Boron Dipyrrin Research Articles

Promising Fast Energy Transfer System via an Easy Synthesis: Bodipy–Porphyrin Dyads Connected via a Cyanuric Chloride Bridge, Their Synthesis, and Electrochemical and Photophysical Investigations

The boron dipyrrin (Bodipy) chromophore was combined with either a free-base or a Zn porphyrin moiety (H(2)P and ZnP respectively), via an easy synthesis involving a cyanuric chloride bridging unit, yielding dyads Bodipy-H(2)P (4) and Bodipy-ZnP (5). The photophysical properties of Bodipy-H(2)P (4) and Bodipy-ZnP (5) were investigated by UV-Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. The comparison of the absorption spectra and cyclic voltammograms of dyads Bodipy-H(2)P (4) and Bodipy-ZnP (5) with those of their model compounds Bodipy, H(2)P, and ZnP shows that the spectroscopic and electrochemical properties of the constituent chromophores are essentially retained in the dyads indicating negligible interaction between them in the ground state. In addition, luminescence and transient absorption experiments show that excitation of the Bodipy unit in Bodipy-H(2)P (4) and Bodipy-ZnP (5) into its first singlet excited state results in rapid Bodipy to porphyrin energy transfer-k(4) = 2.9 × 10(10) s(-1) and k(5) = 2.2 × 10(10) s(-1) for Bodipy-H(2)P (4) and Bodipy-ZnP (5), respectively-generating the first porphyrin-based singlet excited state. The porphyrin-based singlet excited states give rise to fluorescence or undergo intersystem crossing to the corresponding triplet excited states. The title complexes could also be used as precursors for further substitution on the third chlorine atom on the cyanuric acid moiety.

α‐/β‐Formylated Boron–Dipyrrin (BODIPY) Dyes: Regioselective Syntheses and Photophysical Properties

AbstractFormylation has been performed on pyrrole‐unsubstituted dipyrromethanes 1 and boron–dipyrrin (BODIPY) dyes 4 based on a Vilsmeier–Haack reaction. It is highly regioselective and complementary and occurs exclusively at the α‐ and β‐position, respectively, for pyrrole‐unsubstituted dipyrromethanes 1 and BODIPY dyes 4. This regioselective formylation enables the syntheses of a variety of α‐ and β‐substituted BODIPY dyes. The installation of formyl groups affects the electronic properties of the BODIPY chromophore, resulting in red‐ and blueshifts of the absorption and emission maxima, respectively, for the α‐ and β‐formylatedBODIPYs 3 and 5.

Photochemical Charge Separation in Closely Positioned Donor–Boron Dipyrrin–Fullerene Triads

A series of molecular triads, composed of closely positioned boron dipyrrin-fullerene units, covalently linked to either an electron donor (donor(1)-acceptor(1)-acceptor(2)-type triads) or an energy donor (antenna-donor(1)-acceptor(1)-type triads) was synthesized and photoinduced energy/electron transfer leading to stabilization of the charge-separated state was demonstrated by using femtosecond and nanosecond transient spectroscopic techniques. The structures of the newly synthesized triads were visualized by DFT calculations, whereas the energies of the excited states were determined from spectral and electrochemical studies. In the case of the antenna-donor(1)-acceptor(1)-type triads, excitation of the antenna moiety results in efficient energy transfer to the boron dipyrrin entity. The singlet-excited boron dipyrrin thus generated, undergoes subsequent energy and electron transfer to fullerene to produce a boron dipyrrin radical cation and a fullerene radical anion as charge-separated species. Stabilization of the charge-separated state in these molecular triads was observed to some extent.

