Energy Transfer by Way of an Exciplex Intermediate in Flexible Boron Dipyrromethene-Based Allosteric Architectures

Tetraarylpyrrolo[3,2-b]pyrrole-BODIPY dyad: a molecular rotor for FRET-based viscosity sensing

With the aim to develop a FRET-based viscosity sensor, two dyad molecules, 4 and 5, comprising tetraarylpyrrolo[3,2-b]pyrrole (TAPP) (donor) and naked boron-dipyrromethene (BODIPY) dyes (acceptor), were designed. Dyads were synthesized via acid-catalyzed multicomponent reactions followed by Sonogashira coupling. In both dyads, the BODIPY and TAPP moieties are linked through phenylethynyl groups, which allow free rotation of the BODIPY dyes; that is, they can act as molecular rotors. This was supported by X-ray crystallographic and DFT-optimized structures. Spectroscopic studies also confirmed the presence of both TAPP and BODIPY dyes in dyads with no electronic interactions that are suitable for fluorescence resonance energy transfer (FRET). Very high energy transfer efficiency (ETE >99%) from the donor TAPP moiety to the acceptor BODIPY moiety on excitation at the TAPP part was observed. However, due to the non-fluorescent nature of naked BODIPY dyes, no fluorescence emission was observed from the BODIPY moiety in both dyads. With increasing solvent viscosities, emission from the BODIPY moieties increases due to the restricted rotation of the BODIPY moieties. Plotting the logarithms of the fluorescent intensity of dyad 5 and the viscosity of the solution showed a good linear correlation obeying a Förster-Hoffmann equation. Non-fluorescent dyad 5 in methanol became greenish-yellow fluorescent in a methanol/glycerol (1:1) solvent. Furthermore, with an increase in the temperature of the methanol/glycerol (1:1) system, as the viscosity decreases, the fluorescence also starts decreasing. Thus, dyad 5 is capable of sensing the viscosity of the medium via a FRET-based "Off-On" mechanism. This type of viscosity sensor with a very large pseudo-Stokes shift and increased sensitivity will be useful for advancing chemo-bio sensing and imaging applications.

meso-Methyl Amination of BODIPYs by Regiospecific Cross Dehydrogenative Coupling via Direct C(sp3)-N(sp3) Bond Formation

Herein, we report a direct meso-methyl amination of BODIPY dyes by C(sp3)-N(sp3) bond formation using PIDA as an oxidant with a wide range of aliphatic secondary amines. This metal free cross dehydrogenative coupling reaction is regiospecific at the meso-methyl position of BODIPY in the presence of C1, C3, C5, and C7 methyl groups. Detailed nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, and X-ray crystallographic studies were performed to establish the reaction mechanism and the regiospecificity of the reaction. Finally, the photophysical and electrochemical properties of the newly synthesized dyes were evaluated and rationalized.

In house synthesized novel distyryl-BODIPY dye and polymer assembly as deep-red emitting probe for protamine detection

In this contribution, we designed and synthesized a deep-red emitting distyryl-BODIPY dye (dye 3) which is non-fluorescent in aqueous solution due to the formation of non-emissive aggregates. However, in presence of an amphiphilic polymer (polystyrene sulfonate, PSS), the aggregated dye molecules de-aggregate and form dye 3-PSS complex, which significantly modulates the optical features of the bound dye. Interestingly, the dye 3-PSS complex shows turn-on fluorescence response in deep-red region in presence of protamine (Pr) due to the formation of dye 3-PSS-Pr ternary complex. Such enhancement follows a linear trend in the dynamic range of 0-8.75 μM of Pr which has been utilized to determine Pr with limit of detection (LOD) of 15.04(±0.5) nM in phosphate buffer. Furthermore, excellent selectivity of the dye 3-PSS system towards Pr allows us to determine Pr even in complex biological matrix like 1% human serum. Thus, dye 3-PSS system can be applied as a very effective tool for the detection and quantification of Pr in deep-red region, overcoming several limitations encountered with the probes in the shorter wavelength region. This is the first report on BODIPY dye based supramolecular assembly for sensing and quantification of protamine.

