Yang Tao,Xiaoting Liu,Yunping Zhoujin,Panpan Zhou,Sean Parkin,Tonglei Li,Ju Guo,Faquan Yu,Sihui Long
To probe the effect of substitution on the benzoic acid ring on the polymorphism of phenylaminobenzoic acids, five 3-methyl-2-(phenylamino)benzoic acids (MPABAs) were synthesized. A preliminary polymorph screen led to one form for compounds 1–4 and three forms and a solvate (5-I, 5-II, 5-III, and 5-S) for compound 5. This observation is similar to that of the structurally related compounds with no substitution on the benzoic acid ring. All crystal forms were characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), and FT-IR spectroscopy. The polymorphs of compound 5 were investigated in detail experimentally and theoretically. A conformational scan provided insight into the origin of polymorphism of 5. NBO calculations confirmed the composition and nature of the sigma bond character of the two N–C bonds in 5. Hirshfeld analysis accounted for the major intermolecular interactions contributing to the overall stability of the crystals. It is clear that conformational flexibility alone doesn't lead to polymorphism, and substitution position and pattern are the real determinant of polymorphism in the investigated compounds.
Tetraphenylethylene (TPE)–thiophene compounds are promising candidates for stimuli-responsive luminescent materials, yet systematic investigations into the influence of substitution patterns on their photophysical properties remain limited. Herein, four regioisomeric TPE–thiophene derivatives have been synthesized by systematically varying the number and positions of TPE substituents on the thiophene core. A comprehensive spectroscopic characterization reveals that substitution patterns critically modulate the photoluminescence quantum yields (PLQYs). The ortho-monosubstituted isomer exhibits the highest PLQY (52.86% in solid state) compared with the meta-monosubstituted isomer (13.87% in solid state). Interestingly, thiophenes with two or three TPEs substituted at positions 2,5 or 2,3,5 have lower PLQYs, which is rare due to the common understanding that increasing the number of AIE parts should increase the PLQY. Further single-crystal structure analyses show that the key factor impacting the PLQY is the dihedral angles of the TPE subunit, which determines the degree of intramolecular twisting. This work establishes regiochemistry as a powerful design lever for tuning TPE–thiophene photophysics, offering underlying principles for the design of TPE-based thiophene molecules with high photoluminescent performance in the future.
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