Synthesis,Photophysical and Electrochemical Properties of Amide‐Linked Phthalocyanine‐Fullerene Dyad

A new amide‐linked phthalocyanine‐fullerene dyad ZnPc‐C₆₀ was synthesized and characterized. The photophysical and electrochemical properties of the ZnPc‐C₆₀ dyad were investigated. The fluorescence spectrum and quantum yield in different solvents showed the occurrence of photoinduced electron transfer (PET) from the singlet excited ZnPc to C₆₀, which was further confirmed by nanosecond transient absorption spectra and cyclic voltammetry data. The free energy change for charge separation (ΔG_CS) was estimated to be exothermic with ?0.51 eV, which favored the formation of charge‐separation state. The PET from ZnPc to C₆₀ in ZnPc‐C₆₀ made the dyad exhibit stronger reverse saturable absorption performance compared with C₆₀ and the control sample in the Z‐scan experiments, which indicated the synergistic effect of two active moieties in the dyad.     

Photosynthetic Antenna‐Reaction Center Mimicry with a Covalently Linked Monostyryl Boron‐Dipyrromethene–Aza‐Boron‐Dipyrromethene–C60 Triad

An efficient functional mimic of the photosynthetic antenna‐reaction center has been designed and synthesized. The model contains a near‐infrared‐absorbing aza‐boron‐dipyrromethene (ADP) that is connected to a monostyryl boron‐dipyrromethene (BDP) by a click reaction and to a fullerene (C₆₀) using the Prato reaction. The intramolecular photoinduced energy and electron‐transfer processes of this triad as well as the corresponding dyads BDP‐ADP and ADP‐C₆₀ have been studied with steady‐state and time‐resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge‐separated states. Such calculations show that electron transfer from the singlet excited ADP (¹ADP*) to C₆₀ yielding ADP^.+‐C₆₀^.? is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from ¹BDP* to ADP in the dyad BDP‐ADP and electron transfer from ¹ADP* to C₆₀ in the dyad ADP‐C₆₀. Sequential energy and electron transfer have also been clearly observed in the triad BDP‐ADP‐C₆₀. By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10¹¹ s^?1). The dynamics of electron transfer through ¹ADP* has also been studied by monitoring the formation of C₆₀ radical anion at 1000 nm. A fast charge‐separation process from ¹ADP* to C₆₀ has been detected, which gives the relatively long‐lived BDP‐ADP^.+C₆₀^.? with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge‐separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP‐ADP and ADP‐C₆₀, and the triad BDP‐ADP‐C₆₀ are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems.     

Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Azafullerene C59N–Phthalocyanine Dyad: Synthesis,Characterisation and Photoinduced Electron Transfer

The synthesis of a new azafullerene C₅₉N–phthalocyanine (Pc) dyad is described. The key step for the synthesis of the C₅₉N–Pc dyad was the formation of the C₅₉N‐based carboxylic acid, which was smoothly condensed with hydroxy‐modified Pc. The structure of the C₅₉N–Pc dyad was verified by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, UV/Vis spectroscopy and MS measurements. The photophysical and electrochemical properties of the C₅₉N–Pc dyad were investigated in both polar and non‐polar solvents by steady state and time‐resolved photoluminescence and absorption spectroscopy, as well as by cyclic voltammetry. Different relaxation pathways for the photoexcited C₅₉N–Pc dyad, as a result of changing the solvent polarity, were found, thus giving rise to energy‐transfer phenomena in non‐polar toluene and charge‐transfer processes in polar benzonitrile. Finally, the detailed quenching mechanisms were evaluated and compared with that of a C₆₀–Pc dyad, which revealed that the different excited‐state energies and reduction potentials of the two fullerene spheres (i.e. C₅₉N vs. C₆₀) strongly diverged in the deactivation pathways of the excited states of the corresponding phthalocyanine dyads.     

