Porphyrin Fullerene Research Articles

Improvement in photodynamic activity by a porphyrin-fullerene composite system in lipid membranes.

Porphyrin-fullerene composite systems are attracting great attention as photodynamic agents; however, water-soluble derivatives are still scarce. Herein, we prepared noncovalently a lipid membrane-incorporated porphyrin-fullerene composite system with relative stability in aqueous solution. As in the case of porphyrin-fullerene composite systems in nonpolar solvents, efficient formation of singlet oxygen occurred via photoinduced energy transfer between porphyrin and fullerene as the predominant pathway in the photodynamic activity under the hydrophobic conditions of the lipid membranes, resulting in enhanced photodynamic activity toward Colon26 and HeLa cells compared with the individual porphyrin and fullerene components. Furthermore, the porphyrin-fullerene composite system exhibited high selectivity toward HeLa cells over normal mouse fibroblast L929 cells.

Photoinduced Electron Transfer in a Porphyrin-Fullerene Dyad at a Liquid Interface.

The excited-state properties of an amphiphilic porphyrin-fullerene dyad and of its porphyrin analogue adsorbed at the dodecane/water interface are investigated by using surface second-harmonic generation. Although the porphyrin is formally centrosymmetric, the second-harmonic spectra of both compounds are dominated by the intense Soret band of the porphyrin. Polarization-selective measurements and molecular dynamics simulations suggest an angle of about 45° between the donor-acceptor axis and the interfacial plane, with the porphyrin interacting mostly with the nonpolar phase. Time-resolved measurements reveal a marked concentration dependence of the dynamics of both compounds upon Q-band excitation, indicating the occurrence of intermolecular quenching processes. The significant differences in dynamics and spectra between the dyad and the porphyrin analogue are explained by a self-quenching of the excited dyad via an intermolecular electron transfer.

Advanced Nonvolatile Organic Optical Memory Using Self-Assembled Monolayers of Porphyrin-Fullerene Dyads.

Photo-switchable organic field-effect transistors (OFETs) represent an important platform for designing memory devices for a diverse array of products including security (brand-protection, copy-protection, keyless entry, etc.), credit cards, tickets, and multiple wearable organic electronics applications. Herein, we present a new concept by introducing self-assembled monolayers of donor–acceptor porphyrin–fullerene dyads as light-responsive triggers modulating the electrical characteristics of OFETs and thus pave the way to the development of advanced nonvolatile optical memory. The devices demonstrated wide memory windows, high programming speeds, and long retention times. Furthermore, we show a remarkable effect of the orientation of the fullerene–polymer dyads at the dielectric/semiconductor interface on the device behavior. In particular, the dyads anchored to the dielectric by the porphyrin part induced a reversible photoelectrical switching of OFETs, which is characteristic of flash memory elements. On the contrary, the devices utilizing the dyad anchored by the fullerene moiety demonstrated irreversible switching, thus operating as read-only memory (ROM). A mechanism explaining this behavior is proposed using theoretical DFT calculations. The results suggest the possibility of revisiting hundreds of known donor–acceptor dyads designed previously for artificial photosynthesis or other purposes as versatile optical triggers in advanced OFET-based multibit memory devices for emerging electronic applications.

Screening Nanographene‐Mediated Inter(Porphyrin) Communication to Optimize Inter(Porphyrin–Fullerene) Forces

AbstractMultifunctional molecular materials comprising porphyrins and fullerenes have served as perfect prototypes to study key aspects of natural photosynthesis starting at light harvesting and energy transfer processes all the way to charge separation, charge shift, and charge recombination. Herein, hexa‐peri‐hexabenzocoronenes (HBCs) are explored, decorated with one, two, and six porphyrins at their peripheral positions, within the context of replicating key steps of photosynthesis. The major focus of the investigations is to screen inter(porphyrin) communications across the HBC platform as a function of the substitution pattern and to optimize the intermolecular forces with fullerenes. To this end, the ground‐ and excited‐state features are investigated in the absence of C60 and C70 by employing an arsenal of spectroscopic methods. Further insights into inter(porphyrin) communications come from time‐dependent density‐functional theory (TDDFT) calculations. In the presence of C60 and C70, X‐ray crystallography, steady‐state and time‐resolved spectroscopy, and mass spectrometry corroborate exceptionally strong inter(porphyrin–fullerene) interactions in the solid, liquid, and gas phases. The experiments are backed‐up with DFT calculations of the geometrically optimized and energetically stable complex configuration.

