To design ultrabright fluorescent solid dyes, a crystal engineering strategy that enables monomeric emission by blocking intermolecular electronic interactions must be developed. We introduced propylene moieties in distyrylbenzene (DSB) as a bridge between the two phenyl rings around its C=C bonds. The bridged DSB derivatives formed compact crystals and exhibited emission colors similar to those of dilute solutions with high quantum yields. The introduction of flexible seven-membered rings into the DSB core resulted in moderate distortion and steric hindrance in the π-plane of DSB. However, the molecular arrangement could be controlled with almost no decrease in the crystal density relative to that of DSB, and the electronic interactions were suppressed. The crystal structure of bridged DSB was different from those of other DSB derivatives, indicating that bridging afforded novel crystalline systems. This design strategy has important implications in many fields and is more effective than conventional photofunctional crystal design strategies.

Multiple emission colors in solid-state organic fluorophores with the same main skeleton are essential for improving the performance of light-emitting devices/materials. Specifically, emission in the red/near-infrared region is of great importance in the biological field. Previously, we developed di-bridged-distyrylbenzene DBDB[7] with highbrightness solid-state blue and aggregation-induced emissions (AIE) by introducing the bridging structures of a sevenmembered ring into the vinylene groups of distyrylbenzene (DSB). Herein, we synthesize MNDBDMeODB[7] (1), which features substituted methoxy and malononitrile groups as donor and acceptor groups, respectively, in DBDB[7]. In solvents more polar than THF, MNDSDMeOB (3), which has the same main skeleton as 1 but without bridges, shows no emission in the solid state, whereas 1 exhibits highly bright red-orange emission in the solid state owing to the suppression of intermolecular electronic interactions by the bridges and the AIE property. We also synthesize MNDSD(EHO)B (2) in which the methoxy groups of 3 are replaced by ethylhexyloxy groups, thus disrupting the crystallinity of the molecule. 2 exhibits positive fluorescence solvatochromism and has a high fluorescence quantum yield in the solid state as a red-emitting DSB derivative. The solidstate emission properties of 1 and 2 will improve the applicability of DSBs and functionalities of light-emitting devices/materials.

Semiflexible main-chain thermotropic liquid crystalline polyesters (TLCPs) are applied in functional materials like heat dissipation sheets because of their good processability and ability to form nanostructures. Poly­(pentylene 4,4′-bibenzoate) (BB-5) is a commonly investigated biphenyl-based TLCP that forms a SmCA phase. The functional application of BB-5 is limited by its high isotropization temperature (Ti ). This study aims to lower the Ti of BB-5 and enhance the processability of poly­(pentylene 4,4″-terphenyl dicarboxylate) (T-5) compounds, which contain photo/electronic functional mesogens. Six fluorinated BB-5 (F-BB-5) compounds are synthesized with Ti values at least 35 °C lower than that of BB-5. Fluorinated T-5 (F-T-5) compounds show isotropic phases before thermal decompositions, unlike T-5. Moreover, F-BB-5 and F-T-5 form not only amorphous and SmCA phases but also crystalline and higher-order smectic phases, which is unexpected from low-molecular-weight liquid crystals. Mesogenic fluorination of semiflexible TLCPs results in low Ti and even unique morphologies, opening up their new possibilities.

To design ultrabright fluorescent solid dyes, a crystal engineering strategy that enables monomeric emission by blocking intermolecular electronic interactions must be developed. We introduced propylene moieties in distyrylbenzene (DSB) as a bridge between the two phenyl rings around its C=C bonds. The bridged DSB derivatives formed compact crystals and exhibited emission colors similar to those of dilute solutions with high quantum yields. The introduction of flexible seven-membered rings into the DSB core resulted in moderate distortion and steric hindrance in the π-plane of DSB. However, the molecular arrangement could be controlled with almost no decrease in the crystal density relative to that of DSB, and the electronic interactions were suppressed. The crystal structure of bridged DSB was different from those of other DSB derivatives, indicating that bridging afforded novel crystalline systems. This design strategy has important implications in many fields and is more effective than conventional photofunctional crystal design strategies.