Ultrafast excitation transfer and charge stabilization in a newly assembled photosynthetic antenna-reaction center mimic composed of boron dipyrrin, zinc porphyrin and fullerene

A self-assembled supramolecular triad as a model to mimic the light-induced events of the photosynthetic antenna-reaction center, that is, ultrafast excitation transfer followed by electron transfer ultimately generating a long-lived charge-separated state, has been accomplished. Boron dipyrrin (BDP), zinc porphyrin (ZnP) and fullerene (C60), respectively, constitute the energy donor, electron donor and electron acceptor segments of the antenna-reaction center imitation. Unlike in the previous models, the BDP entity was placed between the electron donor, ZnP and electron acceptor, C60 entities. For the construction, benzo-18-crown-6 functionalized BDP was synthesized and subsequently reacted with 3,4-dihydroxyphenyl functionalized ZnP through the central boron atom to form the crown-BDP-ZnP dyad. Next, an alkyl ammonium functionalized fullerene was used to self-assemble the crown ether entity of the dyad via ion–dipole interactions. The newly formed supramolecular triad was fully characterized by spectroscopic, computational and electrochemical methods. Steady-state fluorescence and excitation studies revealed the occurrence of energy transfer upon selective excitation of the BDP in the dyad. Further studies involving the pump–probe technique revealed excitation transfer from the 1BDP* to ZnP to occur in about 7 ps, much faster than that reported for other systems in this series of triads, as a consequence of shorter distance between the entities. Upon forming the supramolecular triad by self-assembling fullerene, the 1ZnP* produced by direct excitation or by energy transfer mechanism resulted in an initial electron transfer to the BDP entity. The charge recombination resulted in the population of the triplet excited state of C60, from where additional electron transfer occurred to produce C60•−:crown-BDP-ZnP•+ ion pair as the final charge-separated species. Nanosecond transient absorption studies revealed the lifetime of the charge-separated state to be ∼100 μs, the longest ever reported for this type of antenna-reaction center mimics, indicating better charge stabilization as a result of the different disposition of the entities of the supramolecular triad.

Ultrafast excitation transfer and charge stabilization in a newly assembled photosynthetic antenna-reaction center mimic composed of boron dipyrrin, zinc porphyrin and fullerene

A self-assembled supramolecular triad as a model to mimic the light-induced events of the photosynthetic antenna-reaction center, that is, ultrafast excitation transfer followed by electron transfer ultimately generating a long-lived charge-separated state, has been accomplished. Boron dipyrrin (BDP), zinc porphyrin (ZnP) and fullerene (C(60)), respectively, constitute the energy donor, electron donor and electron acceptor segments of the antenna-reaction center imitation. Unlike in the previous models, the BDP entity was placed between the electron donor, ZnP and electron acceptor, C(60) entities. For the construction, benzo-18-crown-6 functionalized BDP was synthesized and subsequently reacted with 3,4-dihydroxyphenyl functionalized ZnP through the central boron atom to form the crown-BDP-ZnP dyad. Next, an alkyl ammonium functionalized fullerene was used to self-assemble the crown ether entity of the dyad via ion-dipole interactions. The newly formed supramolecular triad was fully characterized by spectroscopic, computational and electrochemical methods. Steady-state fluorescence and excitation studies revealed the occurrence of energy transfer upon selective excitation of the BDP in the dyad. Further studies involving the pump-probe technique revealed excitation transfer from the (1)BDP* to ZnP to occur in about 7 ps, much faster than that reported for other systems in this series of triads, as a consequence of shorter distance between the entities. Upon forming the supramolecular triad by self-assembling fullerene, the (1)ZnP(*) produced by direct excitation or by energy transfer mechanism resulted in an initial electron transfer to the BDP entity. The charge recombination resulted in the population of the triplet excited state of C(60), from where additional electron transfer occurred to produce C(60)(•-):crown-BDP-ZnP(•+) ion pair as the final charge-separated species. Nanosecond transient absorption studies revealed the lifetime of the charge-separated state to be ~100 μs, the longest ever reported for this type of antenna-reaction center mimics, indicating better charge stabilization as a result of the different disposition of the entities of the supramolecular triad.

