SummaryPhotochromic switches that are able to transmit information in a quick fashion have attracted a growing interest within materials science during the last few decades. Although very fast photochromic switching materials working within hundreds of nanoseconds based on other chromophores, such as spiropyranes, have been successfully achieved, reaching such fast relaxation times for azobenzene-based photochromic molecular switches is still a challenge. This review focuses on the most recent achievements on azobenzene-based light-driven real-time information-transmitting systems. Besides, the main relationships between the structural features of the azo-chromophore and the thermal cis-to-trans isomerisation, the kinetics and mechanism are also discussed as a key point for reaching azoderivatives endowed with fast thermal back-isomerisation kinetics.

No abstract

Synthesis and characterization of new carbazolyl derivatives with a pendant stable radical of the TTM (tris-2,4,6-trichlorophenylmethyl radical) series are reported. The EPR spectra, electrochemical properties, absorption spectra, and luminescent properties of these radical adducts have been studied. All of them show electrochemical amphotericity being reduced and oxidized to their corresponding stable charged species. The luminescence properties of them cover the red spectral band of the emission. The luminescence of the electron-rich carbazole adducts shows the donor-acceptor nature of the excited state. On the other hand, the EPR parameters of these radical adducts show an imperceptible variation with the substituents in the carbazole.

The thermal cis-to-trans isomerisation process has been studied for a series of para-, ortho- and polyhydroxy-substituted azobenzenes in different solvents. The kinetics of the thermal back reaction for the p-hydroxy-substituted azobenzenes depend strongly on the nature of the solvent used, with relaxation times ranging from 200-300 milliseconds in ethanol to half an hour in toluene. Otherwise, the process rate is mainly independent of the solvent nature for the ortho substituted analogues. Polyhydroxy-substituted azobenzenes show very much faster kinetics than the para- and ortho- monohydroxyazoderivatives. With relaxation times of 6-12 milliseconds in ethanol, they are optimal molecules for designing fast optical switching devices. All the hydroxyazoderivatives thermally isomerise from the metastable cis form to the thermodynamically stable trans isomer through a rotational mechanism.