Fluorescence Quenching Study of Zinc Bisporphyrins by Fulleropyrrolidines and Their N-Oxides

Novel phenylene-bridged zinc bisporphyrins （1-4）, fulleropyrrolidines （C60-m, C60-h） and their N-oxides （C60-mo, C60-ho） were synthesized. The fluorescence quenching processes of bisporphyrins in toluene solution by fulleropyrrolidines and their N-oxides were investigated by steady-state fluorescence spectra. The fluorescence quenching constants proved that the fluorescence quenching ability was decreased as reduction of the pyrrolidine functional groups of fullerene surface： C60-h〉C60-m〉C60, and the fluorescence quenching ability was increased about 1.3-7.4 times by utilizing fulleropyrrolidine N-oxides （C60-mo, C60-ho） compared to fulleropyrrolidine compounds （C60-m, C60-h）. The results revealed photoinduced electron transfer （PET） efficiency between bispor-phyrin and fullerene derivatives could be tunable by change of functional groups on fullerene surface.     

Synthesis,photophysical properties,and photochemical activity of the water-soluble dyad based on fullerene С<Subscript>60</Subscript> and chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> derivatives

Chlorin e₆ derivative and water-soluble dyad resulting from covalent bonding of polyanionic fullerene С₆₀ derivative to chlorin e₆ derivative were synthesized and studied for spectral properties and photochemical activity. A considerable change in the absorption spectra and pronounced fluorescence quenching for the chlorin moiety included in the dyad were identified. The singlet excited state of chlorin is quenched via electron transfer from the excited chlorin to the fullerene core. A comparison of the photochemical activities of the test compounds in aqueous solutions showed a tenfold increase in the photochemical activity of the chlorin–fullerene dyad compared with free chlorin per absorbed light quantum.     

Photoinduced Energy and Electron Transfer in Phenylethynyl‐Bridged Zinc Porphyrin–Oligothienylenevinylene–C60 Ensembles

Donor–bridge–acceptor triad (Por‐2TV‐C₆₀) and tetrad molecules ((Por)₂‐2TV‐C₆₀), which incorporated C₆₀ and one or two porphyrin molecules that were covalently linked through a phenylethynyl‐oligothienylenevinylene bridge, were synthesized. Their photodynamics were investigated by fluorescence measurements, and by femto‐ and nanosecond laser flash photolysis. First, photoinduced energy transfer from the porphyrin to the C₆₀ moiety occurred rather than electron transfer, followed by electron transfer from the oligothienylenevinylene to the singlet excited state of the C₆₀ moiety to produce the radical cation of oligothienylenevinylene and the radical anion of C₆₀. Then, back‐electron transfer occurred to afford the triplet excited state of the oligothienylenevinylene moiety rather than the ground state. Thus, the porphyrin units in (Por)‐2TV‐C₆₀ and (Por)₂‐2TV‐C₆₀ acted as efficient photosensitizers for the charge separation between oligothienylenevinylene and C₆₀.     

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY−Fullerene C60 Dyad as Potential Antimicrobial Agent

A covalently linked BODIPY−fullerene C₆₀ dyad (BDP−C₆₀) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C₆₀ to inactivate bacteria. The absorption spectrum of BDP−C₆₀ was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C₆₀. Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 μM BDP−C₆₀ exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP−C₆₀ turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP−C₆₀ is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.     

High‐Potential Perfluorinated Phthalocyanine–Fullerene Dyads for Generation of High‐Energy Charge‐Separated States: Formation and Photoinduced Electron‐Transfer Studies

