Complexation and DFT studies of lower rim hexahomotrioxacalix[3]arene derivatives bearing pyridyl groups with transition and heavy metal cations. Cone versus partial cone conformation

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2‐pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p‐tert‐butylhexahomotrioxacalix[3]arene was studied. Binding was assessed by extraction studies of the metal picrates from water into dichloromethane and by stability constant measurements in acetonitrile and methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of some selected complexes in acetonitrile were performed, as well as proton NMR titrations. Computational methods (density functional theory calculations) were also employed to complement the NMR data. The results are compared with those obtained with the dihomooxacalix[4]arene 2b and the calix[4]arene 3b derivative analogues. Partial cone‐1b is the best extractant for transition and heavy metal cations. Both conformers of 1b exhibit very high stability constants for soft and intermediate cations Pb²⁺, Cd²⁺, Hg²⁺, Zn²⁺ and Ni²⁺, with cone‐1b the strongest binder (ML, log β ≥ 7) and partial cone‐1b the most selective. Both derivatives show a slight preference for Na⁺. Besides the formation of ML complexes, ML₂ and M₂L species were also observed. The former complexes were, in general, formed with the transition and heavy metal cations, whereas the latter were obtained with Ag⁺ and Hg²⁺ and partial cone‐1b. In most cases, these species were corroborated by the proton NMR and density functional theory studies. Copyright © 2013 John Wiley & Sons, Ltd.     

A comparative study of ion-induced damages in C60 and C70 fullerenes

The stability of fullerenes (C₆₀ and C₇₀) under swift heavy ion irradiation is investigated. C₆₀ and C₇₀ thin films were irradiated with 120 MeV Ag ions at fluences from 1×10¹² to 3×10¹³ ions/cm². The damage cross-section and radius of damaged cylindrical zone were found to be higher for C₆₀ than C₇₀ as evaluated by Raman spectroscopy, which shows that the C₇₀ molecule is more stable under energetic ion impact. The higher damage cross-section of the C₆₀ molecule compared with that of the C₇₀ molecule is explained on the basis of thermal conductivity in the framework of the thermal spike model. The surface morphology of pristine C₆₀ and C₇₀ films is studied by atomic force microscopy. UV-visible absorption studies revealed that band gap for C₆₀ and C₇₀ fullerenes thin films decreases with increasing ion fluence. Resistivity of C₆₀ and C₇₀ thin films decreases with increasing ion fluence but the decrease is faster for C₆₀ than C₇₀, indicating higher damage in C₆₀. Irradiation at a fluence of 3×10¹³ ions/cm² results in complete damage of fullerenes (C₆₀ and C₇₀) into amorphous carbon.     

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

Theoretical studies on structure and performance of [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine‐based derivatives

Based on energetic compound [1,2,5]‐oxadiazolo‐[3,4‐d]‐pyridazine, a series of functionalized derivatives were designed and first reported. Afterwards, the relationship between their structure and performance was systematically explored by density functional theory at B3LYP/6‐311 g (d, p) level. Results show that the bond dissociation energies of the weakest bond (N–O bond) vary from 157.530 to 189.411 kJ · mol^?1. The bond dissociation energies of these compounds are superior to that of HMX (N–NO_2, 154.905 kJ · mol^?1). In addition, H1, H2, H4, I2, I3, C1, C2, and D1 possess high density (1.818–1.997 g · cm^?3) and good detonation performance (detonation velocities, 8.29–9.46 km · s^?1; detonation pressures, 30.87–42.12 GPa), which may be potential explosives compared with RDX (8.81 km · s^?1, 34.47 GPa ) and HMX (9.19 km · s^?1, 38.45 GPa). Finally, allowing for the explosive performance and molecular stability, three compounds may be suggested as good potential candidates for high‐energy density materials. Copyright © 2016 John Wiley & Sons, Ltd.     

