Covalent carbon nanodot-azobenzene hybrid photoswitches: the impact of meta/para connectivity and sp3 spacer on photophysical properties

The covalent surface functionalization of carbon nanodots (CNDs) can facilitate the design and development of nanocarbon hybrids with photoswitching properties, which can be applied in a wide range of applications, including sensing, optoelectronics, and even bio-applications. This study underscores the potential utilization of these hybrids as photoresponsive materials, for potential application in optostimulation. In this study, we examine the characteristics of covalent azobenzene-functionalized CNDs, with a particular emphasis on the impact of meta and para connectivity and the additional introduction of a glycine spacer. The CND synthesis process comprises a bottom-up microwave condensation of ethylenediamine and citric acid. Amide coupling to azobenzenes is confirmed through NMR diffusion-ordered spectroscopy and diffusion decay analysis. A comprehensive investigation is conducted into the size and optical properties of the resulting hybrids. Moreover, time-dependent density functional theory computations are employed to understand absorption spectra and charge transfer events. Furthermore, advanced optical characterisation is utilised to examine energy/charge transfer between the constituents. Finally, the switching properties, fatigue resistance, and half-life of the hybrids are studied to evaluate their performance for prospective applications like in optostimulation.