Singlet and Triplet Excitation Management in a Bichromophoric Near-Infrared-Phosphorescent BODIPY-Benzoporphyrin Platinum Complex

Multichromophoric arrays provide one strategy for assembling molecules with intense absorptions across the visible spectrum but are generally focused on systems that efficiently produce and manipulate singlet excitations and therefore are burdened by the restrictions of (a) unidirectional energy transfer and (b) limited tunability of the lowest molecular excited state. In contrast, we present here a multichromophoric array based on four boron dipyrrins (BODIPY) bound to a platinum benzoporphyrin scaffold that exhibits intense panchromatic absorption and efficiently generates triplets. The spectral complementarity of the BODIPY and porphryin units allows the direct observation of fast bidirectional singlet and triplet energy transfer processes (k(ST)((1)BDP→(1)Por) = 7.8 × 10(11) s(-1), k(TT)((3)Por→(3)BDP) = 1.0 × 10(10) s(-1), k(TT)((3)BDP→(3)Por) = 1.6 × 10(10) s(-1)), leading to a long-lived equilibrated [(3)BDP][Por]⇌[BDP][(3)Por] state. This equilibrated state contains approximately isoenergetic porphyrin and BODIPY triplets and exhibits efficient near-infrared phosphorescence (λ(em) = 772 nm, Φ = 0.26). Taken together, these studies show that appropriately designed triplet-utilizing arrays may overcome fundamental limitations typically associated with core-shell chromophores by tunable redistribution of energy from the core back onto the antennae.

Remarkably Efficient Photocurrent Generation Based on a [60]Fullerene-Triosmium Cluster/Zn-Porphyrin/Boron-Dipyrrin Triad SAM

A new artificial photosynthetic triad array, a [60]fullerene-triosmium cluster/zinc-porphyrin/boron-dipyrrin complex (1, Os(3)C(60)/ZnP/Bodipy), has been prepared by decarbonylation of Os(3)(CO)(8)(CN(CH(2))(3)Si(OEt)(3))(mu(3)-eta(2):eta(2):eta(2)-C(60)) (6) with Me(3)NO/MeCN and subsequent reaction with the isocyanide ligand CNZnP/Bodipy (5) containing zinc porphyrin (ZnP) and boron dipyrrin (Bodipy) moieties. Triad 1 has been characterized by various spectroscopic methods (MS, NMR, IR, UV/Vis, photoluminescence, and transient absorption spectroscopy). The electrochemical properties of 1 in chlorobenzene (CB) have been examined by cyclic voltammetry; the general feature of the cyclic voltammogram of 1 is nine reversible one-electron redox couples, that is, the sum of those of 5 and 6. DFT has been applied to study the molecular and electronic structures of 1. On the basis of fluorescence-lifetime measurements and transient absorption spectroscopic data, 1 undergoes an efficient energy transfer from Bodipy to ZnP and a fast electron transfer from ZnP to C(60); the detailed kinetics involved in both events have been elucidated. The SAM of triad 1 (1/ITO; ITO=indium-tin oxide) has been prepared by immersion of an ITO electrode in a CB solution of 1 and diazabicyclo-octane (2:1 equiv), and characterized by UV/Vis absorption spectroscopy, water contact angle, X-ray photoelectron spectroscopy, and cyclic voltammetry. The photoelectrochemical properties of 1/ITO have been investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron donor. The quantum yield of the photoelectrochemical cell has been estimated to be 29 % based on the number of photons absorbed by the chromophores. Our triad 1 is unique when compared to previously reported photoinduced electron-transfer arrays, in that C(60) is linked by pi bonding with little perturbation of the C(60) electron delocalization.

