BODIPY Core Research Articles

Hybridization of triphenylamine to BODIPY dyes at the 3,5,8-positions: A facile strategy to construct near infra-red aggregation-induced emission luminogens with intramolecular charge transfer for cellular imaging

A series of five BODIPY derivatives with triarylamine (TPA) moieties on their 3-, 5-, or 8-positions were reported, which showed wide-range fluorescence emissions across red and near infrared regions in their aggregation states. The influences of numbers and substituted positions of TPA groups on the optical and aggregation-induced emission (AIE) properties of these BODIPYs as well as organelle-specific imaging in live cells were investigated. The TPA groups installed at 3-/5-positions of BODIPY could effectively enlarge the conjugated system and red-shift the absorption and emission bands (λemmax up to 815 nm). In contrast, the TPA group linked to 8-position of BODIPY core has little contribution to decrease the HOMO-LUMO energy gap. Importantly, regardless the substitution positions of TPA groups, all these TPA-substituted BODIPYs (BTs) showed remarkable AIE performance and possessed high molar extinction absorption (up to ∼ 63000 M−1 cm−1), two-photon absorption (up to 171 GM at 870 nm), and large Stokes shifts. The BODIPY with one TPA group (BT1 and FBT1) showed lipid droplets-specific localization while BODIPY with two and three TPA groups (BT2, BT3 and FBT2) preferred to enrich in lysosomes. These BODIPYs all have been successfully used in tracking the dynamic behaviors of lipid droplets or lysosomes in living cells. Furthermore, BT1 and FBT1 can quantitatively detect the overexpression of lipid droplets, and BT3 has been successfully used to observe lysosomes behaviors of lipophagy process in living cells. This work systematically studied the influence of the number and position of TPA units on the optical properties and AIE-activities of BODIPYs, which not only enriched the BODIPY-based AIE NIR probes for organelle-specific imaging in live cells, but also provided a practical strategy for the effective construction of organic dyes with NIR AIE activity.

Synthesis, photophysical properties, anti-Kasha photochemical reactivity and biological activity of vinyl- and alkynyl-BODIPY derivatives

New photoactivable BODIPY fluorescent dyes, which are quinone methide (QM) precursors, were synthesized. The series of BODIPY dyes has a photoreactive group linked to the BODIPY core by vinyl or ethynyl spacers. Molecules have bathochromic shifted absorption and emission maxima and higher fluorescence quantum yields compared to the previously reported BODIPY QM precursors. They show anti-Kasha photochemical reactivity and undergo photomethanolysis reaction upon photoexcitation at λ < 350 nm. Although UV light is needed for the photochemical generation of QMs and attachment to potential bio-targets, bathochromic shifted absorption and emission has advances in sensing and fluorescence labeling. Antiproliferative investigation was conducted for the vinyl derivative against three human cancer lines with the cells kept in dark or irradiated. Upon excitation with visible light antiproliferative activity was enhanced with IC50 values in low micromolar concentration.

Bis-BODIPY-based fluoride and cyanide sensor mediated by unconventional deprotonation of C−H proton

A novel bis-BODIPY-based colorimetric and fluorescent sensor (BODIPY-NN) for F− and CN− recognition with high selectivity and high sensitivity is reported. The designed sensor, BODIPY-NN, was synthesized by a one-step click reaction of azido-BODIPY with N,N′-dipropargylbenzene-1,2-diamine. The BODIPY-NN sensor displays a marked color change from pink to colorless and a remarkable turn-off fluorescence behavior exclusively toward F− and CN− ions. Analysis of 1H, 13C, 19F, 11B NMR and mass spectra, together with theoretical calculations, provides insight into the mechanism of anion binding to BODIPY-NN. The sensing mechanism was found to be unconventional deprotonation at pseudo-benzylic carbons attached to BODIPY cores in the presence of F− and CN− ions, to form the less highly conjugated BODIPY moieties, thereby displaying fluorescence quenching. Addition of water in the BODIPY-NN + F− system regenerates the sensor with restoration of its spectroscopic properties. In contrast, the CN− ions permanently disrupt the BODIPY moieties by nucleophilic displacement at the central boron atoms, which is irreversible upon addition of water. The detection limits for F− and CN− in THF are 83 and 72 nM, respectively. In particular, BODIPY-NN embedded in cetyltrimethylammonium micelles can be used as colorimetric detection of CN− ions in aqueous media.

