Asymmetric Molecular Conformation of Steric Terfluorene toward Constructing Polyhedral Microcrystals for Deep-Blue Lasers

Molecular conformation is crucial for precisely controlling photophysical processing and self-assembly behavior of organic conjugated semiconductors for optoelectronic applications. Herein, we obtained a novel asymmetric molecular conformation of steric terfluorene with torsion angles of -172 and 44° to enable its molecules to self-assemble into a polyhedral microcrystal for deep-blue lasers. Interestingly, significantly different from previous quasi-symmetrical ones, novel asymmetric secondary interactions, including C-H···π and O···H-C hydrogen bonds, are easily observed in our novel crystalline structure and enable DOSFX-SFX molecules to self-organize into an octahedral microcrystal, which is an excellent optical microcavity for organic lasers. Meanwhile, a supramolecular steric encapsulation layer can be induced by large hindrance of SFX nanogroups and simultaneously effectively inhibited intermolecular π-π interactions, allowing for intramolecular photophysical behavior in crystal states. With an intermediated and asymmetric conformation, our DOSFX-SFX molecules exhibited a longer effective conjugated length with a red-shifted 0-1 emission peak at 430 nm than the controlled ones (417 nm) with a larger torsional adjacent angle but a shorter length than the quasi-planar conformational ones (445 nm), confirming the key role of molecular conformation in controlling photophysical behavior. Finally, DOSFX-SFX octahedron-based low-threshold microlasers are also constructed with a 0-1 band emission peak at 417 ± 2 nm, which suggested intramolecular photophysical behavior in crystal states. Our work supported an assumption that molecular conformation is a key factor to control a material's properties and self-assembly behaviors.