Electronic energy harvesting multi BODIPY-zinc porphyrin dyads accommodating fullerene as photosynthetic composite of antenna-reaction center

Efficient electronic energy transfer (EET) in the newly synthesized dyads comprised of zinc porphyrin covalently linked to one, two or four numbers of boron dipyrrin (BDP) entities is investigated. Both steady-state and time-resolved emission as well as transient absorption studies revealed occurrence of efficient singlet-singlet energy transfer from BDP to zinc porphyrin with the time scale ranging between 28 and 48 ps. A decrease in time constants for energy transfer with increasing the number of BDP units is observed revealing better antenna effect of dyads bearing higher number of boron dipyrrin entities. Further, supramolecular triads to mimic the 'antenna-reaction center' functionality of photosynthetic reaction center have been successfully constructed by coordinating fulleropyrrolidine appended with an imidazole ligand to the zinc porphyrin. The structural integrity of the supramolecular triads was arrived by optical, computational and electrochemical studies. Free energy calculations revealed possibility of photoinduced electron transfer from singlet excited zinc porphyrin to fullerene, and the preliminary transient absorption studies involving pump-probe technique are supportive of occurrence of electron transfer from (1)ZnP* to fullerene in the supramolecular triads.

Charge stabilization in a closely spaced ferrocene–boron dipyrrin–fullerene triad

New molecular triads composed of closely spaced ferrocene-boron dipyrrin-fullerene, 1 and triphenylamine-boron dipyrrin-fullerene, 2 are synthesized, and photoinduced electron transfer leading to charge stabilization is demonstrated using a femtosecond transient spectroscopic technique.

Boron Dipyrrin Dyes Exhibiting “Push–Pull–Pull” Electronic Signatures

Manipulating the electronic pathway: A strategy has been devised for functionalizing boron dipyrrin dyes with one or two electroactive ferrocene units at the periphery. Oxidation of one or both ferrocene residues is fully reversible and gives rise to near-IR electrochromism. One-electron oxidation of the bis-derivative transforms the original “push–pull–push” system into a “push–pull–pull” signature.

Photosynthetic Antenna−Reaction Center Mimicry: Sequential Energy- and Electron Transfer in a Self-assembled Supramolecular Triad Composed of Boron Dipyrrin, Zinc Porphyrin and Fullerene

A self-assembled supramolecular triad, a model to mimic the photochemical events of photosynthetic antenna-reaction center, viz., sequential energy and electron transfer, has been newly constructed and studied. Boron dipyrrin, zinc porphyrin, and fullerene respectively constitute the energy donor, electron donor, and electron acceptor segments of the antenna-reaction center mimicry. For the construction, first, boron dipyrrin was covalently attached to a zinc porphyrin entity bearing a benzo-18-crown-6 host segment at the opposite end of the porphyrin ring. Next, an alkyl ammonium functionalized fullerene was used to self-assemble the crown ether entity via ion-dipole interactions. The newly formed supramolecular triad was fully characterized by spectroscopic, computational, and electrochemical methods. Selective excitation of the boron dipyrrin moiety in the dyad resulted in energy transfer over 97% efficiency creating singlet excited zinc porphyrin. The rate of energy transfer from the decay measurements of time-correlated singlet photon counting (TCSPC) and up-conversion techniques agreed well with that obtained by the pump-probe technique and revealed efficient photoinduced energy transfer in the dyad (time constant in the order of 10-60 ps depending upon the conformer). Upon forming the supramolecular triad by self-assembling fullerene, the excited zinc porphyrin resulted in electron transfer to the coordinated fullerene yielding a charge-separated state, thus mimicking the antenna-reaction center functionalities of photosynthesis. Nanosecond transient absorption studies yielded a lifetime of the charge-separated state to be 23 micros indicating charge stabilization in the supramolecular triad. The present supramolecular system represents a successful model to mimic the rather complex "combined antenna-reaction center" events of photosynthesis.

