Mikhail A. Filatov

Fluorescent probes based on photoinduced electron transfer (PET) are widely used to image intracellular environments. Here we report donor–acceptor dyads based on the BODIPY chromophore in which PET is selectively activated upon hydration. Replacing fluorine groups at boron with triethylene glycol (TEG) chains confers aqueous solubility and modulates the electronic properties of the boron‐coordinated core, suppressing PET in polar organic solvents while enabling efficient charge separation in water. This switching arises from hydrogen bonding at the alkoxy oxygens, which strengthens the effective acceptor character of the BODIPY, supported by electrochemistry, transient absorption spectroscopy, and DFT calculations. The mechanism is general across dyads incorporating various aromatic donors and BODIPY substitution patterns. The lead compound, 5‐TEG, displays hydration‐dependent fluorescence lifetimes spanning a 6 ns range. In fluorescence lifetime imaging microscopy (FLIM) of living cells, tumor spheroids, and intestinal organoids, 5‐TEG provides high brightness and lifetime contrast, enabling segmentation of subcellular compartments and reporting on microenvironmental differences. These results establish hydration‐gated PET as a tunable photophysical mechanism for designing fluorescence probes with lifetime‐encoded readouts in complex biological environments.

Fluorescent probes based on photoinduced electron transfer (PET) are widely used to image intracellular environments. Here we report donor–acceptor dyads based on the BODIPY chromophore in which PET is selectively activated upon hydration. Replacing fluorine groups at boron with triethylene glycol (TEG) chains confers aqueous solubility and modulates the electronic properties of the boron‐coordinated core, suppressing PET in polar organic solvents while enabling efficient charge separation in water. This switching arises from hydrogen bonding at the alkoxy oxygens, which strengthens the effective acceptor character of the BODIPY, supported by electrochemistry, transient absorption spectroscopy, and DFT calculations. The mechanism is general across dyads incorporating various aromatic donors and BODIPY substitution patterns. The lead compound, 5‐TEG, displays hydration‐dependent fluorescence lifetimes spanning a 6 ns range. In fluorescence lifetime imaging microscopy (FLIM) of living cells, tumor spheroids, and intestinal organoids, 5‐TEG provides high brightness and lifetime contrast, enabling segmentation of subcellular compartments and reporting on microenvironmental differences. These results establish hydration‐gated PET as a tunable photophysical mechanism for designing fluorescence probes with lifetime‐encoded readouts in complex biological environments.

Fluorescent probes based on photoinduced electron transfer (PET) are widely used to image intracellular microenvironments, yet achieving a selective activation of PET by a single environmental parameter remains a challenge. Here we report donor–acceptor dyads based on the O-BODIPY chromophore in which PET is selectively activated by aqueous hydration rather than by generic solvent polarity. Replacing the fluorine groups at boron with triethylene glycol (TEG) chains confers aqueous solubility and modulates the electronic properties of the boron-coordinated core, suppressing PET in polar organic solvents while enabling efficient charge separation specifically in water. This switching arises from hydrogen bonding at the alkoxy oxygens, which strengthens the effective acceptor character of the BODIPY, as confirmed by electrochemical measurements, transient absorption spectroscopy, and DFT calculations. The mechanism is general across dyads incorporating various donors and can be extended to red-emitting chromophores by substitution of the BODIPY scaffold. The lead compound, 5-TEG, displays hydration-dependent fluorescence lifetimes spanning a 6 ns range. In fluorescence lifetime imaging microscopy (FLIM) of living cells, tumor spheroids, and intestinal organoids, 5-TEG provides exceptional brightness and spatially resolved lifetime contrast, enabling segmentation of subcellular compartments and reporting on microenvironmental differences. These results establish hydration-gated PET as a tunable photophysical mechanism for designing fluorescence probes with lifetime-encoded readouts in complex biological environments.

Fluorescent probes based on photoinduced electron transfer (PET) are widely used to image intracellular microenvironments, yet achieving a selective activation of PET by a single environmental parameter remains a challenge. Here we report donor–acceptor dyads based on the O-BODIPY chromophore in which PET is selectively activated by aqueous hydration rather than by generic solvent polarity. Replacing the fluorine groups at boron with triethylene glycol (TEG) chains confers aqueous solubility and modulates the electronic properties of the boron-coordinated core, suppressing PET in polar organic solvents while enabling efficient charge separation specifically in water. This switching arises from hydrogen bonding at the alkoxy oxygens, which strengthens the effective acceptor character of the BODIPY, as confirmed by electrochemical measurements, transient absorption spectroscopy, and DFT calculations. The mechanism is general across dyads incorporating various donors and can be extended to red-emitting chromophores by substitution of the BODIPY scaffold. The lead compound, 5-TEG, displays hydration-dependent fluorescence lifetimes spanning a 6 ns range. In fluorescence lifetime imaging microscopy (FLIM) of living cells, tumor spheroids, and intestinal organoids, 5-TEG provides exceptional brightness and spatially resolved lifetime contrast, enabling segmentation of subcellular compartments and reporting on microenvironmental differences. These results establish hydration-gated PET as a tunable photophysical mechanism for designing fluorescence probes with lifetime-encoded readouts in complex biological environments.