Acid-Triggered Switchable Near-Infrared/Shortwave Infrared Absorption and Emission of Indolizine-BODIPY Dyes

Fluorescent organic dyes that absorb and emit in the near-infrared (NIR, 700-1000 nm) and shortwave infrared (SWIR, 1000-1700 nm) regions have the potential to produce noninvasive high-contrast biological images and videos. BODIPY dyes are well known for their high quantum yields in the visible energy region. To tune these chromophores to the NIR region, fused nitrogen-based heterocyclic indolizine donors were added to a BODIPY scaffold. The indolizine BODIPY dyes were synthesized via microwave-assisted Knoevenagel condensation with indolizine aldehydes. The non-protonated dyes showed NIR absorption and emission at longer wavelengths than an aniline benchmark. Protonation of the dyes produced a dramatic 0.35 eV bathochromic shift (230 nm shift from 797 nm to 1027 nm) to give a SWIR absorption and emission (λ_max^emis = 1061 nm). Deprotonation demonstrates that material emission is reversibly switchable between the NIR and SWIR.

Light-Harvesting Crystals Formed from BODIPY-Proline Biohybrid Conjugates: Antenna Effects and Excitonic Coupling

A boron dipyrromethene (BODIPY) derivative bearing a cis-proline residue at the meso-position crystallizes in the form of platelets with strong (i.e., Φ_F = 0.34) red fluorescence, but the absorption and emission spectra differ markedly from those for dilute solutions. A key building block for the crystal is a pseudo-dimer where hydrogen bonding aligns the proline groups and separates the terminal chromophores by ca. 25 Å. Comparison with a covalently linked bichromophore suggests that one-dimensional (1D) excitonic coupling between the terminals is too small to perturb the optical properties. However, accretion of the pseudo-dimer forms narrow channels possessing a high density of chromophores. The resultant absorption spectrum exhibits strong excitonic splitting, which can be explained quantitatively using the extended dipole approach and allowing for coupling between ca. 30 BODIPY units. Fluorescence, which decays with a lifetime of 2.2 ns, is assigned to a delocalized and (slightly) super-radiant BODIPY dimer situated at the interface and populated via electronic energy transfer from the interior.

A BODIPY-O-glycoside based near-infrared fluorescent sensor for serum albumin

Highly sensitive and selective near-infrared fluorescent bioprobes for serum albumin detection and quantification are in high demand for biomedical applications. Herein, we report a near-infrared emitting BODIPY-O-glycoside dye as a turn-on emission sensor for serum albumin. To the best of our knowledge, this is the first report of NIR-emitting BODIPY dyes for serum albumin sensing. Despite the various outstanding photophysical properties of the BODIPY dyes, their insolubility in water/biological media restricts their real biomedical applications. To overcome this issue, highly stable unadulterated BODIPY-O-glycoside nanoparticles (BDP-Glu-NPs) were prepared in aqueous solution by self-assembly of amphiphilic BODIPY-O-glycoside dyes. The BDP-Glu-NPs were characterized by spectroscopic, NMR, DLS and TEM studies. The ability of the BDP-Glu-NPs for the detection and quantification of serum albumin was demonstrated. It showed a 150-fold fluorescence enhancement in the presence of serum albumin, with excellent selectivity over other amino acids, porphyrin, proteins and various inorganic salts. Detection of human serum albumin (HSA) in urine samples showed that the bioprobe is applicable to a clinically significant range of the analytes with very low detection limit. These results suggested that the BDP-Glu-NPs can act as potential bioprobe to quantify albumin in biochemical and clinical samples.

Tuning of electron tunneling: a case study using BODIPY molecular layers

Using simple surface chemistry, rectification characteristics can be tuned to reproducible negative differential resistance (NDR) with a very high peak-to-valley ratio (PVR) up to 1000 in BODIPY grafted on Si.

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

We introduce herein boron-dipyrromethene (BODIPY) dyes as a new class of fluorophores for the design of reporter dyes for supramolecular host-guest complex formation with cucurbit[7]uril (CB7). The BODIPYs contain a protonatable aniline nitrogen in the meso-position of the BODIPY chromophore, which was functionalized with known binding motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a host-induced protonation and thus to a fluorescence increase. The possibility to tune binding affinities and pKa values is demonstrated and it is shown that, in combination with the beneficial photophysical properties of BODIPYs, several new applications of host-dye reporter pairs can be implemented. This includes indicator displacement assays with favourable absorption and emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization with fluorophores.

