To disclose the AIE feature of the four compounds, firstly, we measured their emission in the methanol/glycerol mixtures with varied glycerol fractions, since typical AIE molecules generally show enhanced emission in high viscous media due to the RIM mechanism. To our surprise, for all four compounds, increasing viscosity of the mixture had no impact on the fluorescence intensity (Figure and). Then a classical cooling experiment was performed. As shown in Figure and, when gradually decreasing the temperature of BISX dissolved in THF from ambient temperature to -196 °C, its AIE emission peak at 540 nm barely enhanced. Instead, an emission peak at a short wavelength enhanced gradually, and so did the other three compounds (Figure ). These unexpected phenomena indicated that these AIEgens may not be determined by the conventional RIM working mechanism, further arousing our attention. As these cross-shaped molecules are separated by two moieties, the xanthene part and isoquinolinone part, elucidating which part serves as the chromophore became significant to understand the AIE behavior of this non-typical AIE system. As a result, ASX, an analog of xanthene, was designed and prepared from rhodamine B (Figure , Scheme S2a, Figure ). A series of compounds, namely BIPM, IPM, MIPM and MTPM, corresponding to the isoquinolinone part of BISX, ISX, MISX and MTSX were also synthesized, respectively (Figure , Scheme S2b, Figure ). When checking the PL performance of ASX and BIPM, we found both compounds were weakly emissive in the solution and aggregate state, suggesting that the AIE property of BISX originates from neither the upper xanthene core nor the bottom nitrogen heterocyclic part (Figure , Figure ). It was found that both the emission peaks of ASX and BIPM in THF solutions locate at 430 nm, corresponding to the enhanced emission peak of BISX in THF at low temperature, indicating that decreasing temperature restricted the motion of single molecular species and benefited the emission of the localized emission of upper (isoquinolinone) or bottom (xanthene) moieties (Figure ). Same conclusions were also drawn for compounds ISX, MISX and MTSX (Figure ). Then we assumed that their AIE behavior may result from the new chromophore generated by intermolecular throughspace interactions after aggregation. Excitation spectra of the four compounds were measured, respectively (Figure ). For BISX, one set of peaks appeared between 270 nm and 340 nm, corresponding to its absorption spectrum in Figure . Besides, different from its absorption, a weak and broad excitation peak between 350 nm and 400 nm was observed, suggesting some unfavored transition processes may exist within these molecules. The excitation behaviors of ISX, MISX and MTSX were similar to BISX.