Trimethoxyphenyl-BODIPYs as probes for lysosome staining

BODIPYs have been extensively used for biological imaging owing to their high fluorescent quantum yields of stability toward photobleaching. In this work, zwitterionic groups were introduced into trimethoxyphenyl-BODIPY derivatives to improve their water-solubility. The impact of the substitution pattern of the methoxy groups in the phenyl motif and of the alkyl groups at different positions of the BODIPY core was also investigated. Three novel water-soluble trimethoxyphenyl-BODIPYs, herein designated as BDP-12, BDP-13 and BDP-14, were then evaluated as potential markers for lysosome staining. The highest fluorescence quantum yield and molar absorption coefficient were observed for BDP-12. Cellular uptake studies demonstrated that the three BODIPYs are rapidly internalized by cells. It was observed that 5 minutes of incubation time was sufficient to detect BODIPY-associated fluorescence in the treated cells. Cell internalization of the three molecules was inhibited by chloroquine and chlorpromazine, but not by genistein, which indicates that clathrin-mediated endocytosis is the main mechanism of internalization. The three trimethoxyphenyl-BODIPYs displayed excellent biocompatibility, even at high concentrations and in the presence of light. The three BODIPYs accumulate in the lysosomal compartments of live cells and the staining remains stable upon fixation with paraformaldehyde. Due to its optimal optical properties, BDP-12 is suggested as a promising candidate for cell imaging of lysosomes.

Endowing deep-red BODIPY luminophors with enhanced aggregation-induced emission by installing miniature rotor of trifluoromethyl for solution-processed OLEDs

Highly efficient deep-red (DR) organic materials in aggregated state are fundamentally restricted by the serious nonradiative decay rates (k nr ) due to the energy gap law, and the aggregation induced quenching in view of significant intermolecular interaction. Here, two new BODIPY chromophores owning donor−acceptor−donor (D−A−D) structure, namely CF 3 -2TPA and 2CF 3 -2TPA, were designed and synthesized. Trifluoromethyl (CF 3 )-substituted phenyl group was introduced to the meso-position of the BODIPY core, tuning red to DR emission and suppressing intermolecular interaction with the utilization of the steric hindrance of CF 3 . Besides, CF 3 -2TPA and 2CF 3 -2TPA show enhanced aggregation-induced emission (AIE) characteristic, which was ascribed to the CF 3 rotor dissipating the excited-state energy. The OLEDs are fabricated by combining a thermally assisted delayed fluorescence host with a deep-red dye, showing a DR cut-on wavelength of 668 nm and external quantum efficiency of 2.3%. This work provided a rotor strategy to convert BODIPY molecule with obvious AIE property, providing their promising applications in DR-OLEDs. The miniature rotor of trifluoromethyl (CF 3 ) introduced to the meso-position of BODIPY, induced redshifted to deep-red emission, prevented obvious intermolecular interaction and achieved remarkably enhanced aggregation induced emission feature. Deep-red OLED showed an emission wavelength of 668 nm and an EQE max of 2.3%. • The CF 3 units, modifying the meso position of BODIPY, assisted in the deep-red emission. • Depending on the steric hindrance of CF 3 groups, the intermolecular interaction and packing were suppressed. • The enhanced AIE feature of BODIPYs was realized due to the miniature rotor of CF 3 substitutes. • Deep-red OLED showed an emission wavelength of 668 nm and an external quantum efficiency of 2.3%.

Rotor-Tuning Boron Dipyrromethenes for Dual-Functional Imaging of Aβ Oligomers and Viscosity.

Alzheimer's disease (AD), known as a common incurable and elderly neurodegenerative disease, has been widely explored for accurate detection of its biomarker (Aβ oligomers) for early diagnosis. Although great efforts have been made, it is still of great importance to develop fluorescence probes for Aβ oligomers with good selectivity and low background. Herein, starting from BODIPY493/503 (a commercial dye for neutral lipid droplets), which exhibited a small Stokes shift and no response toward Aβ peptides, two fluorescence probes 5MB-SZ and B-SZ with a benzothiazole rotor at the 2-position of the BODIPY core and a methyl or benzyl group at the meso position have been designed and synthesized, which exhibited excellent optical properties/stability and could successfully image β-amyloid fibrils and viscosity. Upon exposure to Aβ oligomers, the fluorescence intensity of 5MB-SZ was enhanced by 43.64-fold with the corresponding fluorescence quantum yields changing from 0.85% to 27.43%. Meanwhile, probe 5MB-SZ showed a highly sensitive viscosity response in both solutions and living cells. In vitro and in vivo experiments confirmed that probe 5MB-SZ exhibited an excellent capacity for imaging β-amyloid fibrils. Therefore, 5MB-SZ, as a rotor-tuning BODIPY analogue, could possibly serve as a highly potential and powerful fluorescence probe for early diagnosis of AD.

