Azobenzene-linked porphyrin-fullerene dyads

Photochromic Carbon Nanomaterials: An Emerging Class of Light-Driven Hybrid Functional Materials

Photochromic molecules have remarkable potential in memory and optical devices, as well as in driving and manipulating molecular motors or actuators and many other systems using light. When photochromic molecules are introduced into carbon nanomaterials (CNMs), the resulting hybrids provide unique advantages and create new functions that can be employed in specific applications and devices. This review highlights the recent developments in diverse photochromic CNMs. Photochromic molecules and CNMs are also introduced. The fundamentals of different photochromic CNMs are discussed, including design principles and the types of interactions between CNMs and photochromic molecules via covalent interactions and non-covalent bonding such as π-π stacking, amphiphilic, electrostatic, and hydrogen bonding. Then the properties of photochromic CNMs, e.g., in photopatterning, fluorescence modulation, actuation, and photoinduced surface-relief gratings, and their applications in energy storage (solar thermal fuels, photothermal batteries, and supercapacitors), nanoelectronics (transistors, molecular junctions, photo-switchable conductance, and photoinduced electron transfer), sensors, and bioimaging are highlighted. Finally, an outlook on the challenges and opportunities in the future of photochromic CNMs is presented. This review discusses a vibrant interdisciplinary research field and is expected to stimulate further developments in nanoscience, advanced nanotechnology, intelligently responsive materials, and devices.

Bridge effect on charge transfer and energy transfer in fullerene-chromophore dyads

Fullerene-chromophore dyads have attracted a great deal of research interest because these complexes can be potentially designed as nanoscale artificial photosynthetic centers, in which the chromophore and fullerene function as the electron donor and acceptor, respectively. The basic operation of this dyad-type artificial reaction center is photoinduced electron transfer from the donor to the acceptor. The fullerene and chromophore are usually covalently linked so that sufficient electronic coupling between these two moieties can facilitate the electron transfer. However, other deactivation pathways for the chromophore excited state, such as energy transfer to the fullerene, may reduce the quantum yield of the photoinduced electron transfer. Here, a series of C60-perylene dyads is exploited to interrogate the effect of the linkage on deactivation mechanisms of the chromophore excited state. For the C60-perylene dyads with a single or double bond bridge, we find that the decay of the singlet state of the chromophore is dominated by the electron transfer, and the corresponding time constant is determined to be 45 ps. On the other hand, for the dyad with a triple bond bridge, the singlet state of the chromophore is quickly quenched through energy transfer to fullerene, and the time constant is as short as 7.9 ps. Our finding suggests that the bond order of the bridge in the fullerene-chromophore dyads can be utilized to control the deactivation pathways of the excited state.

Switching Competition between Electron and Energy Transfers in Porphyrin-Fullerene Dyads

Porphyrin-fullerene dyads were intensively studied as molecular donor-acceptor systems providing efficient photoinduced charge separation (CS). A practical advantage of the dyads is the possibility to tune its CS process by the porphyrin periphery modification, which allows one to optimize the dyad for particular applications. However, this tuning process is typically composed of a series of trial stages involving the development of complex synthetic schemes. To address the issue, we synthesized a series of dyads with properties switching between electron and energy transfer in both polar (benzonitrile) and nonpolar (toluene) media and developed a computation procedure with sufficient reliability by which we can predict the CS properties of the dyad in different media and design new dyads. The dyads photochemistry was established by conducting ultrafast transient absorption studies in toluene, anisole, and benzonitrile. The most crucial step in computational modeling was to establish a procedure for correction of the electronic-state energies obtained by DFT so that the effects of the electron correlation and the long-range interactions are properly incorporated. We also carried out standard electrochemical measurements and show that our computation approach predicts better thermodynamics of the dyads in different solvents.

