The solid-state emission allows to divide the whole series into two groups (Fig. ): acceptor-only-carrying compounds 5, 6, 8 and 9, with emission maximum around 440 nm and acceptor-donor substituted ones with emission at ca. 490 nm (Tab. S1). It is worth to underline the difference in shape and FWHM values for the series (Fig. and). It is clear that the spectra for 6 are practically the same in all the environments, while its FQY increases from THF through aggregate to solid. Taking into account 3 and 7 (Fig. ), their spectra differ to a large extent. For 3, the emission in all surroundings is very similar to one another, putting aside the vibronic progression, while for its isomeric 7 the aggregate/solid spectrum differs much from THF solution. Thus, 7 can be compared with its counterparts of same topology, described by Potopnyk , in which electron acceptors (R=CF3 /R=CF3C6H4 ) and strong donor (R ′ =NMe2) are attached to the fluorophore skeleton. Both 7 and its NMe2-substituted counterpart crystallize in P-1 triclinic space group and exhibit similar head-to-tail crystal packing, retaining planar structure with the phenyl torsion angle below 1 • and similar dye-dye interaction pattern. However, in contrast to 7, R ′ =NMe2-derivative undergoes strong ACQ, decreasing the FQY from 0.61 in THF solution to less than 0.06 in solid state. Since crystal packing in both systems is to the high extend similar, the quenching arises rather from the presence of strong electron-donating dimethylamino group, which develops stronger intramolecular charge transfer than the one due to the milder donating OMe group in 7. The ground state intermolecular interaction estimated for the most stable dimers extracted from the crystal (Fig. and) confirms the similar nature of interactions in all the systems and the analog from . All the dimers are dispersion-governed, with the dispersion-to-electrostatic ratio significantly exceeding 2.0 (Fig. ). This unequivocally proves that the factor determining the ACQ/AIE switching is not the stacking interaction in aggregates itself. The Fig. show that energy constituents in 3 and 7 differ from Potopnyk's [P].