Enhanced electronic communication through a conjugated bridge in a porphyrin–fullerene donor–acceptor couple

The electronic communication between the terminal electron-donor ZnP and electron-acceptor C60 units is enhanced by the conjugated EDOTV-based spacer leading to photoinduced electron transfer over the distance >2 nm in the picosecond time domain.

Fullerene-porphyrin hybrid nanoparticles that generate activated oxygen by photoirradiation.

The preparation of water-dispersible hybrid nanoparticles comprising fullerene and porphyrin from cyclodextrin complexes is described. In the presence of polyethylene glycol, C60 fullerene and porphyrin were expelled from the cyclodextrin cavity to form fullerene–porphyrin hybrid nanoparticles in water. The fullerene–porphyrin hybrid nanoparticles exhibit improved singlet oxygen generation ability under photoirradiation compared with that of C60 nanoparticles.

Decelerating Charge Recombination Using Fluorinated Porphyrins in N,N-Bis(3,4,5-trimethoxyphenyl)aniline—Aluminum(III) Porphyrin—Fullerene Reaction Center Models

In supramolecular reaction center models, the lifetime of the charge-separated state depends on many factors. However, little attention has been paid to the redox potential of the species that lie between the donor and acceptor in the final charge separated state. Here, we report on a series of self-assembled aluminum porphyrin-based triads that provide a unique opportunity to study the influence of the porphyrin redox potential independently of other factors. The triads, BTMPA-Im→AlPorFn-Ph-C60 (n = 0, 3, 5), were constructed by linking the fullerene (C60) and bis(3,4,5-trimethoxyphenyl)aniline (BTMPA) to the aluminum(III) porphyrin. The porphyrin (AlPor, AlPorF3, or AlPorF5) redox potentials are tuned by the substitution of phenyl (Ph), 3,4,5-trifluorophenyl (PhF3), or 2,3,4,5,6-pentafluorophenyl (PhF5) groups in its meso positions. The C60 and BTMPA units are bound axially to opposite faces of the porphyrin plane via covalent and coordination bonds, respectively. Excitation of all of the triads results in sequential electron transfer that generates the identical final charge separated state, BTMPA•+-Im→AlPorFn-Ph-C60•-, which lies energetically 1.50 eV above the ground state. Despite the fact that the radical pair is identical in all of the triads, remarkably, the lifetime of the BTMPA•+-Im→AlPorFn-Ph-C60•- radical pair was found to be very different in each of them, that is, 1240, 740, and 56 ns for BTMPA-Im→AlPorF5-Ph-C60, BTMPA-Im→AlPorF3-Ph-C60, and BTMPA-Im→AlPor-Ph-C60, respectively. These results clearly suggest that the charge recombination is an activated process that depends on the midpoint potential of the central aluminum(III) porphyrin (AlPorFn).

Electron transfer in oriented donor-acceptor dyads, intralayer charge migration, and formation of interlayer charge separated states in multi-layered Langmuir-Schäfer films.