High oxidation potential perfluorinated zinc phthalocyanines (ZnF_nPcs) are synthesised and their spectroscopic, redox, and light‐induced electron‐transfer properties investigated systematically by forming donor–acceptor dyads through metal–ligand axial coordination of fullerene (C₆₀) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine‐ (Py) and phenylimidazole‐functionalised fullerene (C₆₀Im) derivatives to the zinc centre of the F_nPcs. The determined binding constants, K, in o‐dichlorobenzene for the 1:1 complexes are in the order of 10⁴ to 10⁵ M ^?1; nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6‐31G* method. The HOMO and LUMO levels are located on the Pc and C₆₀ entities, respectively; this suggests the formation of ZnF_nPc^.+–C₆₀Im^.? and ZnF_nPc^.+–C₆₀Py^.? (n=0, 8 or 16) intra‐supramolecular charge‐separated states during electron transfer. Electrochemical studies on the ZnPc–C₆₀ dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge‐separated states. The energy of the charge‐separated state for dyads composed of ZnF_nPc is higher than that of normal ZnPc–C₆₀ dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar‐energy harvesting and optoelectronic device building applications.     

Synthesis and Spectroscopic Properties of a Covalently Linked Porphyrin–Fullerene C60 Dyad

A covalently linked porphyrin–fullerene C₆₀ dyad 6 was conveniently synthesized by 1,3‐dipolar cycloaddition using 5‐(4‐carbonylphenyl)‐10,15,20‐tris(4‐methoxylphenyl)porphyrin 5, N‐methylglycine and fullerene C₆₀. Spectroscopic studies show that dyad 6 is a promising architecture with potential application as photoactive organic material.     

A High‐Energy Charge‐Separated State of 1.70 eV from a High‐Potential Donor–Acceptor Dyad: A Catalyst for Energy‐Demanding Photochemical Reactions

A high potential donor–acceptor dyad composed of zinc porphyrin bearing three meso‐pentafluorophenyl substituents covalently linked to C₆₀, as a novel dyad capable of generating charge‐separated states of high energy (potential) has been developed. The calculated energy of the charge‐separated state was found to be 1.70 eV, the highest reported for a covalently linked porphyrin–fullerene dyad. Intramolecular photoinduced electron transfer leading to charge‐separated states of appreciable lifetimes in polar and nonpolar solvents has been established from studies involving femto‐ to nanosecond transient absorption techniques. The high energy stored in the form of charge‐separated states along with its persistence of about 50–60 ns makes this dyad a potential electron‐transporting catalyst to carry out energy‐demanding photochemical reactions. This type of high‐energy harvesting dyad is expected to open new research in the areas of artificial photosynthesis especially producing energy (potential) demanding light‐to‐fuel products.     

Excitation‐Wavelength‐Dependent,Ultrafast Photoinduced Electron Transfer in Bisferrocene/BF2‐Chelated‐Azadipyrromethene/Fullerene Tetrads

Donor–acceptor distance, orientation, and photoexcitation wavelength are key factors in governing the efficiency and mechanism of electron‐transfer reactions both in natural and synthetic systems. Although distance and orientation effects have been successfully demonstrated in simple donor–acceptor dyads, revealing excitation‐wavelength‐dependent photochemical properties demands multimodular, photosynthetic‐reaction‐center model compounds. Here, we successfully demonstrate donor– acceptor excitation‐wavelength‐dependent, ultrafast charge separation and charge recombination in newly synthesized, novel tetrads featuring bisferrocene, BF₂‐chelated azadipyrromethene, and fullerene entities. The tetrads synthesized using multistep synthetic procedure revealed characteristic optical, redox, and photo reactivities of the individual components and featured “closely” and “distantly” positioned donor–acceptor systems. The near‐IR‐emitting BF₂‐chelated azadipyrromethene acted as a photosensitizing electron acceptor along with fullerene, while the ferrocene entities acted as electron donors. Both tetrads revealed excitation‐wavelength‐dependent, photoinduced, electron‐transfer events as probed by femtosecond transient absorption spectroscopy. That is, formation of the Fc⁺–ADP–C₆₀^.? charge‐separated state upon C₆₀ excitation, and Fc⁺–ADP^.?–C₆₀ formation upon ADP excitation is demonstrated.     

