In summary, we have designed three simple isomers which are readily synthesized by the same one-step reaction by locating the Cl group on the ortho-, meta-and para-positions of phenyl unit, respectively. In dilute solutions, these isomers show similar fluorescence and lowtemperature phosphorescence properties, which is indicative of the insignificant effect of positional isomerism on the emissive behaviors of isolated isomeric molecules. In contrast, these isomers exhibit diversified emissive behaviors of AIE, TADF, RTP, dual-RTP, and ML in crystals, among which simultaneous AIE, TADF, and ML properties are realized in o-ClTPA while unique dual-RTP and typical AIE characteristics coexist in p-ClTPA. Moreover, crystal structure analysis and theoretical calculations reveal that distinctive intermolecular interactions and molecular packings should be responsible for diversified luminescent properties of the three isomers in the crystal state given that these isomers have similar intrinsic excited-state electronic structures. Of note, the TADF property of ortho-isomer is attributable to the favorable RISC from the higher T2 to the S1 while its distinctive ML among the three isomers is endowed by the large molecular dipole moment and strong intermolecular interactions with a tight molecular packing motif. More importantly, emission spectra of singlet and triplet states simulated for these isomers in the crystal phase agree well with experimental results, which further verifies the TADF, RTP, and dual-RTP properties of isomers o-ClTPA, m-ClTPA, and p-ClTPA, respectively. To the best of our knowledge, simple organic isomers featuring diversified emissive behaviors of AIE, TADF, RTP, dual-RTP, and ML in the crystal state through the subtle variation in the substitution position are reported for the first time, demonstrating the importance of positional isomerism for tunable photophysical properties within molecular aggregates.