Optical Investigation of Self-Aggregation of a Tetrazole-Substituted Diphenylacetylene Derivative: Steady and Excited State Dynamics in Solid and Solution State

Slow crystallization and fast precipitation of a tetrazole-substituted diphenylacetylene derivative (MPT) led to formation of solids with significantly different photoluminescence efficiencies of 0.06 and 0.33, respectively. A detailed study of the photophysical properties of solutions of MPT as a function of concentration and temperature indicated that the extent of formation of J- and H-aggregates played a significant role in determining the luminescence properties of these materials. Time-resolved emission spectroscopy showed that the lifetime of emission arising from the aggregated species was significantly higher than that of the monomer species. The long-lived emission might be due to the formation of excimer arising from the excitation of ground state J- and H-aggregates. The higher quantum yield of fluorescence in the solids obtained by fast precipitation could be attributed to the presence of increased amounts of J-aggregates similar to that observed in highly concentrated solutions (≥ 4.2 × 10–4 M). The photophysical studies of MPT in various concentrations indicate that J-aggregates are significantly more fluorescent than the H-aggregates. Transient absorption spectra measured by nanosecond laser flash photolysis indicated the formation of a triplet excited state with an absorption maximum of ∼490 nm and a quantum yield of 0.61

Supergelation via Purely Aromatic π–π Driven Self-Assembly of Pseudodiscotic Oxadiazole Mesogens

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 <i>d</i>-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

Self-Assembling and Luminescent Properties of Chiral Bisoxadiazole Derivatives in Solution and Liquid-Crystalline Phases

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)