Highly Efficient Singlet–Singlet Energy Transfer in Light‐Harvesting [60,70]Fullerene–4‐Amino‐1,8‐naphthalimide Dyads

New C₆₀ and C₇₀ fullerene dyads formed with 4‐amino‐1,8‐naphthalimide chromophores have been prepared by the Bingel cyclopropanation reaction. The resulting monoadducts were investigated with respect to their fluorescence properties (quantum yields and lifetimes) to unravel the role of the charge‐transfer naphthalimide chromophore as a light‐absorbing antenna and excited‐singlet‐state sensitizer of fullerenes. The underlying intramolecular singlet–singlet energy transfer (EnT) process was fully characterized and found to proceed quantitatively (Φ_EnT≈1) for all dyads. Thus, these conjugates are of considerable interest for applications in which fullerene excited states have to be created and photonic energy loss should be minimized. In polar solvents (tetrahydrofuran and benzonitrile), fluorescence quenching of the fullerene by electron transfer from the ground‐state aminonaphthalimide was postulated as an additional path.     

Coordinative Interactions between Porphyrins and C60, La@C82, and La2@C80

For the first time, a C₆₀ derivative ( 1 ) and two different lanthanum metallofullerene derivatives, La@C₈₂Py ( 2 ) and La₂@C₈₀Py ( 3 ), that feature a pyridyl group as a coordination site for transition‐metal ions have been synthesized and integrated as electron acceptors into coordinative electron‐donor/electron‐acceptor hybrids. Zinc tetraphenylporphyrin ( ZnP ) served as an excited‐state electron donor in this respect. Our investigations, by means of steady‐state and time‐resolved photophysical techniques found that electron transfer governs the excited‐state deactivation in all of these systems, namely 1/ZnP , 2/ZnP , and 3/ZnP , whereas, in the ground state, notable electronic interactions are lacking. Variation of the electron‐accepting fullerene or metallofullerene moieties provides the incentive for fine‐tuning the binding constants, the charge‐separation kinetics, and the charge‐recombination kinetics. To this end, the binding constants, which ranged from log K_assoc=3.94–4.38, are dominated by axial coordination, with minor contributions from the orbital overlap of the curved and planar π systems. The charge‐separation and charge‐recombination kinetics, which are in the order of 10¹⁰ and 10⁸ s^?1, relate to the reduction potential of the fullerene and metallofullerenes, respectively.     

A Ruthenium Complex–Porphyrin–Fullerene‐Linked Molecular Pentad as an Integrative Photosynthetic Model

A ruthenium complex, porphyrin sensitizer, fullerene acceptor molecular pentad has been synthesized and a long‐lived hole–electron pair was achieved in aqueous solution by photoinduced multistep electron transfer: Upon irradiation by visible light, the excited‐state of a zinc porphyrin (¹ZnP*) was quenched by fullerene (C₆₀) to afford a radical ion pair, ^1,3(ZnP^.+‐C₆₀^.−). This was followed by the subsequent electron transfer from a water oxidation catalyst unit (Ru^II) to ZnP^.+ to give the long‐lived charge‐separated state, Ru^III‐ZnP‐C₆₀^.−, with a lifetime of 14 μs. The ZnP worked as a visible‐light‐harvesting antenna, while the C₆₀ acted as an excellent electron acceptor. As a consequence, visible‐light‐driven water oxidation by this integrated photosynthetic model compound was achieved in the presence of sacrificial oxidant and redox mediator.     

Intramolecular electronic communication in a dimethylaminoazobenzene–fullerene C60 dyad: An experimental and TD‐DFT study