Fine-Tuning the Electronic Properties of Azo Chromophore-Incorporated Perylene Bisimide Dyads

Perylene bisimide (PBI) and azo-compounds are fascinating molecules with interesting optical properties. Here, we combine the two chromophores to prepare nonconjugated and conjugated stable azo-PBI dyes. The detailed structural characterization, comparison of properties, and solid-state self-assembly of the compounds are discussed. The incorporation of azo groups at the bay side of PBI led to significant changes in optical properties as compared to the model PBIs (M₁ and M₂). All new azo-PBIs showed photoinduced isomerization, which caused disaggregation and enhancement in fluorescence. The amine-incorporated azo-PBIs (3 and 6) reduced chloroauric acid into gold nanoparticles. The current study offers a simple synthetic strategy and comparison of the properties of conjugated and nonconjugated azo-PBIs, which could be useful in photoelectronic devices.

Rigid axially symmetrical C60-BODIPY triplet photosensitizers: effect of bridge length on singlet oxygen generation

Two rigid axially symmetrical C₆₀-BODIPY systems with different bridge lengths have been synthesized and the dyad with short bridge generates a higher quantum yield of singlet oxygen.

Sc3N@Ih-C80 based donor–acceptor conjugate: role of thiophene spacer in promoting ultrafast excited state charge separation

Photoinduced charge separation and dark charge recombination occurring within picoseconds is observed in newly synthesized triphenylamine–thiophene-Sc₃N@I_h-C₈₀ and triphenylamine–thiophene-C₆₀ conjugates.

Excitation-dependent electron exchange energy and electron transfer dynamics in a series of covalently tethered N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline - [C60] fullerene dyads via varying π-conjugated spacers

Femtosecond time-resolved fluorescence and transient absorption studies are reported for three newly synthesized covalently linked N,N-bis(4'-tert-butylbiphenyl-4-yl)aniline (BBA) and pyrrolidinofullerenes (C60)-based donor-π conjugated bridge-acceptor dyads (D-B-A) as functions of the bridge length (7.1, 9.5 and 11.2 Å for Dyad-1, Dyad-2 and Dyad-3), dielectric constants of the medium and pump wavelengths. In polar solvent, ultrafast fluorescence quenching (kEET ≥ 2 × 1012 s-1) of the BBA moiety upon excitation of the BBA moiety (320 nm) is observed in the dyads and is assigned to a mechanism involving electron exchange energy transfer (EET) from 1BBA* to C60 followed by electron transfer from BBA to 1C60*. Cohesive rise and decay dynamics of conjugated BBA˙+-C60˙- anion pairs confirm the involvement of a distance independent adiabatic charge-separation (CS) process (kCS ≥ 2.2 × 1011 s-1) with near unity quantum efficiency (φCS ≥ 99.7%) and a distance-dependent non-adiabatic charge-recombination (CR) process [kCR ∼ (1010-108) s-1]. In contrast, excitation of the C60 moiety (λex = 430 to 700 nm) illustrates photoinduced electron transfer from BBA to 1C60*, involving non-adiabatic (diabatic) and distance-dependent CS (kCS in the range of 0.59-1.78 × 1011 s-1) with 98.86-99.6% (Dyad-3-Dyad-1) quantum efficiency and a CR process with kCR values [kCR ∼ (1010-108) s-1] up to three orders greater than kCS of the respective dyads. Both the processes, CS and CR, upon C60 excitation and the CR process upon BBA excitation show distance dependent rate constants with exponential factor β ≤ 0.5 Å-1, and electron transfer is concluded to occur through a covalently linked conjugated π bridge. Global and target analysis of fsTA data reveal the occurrence of two closely lying CS states, thermally hot (CShot) and thermally relaxed (CSeq) states, and two CR processes with two orders of different rate constants. Careful analysis of the kinetic and thermodynamic data allowed us to estimate the total reorganization energy and electronic coupling matrix (V), which decrease exponentially with distance. These novel features of the distance independent adiabatic CS process and the distance-dependent diabatic CR process upon donor excitation are due to extending the π-conjugation between BBA and C60. The demonstrated results may provide a benchmark in the design of light-harvesting molecular devices where ultrafast CS processes and long-lived CS states are essential requirements.

