Tunable Yellow to Near-Infrared Fluorescent Boron-Amino-Chelating Complexes with Stokes Shifts >100 nm

A series of diphenylboron-chelating N-substituent 8-aminoquinoline, 5-aminoquinoxaline, and 1-aminophenazine were prepared. They exhibit lowest energy absorption peaks of 444-766 nm, emission peaks of 563-820 nm, and quantum yields of up to 46.5%. Electrochemical and theoretical studies indicate that the N-substituent mainly determines the HOMO and the framework determines the LUMO, thus allowing for a wide-tuning of absorptions/emissions. Intramolecular charge transfer transition leads to large Stokes shifts of up to 166 nm. One selected compound showed satisfactory cytocompatibility and cytoplasm-targeting cell imaging ability.

Aryl/Heteroaryl Substituted Boron-Difluoride Complexes Bearing 2-(Isoquinol-1-yl)pyrrole Ligands Exhibiting High Luminescence Efficiency with a Large Stokes Shift

A series of 2-(isoquinol-1-yl)pyrrole-boron complexes possessing (hetero)aryl substituents on the pyrrole and/or isoquinoline moiety were prepared. These compounds exhibited the fluorescence emission character in both solution and solid state. In most cases, the large Stokes shift and high fluorescence quantum yield in the solution were compatible. Furthermore, the structural diversity allowed the precise tuning of emitting colors from light blue to red with strong emission intensity. The present paper describes their comprehensive optical characteristics dependent on the type and position of the substituted aryl groups by the experimental and computational studies.

Aromatic [b]-fused BODIPY dyes as promising near-infrared dyes

Far-red and near-infrared (NIR) absorbing/emitting dyes have found diverse applications in biomedicine and material science. However, the absorption and emission of classical BODIPY chromophores at short wavelength hamper their applications. Several strategies have been adopted to modify the structure of the BODIPY core to design NIR dyes. Among these, the most efficient approach to expand the π-conjugation of the BODIPY core is via fusion of aromatic rings. So far, many novel BODIPY skeletons fused to aromatic hydrocarbons and heterocycles at the b bond have been reported. This review comprehensively describes the recent advances regarding the development of aromatic [b]-fused BODIPY dyes with the focus on the design and synthesis, the relationships between their photophysical/spectroscopic properties and molecular structures, and the potential applications in bioassays and optoelectronic devices.

Theoretical predictions of the spectroscopic properties of BODIPY dyes: Effects of the fused aromatic and heteroaromatic rings at the b, g bonds

The fusion of aryl and heteroaryl moieties in the BODIPY skeleton is the important route to design BODIPYs exhibiting absorption and fluorescence in red or near infra-red regions. Despite the importance of this approach, little is known about the influence of aryl and heteroaryl rings on the position of the energy levels of the lower electronic states of such dyes. In this paper, the influence of benzene (B), thiophene (T) and furan (F) rings fused in the BODIPY core (b) at both b and g bonds on the optical properties of the symmetric BbB, TbT and FbF and asymmetric TbF, BbF and BbT dyes have been investigated by TD-CAM-B3LYP and RI-CC2 calculations. We have shown that in contrast to the locally excited (LE0-type) main vertical state, energy of which is nearly the same for all the substituents at the b and g bonds, energy of the next two states of the LE1- and LE2-type for the symmetric dyes or the charge transfer (CT1- and CT2-type) for the asymmetric dyes depends strongly on the nature of the rings at the b and g bonds. The benzene-fused dyes (BbF, BbT, BbB) have the lowest energy of the excited levels of the LE-type (or CT1-type) states, and inversion with LE0-type levels occurs. As a result, the dramatic decrease of the fluorescence quantum yield is expected in these cases. The identification of these effects provides a quality framework for understanding of how fused substituents regulate photophysical processes of BODIPYs.

Absorption and fluorescence properties of non-symmetric benzo-, furo-, and thieno-fused structures at the b bonds in the BODIPY frame

The influence of furo-, thieno-, and benzo-fused structures at the b bonds in the BODIPY frame on the optical properties is investigated by TD-CAM-B3LYP and RI-CC2 calculations. The most important result is that substituents at the b bond of the BODIPY core affect strongly the S₁-S₂ gaps. In contrast to the S₁ (local excited (LE-type)) state, energy of which is nearly the same for all the substituents at the b bond, energy of the S₂ (charge transfer (CT-type)) state depends strongly on the nature of the substituent and decreases in the following order: furo-fused > thieno-fused > benzo-fused. In the last case the inversion of S₁ and S₂ levels occurs. No red shift of the main long-wave absorption transition and no substantial changes in its intensity can be predicted by the calculations for benzo[b]-derivative (vertical energy (E_v) is 2.95 eV, oscillator strength (f) is 0.80) relative to furo- (E_v = 2.97 eV, f = 0.69) and thieno-derivatives (E_v = 2.95 eV, f = 0.65). However, the dramatic decrease of the fluorescence quantum yield is expected owing to positions of their LE-type (E_v = 2.95 eV, f = 0.80) and CT-type (E_v = 2.79 eV, f = 0.01) transitions. In the case of thieno-fused BODIPY, owing to the approach of the energy levels of the vertical S₂ and S₁ states, the energy equilibrium of the [1]CT-type state becomes lower than that of the [1]LE state, and Φ_f of the thieno-derivative may be substantially lower than Φ_f of the furo-derivative.