Functionalization of Boron Dipyrrin (BODIPY) Dyes through Iridium and Rhodium Catalysis: A Complementary Approach to α‐ and β‐Substituted BODIPYs

Iridium-catalyzed direct borylation has been applied to meso-substituted dipyrromethane and boron dipyrrin (BODIPY) dyes. Borylation is highly regioselective and complementary: it occurs exclusively at the alpha position for meso-mesityldipyrromethane and at the beta positions for meso-mesityl BODIPY dye. This regioselective borylation enables a variety of alpha- and beta-substituted BODIPY dyes to be synthesized. Introduction of alpha,beta-enoate and alpha,beta,gamma,delta-dienoate functions into BODIPY dyes at the alpha or beta positions was achieved by rhodium-catalyzed Heck-type addition of the borylated compounds to acrylate and 2,4-pentadienoate esters. This functionalization has a significant effect on the electronic properties of BODIPY dyes, as seen in substantial redshift of the absorption and emission spectra. Comparative studies showed that the alpha- and beta-substituted series of BODIPY dyes show substantially different photophysical properties, and thus the importance of the position to be functionalized is highlighted.

Membrane-Bound Molecular Rotors Measure Viscosity in Live Cells via Fluorescence Lifetime Imaging

We report intracellular fluorescence lifetime imaging (FLIM) and fluorescence anisotropy measurements of two meso-substituted fluorophores based on the boron−dipyrrin (BODIPY) structure. Both dyes incorporate hydrophobic groups, which render them membrane-soluble. We have obtained values for quantum yields, radiative and nonradiative rate constants, fluorescence lifetimes, and time-resolved anisotropy data for the dyes in homogeneous methanol/glycerol solutions of varying viscosities from 0.6 to 950 cP. We find that the fluorescence lifetimes and rotational correlation times for both dyes increase with increasing viscosity, as predicted by theory. These molecules can thus serve as fluorescent molecular rotors to report on local microviscosity, including that in live cells. The dyes are readily taken up by cells as imaged using confocal fluorescence microscopy. Using FLIM, we have detected two distinct fluorescence lifetime populations for both dyes in live SK-OV-3 human ovarian carcinoma cells, correspond...

Convenient and highly efficient synthesis of boron–dipyrrins bearing an arylboronate center

Novel boron–dipyrrins bearing an aryl group and a phenyloxy group linked directly to the boron center have been prepared in high yields from arylboronic acid. The unique coordination geometry around the boron was determined by an X-ray crystallographic analysis. The complexes showed a strong fluorescence, and alkylation of the OH group shifted the emission to a longer wavelength with a larger Stokes shift.

BF2‐Chelate Complexes of 6‐(4‐Iodophenyl)‐2,3,4,8,9,10‐hexamethyldipyrrin and 2‐(4‐Iodobenzoyl)‐3,4,5‐trimethylpyrrole: Fluorescent Dyes with a Chemical Anchor Group

AbstractThe one‐pot condensation/coordination reaction of 4‐iodobenzoylchloride, 2,3,4‐trimethylpyrrole and BF3 × Et2O yields the BF2 chelate complexes of the 1:1 condensation product 2‐(4‐iodobenzoyl)‐3,4,5‐trimethylpyrrole and of the 1:2 product 6‐(4‐iodophenyl)‐2,3,4,8,9,10‐hexamethyldipyrrin, as separable compounds in 6 and 38 % yield, respectively. Both new boron derivatives are fluorescent already upon exitation with ambient light. While the fluorescence quantum yield of the benzoyl derivative is very low, this value is significantly higher for the related boron dipyrrin (BODIPY) derivative. Single crystal X‐ray diffraction studies of both compounds reveal that the reason for these deviating physical properties are structural in nature. For the BODIPY an essentially flat structure of the fluorophor has been established, in addition to restricted rotation of the 4‐iodophenyl substituent, so that no conformational dynamic facilitates radiationless deactivations. The 1:1 condensation product on the other hand allows a fast equilibration of the photophysical exitation by dynamic processes and therefore exhibits a low fluorescence quantum yield. Both luminophores contain an iodoaryl moiety with potential uses for further functionalization and bioconjugation.

