Aggregation-Induced Fluorescence Behavior of Triphenylamine-Based Schiff Bases: The Combined Effect of Multiple Forces

Abstract

Eight triphenylamine (TPA)-based Schiff bases that exhibit different aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ) behavior in tetrahydrofuran (THF)/water mixtures have been synthesized and characterized. The photophysical properties in solution, aqueous suspension, film, and the crystalline state along with their relationships were comparatively investigated. The single-crystal structures of 1-8 indicate that compact π···π stacking or excimers induce fluorescence quenching of 1, 2, 5, and 7. However, the existence of J aggregates or multiple intra- and intermolecular interactions restrict the intramolecular vibration and rotation, enabling compounds 3, 4, 6, and 8 to exhibit good AIE character. The size and growth process of particles with different water fractions were studied using scanning electron microscopy, which demonstrated that smaller uniformly dispersed nanoparticles in the THF/water mixtures favor fluorescence emission. The above results suggest that the combined effects of multiple forces caused by structural variation have a great influence on their molecular packing, electronic structure, and aggregation-induced fluorescence properties. In addition, piezofluorochromic experiments verified the potential applications of 4 and 6.

Carbazole-functionalized polyphenylene-decorated solid state emissive D–A–D molecules: reduced donor–acceptor interaction and enhanced emission in the solid state

“…Crystalline particles leads to enhancement while amorphous leads to reduction in emission intensity. 72 TEM images show formation of nano rods in 60% water fraction with clear diffraction spots in ED spectra which confirm the crystalline nature of aggregates (See Fig. S13, ESI), while in 90% water only amorphous spherical aggregates are observed giving only an obscure diffuse halo in ED spectra (See Fig.…”

Aza‐Macrocyclic Triphenylamine Ligands for G‐Quadruplex Recognition

“…Non‐protic, low‐polarity solvents enhance the supramolecular interactions between the molecules with the concomitant formation of aggregates. These aggregates lead to an RIR effect, producing an enhancement and redshift of the emission …”

“…Non-protic, low-polarity solvents enhancet he supramolecular interactions between the molecules with the concomitant formation of aggregates.T hese aggregates lead to an RIR effect, producing an enhancement and redshift of the emission. [26] To confirmt his aggregation process in non-polar solvents, we recorded the emission spectra in different H 2 O/THF solvent mixtures. All the TPA-PY ligands exhibited as trong enhancement of the emission at 480 nm (l ex = 314 nm) with increasing percentage of THF.M oreover,u pon excitation at 375 nm, both TPA2PY and TPA3PY showedavery large increase in the fluo-rescence intensity at 480 nm, which corresponds to the formation of the aggregate state ( Figure 7a nd FiguresS5a nd S6 in the Supporting Information).…”

A Facile Route to Bis(pyridyl‐1,3,5‐triazine) Ligands with Fluorescing Properties

“…In fact, ESI‐MS of 10 revealed the presence of a dimer, whereas 9 does not show any type of aggregation in the gas phase as examined by mass spectrometry. Such π‐π interactions in extended π‐conjugated systems are associated with an effect called aggregation‐caused quenching (ACQ), which is also responsible for weak or non‐emissive luminescence properties in solid state 28…”