This article reports the enhanced photoluminescent properties observed in the crystals of a cube-plane-cube shape amphiphile composed of perylene diimide (PDI) tethered with polyhedral oligomeric silsesquioxanes (POSS) at the imide position via either rigid or flexible linkages (POSS-PDI-POSS). The fluorescence quantum yields (Φ_f) of the conjugates in crystal (∼0.48) are much higher than that of the more amorphous samples (∼0.17) and that of the reference compound without pendant POSS cage (∼0.12). The enhancement was understood in three ways. First, their self-assembly behaviors in gaseous phase were studied by tandem mass spectrometry coupled with traveling wave ion mobility separation; second, their self-assembly behaviors in solution were revealed by concentration- and solvent-dependent experiments using UV/vis absorption and fluorescence spectrometry; and third, the molecular packing in crystals was determined by wide angle X-ray diffraction and transmission electron microscope. The results demonstrate the conjugates' strong tendency toward dimer formation in solution and show a unique molecular packing of discrete dimeric motifs in the solid states. It suggests that the high Φ_f of these conjugates can be attributed to the discontinuous π–π stacking, which results in a weaker electron interaction between the dimers, and the relatively fixed position of the PDI, which prohibits the common structural relaxation of PDIs π-planes.

It remains challenging to understand the structural evolution of conjugated polymers from single chains to solvated aggregates and film microstructures, although it underpins the performance of optoelectrical devices fabricated via the mainstream solution processing method. With several ensemble visual measurements, here we unravel the morphological evolution process of a model system of isoindigo-based conjugated molecules, including the hidden molecular assembly pathways, the mesoscale network formation, and their unorthodox chain dependence. Short chains show rigid chain conformations forming discrete aggregates in solution, which further grow to form a highly ordered film that exhibits poor electrical performance. In contrast, long chains exhibit flexible chain conformations, creating interlinked aggregates networks in solution, which are directly imprinted into films, forming interconnective solid-state microstructure with excellent electrical performance. Visualizing multi-level assembly structures of conjugated molecules provides a deep understanding of the inheritance of assemblies from solution to solid-state, accelerating the optimization of device fabrication.