Photoinduced intra- and interlayer electron transfer (ET) of doubly bridged donor-acceptor molecule, porphyrin-fullerene dyad (PF), was studied in single- and multi-layered Langmuir-Schäfer (LS) films and in LS films, where PF and an efficient electron donating polymer polyhexyltiophene (PHT) formed a bilayer PHT/PF and multi-layered PHT/PF structures. The ET through layers were investigated by a method, which measures the photovoltaic (PV) response proportional to the number of charge-separated (CS) states and to the CS distance between the electrons and holes formed in pulsed photo-excitation. Primary conclusions were, that ET starts as formations of CS dyads (P+F-) in single-layers, continues as long-range intra-layer charge migrations following interlayer CS between two adjacent monolayers. Quantitative conclusions were, that the interlayer ET efficiency is 100% in the bi-layered PF structure (2PF), where two CS dyads in adjacent layers forms CS complexes (P+F/PF-) and that the probability to form longer or higher order of CS complexes follows an expression of a convergent geometric series, with a converting factor of 2/3. In the PHT/PF bilayer structure the ET efficiency was one order of magnitude higher, than that for the 2PF structure due to the ET from the CS dyads to ground state electron donor PHT, with an acceptor density, much higher than that of (P+F-).

Panchromatic light funneling through the synergy in hexabenzocoronene-(metallo)porphyrin-fullerene assemblies to realize the separation of charges.

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data.

Porphyrinoid–Fullerene Hybrids as Candidates in Artificial Photosynthetic Schemes

Natural photosynthesis inspired the scientific community to design and synthesize molecular assemblies that possess advanced light-harvesting and electron-transfer features. In this review, we present the preparation and the photophysical investigation of novel porphyrin–fullerene hybrids acting as artificial photosynthetic systems. Porphyrinoids stand as chlorophyll analogues and have emerged as suitable photosensitizers in supramolecular electron donor–acceptor hybrids. Fullerenes (C60) are versatile electron acceptors with small reorganization energy and low reduction potentials. The novel derivatives presented herein mimic the fundamental features of the photosynthetic reaction center, namely, light harvesting, charge separation, and charge transport. To this end, a comprehensive analysis on these key processes that occur in various porphyrin–fullerene entities is illustrated in this work.

(Invited) Triplet Sensitizer Derived, Nanocarbon Bearing Donor-Acceptor Conjugates for High Potential, Long-Lived Charge Separation

Donor-acceptor conjugates capable of producing high potential, long-lived charge separated states are invaluable for artificial photosynthesis of converting light energy into either electricity or environmentally friendly fuels. The majority of the donor-acceptor conjugates designed for this purpose are derived mainly from singlet sensitizers.1,2 In such conjugates, charge separation from the singlet excited donor or acceptor due to rapid charge separation and recombination processes results in a short-lived charge separated state of singlet spin character. Utilization of high energy triplet sensitizers instead of the traditionally employed singlet sensitizers could be an elegant approach to generate long-lived charge separated states. The radical ion-pairs of triplet spin character charge recombine to the ground state slowly due to spin forbidden nature of the process. However, witnessing such a process purely from the triplet excited state without the interference of the singlet excited state and other competing photochemical events such as excitation energy transfer has been challenging to establish.3-5 In the present contribution, we summarize our efforts to derive and witness donor-acceptor conjugates where excited state electron transfer exclusively occurs from the triplet excited state. To achieve the goal, two triplet sensitizers, viz., palladium porphyrin and platinum porphyrin are covalently linked to either fullerene, C60 3-5 or (6,5) or (7,6) enriched single wall carbon nanotubes (SWCNTs).6 Using transient absorption spectral studies covering wide temporal and spatial regions, and time-resolved electron paramagnetic resonance (TR-EPR) studies, photoinduced electron transfer from 1MP* (M = Pd or Pt) to C60 in a series of dyads, leading to the formation of MP•+-C60 •- charge separated state of triplet spin character will be demonstrated. Similarly, the role of triplet sensitizers in promoting charge separation in PdP-SWCNT(6,5) and PdP-SWCNT(7,6) in solvents of different polarity will be highlighted. 1. C. B. KC, F. D’Souza, ‘Design and photochemical study of supramolecular donor-acceptor systems assembled via metal-ligand axial coordiation’ Coord. Chem. Rev. 2016, 322, 104-141.2. F. D’Souza, and O. Ito ‘Photosensitized electron transfer processes of nanocarbons applicable to solar cells’ Chem. Soc. Rev. 2012, 41, 86-96.3. C. Obondi, G. N. Lim, F. D’Souza, Triplet-Triplet Excitation Transfer in Palladium Porphyrin – Fullerene and Platinum Porphyrin – Fullerene Dyads’ J. Phys. Chem. C 2015, 119, 176-185.4. C. Obondi, G. N. Lim, B. Churchill, P. K. Poddutoori, A. van der Est, and F. D’Souza, ‘Modulating the generation of long-lived charge separated states exclusively from the triplet excited states in palladium porphyrin–fullerene conjugates’, Nanoscale, 2016, 8, 8333-8344.5. P. K. Poddutoori, Y. E. Kandrashkin, C. O. Obondi, F. D’Souza and A. van der Est, Triplet Electron Transfer and Spin Polarization in a Palladium Porphyrin–Fullerene Conjugate, Phys. Chem. Chem. Phys. 2018, 20, 28223-28231.6. L. M. Arellano, H. B. Gozebe, M. J. Gómez-Escalonilla, J. L. G. Fierro, F. D’Souza and F. Langa, Photoinduced charge separation in PdP-SWCNT(6,5) and PdP-SWCNT(7,6) donor-acceptor hybrids, manuscript in preparation.