Novel phthalocyanines containing azo chromophores; synthesis, characterization, photophysical, and electrochemical properties

A series of novel metal-free and zinc (II), copper (II), cobalt (II), and manganese (III) phthalocyanine complexes bearing peripheral 2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenoxy units have been synthesized. Novel phthalonitrile derivative required for the preparation of these phthalocyanine complexes was prepared by a base-catalyzed nucleophilic aromatic nitro displacement of 4-nitrophthalonitrile with 2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenol. The structures of these new compounds were characterized by using elemental analyses, proton and carbon nuclear magnetic resonance, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and mass spectrometry. The photophysical properties of metal-free and zinc(II) phthalocyanines were studied in tetrahydrofuran. The electrochemical properties of the phthalocyanine complexes were investigated by cyclic and square wave voltammetry.

Azo group(s) in selected macrocyclic compounds

Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans-cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds' structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed.

Efficient Photoinduced Energy and Electron Transfer in ZnII -Porphyrin/Fullerene Dyads with Interchromophoric Distances up to 2.6 nm and No Wire-like Connectivity

The dyads 1-3 made of an alkynylated Zn^II -porphyrin and a bis-methanofullerene derivative connected through a copper-catalyzed azide-alkyne cycloaddition have been synthesized. The porphyrin and fullerene chromophores are separated through a bridge made of a bismethanofullerene tether linked to different spacers conjugated to the porphyrin moiety [i.e., m-phenylene (1), p-phenylene (2), di-p-phenylene-ethynylene (3)]. Compounds 1-3 exhibit relatively rigid structures with an interchromophoric separation of 1.7, 2.0, and 2.6 nm, respectively, and no face-to-face or direct through-bond conjugation. The photophysical properties of compounds 1-3 have been investigated in toluene and benzonitrile with steady-state and time-resolved techniques as well as model calculations on the Förster energy transfer. Excited-state interchromophoric electronic interactions are observed with a distinct solvent and distance dependence. The latter effect is evidenced in benzonitrile, where compounds 1 and 2 exhibit a photoinduced electron transfer in the Marcus-inverted region, with charge-separated (CS) states living for 0.44 and 0.59 μs, respectively, whereas compound 3 only undergoes energy transfer, as in apolar toluene. The quantum yield of the charge separation (φ_CS ) of compounds 1 and 2 in benzonitrile is ≥0.75. It is therefore demonstrated that photoinduced energy and electron transfers in porphyrin-fullerene systems with long interchromophoric distances may efficiently occur also when the bridge does not provide a wire-like conjugation and proceed through the triplet states of the chromophoric moieties.

Self-Assembled Ruthenium(II)Porphyrin-Aluminium(III)Porphyrin-Fullerene Triad for Long-Lived Photoinduced Charge Separation

A very efficient metal-mediated strategy led, in a single step, to a quantitative construction of a new three-component multichromophoric system containing one fullerene monoadduct, one aluminium(III) monopyridylporphyrin, and one ruthenium(II) tetraphenylporphyrin. The Al(III) monopyridylporphyrin component plays the pivotal role in directing the correct self-assembly process and behaves as the antenna unit for the photoinduced processes of interest. A detailed study of the photophysical behavior of the triad was carried out in different solvents (CH₂Cl₂, THF, and toluene) by stationary and time-resolved emission and absorption spectroscopy in the pico- and nanosecond time domains. Following excitation of the Al-porphyrin, the strong fluorescence typical of this unit was strongly quenched. The time-resolved absorption experiments provided evidence for the occurrence of stepwise photoinduced electron and hole transfer processes, leading to a charge-separated state with reduced fullerene acceptor and oxidized ruthenium porphyrin donor. The time constant values measured in CH₂Cl₂ for the formation of charge-separated state Ru-Al⁺-C₆₀^- (10 ps), the charge shift process (Ru-Al⁺-C₆₀^- → Ru⁺-Al-C₆₀^-), where a hole is transferred from Al-based to Ru-based unit (75 ps), and the charge recombination process to ground state (>5 ns), can be rationalized within the Marcus theory. Although the charge-separating performance of this triad is not outstanding, this study demonstrates that, using the self-assembling strategy, improvements can be obtained by appropriate chemical modifications of the individual molecular components.

