Tunable Nano‐Bending Structures of Loosened/Tightened Lassos with Bi‐Stable Vibration‐Induced Emissions for Multi‐Manipulations of White‐Light Emissions and Sensor Applications

Abstract

AbstractThe first tunable nano‐bending structures of [1]rotaxane containing a single‐fluorophoric N,N′‐diphenyl‐dihydrodibenzo[a,c]phenazine (DPAC) moiety (i.e., [1]RA) are developed as a loosened lasso structure to feature the bright white‐light emission [CIE (0.27, 0.33), Φ = 21.2%] in THF solution, where bi‐stable states of bending and twisted structures of DPAC unit in [1]RA produce cyan and orange emissions at 480 and 600 nm, respectively. With acid/base controls, tunable loosened/tightened nano‐loops of corresponding [1]rotaxanes (i.e., [1]RA/[1]RB) can be achieved via the shuttling of macrocycles reversibly, and thus to adjust their respective white‐light/cyan emissions, where the cyan emission of [1]RB is obtained due to the largest conformational constraint of DPAC moiety in its bending form of [1]RB with a tightened lasso structure. Additionally, the non‐interlocked analog M‐Boc only shows the orange emission, revealing the twisted form of DPAC fluorophore in M‐Boc without any conformational constraint. Moreover, the utilization of solvents (with different viscosities and polarities), temperatures, and water fractions could serve as effective tools to adjust the bi‐stable vibration‐induced emission (VIE) colors of [1]rotaxanes. Finally, tuning ratiometric emission colors of adaptive conformations of DPAC moieties by altering nano‐bending structures in [1]rotaxanes and external stimuli can be further developed as intelligent temperature and viscosity sensor materials.