Dual-responsive molecular systems via π-bridge engineering: Visible-light photochromism, electrofluorochromism and differential emission switching

Smart stimuli-responsive materials have attracted considerable attention due to their crucial role in advancing next-generation technologies. Optical and electrical stimuli are particularly valuable owing to their high sensitivity and rapid response kinetics. In this study, we develop an innovative multi-stimuli-responsive molecular system through π-conjugation engineering. This system integrates electroactive triphenylamine (TPA) and photoactive phenanthrene motifs using both direct linkage and benzene-ring-bridged strategies. Systematic investigations reveal that π-conjugation extension plays a decisive role in governing the photochemical and electrochemical properties: Benzene-bridged derivatives enable visible-light-driven photochromism (activation at 400–410 nm), overcoming the limitations associated with conventional UV-dependent activation; directly linked TPA–phenanthrene conjugates exhibit rapid electrochromism through the formation of TPA^+• radicals, and bidirectional fluorescence modulation. Notably, the engineered diarylethenes demonstrate synergistic photochromic–electrochromic coupling within a single molecular scaffold, as evidenced by the successful fabrication of an electrochromic device. This integrated optical and electrical responsiveness provides a novel molecular engineering strategy for the development of adaptive, multifunctional smart materials.