(Invited) What Determines the Composition of Fullerene Porphyrin Cocrystals?

Cocrystallization of endohedral fullerenes and empty cage fullerenes with Ni(octaethylporphyrin) has become a widely used method to obtain X-ray structural information on these molecules. However, the stoichiometry of composition of these materials is difficult to predict. here we will report some new structures and studies of factors that effect the composition of these cocrystals.

Photogalvanic eff ect in porphyrin-pyrrolo[3′,4′:1,9]-(C60-Ih)[5,6]fullerene-2′,5′-dicarboxylate systems

The influence of molecular structural factors of covalently bound porphyrin-fullerene dyads and porphyrin—fullerene binary mixtures on photocurrent in model photoelectrochemical cells was studied. It was found that the photocurrent increased either by introducing solubilizing alkyl groups into the donor (porphyrin) or acceptor (fullerene) fragments, or by covalent binding porphyrin and fullerene into a donor-acceptor dyad.

High-Energy Charge-Separated States by Reductive Electron Transfer Followed by Electron Shift in the Tetraphenylethylene–Aluminum(III) Porphyrin–Fullerene Triad

A high-potential supramolecular triad (TPE-AlPor ← Im-C60) composed of aluminum(III) porphyrin (AlPor), fullerene (C60), and tetraphenylethylene (TPE) has been constructed. The fullerene and tetraphenylethylene units are bound axially to opposite faces of the porphyrin plane via coordination and covalent bonds, respectively. The ground and excited-state properties of the triad and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The transient data show that photoexcitation results in charge separation from tetraphenylethylene to the excited singlet state of the porphyrin (1AlPor*), generating a high-energy (2.14 eV) charge-separated state, (TPE)•+-(AlPor)•–, in toluene. A subsequent electron migration from the AlPor–• to fullerene generates a second high-energy (1.78 eV) charge-separated state (TPE)•+-AlPor ← Im-(C60)•–. The lifetime of the charge separation is about 25 ns. The high energy stored in the form of charge-separated states along with their reasonable l...

