Recent advances in photoresponsive fluorescent materials based on [2+2] photocycloaddition reactions

The development of light responsive fluorescent materials with nondestructive and high-contrast signaling properties has attracted much attention due to their potential use in a variety of areas, such as optical sensing, data storage, smart display, and advanced anti-counterfeiting. In general, most light responsive fluorescent materials are built on intramolecular Z/E photoisomerisation and photocyclisation of a single molecule, making them more suitable for solution-based systems due to the aggregation-caused quenching effect. Recent advances demonstrated that intermolecular [2+2] photocycloaddition reactions could be exploited to construct a new class of light responsive fluorescent materials whose solid-state fluorescence can be dramatically photoactivated. Such a conversion of solid-state emission from quenched to enhanced emission provides a promising solution to overcome the notorious aggregation-caused quenching effect, making these smart molecules more suitable for surface/interface-involved applications. This review systematically summarized recent advances in photoresponsive fluorescent molecules based on intermolecular [2+2] photocycloaddition reactions. The molecules were classified into four groups based on their molecular skeletons: diarylethenes, cyanodiarylethenes, benzoheterocycles, and diaryl acetylenes. We highlighted the structural design of these smart molecules, controlled molecular aggregation in different environments, including ordered crystals, disordered polymers, order-dependent liquid crystals, and caves of specific supramolecules, and their distinct photoactivation mechanisms of solid-state fluorescence. Finally, we analyse the challenges and opportunities for the future development of light responsive fluorescent materials based on intermolecular [2+2] photocycloaddition as a promising class of smart materials.

Automated summary

The development of light responsive fluorescent materials with nondestructive and high-contrast signaling properties has attracted much attention. Recent advances in intermolecular [2+2] photocycloaddition reactions have led to the construction of a new class of light responsive fluorescent materials with enhanced solid-state fluorescence. This review summarizes the recent advances in structural design, controlled molecular aggregation, and distinct photoactivation mechanisms of these smart materials, and discusses the challenges and opportunities for future development.