Tuning optical properties of aromatic near-infrared fluorescent switch through engineering functional heterocycle on donor moiety

Abstract

Near-infrared (NIR) emissive fluorophores with donor−acceptor−donor (D−A−D) structures are attractive for deep tissue in vivo bioimaging and sensing, owing to their low background autofluorescence and deep penetration depth. In this study, we constructed a series of nitric oxide (NO)-responsive fluorescent switches with D−A−D structure, in which functional heterocycles act as donor moiety, resulting in the modification of fluorescence wavelengths from NIR-I (750–950 nm) to NIR-II (1000–1700 nm) region. Specifically, the NIR-I fluorescence can be achieved by using furan, thiophene and selenophene as the donor moiety. By using pyrrole as the donor moiety, NIR-II fluorescence can be achieved due to the strong N–H⋯N hydrogen bond interaction and tunable intramolecular charge transfer (ICT) process. Based on our findings, tailoring electronegativity of donor moiety could controllably tune the fluorescence wavelength from NIR-I to NIR-II region, proposing a practical design strategy for developing NIR-II fluorescent switches.