A Highly Emissive Diarylethene Photoswitch with Efficient Reversible Switching in Solution and the Solid State

A highly emissive diarylethene photoswitch was developed by introducing a phenyl substituent into a benzophosphole-containing framework. The closed-ring isomer exhibited high fluorescence quantum yields in cyclohexane (Φf = 0.72) and powder (Φf = 0.96), while retaining sufficient cycloreversion reactivity (ΦCO = 3.7 × 10−2) and reversible photoswitching. Analysis of the excited-state decay processes revealed that the enhanced fluorescence primarily originates from suppressed non-radiative deactivation, demonstrating efficient emission in both solution and the solid state with reversible photoswitching.