Synthesis, characterization and optical properties of novel dendronized azo-dyes containing a fullerene C60 unit and well-defined oligo(ethylene glycol) segments

Herein, we report the preparation and characterization of a novel series of dendronized azo-dyes containing a fullerene C₆₀ unit and well-defined oligo(ethylene glycol) spacers.

Synthesis and Properties of Axially Symmetrical Rigid Visible Light-Harvesting Systems Containing [60]Fullerene and Perylenebisimide

Two visible light-harvesting perylenebisimide (PDI)-[60]fullerene (C₆₀) systems, dyad P1 with one C₆₀ unit and triad P2 with two C₆₀ units, have been synthesized. Both systems are axially symmetrical with a rigid biphenyl linker, ensuring a relatively fixed spatial distance between the donor and acceptor, preventing through-space interaction, and enhancing energy transfer. Steady-state and transient spectroscopy, electrochemistry, as well as theoretical calculations have been used to investigate the electrochemical and photophysical properties of the two systems. Steady-state and time-resolved spectroscopy demonstrate that the excited state is featured by an efficient intramolecular energy transfer from PDI to C₆₀. Then, the high efficient intrinsic intersystem crossing of C₆₀ eventually leads to the production of the triplet C₆₀. The extensive visible light absorption of PDI in the range of 400-650 nm and the final localization of the excited energy at the triplet C₆₀ make these compounds ideal singlet oxygen inducers. Further investigation shows that the photooxidation capability for both compounds is significantly enhanced with respect to either PDI or C₆₀ and even better than that of the commonly used triplet photosensitizer methylene blue (MB). The double C₆₀ moieties in P2 display a better result, and the photooxidation efficiency of P2 increases 1.3- and 1.4-fold compared to that of P1 and MB, respectively. The combination of a light-harvesting unit with an intersystem crossing unit results in a highly efficient photooxidation system, which opens up a new way to triplet photosensitizer design.

Stabilising the lowest energy charge-separated state in a {metal chromophore - fullerene} assembly: a tuneable panchromatic absorbing donor-acceptor triad

Photoreduction of fullerene and the consequent stabilisation of a charge-separated state in a donor-acceptor assembly have been achieved, overcoming the common problem of a fullerene-based triplet state being an energy sink that prevents charge-separation. A route to incorporate a C60-fullerene electron acceptor moiety into a catecholate-Pt(ii)-diimine photoactive dyad, which contains an unusually strong electron donor, 3,5-di-tert-butylcatecholate, has been developed. The synthetic methodology is based on the formation of the aldehyde functionalised bipyridine-Pt(ii)-3,5-di-tert-butylcatechol dyad which is then added to the fullerene cage via a Prato cycloaddition reaction. The resultant product is the first example of a fullerene-diimine-Pt-catecholate donor-acceptor triad, C60bpy-Pt-cat. The triad exhibits an intense solvatochromic absorption band in the visible region due to catechol-to-diimine charge-transfer, which, together with fullerene-based transitions, provides efficient and tuneable light harvesting of the majority of the UV/visible spectral range. Cyclic voltammetry, EPR and UV/vis/IR spectroelectrochemistry reveal redox behaviour with a wealth of reversible reduction and oxidation processes forming multiply charged species and storing multiple redox equivalents. Ultrafast transient absorption and time resolved infrared spectroscopy, supported by molecular modelling, reveal the formation of a charge-separated state [C60˙-bpy-Pt-cat˙+] with a lifetime of ∼890 ps. The formation of cat˙+ in the excited state is evidenced directly by characteristic absorption bands in the 400-500 nm region, while the formation of C60˙- was confirmed directly by time-resolved infrared spectroscopy, TRIR. An IR-spectroelectrochemical study of the mono-reduced building block (C60-bpy)PtCl2, revealed a characteristic C60˙- vibrational feature at 1530 cm-1, which was also detected in the TRIR spectra. This combination of experiments offers the first direct IR-identification of C60˙- species in solution, and paves the way towards the application of transient infrared spectroscopy to the study of light-induced charge-separation in C60-containing assemblies, as well as fullerene films and fullerene/polymer blends in various OPV devices. Identification of the unique vibrational signature of a C60-anion provides a new way to follow photoinduced processes in fullerene-containing assemblies by means of time-resolved vibrational spectroscopy, as demonstrated for the fullerene-transition metal chromophore assembly with the lowest energy charge-separated excited state.