The electronic structures and excitation properties of three meso-pentafluorophenyl substituted zinc porphyrin–fullerene dyad

Understanding electronic structures and excitation properties is a fundamental issue to develop novel electron donor (D) and acceptor (A) molecular dyad that can be applied in optoelectronic systems. Here, the geometry, electronic structures, and excitation properties of three meso-pentafluorophenyl substituted zinc porphyrin fullerene ((F15P)ZnPC60) dyad were analyzed based on density functional theory (DFT) and time dependent DFT (TDDFT) calculations. The geometrical parameters provide the D-A distance is about 18.19 Å. The electronic structure analysis indicates that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in porphyrin core and C60, respectively. The transition configurations and the MOs suggest the excited states at the absorption maxima are local excited states, while the charge transfer (CT) states are transient intermediates. The population analysis supports the first singlet/triplet excited states are local excitations in porphyrin (LEP). Quasi-degeneracy of excited states between LEP and local excitation in C60 (LEC) enable the partial delocalization of eigenstates and excitation-energies over the D and A in dyad, while the quasi-degeneracy between CT and LEP generate synergistic enhancement effects for CT. The results of this work could be helpful to understand optoelectronic properties of (F15P)ZnPC60 dyad.

Porphyrin–Fullerene Dyad Based on Indium(III) Complex. Donor–Acceptor Complex Formation Equilibrium

Formation kinetics and spectral properties of the donor–acceptor complexes of (5,10,15,20- tetra(2-methoxyphenyl)porphinato)chloroindium(III) with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin- 2-yl)methylpyrrolidinyl[3′,4′:1,2][60]fullerene were studied. The formation of the donor–acceptor dyad [(Py3F)InTPP(2-OCH3)4]+Cl– occurs as a two-step reaction, including fast reversible coordination of the fullerene base molecule and slow irreversible displacement of the axial chloride ion to the second coordination sphere. Quantitative characteristics for the reaction rate and equilibrium were obtained. The reaction products were identified by IR and 1H NMR spectroscopy. The most important electron optical and stability parameters of the porphyrin–fullerene dyads with inner- and outer-sphere chloride ions were determined. These results are important for studies of the photophysics of porphyrin–fullerene dyads and development of photoconverters based on them.

Triplet electron transfer and spin polarization in a palladium porphyrin-fullerene conjugate.

Transient electron paramagnetic resonance (TREPR) spectroscopy is used to investigate the pathway and dynamics of electron transfer in a palladium porphyrin-fullerene donor-acceptor conjugate. The heavy Pd atom in the porphyrin greatly enhances the rate of intersystem crossing and as a result, electron transfer from the porphyrin to fullerene occurs via the porphyrin triplet state. The sign of the polarization pattern of the radical pair generated by the electron transfer is opposite in benzonitrile and the liquid crystal 5CB. This difference is the result of a change in sign of the spin-spin coupling, which allows the values of the dipolar and exchange couplings between the electrons in the charge-separated state to be estimated. In addition to the radical pair, signals from the fullerene triplet state are also observed. The polarization of the fullerene triplet state inverts with time, while the radical pair signal decays to a multiplet pattern that persists for times longer than the spin-lattice relaxation time. A kinetic model, developed to explain these effects, reveals that forward and reverse electron transfer between the charge-separated state and the fullerene takes place. This process, combined with singlet recombination of the radical pair accounts for the inversion of the fullerene triplet state polarization and the long-lived multiplet polarization of the radical pair.

Effect of the triazole ring in zinc porphyrin-fullerene dyads on the charge transfer processes in NiO-based devices.

