Design of Azobenzene beyond Simple On–Off Behavior

Abstract

Azobenzenes are without a doubt the most widely used light-induced switching units, and there is a plethora of application examples ranging from supramolecular chemistry to material science and biological chemistry. Here, we present a smart azobenzene, in which the photoswitching capability of the azobenzene moiety can be reversibly switched on and off using a second unit (redox switch). This second switching unit is based on the variation of the strength of a chalcogen bond between the azo group and a Te–Ph unit in ortho position to the azo group. This allows the selective switching of only one azobenzene unit in the presence of other azobenzene switches. The entire double-switch is a very simple, small system that can also be easily synthesized. As a result, this double-switch can be used as a smarter replacement for the established azobenzene system in the future. For example, in contrast to the latter this double-switch could be employed to store state information analogous to a flip-flop in digital electronic systems.

Bridging D–A type photosensitizers with the azo group to boost intersystem crossing for efficient photodynamic therapy

“…Since azo-bridging of two molecules of TPA-Th(+) generated an azobenzene structure, the resulting Azo-TPA-Th(+) could respond to UV irradiation by experiencing trans-to-cis isomerization. [46][47][48] According to the theoretical calculations, cis-Azo-TPA-Th(+) should be potentially efficient in fluorescence emission rather than ROS generation. To verify our hypothesis, we studied the photophysical properties of Azo-TPA-Th(+) in phosphate buffered saline (PBS) before and after UV irradiation.…”

Fast relaxing red and near-IR switchable azobenzenes with chalcogen and halogen substituents: periodic trends, tuneable thermal half-lives and chalcogen bonding

“…Further evidence for this X•••N chalcogen bonding interaction can be inferred from the inherent preference for 5 membered intramolecular X•••N interactions over 4 membered (dX•••N < dX•••N'), where the highly directional chalcogen bond overlap is more feasible (Figure 5d). 43 Conversely, the halogens have no preference between 4 or 5 membered interactions because the halogen centred σhole is on the pole of the halogen atom and therefore cannot interact with the azo N via a linear halogen bond. Conformations where steric clash is minimised are therefore favoured (dX…”

Interplay between chalcogen bonds and dynamic covalent bonds

“…Energy decomposition analysis (EDA) has been gaining increasing popularity in exploring the nature of non-covalent interactions. [57][58][59][60][61][62][63][64] To probe intramolecular contact, generalized Kohn-Sham energy decomposition analysis (GKS-EDA) [65][66][67] was used to calculate the total interaction energy of 1/2 and dissect the contributing factors to chalcogen bonding by the modified GAMESS package. 68 GKS-EDA divides the total interaction energy (ΔE TOT ) into electrostatic (ΔE ele ), exchange-repulsion (ΔE ex-rep ), polarization (ΔE pol ), correlation (ΔE corr ), and dispersion (ΔE disp ) terms as follows in eqn (1).…”