Control of self-assembly of twin-tapered dihydrazide derivative: mesophase and fluorescence-enhanced organogels

Abstract

A twin-tapered (six-chained) low-molecular-mass organic gelator bearing hydrazine linkage and end-capped by phenyl, 1,4-bis[(3,4,5-trihexyloxy phenyl)hydrazide]phenylene (TC6) was designed and synthesized. Quadruple hydrogen bonds between the dihydrazide units are the main driving force in forming supramolecular liquid crystals and organogels. The association constants (K) of the quadruple hydrogen bonds between the hydrazide units in chloroform are 7.13 × 10³ M⁻¹ and 1.53 × 10³ M⁻¹ on the basis of NH-1 and NH-2, respectively. Depending on the environmental conditions, compound TC6 can self-assemble into a hexagonal columnar mesophase in the condensed state, in which two molecules constitute the slice of the column, or into a smectic mesomorphic-like organization in the presence of apolar solvents such as 1,2-dichloroethane, or into a rectangular columnar mesomorphic-like organization in the presence of polar solvents such as ethanol, in which one molecule constitutes the slice of the column. Aggregation-induced emission enhancement (AIEE) has been observed after gelation though conventional chromophore units are not incorporated in TC6.