Unveiling the Photophysical Properties of Boron-dipyrromethene Dyes Using a New Accurate Excited State Coupled Cluster Method

Boron-dipyrromethene (BODIPY) molecules form a class of fluorescent dyes known for their exceptional photoluminescence properties. Today, they are used extensively in various applications from fluorescent imaging to optoelectronics. The ease of altering the BODIPY core has allowed scientists to synthesize dozens of analogues by exploring chemical substitutions of various kinds or by increasing the length of conjugated groups. However, predicting the impact of any chemical change accurately is still a challenge, especially as most computational methods fail to describe correctly the photophysical properties of BODIPY derivatives. In this study, the recently developed coupled cluster method called "domain-based local pair natural orbital similarity transformed equation of motion-coupled cluster singles and doubles" (DLPNO-STEOM-CCSD) is employed to compute the lowest vertical excitation energies of more than 50 BODIPY molecules. The method performs remarkably well yielding an accuracy of about 0.06 eV compared to the experimental absorption maxima. We also provide an estimate to the error made by neglecting vibronic effects in the computed spectra. The dyes selected for investigation here span a large range of molecular sizes and chemical functionalities and are embedded in solvents with different polarities. We have also investigated if the method is able to correctly reproduce the impact of a single chemical modification on the absorption energy. To characterize the method in more specific terms, we have studied four large BODIPY analogues used in real-life applications due to their interesting chemical properties. These examples should illustrate the capacity of the DLPNO-STEOM-CCSD procedure to become a method of choice for the study of photophysical properties of medium to large organic compounds.

Ultraspecific live imaging of the dynamics of zebrafish neutrophil granules by a histopermeable fluorogenic benzochalcone probe

Neutrophil granules (NGs) are key components of the innate immune response and mark the development of neutrophilic granulocytes in mammals. However, there has been no specific fluorescent vital stain up to now to monitor their dynamics within a whole live organism. We rationally designed a benzochalcone fluorescent probe (HAB) featuring high tissue permeability and optimal photophysics such as elevated quantum yield, pronounced solvatochromism and target-induced fluorogenesis. Phenotypic screening identified HAB as the first cell- and organelle-specific small-molecule fluorescent tracer of NGs in live zebrafish larvae, with no labeling of other cell types or organelles. HAB staining was independent of the state of neutrophil activation, labeling NGs of both resting and phagocytically active neutrophils with equal specificity. By high-resolution live imaging, we documented the dynamics of HAB-stained NGs during phagocytosis. Upon zymosan injection, labeled NGs were rapidly recruited to the forming phagosomes. Despite being a reversible ligand, HAB could not be displaced by high concentrations of pharmacologically relevant competing chalcones, indicating that this specific labeling was the result of the HAB's precise physicochemical signature rather than a general feature of chalcones. However, one of the competitors was discovered as a promising interstitial fluorescent tracer illuminating zebrafish histology, similarly to BODIPY-ceramide. As a yellow-emitting histopermeable vital stain, HAB functionally and spectrally complements most genetically incorporated fluorescent tags commonly used in live zebrafish biology, holding promise for the study of neutrophil-dependent responses relevant to human physiopathology such as developmental defects, inflammation and infection. Furthermore, HAB intensely labeled isolated live human neutrophils at the level of granulated subcellular structures consistent with human NGs, suggesting that the labeling of NGs by HAB is not restricted to the zebrafish model but also relevant to mammalian systems.

Phase partitioning, solvent-switchable BODIPY probes for high contrast cellular imaging and FCS

Lipophilic BODIPY fluorphores, in which the BODIPY core bears pendant dipyrido[3,2-a:2′,3′-c]phenazine (Dppz) or naphthyridyl and cholesterol substituents were designed and prepared as lipid probes for both liposomes and live cell imaging.

Naphtho[b]-fused BODIPYs: one pot Suzuki–Miyaura–Knoevenagel synthesis and photophysical properties

The facile one-pot synthesis of naphtho[b]-fused BODIPYs and their photophysical properties are reported.

Azadipyrromethene cyclometalation in neutral RuII complexes: photosensitizers with extended near-infrared absorption for solar energy conversion applications

In the on-going quest to harvest near-infrared (NIR) photons for energy conversion applications, a novel family of neutral ruthenium(ii) sensitizers has been developed by cyclometalation of an azadipyrromethene chromophore.