Aggregation-induced emission properties of pyridyl-containing tetra-arylethenes

New pyrrolo[3,2-b]pyrroles with AIE characteristics for detection of dichloromethane and chloroform

Three new pyrrolo[3,2-b]pyrrole derivatives containing methoxyphenyl, pyrene or tetraphenylethylene (TPE) units (compounds 1-3) have been designed, synthesized and fully characterized. The aggregation-induced emission (AIE) properties of compounds 1-3 were tested in different water fraction (fw ) of tetrahydrofuran (THF). The pyrrolo[3,2-b]pyrrole derivative 3 containing TPE units exhibited typical AIE features with an enhanced emission (∼32-fold) in the solid state versus in solution; compounds 1 and 2 exhibited an aggregation-caused quenching effect. In addition, the steric and electronic effects of the peripheral moieties on the emission behavior, both in solution and in the solid state, have been investigated. Moreover, pyrrolo[3,2-b]pyrrole 1 exhibits high sensitivity and selectivity for dichloromethane and chloroform solvents, with the system displaying a new emission peak and fast response time under ultraviolet irradiation.

Fluorescent styryl pyridine-N-oxide probes for imaging lipid droplets

Lipid droplets (LDs) have emerged as major regulators of cellular metabolism, encompassing lipid storage, membrane synthesis, viral replication, and protein degradation. Exclusive studies have suggested a direct link between LDs and cancer, as a notable abundance of LDs is found in cancerous cells. Therefore, monitoring the location, distribution, and movements of LDs is of paramount importance for understanding their involvement in biological processes. To target LDs, we designed and synthesized fluorophores with a styryl scaffold bearing electron-donating amino groups and pyridine-N-oxide, a zwitterionic acceptor moiety. We explored their photophysical properties in various solvents and conducted systematic DFT calculations on the synthesized fluorescent molecules, comparing them with neutral pyridine and cationic pyridinium styryl dyes. The results demonstrate that diphenylaminostyryl pyridine-N-oxide (TNO) shows excellent imaging of LDs, in contrast to the behavior of cationic styrylpyridinium (TNC), which primarily localizes within the mitochondria. Notably, pyridine N-oxide offers several benefits: an increased dipole moment facilitating charge separation between donors and acceptors, substantial HOMO and LUMO stabilization, improved water solubility, favorable redox properties, and bathochromic-shifted absorption/emission spectra, showing promise as a fluorescent tool for probing the cellular-biological realm.