Naphthalimide-BODIPY dyads: Synthesis, characterization, photophysical properties, live cell imaging and antimicrobial effect

Naphthalimide-Borondipyrromethene (NI-BODIPY) dyads, bearing NI unit on the meso and styryl positions of BODIPY core were designed and subjected to photophysical, in vitro cell imagining and antimicrobial activity studies. The identities of synthesized compounds (3-5) were confirmed by using FT-IR, 1H, 13C NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The structure of the NI-BODIPY dyad (3) was also characterized by means of X-ray diffraction. Spectroscopic properties of dyad systems were explored in detail via UV-vis absorption and fluorescence emission spectroscopies. Mono- and distyryl- derivatives (4 and 5) revealed a substantial conjugation effect manifested by an expected bathochromic shift in absorption and emission spectra relative to dyad 3. The use of NI-BODIPYs for live cell lines is demonstrated by flow cytometry and confocal microscopy in which compound 3 produced the brightest fluorescence in confocal microscopy. Furthermore in vitro antimicrobial activities were evaluated on Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Noticeably, the distyryl- derivative 5 functionalized with three NI units displayed superior antibacterial activity against both E. coli and S. aureus with MIC values of 76 and 110 μM, respectively. Naphthalimide decorated BODIPY dyads have been proposed as both antibacterial and cell imaging agents.

β-Boronic Acid-Substituted Bodipy Dyes for Fluorescence Anisotropy Analysis of Carbohydrate Binding.

Boronic acids are widely used for labeling catechols and carbohydrates in analytical (bio)chemistry due to their high binding affinities for diols. Here, we present two asymmetrically substituted Bodipy dyes with a boronic acid at the β-position (BBB). We present a green-emitting BBB, gBBB, and, by expanding the conjugated system of the Bodipy core at α-position, a red-emitting rBBB. Especially, gBBB shows a bathochromic shift of the electronic spectra upon binding to saccharides and polyols, whereas the fluorescence lifetime of rBBB is more sensitive to hydroxy-ligand binding. Moreover, gBBB constantly shows higher binding affinities than rBBB, reaching Kb ≈ 103 M-1 at pH 8.5 for fructose. Finally, time-resolved fluorescence anisotropy allows to distinguish the number of saccharide units of oligosaccharides as the bond along the transition dipole moment ensures that the fluorescence anisotropy only decays due to the rotational diffusion of labeled carbohydrates. β-substituted BODIPY dyes are, thus, foreseen as fluorescence anisotropy labels for macromolecule sizing, where conventional fluorophores fail to discriminate due to the chemical similarity of recognition sites.

Rational design and synthesis of a novel BODIPY-based probe for selective imaging of tau tangles in human iPSC-derived cortical neurons

Numerous studies have shown a strong correlation between the number of neurofibrillary tangles of the tau protein and Alzheimer's disease progression, making the quantitative detection of tau very promising from a clinical point of view. However, the lack of highly reliable fluorescent probes for selective imaging of tau neurofibrillary tangles is a major challenge due to sharing similar β–sheet motifs with homologous Amyloid-β fibrils. In the current work, we describe the rational design and the in silico evaluation of a small-size focused library of fluorescent probes, consisting of a BODIPY core (electron acceptor) featuring highly conjugated systems (electron donor) with a length in the range 13–19 Å at C3. Among the most promising probes in terms of binding mode, theoretical affinity and polarity, BT1 has been synthesized and tested in vitro onto human induced pluripotent stem cells derived neuronal cell cultures. The probe showed excellent photophysical properties and high selectivity allowing in vitro imaging of hyperphosphorylated tau protein filaments with minimal background noise. Our findings offer new insight into the structure-activity relationship of this class of tau selective fluorophores, paving the way for boosting tau tangle detection in patients possibly through retinal spectral scans.

