Through‐Space CBr···π Halogen Interaction: Efficient Modulation of Reaction‐Based Photochromism and Photoluminescence at Crystalline States for Irradiation Time‐Dependent Anti‐Counterfeiting

Abstract Reaction‐based photo‐responsive molecular systems have been used as a reliable platform for building intelligent materials, but often suffer from high inactivity in terms of conversion efficiency and reversibility when it comes to solid‐state applications. Herein, a class of Spiro‐conjugated diphenylindene (DPI) aggregation‐induced emission materials that exhibit solid‐state photocyclization‐based photochromism and photoluminescence, achieved by manipulating through‐space CBr···π halogen interactions is reported. In the crystalline state, the Spiro bridge enables a pair of perpendicularly configured CBr···π interactions that suppress photoluminescence while activating a highly reversible (>10 000 cycles) and efficient photochromism based on photocyclization. After breaking this intermolecular CBr···π interaction, for example, by grinding, the solid‐state photochromic properties are sensitively de‐activated. In addition, this spontaneously reversible photochromism behavior gives a controllable decolorization time (from a few seconds to a few minutes), depending on the light exposure conditions, while displaying a luminescence change. In a proof‐of‐principle study, these photo‐function features demonstrate an attractive potential for novel anti‐counterfeiting applications. This work reveals the efficient regulation of CBr···π halogen interactions for spatial molecular packing, molecular electronic transitions, and chemical transformations, paving the way for the development of solid‐state intelligent materials with good reversibility.