Experimental Characterization and Modeling of Photon Upconversion in Azobenzene Photomechanical Polymers

Abstract

Azobenzene polymers show promising photostrictive behavior for a broad range of applications in flow control, robotics, and energy harvesting applications. The conversion of solar energy directly into mechanical work provides unique capabilities in adaptive structures; however, the energy conversion of visible light into mechanical work presents several material chemistry challenges. Azobenzene strongly absorbs ultraviolet (UV) light and blue/green light which limits the efficiency of the photomechanical response under solar irradiation. Photon upconversion — combining two or more low energy photons (longer wavelength) to generate a higher energy excited state (shorter wavelength), provides an intriguing strategy to drive these high energy photochemical reactions with low energy light. We present an experimental study showing the feasibility to drive azobenzene photoisomerization using visible light via select up-conversion molecules in the fluidic state. Multi-physics modeling is then used to predict advances in photomechanical energy conversion when up-conversion molecules are introduced within an azobenzene polymer.