An electronically push–pull type dimethylaminoazobenzene–fullerene C₆₀ hybrid was designed and synthesized by tailoring N,N‐dimethylaniline as an electron donating auxochrome that intensified charge density on the β‐azonitrogen, and on N‐methylfulleropyrrolidine (NMFP) as an electron acceptor at the 4 and 4′ positions of the azobenzene moiety, respectively. The absorption and charge transfer behavior of the hybrid donor‐bridge‐acceptor dyad were studied experimentally and by performing TD‐DFT calculations. The TD‐DFT predicted charge transfer interactions of the dyad ranging from 747 to 601 nm were experimentally observed in the UV‐vis spectra at 721 nm in toluene and dichloromethane. A 149 mV anodic shift in the first reduction potential of the N?N group of the dyad in comparison with the model aminoazobenzene derivative further supported the phenomenon. Analysis of the charge transfer band through the orbital picture revealed charge displacement from the n_(N?N) (nonbonding) and π _(N?N) type orbitals centered on the donor part to the purely fullerene centered LUMOs and LUMO+n orbitals, delocalized over the entire molecule. The imposed electronic perturbations on the aminoazobenzene moiety upon coupling it with C₆₀ were analyzed by comparing the TD‐DFT predicted and experimentally observed electronic transition energies of the dyad with the model compounds, NMFP and (E)‐N,N‐dimethyl‐4‐(p‐tolyldiazenyl)aniline (AZNME). The n_(N?N) → π*_(N?N) and π_(N?N) → π*_(N?N) transitions of the dyad were bathochromically shifted with a significant charge transfer character. The shifting of π_(N?N) → π*_(N?N) excitation energy closer to the n → π*_(N?N) in comparison with the model aminoazobenzene emphasized the predominant existence of charge separated quinonoid‐like ground state electronic structure. Increasing solvent polarity introduced hyperchromic effect in the π_(N?N) → π*_(N?N) electronic transition at the expense of transitions involved with benzenic states, and the extent of intensity borrowing was quantified adopting the Gaussian deconvolution method. On a comparative scale, the predicted excitation energies were in reasonable agreement with the observed values, demonstrating the efficiency of TD‐DFT in predicting the localized and the charge transfer nature of transitions involved with large electronically asymmetric molecules with HOMO and LUMO centered on different parts of the molecular framework. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Ultrafast Photoinduced Electron Transfer and Charge Stabilization in Donor–Acceptor Dyads Capable of Harvesting Near‐Infrared Light

To harvest energy from the near‐infrared (near‐IR) and infrared (IR) regions of the electromagnetic spectrum, which constitutes nearly 70 % of the solar radiation, there is a great demand for near‐IR and IR light‐absorbing sensitizers that are capable of undergoing ultrafast photoinduced electron transfer when connected to a suitable electron acceptor. Towards achieving this goal, in the present study, we report multistep syntheses of dyads derived from structurally modified BF₂‐chelated azadipyrromethene (ADP; to extend absorption and emission into the near‐IR region) and fullerene as electron‐donor and electron‐acceptor entities, respectively. The newly synthesized dyads were fully characterized based on optical absorbance, fluorescence, geometry optimization, and electrochemical studies. The established energy level diagram revealed the possibility of electron transfer either from the singlet excited near‐IR sensitizer or singlet excited fullerene. Femtosecond and nanosecond transient absorption studies were performed to gather evidence of excited state electron transfer and to evaluate the kinetics of charge separation and charge recombination processes. These studies revealed the occurrence of ultrafast photoinduced electron transfer leading to charge stabilization in the dyads, and populating the triplet states of ADP, benzanulated‐ADP and benzanulated thiophene‐ADP in the respective dyads, and triplet state of C₆₀ in the case of BF₂‐chelated dipyrromethene derived dyad during charge recombination. The present findings reveal that these sensitizers are suitable for harvesting light energy from the near‐IR region of the solar spectrum and for building fast‐responding optoelectronic devices operating under near‐IR radiation input.     

Mono‐ and Bis(pyrrolo)tetrathiafulvalene Derivatives Tethered to C60: Synthesis,Photophysical Studies,and Self‐Assembled Monolayers

