Computational chemistry modeling and design of photoswitchable alignment materials for optically addressable liquid crystal devices II: Transition state modeling in azobenzene and spiropyran oligomers (Conference Presentation)

Computational chemistry tools such as density functional theory (DFT) have seen increasing application in the design and development of new organic optical materials, organic light emitting diodes (OLED) and liquid crystals. In previous work, we employed DFT to model the trans–cis isomerization state energies in a series of methacrylate and acrylamide photoswitchable polymer alignment materials functionalized with azobenzene pendants connected through a flexible alkyl chain (tether). Such photoswitchable alignment materials are of interest for LC devices for beam shaping due to their remarkable 1054 nm, 1 ns laser damage thresholds (28 to 67 J/cm2) and their ability to support spatially-varying write-erase capability. These modeling efforts were confined to a small representative section of the photoaligment polymer (an oligomer) composed of one tethered chromophore and four repeat backbone segments to reduce the large amounts of computational resources and time that would be required to accurately model a complete polymer system. Twenty-two different terminal functional groups were evaluated computationally to determine their individual effects on the trans and cis isomerization-state energies of the methacrylate and acryamide oligomers when used as substituents on azobenzene cores linked through a four-carbon tether to methacrylate and acrylamide backbones. The contribution of the alkyl tether to the isomerization-state energies of the methacrylate and acrylamide oligomers was also investigated computationally. This work extends the previous study by using DFT to evaluate the effect of molecular structure and tether length on the transition state energy barrier separating the pendant’s isomeric switching states, which can have a large effect on bistability, write-erase fatigue, and switching energy requirements. Both oligomers containing azobenzene and spiropyran photoswitchable pendants were modeled in this study.