Herein, the synthesis of three covalently linked donor-acceptor zinc porphyrin-fullerene (ZnP-C60) dyads (C60trZnPCOOH, C60trZnPtrCOOH and C60ZnPCOOH) is described, and their application as sensitizers in NiO-based dye-sensitized solar cells (DSCs) is discussed. To the best of our knowledge, this is the first example where covalently linked ZnP-C60 dyads have been used as chromophores in NiO-based DSCs. In an effort to examine whether the distance of the chromophore from the electron acceptor entity and/or the NiO surface affects the performance of the cells, a triazole ring was introduced as a spacer between ZnP and the two peripheral units C60 and -COOH. The triazole ring was inserted between ZnP and C60 in dyad C60trZnPCOOH, whereas both the anchoring group and C60 were connected to ZnP through triazole spacers in C60trZnPtrCOOH, and dyad C60ZnPCOOH did not contain any triazole linker. Photophysical investigation performed by ultrafast transient absorption spectroscopy in solution and on the NiO surface demonstrated that all the porphyrin-fullerene dyads exhibited long-lived charge-separated states due to electron shifts from the reduced porphyrin core to C60. The transient experiments performed in solution showed that the presence of triazole ring influenced the photophysical properties of the dyads C60trZnPCOOH and C60trZnPtrCOOH and in particular, increased the lifetime of the charge-separated states compared to that of the C60ZnPCOOH dyad. On the other hand, the corresponding studies on the NiO surface proved that the triazole spacer has a rather moderate impact on the charge separation (NiO-ZnP˙+-C60˙-) and charge recombination (NiO-3*ZnP-C60) rate constants. All three dyads exhibited enhanced performance in terms of photovoltaic measurements with more than threefold increase compared to the reference compound PhtrZnPCOOH in which the C60 acceptor is absent. Two different electrolytes were examined (I3-/I- and CoIII/II) and in most cases, the presence of the triazole ring enhanced their photovoltaic performance. The best performing dyad in I3-/I- was C60trZnPCOOH (PCE = 0.076%); in CoIII/II, the best performing dyad was C60trZnPtrCOOH (PCE = 0.074%).

Strategy to Attain Remarkably High Photoinduced Charge-Separation Yield of Donor–Acceptor Linked Molecules in Biological Environment via Modulating Their Cationic Moieties

A series of ferrocene–porphyrin–fullerene linked triads (TC1, TC2, and TC4) possessing different numbers of cationic moieties were designed and prepared to achieve a high photoinduced charge-separation (CS) yield in a biological environment. In a solution, TC1, TC2, and TC4 demonstrated the formation of their nanoaggregates. Among the new triads, TC4 possessing the four cationic moieties exhibited the formation of a long-lived charge-separated state with the highest CS yield (86%) ever reported in cell membrane-like lipid bilayers, which is consistent with the largest change in the cell membrane potential of PC12 cells via the photoinduced CS under green light illumination. The highest CS yield in the biological environment can be rationalized by the well-tailored balance in hydrophobicity and hydrophilicity of TC4. This finding provides a strategy to improve greatly the photoinduced charge-separation yield of donor–acceptor linked molecules in the biological environment and also will be informative for e...

Comparative charge transfer studies in nonmetallated and metallated porphyrin fullerene dyads

AbstractSingle material organic solar cells become an interesting area of research to overcome the challenges with efficient charge separation efficiencies in conventional organic solar cells. In this article, we have synthesized nonmetallated and metallated porphyrin‐fullerene dyad materials (H2P‐C60 and ZnP‐C60, respectively) with simple structure, comprehensively studied their charge transfer mechanism, and established a proof of concept that nonmetallated porphyrin‐fullerene dyads are better candidates to be used in organic solar cells compared with metallated dyads. Absorption and electrochemical analysis revealed the ground state electronic interactions between donor‐acceptor moieties in both types of dyads. Driving force (−ΔGoET) for intramolecular electron transfer process was calculated by first oxidation and reduction potentials of dyads. The excited state electronic interactions were characterized by time‐resolved fluorescence and pump‐probe transient absorption experiments. Strong fluorescence quenching of porphyrin along with reduced lifetimes in dyads due to deactivation of singlet excited states by photoinduced charge transfer process between porphyrin/Zn‐porphyrin core and fullerene in different polarity solvents was observed. Transient absorption spectroscopy was also applied to identify the transient spectral features, ie, cationic (H2P+/ZnP+) and anionic (C60−) radicals formed because of the charge separation in both types of dyads. Finally, organic solar cell device was also fabricated using the dyads. We obtained higher Voc, Jsc, and fill factor in single material organic solar cell using H2P‐C60 compared to previous reports.