Rigid donor–acceptor dyads with a conformationally locked [2.2.2]bicyclooctane bridge reveal interesting excited-state dynamics: charge separation proceeds efficiently, but triplet formation via the charge-transfer state is fully suppressed.

The photoinitiating system (PIS) is a key component of holographic materials which needs to be carefully selected and optimized to achieve efficient photopolymerization and, as a result, highly efficient holographic structures. Recently, boron dipyrromethene (BODIPY) dyes have been introduced as a new class of photosensitizers for holographic materials, including photopolymerizable glass, which is characterized by excellent environmental stability. Here, we present a study of the holographic recording capability of a photopolymerizable glass, where PIS was optimized using two approaches: (1) adding a second co‐initiator, diphenyl iodonium hexafluorophosphate (DPIHFP) and (2) exploring a range of BODIPY structures, such as anthracene‐ and pyrene‐BODIPYs. The performance of a novel pyrene‐BODIPY dyad was compared with commercially available Erythrosine B, used as a reference. Remarkably, a 9‐fold increase in the diffraction efficiency and refractive index modulation (RIM) was achieved by replacing Erythrosine B with pyrene‐BODIPY dyads, indicating enhanced photopolymerization kinetics with BODIPY sensitization. In addition, incorporating a second co‐initiator, DPIHFP, further increases the exposure sensitivity by a factor of three. These results demonstrate the high efficiency of BODIPY‐based PIS formulations and underscore photopolymerizable glass as a promising platform for developing highly efficient holographic optical elements.

In the past decade, quantitative structure–property relationship (QSPR) techniques combined with machine learning (ML) have gained significant traction in photochemistry and photophysics, offering new strategies for the rational design of photoactive molecules. This progress has been driven by advances in artificial intelligence, automation of research workflows, and the availability of large, curated datasets containing experimental and computational data on molecular structures, electronic transitions, spectra, and related properties. These developments enable pre‐synthetic screening, reducing time, cost, and material consumption in experimental studies. QSPR and ML have emerged as powerful tools for accelerating discovery in optical materials and functional dyes design, with applications ranging from UV–vis absorption and fluorescence to intersystem crossing (ISC), singlet oxygen generation, photosensitization efficiency, and phototoxicity prediction. Such models help prioritize candidates and eliminate low‐potential compounds early in development. This review summarizes recent advances in the application of QSPR and ML to molecular photonics, highlighting the most effective statistical methods and ML architectures. Best practices in model development and validation are outlined, and the most informative molecular descriptors and fingerprints for different photochemical processes are identified, providing practical guidance for integrating ML into photonic materials research.

Switchable intersystem crossing (sISC) is a novel concept in the design of functional dyes that enables dynamic modulation of fluorescence and triplet state formation in response to changes in the dye's environment. Unlike conventional dyes, where intersystem crossing and fluorescence rates are entirely determined by molecular structure, sISC dyes allow reversible switching between these functions based on external factors, such as solvent polarity. sISC can arise from various photophysical mechanisms involving charge–transfer states, whose energies are sensitive to the surrounding environment. Mechanisms such as thermally activated delayed fluorescence and spin–orbit charge transfer intersystem crossing can be employed to design sISC dyes. The ability to fine‐tune photophysical processes without chemical modification of the dye's structure opens new possibilities for biomedical applications, including bioimaging, photodynamic therapy, and optogenetic control. This paper introduces the concept of sISC, provides key examples of dyes exhibiting this behavior, and discusses approaches for their design.

A series of unsymmetrically substituted BODIPY dyes featuring fused benzo- or naphtho-fragments on one pyrrolic unit were synthesized from the corresponding pyrrolic precursors. The synthetic route was optimized using a modular approach based on the condensation of formylpyrroles with alkylpyrroles, enabling the identification of precursor combinations that minimize byproduct formation and improve preparative yields. The resulting benzo- and naphtho-fused BODIPYs display intense fluorescence in the red region, with emission maxima spanning 590-680 nm and fluorescence quantum yields ranging from 0.27 to 0.84. Their two-photon absorption (2PA) properties were studied both experimentally and computationally. An increase in the two-photon absorption cross-section with an increase in the size of the π-conjugated system was observed, reaching 80 GM for the naphthoBODIPY derivative. These findings demonstrate the potential of π-extended BODIPY scaffolds as NIR-active fluorophores with enhanced nonlinear optical properties.