Substitution effects in distyryl BODIPYs for near infrared organic photovoltaics

In this research, four new conjugated Bodipy (boron dipyrromethene) structures absorbing in the near IR region have been synthesized and their photophysical, electrochemical, morphological properties and their potential for organic photovoltaics (OPV) have been investigated. All the compounds were substituted with bithiophene units in their 3- and 5- positions. Besides, the meso (8-) and 2-, 6- positions were substituted with different groups, and it allowed analysis of substitution effects in these positions on the performance of organic photovoltaics. Among the synthesized compounds, BTT has better photovoltaic performance than others with 1.3% power conversion efficiency (PCE) value when an organic solar cell with PC71BM acceptor compound was formed under the optimized conditions. Experimental and theoretical studies demonstrated that photovoltaic performance is largely affected by the units on the meso position under the compounds studied and the electronic distributions of the frontier molecular orbitals which are presumably dictated by the orientation of the side groups around the Bodipy core. We believe, with the light of the studies performed novel substitution transformations would enhance implementation of these types of compounds in near infrared photovoltaics.

Photophysical properties of BODIPYs with sterically-hindered nitrophenyls in meso-position

During recent years, the BODIPY core became a popular scaffold for designing of dyes with desirable properties. In this paper, we extend the library of possible modification of BODIPYs, presenting experimental data for a new family meso-substituted with nitrophenyl groups. We also present quantum chemical calculations, which complement the experimental data and give additional insight in the underlying photochemical and photophysical processes. Optical properties of novel compounds are characterized. It is shown that the fluorescence quantum yield and the efficiency of singlet oxygen generation differs by two orders of magnitude across the family. In aqueous solution, red-shifted fluorescence emission band is detected, corresponding to aggregates. This band has shorter decay time and wide excitation spectrum. We show that photolysis is not accompanied by the release of nitric oxide (NO) which was observed earlier for some dyes with nitrophenyl substituents. The experimental data presented in this paper may be useful for further designing of BODIPY dyes and NO photodonors.

BODIPY nanoparticles functionalized with lactose for cancer-targeted and fluorescence imaging-guided photodynamic therapy

A series of four lactose-modified BODIPY photosensitizers (PSs) with different substituents (-I, -H, -OCH3, and -NO2) in the para-phenyl moiety attached to the meso-position of the BODIPY core were synthesized; the photophysical properties and photodynamic anticancer activities of these sensitizers were investigated, focusing on the electronic properties of the different substituent groups. Compared to parent BODIPY H, iodine substitution (BODIPY I) enhanced the intersystem crossing (ISC) to produce singlet oxygen (1O2) due to the heavy atom effect, and maintained a high fluorescence quantum yield (ΦF) of 0.45. Substitution with the electron-donating methoxy group (BODIPY OMe) results in a significant perturbation of occupied frontier molecular orbitals and consequently achieves higher 1O2 generation capability with a high ΦF of 0.49, while substitution with the electron-withdrawing nitro group (BODIPY NO2) led a perturbation of unoccupied frontier molecular orbitals and induces a forbidden dark S1 state, which is negative for both fluorescence and 1O2 generation efficiencies. The BODIPY PSs formed water-soluble nanoparticles (NPs) functionalized with lactose as liver cancer-targeting ligands. BODIPY I and OMe NPs showed good fluorescence imaging and PDT activity against various tumor cells (HeLa and Huh-7 cells). Collectively, the BODIPY NPs demonstrated high 1O2 generation capability and ΦF may create a new opportunity to develop useful imaging-guided PDT agents for tumor cells.