A series of mono‐ (MPTTF) and bis(pyrrolo)tetrathiafulvalene (BPTTF) derivatives tethered to one or two C₆₀ moieties was synthesized and characterized. The synthetic strategy for these dumbbell‐shaped compounds was based on a 1,3‐dipolar cycloaddition reaction between aldehyde‐functionalized MPTTF/BPTTF derivatives, two different tailor‐made amino acids, and C₆₀. Electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties was studied by a variety of techniques including cyclic voltammetry and absorption spectroscopy. These solution‐based studies indicated no observable electronic communication between the MPTTF/BPTTF units and the C₆₀ moieties. In addition, femtosecond and nanosecond transient absorption spectroscopy revealed, rather surprisingly, that no charge transfer from the MPTTF/BPTTF units to the C₆₀ moieties takes place on excitation of the fullerene moiety. Finally, it was shown that the MPTTF–C₆₀ and C₆₀–BPTTF‐C₆₀ dyad and triad molecules formed self‐assembled monolayers on a Au(111) surface by anchoring to C₆₀.     

Multistep Energy and Electron Transfer in a “V‐Configured” Supramolecular BODIPY–azaBODIPY–Fullerene Triad: Mimicry of Photosynthetic Antenna Reaction‐Center Events

A new photosynthetic antenna‐reaction‐center model compound composed of covalently linked BF₂‐chelated dipyrromethene (BODIPY), BF₂‐chelated azadipyrromethene (azaBODIPY), and fullerene (C₆₀), in a “V‐configuration”, has been newly synthesized and characterized by using a multistep synthetic procedure. Optical absorbance and steady‐state fluorescence, computational, and electrochemical studies were systematically performed in nonpolar, toluene, and polar, benzonitrile, solvents to establish the molecular integrity of the triad and to construct an energy‐level diagram revealing different photochemical events. The geometry obtained by B3LYP/6‐31G* calculations revealed the anticipated V‐configuration of the BODIPY‐azaBODIPY‐C₆₀ triad. The location of the frontier orbitals in the triad tracked the site of electron transfer determined from electrochemical studies. The different photochemical events originated from ¹BODIPY* were realized from the energy‐level diagram. Accordingly, ¹BODIPY* resulted in competitive ultrafast energy transfer to produce BODIPY–¹azaBODIPY*–C₆₀ and electron transfer to produce BODIPY ^{. +}–azaBODIPY–C₆₀ ^{. ?} as major photochemical events. The charge‐separated state persisted for few nanoseconds prior populating ³C₆₀*, which in turn revealed an unusual triplet–triplet energy transfer to produce ³azaBODIPY* prior returning to the ground state. These findings delineate the importance of multimodular systems in energy harvesting, and more importantly, their utility in building multifunction performing optoelectronic devices.     

BOPHY-Fullerene C60 Dyad as a Photosensitizer for Antimicrobial Photodynamic Therapy

A novel BOPHY–fullerene C₆₀ dyad ( BP-C₆₀ ) was designed as a heavy-atom-free photosensitizer (PS) with potential uses in photodynamic treatment and reactive oxygen species (ROS)-mediated applications. BP-C₆₀ consists of a BOPHY fluorophore covalently attached to a C₆₀ moiety through a pyrrolidine ring. The BOPHY core works as a visible-light-harvesting antenna, while the fullerene C₆₀ subunit elicits the photodynamic action. This fluorophore–fullerene cycloadduct, obtained by a straightforward synthetic route, was fully characterized and compared with its individual counterparts. The restricted rotation around the single bond connecting the BOPHY and pyrrolidine moieties led to the formation of two atropisomers. Spectroscopic, electrochemical, and computational studies disclose an efficient photoinduced energy/electron transfer process from BOPHY to fullerene C₆₀. Photodynamic studies indicate that BP-C₆₀ produces ROS by both photomechanisms (type I and type II). Moreover, the dyad exhibits higher ROS production efficiency than its individual constitutional components. Preliminary screening of photodynamic inactivation on bacteria models (Staphylococcus aureus and Escherichia coli) demonstrated the ability of this dyad to be used as a heavy-atom-free PS. To the best of our knowledge, this is the first time that not only a BOPHY–fullerene C₆₀ dyad is reported, but also that a BOPHY derivative is applied to photoinactivate microorganisms. This study lays the foundations for the development of new BOPHY-based PSs with plausible applications in the medical field.