Conformational Effect of Polymorphic Terfluorene on Photophysics, Crystal Morphologies, and Lasing Behaviors

Abstract

Molecular conformation is an important factor in flexible organic molecules and deeply influences their physical and chemical properties. Here, a model fluorene trimer, 2,2′:7′,2″-ter­(9,9-di­methyl­fluorene) (TDMeF), was designed and synthesized to investigate the effect of conformational diversity of oligofluorene on the morphologies of microcrystals and photophysical properties. Single crystal X-ray diffraction analysis indicates that TDMeF has four polymorphs with different molecular conformations, and crystalline polymorphism is first observed in oligofluorenes. Moreover, the slight change in molecular conformation leads to form different crystal morphologies, namely, ribbon and rodlike microcrystals, in virtue of different intermolecular interactions. Finally, although both microcrystals display deep blue lasing behaviors, the rodlike microcrystal shows a threshold of 114 W/cm2, which is twice times lower than that of the ribbon-like one due to the effect of molecular orientation and optical microcavity.

Hierarchical Uniform Supramolecular Conjugated Spherulites with Suppression of Defect Emission

“…Similarly, the maximum absorption peak of DSFX-OSFX is red-shifted from 357 to 390 nm. The above results indicate that molecular conformations are ordering and planarizing in the annealed film, resulting in a longer effective conjugation length (Bai et al., 2017, Ou et al., 2017a, Yu et al., 2018). Besides, the maximum emission peaks are bathochromic from 430 to 448 nm.…”

“…Frequently, noncovalent interactions among H, S, F, and O are useful to stabilize planar conformations and enhance crystallinity (Kim et al., 2013). According to our previous works, diverse and strong hydrogen-bonding interactions were observed in the SFXSO units (S=O···H-C), which could confer photophysical properties in aggregate state (Ou et al., 2017a, Ou et al., 2017b). Therefore, DOSFX-SFX was designed and prepared to determine the effect of this promising noncovalent interaction on conformation and crystalline properties.…”

Self‐assembly into Polymorphic 2D Nanosheets with Crystallization‐Induced Emission Enhancement

“…Organic micro/nanocrystals with polymorphic tunability have attracted a great deal of interest in widespread applications, such as pharmaceuticals separation, [ 1 ] organic field effect transistors (OFET), [ 2‐4 ] colorful organic solid‐state lasers (OSSLs) [ 5‐7 ] or light‐ emitting devices, [ 8‐10 ] and so on. [ 11‐13 ] For building blocks with different molecular conformations, their polymorphism offers an opportunity to explore the effects of molecular packing on exciton behaviors under the same chemical structures, and flexibly tune extraordinary optoelectronic performances.…”

Organic Semiconductor Micro/Nanocrystals for Laser Applications

“…These inhomogeneities lead to multiple scattering and formation of resonances via random walk. They often display multiple lasing modes and their emission cannot be controlled though crystal design owing to their disorder nature [ 115 , 116 , 117 ].…”