Structure–Property Relationship on Aggregation-Induced Enhanced Emission of the Spirobifluorene Derivatives including Herringbone, T, and Helical Aggregation Mode in Solid-Phase: Synthesis, Crystallography, Density Functional Theory, Optical, and Thermal Properties

The development of efficient luminescent materials in the solid state attracts great attention for their potential applications. Based on this importance, we presented the structure–property relationship of the spirobifluorene (SBF) derivative molecules by photophysical studies and single-crystal X-ray crystallography and very important luminogens having aggregation-induced emission behavior in the solid state. Also, cyclic voltammetry (CV), thermogravimetric analysis (TGA), spectroscopic, and theoretical studies of these molecules are presented. We show that the molecular structure, conformational twisting, structural rigidity, and supramolecular packing play significant roles in the SBF molecules’ photoluminescence behavior, especially in determining whether they are aggregation-induced emission -active. These molecules demonstrated enhanced emission in the supramolecular aggregate state created by herringbone-, helical-, and T-type π···π stacking interactions compared to that of the solution phase. Moreover, the restricted intramolecular rotation has been demonstrated to play a significant role in the aggregation-induced enhanced emission properties of the SBF molecules. The most increasing in PL intensity was observed in the molecule SBF1 and SBF3 with the T- and helical-type stacking interactions, respectively. We concluded that the helical- and T-type stacking modes with a small perpendicular distance result in high fluorescence intensity in the SBF molecules’ aggregate state. This study will provide an overview of supramolecular arrangements on the solid-state optoelectronic properties of SBF derivatives. Also, it would suggest new pathways toward targeted molecular design strategies.