the experimental values.