Coupling carbon nanomaterials with photochromic molecules for the generation of optically responsive materials

Multifunctional carbon-based nanomaterials offer routes towards the realization of smart and high-performing (opto)electronic (nano)devices, sensors and logic gates. Meanwhile photochromic molecules exhibit reversible transformation between two forms, induced by the absorption of electromagnetic radiation. By combining carbon-based nanomaterials with photochromic molecules, one can achieve reversible changes in geometrical structure, electronic properties and nanoscale mechanics triggering by light. This thus enables a reversible modulation of numerous physical and chemical properties of the carbon-based nanomaterials towards the fabrication of cognitive devices. This review examines the state of the art with respect to these responsive materials, and seeks to identify future directions for investigation.

Chemical physics behind formation of efficient charge-separated state for complexation between PC70BM and designed diporphyrin in solution

The present work reports supramolecular interaction of [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) with two designed diporphyrin molecules having dithiophene (1) and carbazole (2) spacer in solvent having varying polarity. Studies on complex formation reveal relatively higher binding constant for PC70BM/2 complex in all the solvent studied. Solvent dependence of charge separation and charge recombination processes in PC70BM/diporphyrin non-covalent complexes has been well established in present work. Donor-acceptor geometry and stabilization of the singlet excited state of the diporphyrin during charge recombination are considered to be the possible reasons for this behavior.

Flat-on ambipolar triphenylamine/C60 nano-stacks formed from the self-organization of a pyramid-sphere-shaped amphiphile

The study identified the flat-on dual-channel nano-structure and the ambipolar characteristics of a novel giant pyramid-sphere shape amphiphile.

A giant amphiphile, which is constructed with an amorphous nano-pyramid (triphenylamine, TPA) and a crystalline nano-sphere (C₆₀), was synthesized. Structural characterization indicates that this pyramid-sphere-shaped amphiphile (TPA–C₆₀) forms a solvent-induced ordered phase, in which the two constituent units self-assemble into alternating stacks of two-dimensional (2D) TPA and C₆₀ nano-sheets. Due to the complexity of the molecular structure and the amorphous nature of the nano-pyramid, phase formation was driven by intermolecular C₆₀–C₆₀ interactions and the ordered phase could not be reformed from the TPA–C₆₀ melt. Oriented crystal arrays of TPA–C₆₀, which contain flat-on TPA/C₆₀ nano-stacks, can be obtained via a PDMS-assisted crystallization (PAC) technique. The flat-on dual-channel supramolecular structure of TPA–C₆₀ delivered ambipolar and balanced charge-transport characteristics with an average μ_e of 2.11 × 10^–4 cm² V^–1 s^–1 and μ_h of 3.37 × 10^–4 cm² V^–1 s^–1. The anisotropic charge-transport ability of the pyramid-sphere-shaped amphiphile was further understood based on the lattice structure and the lattice orientation of TPA–C₆₀ revealed from electron diffraction analyses.

