Promoting Z-to-E Thermal Isomerization of Azobenzene Derivatives by Noncovalent Interaction with Phosphorene: Theoretical Prediction and Experimental Study

The ability to modulate the rate of Z/E isomerization of azobenzene (AB) derivatives is crucial to the practical applications of biological and photofunctional systems. Four kinds of AB-OC4H8-R derivatives (AB-1, R = NMe3+I-; AB-2, R = NH2; AB-3, R = C6H13; AB-4, R = SH) were incorporated into liquid-exfoliated black phosphorus (BP) nanosheets through noncovalent functionalization. Experiments indicated that the switching process between the two states, trans (E) and cis (Z), especially the Z-to-E thermal conversion of AB derivatives, was accelerated 2-23 times by the presence of phosphorene at temperatures of 293-313 K. The acceleration phenomenon was rationalized by density functional theory (DFT) calculations, which reveals that the interaction between phosphorene and AB derivatives stabilized the Z isomer and transition state of azobenzene in a less degree than the E isomer, hence lowering the activation energy (E-a) of the Z-to-E isomerization. A close correlation is shown between the extent of charge transfer, the binding energy, and the Z-to-E thermal activation energy. The reactive molecular dynamics simulations also demonstrated a threefold faster isomerization process for AB@BP hybrids to accomplish the thermal relaxation relative to the free-standing AB. The predicted energy difference between E and Z isomers of AB@BP hybrids are enhanced 2-3 times upon deposition on the BP substrate. The photoresponsive AB@BP system suggests a new platform for energy conversion and potential applications in the biological field.