Circularly Polarized Luminescence Inversion in AIE-Active Crystal Enabled by Solvent-Induced Transition Dipole Moment Regulation

Abstract

Control of the dissymmetry of circularly polarized luminescence (CPL) is intriguing and has great potential for applications in the field of optics. The traditional control strategy involves using the opposite enantiomers to achieve reversal of CPL signs. However, regulating CPL reversal by controlling only the transition dipole moments without changing molecular or supramolecular chirality remains a challenge. Herein, we developed a couple of crystal materials based on axially chiral aggregation-induced emission luminogens (AIEgens). These materials exhibit achiral solvent-induced CPL sign inversion with identical helical structures and molecular chirality in their crystalline states. (R)-BPAuCz^T displays (+)-CPL with a dissymmetry factor of luminescence (g_lum) value of +9.81 × 10⁻⁴ (560 nm), while (R)-BPAuCz^C exhibits (−)-CPL with a g_lum value of −1.02 × 10⁻³ (560 nm). Time-dependent density functional theory calculations show that the magnetic and electric transition dipole moments at S₁ → S₀ of the (R)-BPAuCz^C unit cell are considerably influenced by the cocrystallized solvent molecules, revealing a solvent-induced CPL inversion mechanism. The nonbonding interactions between the solvent molecules (i.e., tetrahydrofuran or CDCl₃) and AIEgens in the crystal play a crucial role in the manipulation of the transition dipole moment of these crystal materials. Moreover, microrods of (R)-BPAuCz^T, (R)-BPAuCz^C, and (R)-BPAuCz^DCE exhibit optical waveguide properties with relatively low optical-loss coefficients of 187.3, 567.4, and 65.2 dB/cm, respectively. These findings can help in developing a new strategy toward controlling CPL signals and providing a potential application for future integrated photonic circuits.