RESUMO
Herein, we report the synthesis, self-assembly, and electroluminescence characteristics of a new green-emitting, pseudodiscoid chiral molecule, OXDC, containing an electron-donating stilbene core and an electron-accepting oxadiazole substituent. The helical organization and specific interaction of the chiral pseudodiscoid molecule resulted in the formation of self-assembled nanofibers with a columnar superstructure. Macroscopic chirality was observed in both the liquid-crystalline phases and the self-assembled nanofibers of OXDC, a feature which was absent in the analogous achiral oxadiazole derivative reported earlier [ Sivadas , A. P. ; Supergelation via Purely Aromatic π-π Driven Self-Assembly of Pseudodiscotic Oxadiazole Mesogens . J. Am. Chem. Soc. 2014 , 136 , 5416 - 5423 ]. A high-performance organic light-emitting device was demonstrated using OXDC as the emitting material, with a luminous intensity of 10 115 cd m-2 at 5 V and chromaticity coordinates of (0.32, 0.51).
RESUMO
A series of highly luminescent oxadiazole-based stilbene molecules (OXD4, OXD8, OXD10, and OXD12) exhibiting interesting enantiotropic liquid crystalline and gelation properties have been synthesized and characterized. The molecules possessing longer alkyl substituents, OXD10 and OXD12, possess a pseudodisc shape and are capable of behaving as supergelators in nonpolar solvents, forming self-standing gels with very high thermal and mechanical stability. Notably the self-assembly of these molecules, which do not possess any hydrogen-bonding motifs normally observed in most reported supergelators, is driven purely by π-stacking interactions of the constituent molecules. The d-spacing ratios estimated from XRD analysis of OXD derivatives possessing longer alkyl chains show that the molecules are arranged in a columnar fashion in the mesogens and the self-assembled nanofibers formed in the gelation process.
RESUMO
Star-shaped molecules consisting of a 1,3,4-oxadiazole core derivatized with alkoxy-substituted phenyl ethynylenes, FD12 (dodecyl) and FD16 (hexadecyl) were synthesized. These molecules exhibited enantiotropic columnar mesophases over a wide temperature range, with the liquid crystalline phases exhibiting strong blue fluorescence. On cooling, FD12 transformed into a transparent glass at room temperature wherein the liquid crystalline texture was retained. The glassy film remained stable over a period of one year and exhibited blue luminescence with an absolute quantum yield of 26%. The oxadiazole derivatives formed stable luminescent gels in decane and study of their morphology by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated formation of interlocked network of self-assembled fibers. X-ray diffraction (XRD) analysis of the xerogel of these derivatives indicated oblique columnar ordering of the molecules within the fibers. The length of the alkyl substituent was observed to have a significant effect on the absorption and fluorescence properties of the gels, which was attributable to the role of the alkyl substituents in controlling the nature of the molecular packing within the self -assembled fibers of the gels.
