Dipyrroethene-Based Red-Light Emissive AIEgens

Aggregation-induced emission (AIE) molecules find myriads of applications in various fields ranging from biomedical probes and chemical sensors to optoelectronics. In this domain, tetraphenylethene (TPE) and its derivatives have long been a benchmark due to their unique luminescent properties in aggregated states. However, the limited tunability through further functionalization and the absorption and emission spectrum in higher-energy regions constrain their applications from multiple domains. To address these limitations, we have designed a new class of highly symmetric red-light emissive AIE-active molecules by structurally engineering the <i>E</i>-dipyrroethene (DPE) skeleton. This design enables pre- and postsynthetic modification opportunities through the two pyrrole rings and multiple heteroatoms, facilitating tunable photophysical properties. In this context, DPE-based AIEgens <b>Tz</b> and <b>BTz</b> were synthesized through the selective α,α-diformylation of DPE followed by condensation with 2-aminothiazole and 2-aminobenzothiazole, respectively. The π-extended conjugation systems in <b>Tz</b> and <b>BTz</b> containing multiple heteroatoms tune the excitation spectra in visible wavelength and emission spectra above 600 nm with a large Stokes shift in the range of 3632-5058 cm^-1. Moreover, this modification provides a great platform for numerous noncovalent interactions, which significantly enhance aggregation- and solid-state fluorescence properties. Furthermore, various experimental, spectroscopic, and theoretical studies and X-ray crystallography measurements elucidate the structure-property relationships of these molecules, which pave the way for the development of novel materials with various applications in sensing and bioimaging. As a proof of concept, the potential of these molecules has been successfully demonstrated for the development of vapor- and solution-phase dynamic acid-base stimuli-responsive smart sensors, as well as the application of the <b>BTz</b> molecule in live-cell imaging.