Triazole linked ruthenium(ii)–porphyrin: influence of the connectivity pattern on photophysical and electrochemical properties

A family of inverse and regular triazolyl–pyridyl porphyrin–ruthenium(ii) conjugates display an energy transfer from porphyrin to the ruthenium bipyridyl moiety and a narrow HOMO/LUMO energy band gap is responsible for enhanced electronic coupling.

Photoisomerization and optical properties of a subphthalocyanine–azobenzene–subphthalocyanine triad

A novel subPc–AB–subPc triad exhibits on–off switching of the fluorescence emission intensity upon reversible trans ↔ cis photoisomerization of the azobenzene moiety. NMR spectroscopy provides additional evidence for the conformational change.

On-off switch of charge-separated states of pyridine-vinylene-linked porphyrin-C60 conjugates detected by EPR

The design, synthesis, and electronic properties of a new series of D-π-A conjugates consisting of free base (H2P) and zinc porphyrins (ZnP) as electron donors and a fullerene (C60) as electron acceptor, in which the two electroactive entities are covalently linked through pyridine-vinylene spacers of different lengths, are described. Electronic interactions in the ground state were characterized by electrochemical and absorption measurements, which were further supported with theoretical calculations. Most importantly, charge-transfer bands were observed in the absorption spectra, indicating a strong push-pull behavior. In the excited states, electronic interactions were detected by selective photoexcitation under steady-state conditions, by time-resolved fluorescence investigations, and by pump probe experiments on the femto-, pico-, and nanosecond time scales. Porphyrin fluorescence is quenched for the different D-π-A conjugates, from which we conclude that the deactivation mechanisms of the excited singlet states are based on photoinduced energy- and/or electron transfer processes between H2P/ZnP and C60, mediated through the molecular spacers. The fluorescence intensity decreases and the fluorescence lifetimes shorten as the spacer length decreases and as the spacer substitution changes. With the help of transient absorption spectroscopy, the formation of charge-separated states involving oxidized H2P/ZnP and reduced C60 was confirmed. Lifetimes of the corresponding charge-separated states, which ranged from ∼400 picoseconds to 165 nanoseconds, depend on the spacer length, the spacer substitution, and the solvent polarity. Interestingly, D-π-A conjugates containing the longest linkers did not necessarily exhibit the longest charge-separated state lifetimes. The distances between the electron donors and the acceptors were calculated by molecular modelling. The longest charge-separated state lifetime corresponded to the D-π-A conjugate with the longest electron donor-acceptor distance. Likewise, EPR measurements in frozen media revealed charge separated states in all the D-π-A conjugates investigated. A sharp peak with g values ∼2.000 was assigned to reduced C60, while a broader, less intense signal (g ∼ 2.003) was assigned to oxidized H2P/ZnP. On-off switching of the formation and decay of the charge-separated states was detected by EPR at 77 K by repeatedly turning the irradiation source on and off.

Absorption spectrophotometric, fluorescence and quantum chemical investigations on non-covalent interaction between PC₇₀BM and designed diporphyrin in solution

Present work reports the photophysical insights on supramolecular interaction of a C₇₀ derivative, namely, [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₀BM), with two designed diporphyrin molecules having dithiophene (1) and carbazole (2) spacer in toluene and benzonitrile. Both absorption spectrophotometric and steady state fluorescence investigations reveal efficient complexation of PC₇₀BM with 1 and 2 in both toluene and benzonitrile. The magnitude of average value of binding constant, viz., Kav, for the complexes of PC₇₀BM with 1 and 2 in toluene (benzonitrile) are estimated to be 2.185 × 10(3)dm(3)mol(-1) (3.215 × 10(3)dm(3)mol(-1)) and 10.180 × 10(3)dm(3)mol(-1) (25.405 × 10(3)dm(3)mol(-1)), respectively. Selectivity in binding for the complexation process of PC₇₀BM with 1 and 2 is estimated to be ∼4.6 and ∼7.90 as observed in toluene and benzonitrile, respectively. The complexation between PC₇₀BM and diporphyrin is well accounted by a theoretical model which takes into account the electronic subsystems of both acceptor and donor. Ab initio calculations in vacuo establish that size selective orientation pattern of PC₇₀BM towards the cavity of diporphyrin dictates the magnitude of binding and electronic structure of the PC₇₀BM/diporphyrin complexes.

