Liquid-Crystalline Star-Shaped Supergelator Exhibiting Aggregation-Induced Blue Light Emission

Abstract

A family of closely related star-shaped stilbene-based molecules containing an amide linkage are synthesized, and their self-assembly in liquid-crystalline and gel states was investigated. The number and position of the peripheral alkyl tails were systematically varied to understand the structure-property relation. Interestingly, one of the molecules with seven peripheral chains was bimesomorphic, exhibiting columnar hexagonal and columnar rectangular phases, whereas the rest of them stabilized the room-temperature columnar hexagonal phase. The self-assembly of these molecules in liquid-crystalline and organogel states is extremely sensitive to the position and number of alkoxy tails in the periphery. Two of the compounds with six and seven peripheral tails exhibited supergelation behavior in long-chain hydrocarbon solvents. One of these compounds with seven alkyl chains was investigated further, and it has shown higher stability and moldability in the gel state. The xerogel of the same compound was characterized with the help of extensive microscopic and X-ray diffraction studies. The nanofibers in the xerogel are found to consist of molecules arranged in a lamellar fashion. Furthermore, this compound shows very weak emission in solution but an aggregation-induced emission property in the gel state. Considering the dearth of solid-state blue-light-emitting organic materials, this molecular design is promising where the self-assembly and emission in the aggregated state can be preserved. The nonsymmetric design lowers the phase-transition temperatures.The presence of an amide bond helps to stabilize columnar packing over a long range because of its polarity and intermolecular hydrogen bonding in addition to promoting organogelation.

Novel Luminescent Diazafluorenone Liquid Crystals

“…Therefore, the presence of an ordered rectangular columnar (Col ro ) mesophase at ambient temperature, but a disordered rectangular columnar (Col rd ) mesophase at higher temperatures seems to be reasonable. The observed phase sequence of one (or two) rectangular columnar phases at lower temperatures followed by a hexagonal columnar phase at higher temperatures is in good agreement with similar phase behavior of non-discoid [66][67][68][69][70] and discoid mesogens 71,72 and has been examined theoretically. [73][74][75] However, the lattice parameters changed slightly during the Col ro -Col rd transition (a = 0.7 Å, b = 0.2 Å), although a small but distinct endothermal peak was visible in the DSC curve (Figure 5c, H = 1.3 kJ mol -1 ).…”

Transforming a C3-Symmetrical Liquid Crystal to a π-Gelator by Alkoxy Chain Variation

“…C 3 OPV2 , a molecule with alkoxy chains at 3,4-positions is able to gelate organic solvents, whereas C 3 OPV3 , a molecule with alkoxy chains at 3,5-positions, neither forms gel nor shows any LC properties. This study illustrates the important role of alkoxy chains in the design of functional molecules with distinctly different properties 48,66−68 and hence can be applied to several of the existing systems for their rational conversion to functional soft materials.…”

Mesogens with aggregation‐induced emission properties: Materials with a bright future

“…In 2016, Pathak et al synthesized a series of star-shaped liquid crystalline gelators based on the stilbene-structure showing AIE activity (STI-1-5) in the gel state as well as in the mesophase and the solid state (Figure 28A). [68] A crucial structural element of the mesogens is the amide linkages, which induces columnar stacking of the mesogens by intermolecular hydrogen bonding. A comprehensive structure-property relationship study revealed that the nature and thermal stability of the mesophase strongly depend on the number and length of the peripheral alkyl chains.…”