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Fluorescent probes have become an indispensable tool in the detection and imaging of biological and disease-related analytes due to their sensitivity and technical simplicity. In particular, fluorescent probes with far-red to near-infrared (FR-NIR) emissions are very attractive for biomedical applications. However, many available FR-NIR fluorophores suffer from small Stokes shifts and sometimes low quantum yields, resulting in self-quenching and low contrast. In this work, we describe the rational design and engineering of FR-NIR 2,4,6-triphenylpyrylium-based fluorophores (TPP-Fluors) with the help of theoretical calculations. Our strategy is based on the appending of electron-donating substituents and fusing groups onto 2,4,6-triphenylpyrylium. In contrast to the parent TPP with short emission wavelength, weak quantum yields, and low chemical stability, the obtained novel TPP-Fluors display some favorable properties, such as long-wavelength emission, large Stokes shifts, moderate to high quantum yields, and chemical stability. TPP-Fluors demonstrate their biological value as mitochondria-specific labeling reagents due to their inherently positive nature. In addition, TPP-Fluors can also be applied to develop ratiometric fluorescent probes, as the electron-donating ability of the 2,6-phenyl substituents is closely correlated with their emission wavelength. A proof-of-concept ratiometric probe has been developed by derivatizing the amino groups of TPP-Fluor for the detection and imaging of nitroreductase in vitro and in hypoxic cells., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two-photon imaging is an emerging tool for biomedical research and clinical diagnostics. Electron donor-acceptor (D-A) type molecules are the most widely employed two-photon scaffolds. However, current D-A type fluorophores suffer from solvatochromic quenching in aqueous biological samples. To address this issue, we devised a novel class of D-A type green fluorescent protein (GFP) chromophore analogues that form a hydrogen-bond network in water to improve the two-photon efficiency. Our design results in two-photon chalcone (TPC) dyes with 0.80 quantum yield and large two-photon action cross section (210 GM) in water. This strategy to form hydrogen bonds can be generalized to design two-photon materials with anti-solvatochromic fluorescence. To demonstrate the improved in vivo imaging, we designed a sulfide probe based on TPC dyes and monitored endogenous H 2 S generation and scavenging in the cirrhotic rat liver for the first time., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)