Complex chiral columns made of achiral quinoxaline derivatives with semi-flexible cores

TL;DR

This study reports on achiral quinoxaline derivatives forming complex 3D chiral columnar structures with tunable fluorescence and electronic properties, influenced by molecular flexibility and conjugation.

Contribution

It introduces a new class of mesogenic materials with semi-flexible cores forming unique 3D chiral columns and explores their optical and electronic behaviors.

Findings

Achiral quinoxaline derivatives form 3D columnar structures with Fddd symmetry.

Flexible molecules exhibit up to 25% fluorescence quantum yield.

Rigid molecules show strong hole photocurrent and bipolar charge transfer.

Abstract

Mesogenic materials, quinoxaline derivatives with semi-flexible cores, are reported to form new type of 3D columnar structure with large crystallographic unit cell and Fddd symmetry below columnar hexagonal phase. The 3D columnar structure is a result of frustration imposed by arrangement of helical columns of opposite chirality into triangular lattice. The studied materials exhibit fluorescent properties that could be easily tuned by modification of molecular structure, compounds with the extended {\pi} electron conjugated systems form aggregates and fluorescence is quenched. For molecules with flexible structure the fluorescence quantum yield reaches 25%. On the other hand, compounds with more rigid mesogenic core, for which fluorescence is suppressed show strong hole photocurrent. For some materials also bi-polar: hole and electron transfer was observed.