Halogenated BODIPY photosensitizers: Photophysical processes for generation of excited triplet state, excited singlet state and singlet oxygen

We have systematically examined the formation of singlet oxygen O2(1Δg), the excited triplet state (T1), and excited singlet state (S1) for halogenated BODIPY photosensitizers (halogen = Cl, Br, and I) in eight solvents to understand how halogen atoms and solvent affect these properties. The phosphorescence spectra and lifetimes of singlet oxygen generated by these halogenated BODIPYs have been measured by steady state/time resolved NIR emission, while the formation quantum yield of singlet oxygen (ΦΔ) has been determined by chemical method using diphenylisobenzofuran (DPBF) as the trapping agent. The formation quantum yield ΦΔ of singlet oxygen can be as high as 0.96 for iodinated BODIPY and 0.71 for brominated BODIPY. The triplet state T1 absorption spectra of brominated and iodinated BODIPYs have been recorded by laser flash photolysis method, in which T1 shows high formation efficiency and long lifetime. The formation and decay of excited singlet state S1 of four BODIPYs have been measured by ground state (S0) absorption and steady state/time resolved fluorescence. The results show that larger halogen atoms on BODIPY core lead to smaller fluorescence quantum yield, shorter fluorescence lifetime and higher singlet oxygen formation quantum yield due to heavy atom effect that promotes the formation of triplet state. On the other hand, higher solvent polarity causes lower singlet oxygen formation quantum yield, smaller fluorescence quantum yield, and shorter fluorescence lifetime. This solvent effect is explained by the presence of photoinduced charge transfer (ICT) process from halogen atoms to BODIPY. The ICT efficiency has been estimated and the results are agreed with ICT theory. ICT process in halogenated BODIPYs has never been revealed in literature. HOMO/LUMO obtained from DFT calculation also supports the presence of ICT. The involvement of ICT in the photosensitizing process of halogenated BODIPYs provides new insights for designing BODIPY photosensitizers for photodynamic therapy of tumor.

Effect of the iodine atom position on the phosphorescence of BODIPY derivatives: a combined computational and experimental study.

A new BODIPY derivative (o-I-BDP) containing an iodine atom in the ortho position of the meso-linked phenyl group was prepared. Photophysical and electrochemical properties of the molecule were compared to previously reported iodo BODIPY derivatives, as well as to the non-iodinated analog. While in the case of derivatives featuring iodine substituents in the BODIPY core, efficient population of the triplet state is accompanied by a substantial positive shift of the reduction potential compared to pristine BODIPY, o-I-BDP displays phosphorescence and simultaneously maintains the electrochemical properties of unsubstituted BODIPYs. A theoretical investigation was settled to analyze results and rationalize the influence of iodine position on electronic and photophysical properties, with the purpose of preparing a fully organic phosphorescent BODIPY derivative. TD-DFT and spin-orbit coupling calculations shed light on the subtle effects played by the introduction of iodine atom in different positions of BODIPY.

Photophysical properties regulation and applications of BODIPY-based derivatives with electron donor-acceptor system

As a class of important fluorescence dyes, BODIPY and its derivatives have the advantages of high quantum yield, good biocompatibility and easy structure adjustment, etc. In view of the structural characteristics of BODIPY, through the methods of introducing electron donors and electron acceptors into BODIPY core, the photophysical properties can be adjusted effectively through the push–pull electron effect. In this review, based on different fluorescence regulation mechanisms and the BODIPY electronic roles as donating, withdrawing or linkage parts in the molecular structures, we summarized the research progress and application directions of BODIPY-based derivatives with donor–acceptor electron system.

Photophysical challenges and antenna effect between click reaction-based Bodipy derivatives manufactured from Knorr pyrrole

In this paper, a series of click reaction-based Bodipy derivatives have been synthesized as part of a preliminary study. Following the characterization of the four challenger molecules, the photophysical properties (absorption, emission, excitation, molar absorption coefficient, quantum yield, etc.) were examined in various organic solvents. The results showed that the energy transfer from the Bodipy cores to other moieties was calculated between 71% and 93% depending on different π-electron configurations and chromophore groups.

Design of a graphene oxide-BODIPY conjugate for glutathione depletion and photodynamic therapy

