Achieving highly efficient aggregation-induced emission, reversible and irreversible photochromism by heavy halogen-regulated photophysics and D-A molecular pattern-controlled photochemistry of through-space conjugated luminogens

It is extremely challenging but desirable to regulate the photophysical and photochemical processes of aggregation-induced emission luminogens (AIEgens) in distinct states in a controllable manner. Herein, we design two groups of AIEgens based on a triphenylacrylonitrile (TPAN) skeleton with through-space conjugation (TSC) property, demonstrate controlled regulation of photophysical emission efficiency/color and photochemical photochromic and photoactivatable fluorescence behaviours of these compounds, and further validate design principles to achieve highly efficient and emission-tuning AIEgens and to accomplish photo-dependent color switches and fluorescence changes. It is surprisingly found that the introduction of heavy halogens like bromine into a TPAN skeleton dramatically enhances the emission efficiency, and such an abnormal phenomenon against the heavy-atom effect is attributed to the specific through-space conjugation nature of the AIE-active skeleton, effective intermolecular halogen-bond-induced restriction of intramolecular motions, and heavy atom-induced vibration reduction. The incorporation of two electron-donating amino groups into the TPAN skeleton cause the luminogens to undergo a bathochromic shifted emission due to the formation of a D-A pattern. Apart from the regulation of photophysical processes in the solid state, the construction of the D-A pattern in luminogens also results in extremely different photochemical reactions accompanying reversible/irreversible photochromism and photoactivatable fluorescence phenomena in a dispersed state. It is revealed that photo-triggered cyclization and decyclization reactions dominantly contribute to reversible photochromism of the TPAN family, and the photo-induced cyclization-dehydrogenation reaction is responsible for the irreversible color changes and photoactivatable fluorescence behaviours of the NTPAN family. The demonstrations of multiple-mode signaling in photoswitchable patterning and information encryption highlight the importance of controlled regulation of photophysics and photochemistry of fused chromic and AIE-active luminogens in distinct states.

Automated summary

This study successfully demonstrates the controllable regulation of photophysical and photochemical processes by designing new AIEgens, including emission efficiency, color tuning, and photochemical reactions. By introducing heavy halogens and electron-donating groups, efficient emission control and color changes in the luminogens are achieved.