The systematic modification of the dye environment, from the solution with dominating dye-solvent interactions, via aggregate, where the influence of solvent molecules is reduced in favour of dye-dye interaction, can be concluded with the crystal structure, appearing as the extreme aggregate case in the absence of solvent molecules. While for most of aromatic, planar and rigid fluorophores, usually fluorescent in solution, the emission in solid deteriorates due to stacking-assisted ACQ , the main principle in design of AIE molecules is based on the introduction of solution-flexible molecular structures , which minimize intramolecular motion when aggregated. This limits the non-radiative transition pathways, shifting towards radiative decay and thus increasing FQY. On the other hand, from the structural point of view, sterically hindered substituents can prevent close packing leading to reduced intermolecular interactions and suppression of ACQ.