•Cy7-NphS is a near-infrared probe for HClO/MPO sensing.•Cy7-NphS merit fast response time and high sensitivity.•Cy7-NphS could be used for real-time HClO imaging in living cells.•Cy7-NphS could respond to MPO activity linearly within the clinical range.•Cy7-NphS was mitochondria targeted.Hyperchlorous acid (HClO), produced from MPO, is recognized as a host defense that kills pathogens; a signaling molecule that initiates cell apoptosis; and a harmful agent when overproduced. Thus, measuring of endogenous HClO and MPO will always find its great importance in revealing biological roles under complex biological conditions. In this study, a turn-on near infrared (NIR) fluorescent probe Cy7-NphS has been designed and developed for highly selective and sensitive sensing of HClO and Myeloperoxidase (MPO) with fast response time. The newly developed probe has been successfully applied in real-time monitoring of HClO and MPO activity in PBS solutions and living HL-60 cells. When applied in MPO activity determination, the probe showed very high sensitivity with a detection limit of as low as 3.69×10−3 U/mL. Furthermore, the living cell imaging study suggested that this probe could detect HClO in mitochondria.

The dynamic overall perspective of an excited-state proton transfer (ESPT) process for 2,8-diphenyl-3,7-dihydroxy-4H,6H-pyrano[3,2-g]-chromene-4,6-dione (D3HF) is investigated based on a time-dependent density functional theory (TDDFT) method. The intramolecular hydrogen bonds of D3HF (O1–H2⋯O3 and O4–H5⋯O6) are demonstrated to be strengthened in the first excited state, which provides the possibility for an ESPT process. Frontier molecular orbitals (MOs) indicate the nature of the intramolecular charge transfer. The corresponding Mulliken’s charge distribution and natural bond orbital (NBO) analysis as well as the Wiberg bond order can be used as reasonable evidence that the ESPT process occurs due to charge transfer. The reduced dimensionality potential energy surfaces (PESs) of the S0 and S1 states have been constructed to explain whether a single or double proton transfer process occurs. The heights of potential barriers among the local minima on the S1 PES indicate that an excited-state single proton transfer mechanism occurs for D3HF. In turn, through the process of radiative transition, the single proton-transfer SPT-D3HF structure returns to the ground state with 582.5 nm fluorescence. Eventually, the almost negligible low barrier facilitates a reversed GSIPT process.

•A lysosome-targetable fluorescent probe for HOCl was synthesized.•It showed a fast fluorescence response to HOCl in aqueous solution.•The probe displayed a large fluorescence enhancement.•Imaging of exogenous HOCl in lysosomes of living cells was achieved using fluoresce microscope.The development of fluorescent probes for hypochlorous acid (HOCl) has received intense attention because of the biological significance of HOCl. In this work, a novel fluorescent probe based on a selenide switch for the detection of HOCl in lysosomes has been designed and synthesized on a 1,8-naphthalimide scaffold. The probe exhibited a high selectivity for HOCl over various reactive oxygen species (ROS) with a fast response and a large fluorescence enhancement in aqueous media. Confocal microscopy imaging of living cells indicated that the probe was able to accumulate in lysosomes and was successfully applied to imaging exogenous HOCl in living cells. Attempts of using Lyso-NI-Se to image HOCl in stimulated RAW264.7 cells failed, probably due to the absence of endogenous HOCl in lysosomes or the undesirable detection limit.

The pH-related fluorescence quenching mechanism of 2-amino-4-hydroxypteridine (pterin), a biologic functional molecule, in the presence of acetate ion has been fully investigated for the first time. Using a combined experimental and theoretical approach, we discover that the fluorescence quenching observed in acid condition originated from a barrierless excited-state proton-transfer process. The proton on the acid form of pterin is transferred to acetate after photoexcitation. The hydrogen-bonding patterns are found to change with the pH values that govern the occurrence of excited-state proton transfer (ESPT). As revealed by investigating the excitation and relaxation processes of pterin, this ESPT process shows impressive site specificity intrinsically due to the photoinduced acidic center shifting. The experimentally observed fluorescence quenching and lifetime shortening of pterin in acid condition are thus attributed to the site-specific proton transfer from the N5 site. Pterin exists extensively in living organisms and has been found to show favorable proton-donating ability, which may transfer its proton to biofunctional molecules with hydrogen-accepting groups and induce related bioeffects.

Intermolecular dihydrogen bonding in the electronically excited states of a phenol–diethylmethylsilane (DEMS) complex was studied theoretically using the time-dependent density functional theory (TDDFT) method. Analysis of the frontier molecular orbitals revealed a locally excited S1 state for the dihydrogen-bonded phenol–DEMS complex in which only the phenol moiety is electronically excited. The calculated infrared spectrum of the phenol–DEMS complex is quite different from that of previously studied S1 state of a dihydrogen-bonded phenol–borane-trimethylamine complex. The O–H and Si–H stretching vibrational modes appear as intense, sharp peaks for the S1 state which are slightly red-shifted compared with those predicted for the ground state. Upon electronic excitation to the S1 state, the O–H and Si–H bonds involved in the dihydrogen bond O–H⋯H–Si lengthen slightly, while the C–O bond shortens. The calculated H⋯H distance is significantly shorter in the S1 state than in the ground state. Thus, the intermolecular dihydrogen bond of the phenol–DEMS complex is stronger in the electronically excited state than in the ground state.