Tailored-BODIPY/Amphiphilic Cyclodextrin Nanoassemblies with PDT Effectiveness

Amphiphilic cyclodextrins (aCDs) are an intriguing class of carrier systems which, recently, have been proposed to deliver porphyrinoids and anticancer drugs or combined dose of both for dual therapeutic applications. The design of nanoassemblies based on aCD and photosensitizers (PSs) aims to preserve the photodynamic therapy (PDT) efficacy of PS, reducing the tendency of PS to self-aggregate, without affecting the quantum yield of singlet oxygen (¹O₂) production, and, not less importantly, minimizing dark toxicity and reducing photosensitization effects. With this idea in mind, in this paper, we focus on nanoassemblies between a non-ionic aCD (SC6OH) and halo-alkyl tailored iodinated boron-dipyrromethenes (BODIPY) dye, a class of molecules which recently have been successfully proposed as a stimulating alternative to porphyrinoids for their high photodynamic efficacy. Nanoassemblies of BODIPY/aCD (BL01I@SC6OH) were prepared in different aqueous media by evaporation of mixed organic film of aCD and BODIPY, hydration, and sonication. The nanostructures were characterized, measuring their hydrodynamic diameter and ξ-potential and also evaluating their time-stability in biological relevant media. Taking advantage of emissive properties of the not-iodinated BODIPY analogue (BL01), nanoassemblies based on aCD and BL01 were investigated as model system to get insight on entanglement of BODIPY in the amphiphile in aqueous dispersion, pointing out that BODIPY is well-entrapped in monomeric form (τ ≅ 6.5 ns) within the colloidal carriers. Also morphology and fluorescence emission properties were elucidated after casting the solution on glass. BL01@SC6OH is easily detectable in cytoplasm of HCT116 cell lines, evidencing the remarkable intracellular penetration of this nanoassembly similar to free BODIPY. On the same cell lines, the photodynamically active assembly BL01I/aCD shows toxicity upon irradiation. Despite the fact that free BL01I is more PDT active than its assembly, aCD can modulate the cell uptake of BODIPY, pointing out the potential of this system for in vivo PDT application.

End-to-end communication in a linear supermolecule with a BOPHY centre and N,N-dimethylanilino-based terminals

Long-range electrostatic interactions are sufficient to cause sequential ionization of the terminal groups in a BOPHY-based supermolecule.

Photocatalysis and self-catalyzed photobleaching with covalently-linked chromophore-quencher conjugates built around BOPHY

Two Chromophore-Quencher Conjugates (CQCs) have been synthesized by covalent attachment of the anti-oxidant dibutylated-hydroxytoluene (BHT) to a pyrrole-BF₂ chromophore (BOPHY) in an effort to protect the latter against photofading.

Enhanced fluorescence of aqueous BODIPY by interaction with cavitand cucurbit[7]uril

Host–guest interactions of the host cucurbit[7]uril (CB[7]) with a water soluble cationic BODIPY dye 2 are scarcely reported.

Congeners of Pyrromethene-567 Dye: Perspectives from Synthesis, Photophysics, Photostability, Laser, and TD-DFT Theory

In an attempt to develop photostable and efficient BODIPY (PM) dyes for use in liquid dye lasers, three new congeners of widely used laser dye, PM567, were synthesized and their photophysical properties in various organic solvents, laser performances, and photostabilities in a selected solvent, 1,4-dioxane, have been investigated using a frequency doubled Q-switched (10 Hz) Nd:YAG laser at 532 nm. The results of photostability study in nonpolar 1,4-dioxane revealed the remarkable enhancement in stability of the novel dyes compared to that of PM567 as well as improved laser performances. Cyclic voltammetry study strongly supports the observed enhancement in photostability of the novel dyes compared to that of PM567. The observed properties of the novel dyes in relation to those of PM567 have been rationalized by extensive use of DFT and TD-DFT using the B3LYP/6-31G(d) method of theory.

Quinone–Bodipy H-bonding interaction over π-stacking in toluene

Quinone type compounds (o-chloranil, p-chloranil and DDQ) demonstrate excellent H-bonding interactions with a meso-phenol Bodipy dye (1) in both ground and excited state in a non-polar toluene medium.

Thiocyanation of BODIPY dyes and their conversion to thioalkylated derivatives

Thiocyanation and formation of thioalkylated BODIPYs is a simple and reliable way for their chemical modification and photophysical tuning.