Synthesis and study of crown ether-appended boron dipyrrin chemosensors for cation detection

Boron dipyrrin (BDP) bearing crown ethers of varying cavity sizes, namely, 15-crown-5, 18-crown-6, and 21-crown-7, at the meso-position are synthesized and employed as chemosensors for cation detection in solution. In the absence of metal cations, the emission of the BDP moiety is found to be quenched to some extent by an intramolecular charge transfer (ICT) process from the donor oxygen atoms to the acceptor BDP unit. Coordination of metal ions to the oxygen donor atoms in the crown ether cavity inhibits intramolecular charge transfer to the BDP acceptor, leading to cation-induced fluorescence enhancement. The fluorescence enhancement is systematically probed as a function of crown ether cavity and metal ion sizes to achieve metal ion selectivity.

Light Harvesting and Efficient Energy Transfer in a Boron-dipyrrin (BODIPY) Functionalized Perylenediimide Derivative

[reaction: see text] Click chemistry has been successfully applied in the synthesis of a bay region tetraboron-dipyrrin (BODIPY) appended perylenediimide (PDI). This light-harvesting molecule presents a large cross section for the absorption of light in the visible region. Excitation energy is efficiently channeled to the perylenediimide core. This novel antenna system is the first demonstration of the efficiency of energy transfer in a BODIPY-PDI bichromophoric system and appears to be highly promising for the design and synthesis of similar dendritic structures.

Energy transfer followed by electron transfer in a supramolecular triad composed of boron dipyrrin, zinc porphyrin, and fullerene: a model for the photosynthetic antenna-reaction center complex.

The first example of a working model of the photosynthetic antenna-reaction center complex, constructed via self-assembled supramolecular methodology, is reported. For this, a supramolecular triad is assembled by axially coordinating imidazole-appended fulleropyrrolidine to the zinc center of a covalently linked zinc porphyrin-boron dipyrrin dyad. Selective excitation of the boron dipyrrin moiety in the boron dipyrrin-zinc porphyrin dyad resulted in efficient energy transfer (k(ENT)(singlet) = 9.2 x 10(9) s(-)(1); Phi(ENT)(singlet) = 0.83) creating singlet excited zinc porphyrin. Upon forming the supramolecular triad, the excited zinc porphyrin resulted in efficient electron transfer to the coordinated fullerenes, resulting in a charge-separated state (k(cs)(singlet) = 4.7 x 10(9) s(-)(1); Phi(CS)(singlet) = 0.9). The observed energy transfer followed by electron transfer in the present supramolecular triad mimics the events of natural photosynthesis. Here, the boron dipyrrin acts as antenna chlorophyll that absorbs light energy and transports spatially to the photosynthetic reaction center, while the electron transfer from the excited zinc porphyrin to fullerene mimics the primary events of the reaction center where conversion of the electronic excitation energy to chemical energy in the form of charge separation takes place. The important feature of the present model system is its relative "simplicity" because of the utilized supramolecular approach to mimic rather complex "combined antenna-reaction center" events of photosynthesis.

Synthesis of 21-thia and 21-oxaporphyrin building blocks and boron–dipyrrin appended systems

A series of 21-thia and 21-oxaporphyrin building blocks bearing iodo-, ethynyl-and aldehyde functional groups were synthesized and characterized. These porphyrins are ideal building blocks for the construction of unsymmetrical porphyrin arrays containing two dissimilar porphyrin cores. The building blocks were used to construct boron–dipyrrin appended core-modified porphyrin systems under mild palladium coupling conditions. A preliminary steady state fluorescence measurements suggested that boron–dipyrrin unit transfers the energy to both 21-oxaporphyrin and 21-thiaporphyrin and the efficiency depends on the orientation of the boron–dipyrrin units and the core structure of the porphyrin.

Synthesis and Crystal Structure of a Calix[4]arene-Based Dual Boron–Dipyrrin System.

Abstract The preparation of a calix[4]arene-based dual boron–dipyrrin system was accomplished by the condensation of diformylcalix[4]arene and pyrrole followed by a treatment with DDQ and diethyl ether–boron trifluoride (1/1). An X-ray crystal structure analysis and spectroscopic measurements revealed that the cone conformation of calix[4]arene serves to define 14.9 Å as the center-to-center boron–dipyrrin separation.