Interestingly, upon scratching the crystals of the three isomers by a metal rod, only o-ClTPA can emit bright blue light without UV irradiation, which is indicative of the unique ML property of o-ClTPA in crystals (Video 1). As shown in Figure , the ML and PL spectra of o-ClTPA are overlapped well with each other, implying that the ML is stemmed from the intrinsic fluorescence of o-ClTPA rather than other species. It should be noted that the much higher photoluminescence quantum yield of o-ClTPA among the three isomers also contributes to the simultaneous TADF and ML properties in the crystal state because of reduced nonradiative relaxations (Table ). These experimental results demonstrate that the subtle variation in the substituent position has a profound impact on the luminescent properties of these isomers at the aggregate level. Given that these isomers display similar photophysical properties at the molecular level, single-crystal structure analysis is performed to understand the impact of intermolecular interactions and molecular packings on their crystal-state luminescent properties. As depicted in Figure , these isomers show similar distorted molecular geometries in the gas phase, which become different but less distorted in the crystal phase due to the positive effect of intermolecular interactions and molecular packings. Indeed, different types of intermolecular interactions are formed in the crystal structures of these isomers (Table ). As illustrated in Figure , a single o-ClTPA molecule is involved in ten intermolecular interactions including