Pyrene-fullerene C60 dyads as light-harvesting antennas

A series of pyrene-fullerene C₆₀ dyads bearing pyrene units (PyFC₁₂, PyFPy, Py₂FC₁₂ and PyFN) were synthesized and characterized. Their optical properties were studied by absorption and fluorescence spectroscopies. Dyads were designed in this way because the pyrene moeities act as light-harvesting molecules and are able to produce “monomer” (PyFC₁₂) or excimer emission (PyFPy, Py₂FC₁₂ and PyFN). The fluorescence spectra of the dyads exhibited a significant decrease in the amount of pyrene monomer and excimer emission, without the appearance of a new emission band due to fullerene C₆₀. The pyrene fluorescence quenching was found to be almost quantitative, ranging between 96%–99% depending on the construct, which is an indication that energy transfer occurred from one of the excited pyrene species to the fullerene C₆₀.

Role of charge transfer interaction and the chemical physics behind effective fulleropyrrolidine/porphyrin non-covalent interaction in solution

The present paper reports the photophysical insights on supramolecular interaction of a monoporphyrin derivative, namely, 1, with C60 pyrrolidine tris-acid ethyl ester (PyC60) in toluene and benzonitrile. The ground state interaction between PyC60 and 1 is facilitated through charge transfer interaction. Both UV-Vis and steady state measurements elicit almost similar magnitude of binding constant for the PyC60/1 complex in toluene and benzonitrile, viz., 6825 and 6540 dm(3 )mol(-1), respectively. Life time measurement evokes that rate of charge separation is fast in benzonitrile. Both hybrid-DFT and DFT calculations provide very good support in favor of electronic charge-separation in PyC60/1 system in vacuo.

A metallofullerene electron donor that powers an efficient spin flip in a linear electron donor-acceptor conjugate

The dream target of artificial photosynthesis is the realization of long-lived radical ion pair states that power catalytic centers and, consequently, the production of solar fuels. Notably, magnetic field effects, especially internal magnetic field effects, are rarely employed in this context. Here, we report on a linear Lu3N@Ih-C80-PDI electron donor-acceptor conjugate, in which the presence of the Lu3N cluster exerts an appreciable electron nuclear hyperfine coupling on the charge transfer dynamics. As such, a fairly efficient radical ion pair intersystem crossing converts the initially formed singlet radical ion pair state, (1)[(Lu3N@Ih-C80)(•+)-PDI(•-)], to the corresponding triplet radical ion pair state, (3)[(Lu3N@Ih-C80)(•+)-PDI(•-)]. Most notably, the radical ion pair state lifetime of the latter is nearly 1000 times longer than that of the former.

Synthesis, electrochemical and photophysical properties of covalently linked porphyrin-polyoxometalates

Two covalently linked porphyrin-polyoxometalate hybrids have been prepared: an Anderson-type hexamolybdate [N(C(4)H(9))(4)](3)[MnMo(6)O(18){(OCH(2))(3)CNHCO(ZnTPP)}(2)] with two pendant zinc(II)-tetraphenylporphyrins, and a Dawson-type vanadotungstate [N(C(4)H(9))(4)](5)H[P(2)V(3)W(15)O(59){(OCH(2))(3)CNHCO(ZnTPP)}] with one porphyrin. Electrochemical studies show independent redox processes for the organic and inorganic parts at usual potentials. Photophysical studies reveal an electron transfer from the excited porphyrin to the Dawson polyoxometalate, but not to the Anderson polyoxometalate. Time resolved absorption spectroscopy allows the identification of the electron transfer pathways and the determination of the time constants.

Charge transfer excitations in cofacial fullerene-porphyrin complexes

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C(60) and C(70). The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 Å. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C(60) by C(70) in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.