Boron dipyrromethene derivates (BODIPYs) are promising photosensitisers (PSs) for cancer treatment using photodynamic therapy (PDT). This study investigates the functionalisation of graphene oxide (GO) with a BODIPY derivate for glutathione (GSH) depletion and PDT. The functionalisation of GO with a 3,5-dichloro-8-(4-boronophenyl) BODIPY via a diol derivatisation with the phenyl boronic acid moiety at the meso position of the BODIPY core, allowed to preserve the intrinsic properties of GO. We demonstrated that both chlorine atoms were substituted by GSH in the presence of glutathione transferase (GST), inducing a relevant bathochromic shift in the absorption/emission features and thus generating the active PS. Ex vitro assessment using cell lysates containing cytoplasmatic GST revealed the intracellular catalytic mechanism for the nucleophilic substitution of the GO-BODIPY adduct with GSH. Confocal microscopy studies showed important differences in the cellular uptake of free BODIPY and GO-BODIPY and revealed the coexistence of GO-BODIPY, GO-BODIPY-GS, and GO-BODIPY-GS2 species inside vesicles and in the cytoplasm of the cells after 24 h of incubation. In vitro biocompatibility and safety of GO and GO-BODIPY were evaluated in 2D and 3D models of prostate adenocarcinoma cells (PC-3), where no toxicity was observed up to 100 µg ml−1 of GO/GO-BODIPY in all treated groups 24 h post-treatment (cell viability > 90%). Only a slight decrease to 80% at 100 µg ml−1 was observed after 48 h of incubation. We demonstrated the efficacy of a GO adduct containing an α-chlorine-substituted BODIPY for the simultaneous depletion of intracellular GSH and the photogeneration of reactive oxygen species using a halogen white light source (5.4 mW cm−2) with a maximum in the range of 500–800 nm, which significantly reduced cell viability (<50%) after irradiation. Our study provides a new vision on how to apply BODIPY derivates and potentiate the toxicity of PDT in prostate and other types of cancer.

Give or Take: Effects of Electron-Accepting/-Withdrawing Groups in Red-Fluorescent BODIPY Molecular Rotors.

Mapping microviscosity, temperature, and polarity in biosystems is an important capability that can aid in disease detection. This can be achieved using fluorescent sensors based on a green-emitting BODIPY group. However, red fluorescent sensors are desired for convenient imaging of biological samples. It is known that phenyl substituents in the position of the BODIPY core can shift the fluorescence spectra to longer wavelengths. In this research, we report how electron-withdrawing (EWG) and -donating (EDG) groups can change the spectral and sensory properties of -phenyl-substituted BODIPYs. We present a trifluoromethyl-substituted (EWG) conjugate with moderate temperature sensing properties and a methoxy-substituted (EDG) molecule that could be used as a lifetime-based polarity probe. In this study, we utilise experimental results of steady-state and time-resolved fluorescence, as well as quantum chemical calculations using density functional theory (DFT). We also explain how the energy barrier height () for non-radiative relaxation affects the probe’s sensitivity to temperature and viscosity and provide appropriate ranges for the best possible sensitivity to viscosity and temperature.

A new 3-substituted BODIPY dye: Synthesis, crystal structure, photophysical, non-linear optic and OLED properties

A BODIPY derivative (compound 2), substituted with 4-nitrophenyl at the meso position and its 3-pyrrole substituted derivative (compound 3) were synthesized and characterized. The structure of compound 3 was elucidated by single crystal X-ray diffraction study. The Photophysical properties of compounds 2 and 3 were studied in various solvents with different polarities. The expansion of the π-conjugation by introduction of the pyrrole ring to 3-position of the BODIPY core results in a considerable red shift in the absorption and emission bands. Also, photophysical properties of compounds 2 and 3 was affected by the solvent polarity. Compound 3 showed stronger fluorescence in non-polar solvents (ΦF = 0.049 in Hexane). In order to establish the effect of the pyrrole attachment, the synthesized compounds 2 and 3 were optimized at the level of computational chemistry, DFT/B3LYP/6–31+G(d,p). The highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital (ELUMO), the energy gap (ΔE) parameters and contour diagrams obtained from the optimized structures were investigated. The nonlinear optical (NLO) and light emission (OLED) properties of the compounds were investigated computationally on the basis of polarizability parameters and Marcus theory, respectively.

Quinoline-functionalized BODIPY dyes: Structural and photophysical properties

BODIPYs at different positions of quinolines show similar absorption spectra but very different visible emission efficiency. Single-crystal structures show different tilting angles of quinoline groups and BODIPY core structure. The emission efficiency decreases as the torsion angle between BODIPY core and quinoline becomes smaller in the order of 4-Q-BDP > 3-Q-BDP > 2-Q-BDP ≈ 2,9-Phen-BDP. The restoration of fluorescence in the presence of methanol and theoretical calculations indicate the photoinduced electron transfer from quinoline N to BODIPY core could be responsible for such a gradual fluorescence change.