Theory studies of the local lattice distortions and the EPR parameters for Cu2+, Mn2+ and Fe3+ centres in ZnWO4

The local lattice distortions and the electron paramagnetic resonance (EPR) parameters (g factors, hyperfine structure constants and zero-field splittings) for Cu²⁺, Mn²⁺ and Fe³⁺ in ZnWO₄ are theoretically studied based on the perturbation calculations for rhombically elongated octahedral 3d⁹ and 3d⁵ complexes. The impurity centres on Zn²⁺ sites undergo the local elongations of 0.01, 0.002 and 0.013 Å along the C₂ axis and the planar bond angle variations of 8.1°, 8.0° and 8.6° for Cu²⁺, Mn²⁺ and Fe³⁺, respectively, due to the Jahn–Teller effect and size and charge mismatch. In contrast to the host Zn²⁺ site with obvious axial elongation (～0.31 Å) and perpendicular (angular) rhombic distortion, all the impurity centres demonstrate more regular octahedral due to the above local lattice distortions. The copper centre exhibits significant Jahn–Teller reductions for the spin-orbit coupling and orbital angular momentum interactions, characterised by the Jahn–Teller reduction factor J (≈0.29 ? 1). The calculated EPR parameters agree well with the experimental results. The local structures of the impurity centres are analysed in view of the corresponding lattice distortions.     

Determination of the reaction rate constant and activation energy for pressure-induced 2+2 cycloaddition of the C60 fullerene

The kinetics of fullerene solid-phase dimerization proceeding through the 2+2 cycloaddition of C₆₀ at a pressure of 1.5 GPa is investigated by vibrational spectroscopy in the temperature range 373–473 K. Kinetic curves for the formation of (C₆₀)₂ dimers are obtained using the analytical band at 796 cm^?1 in the IR spectra of the (C₆₀)₂ dimer molecule. Under the assumption that the pressure-induced dimerization of C₆₀ is an irreversible second-order reaction, the reaction rate constants are determined at different temperatures. The activation energy and the preexponential factor are found to be equal to 134±6 kJ/mol and (1.74±0.24)×10¹⁴ s^?1, respectively.     

Density functional investigation of metal encapsulated X@C12Si8 heterofullerene (X=Li, Na, K, Be, Mg, Ca, Al, Ga)

The stability and the possible application of our recently reported SiC heterofullerenes inspire the investigation of their further stabilization through ion encapsulation. The endohedral complexes X@C₁₂Si₈, where X=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Al³⁺, and Ga³⁺, are probed at the MPWB1K/6-311G? and B3LYP/6-311G* levels of theory. The optimized geometries show the expanding or contracting capability of C₁₂Si₈ in order to accommodate metal ion guests. The inclusion energies indicate the stability of the complexes compared to the components. Meanwhile, the calculated binding energies show the stabilization of C₁₂Si₈ through the inclusion of Be²⁺, Mg²⁺, Al³⁺, and Ga³⁺. The host-guest interaction that is probed through NBO atomic charges supports the obtained results. This study refers to “metal ion encapsulation” as a strategy for stabilization of SiC heterofullerenes.     

Kinetics and mechanism for acid‐catalyzed disproportionation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl

Disproportionation of cyclic nitroxyl radicals (NRs) in acid solutions is of key importance for the chemistry of these compounds. Meanwhile, the data reported on the mechanism of this reaction in dilute acids are inconsistent with those on the stability of NRs in concentrated acids. Here we have examined the kinetics and stoichiometry for the disproportionation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl ( 1 ) in aqueous H₂SO₄ (1.0–99.3 wt%) and found that (1) the disproportionation of 1 proceeds by the same mechanism over the entire range of acid concentrations, (2) the effective rate constant of the process exhibits a bell‐shaped dependence on the excess acidity function X peaked at X = ?pK _1H+ = 5.8 ± 0.3, (3) a key step of the process involves the oxidation of 1 with its protonated counterpart 1H ⁺ yielding oxopiperidinium cation 2 and hydroxypiperidine 3 at a rate constant of (1.4 ± 0.8) × 10⁵ M^?1 · s^?1, and (4) the reaction is reversible and, upon neutralization of acid, disproportionation products 2 and 3H ⁺ comproportionate to starting 1 . In highly acidic media, the protonated form 1H ⁺ is relatively stable due to a low disproportionation rate. Based on the known and newly obtained values of equilibrium constants, both the standard redox potential for the 1H ⁺ / 3 pair (955 ± 15 mV) and the pH‐dependences have been calculated for the reduction potentials of 1 and 2 to hydroxylamine 3 that is in equilibrium with its protonated 3H ⁺ and deprotonated 3 ^? forms. The data obtained provide a deeper insight into the mechanism of nitroxyl‐involving reactions in chemical and biological systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Single‐molecule surface‐enhanced Raman scattering of fullerene C60

We achieved single‐molecule surface‐enhanced Raman scattering (SM‐SERS) spectra from ultralow concentrations (10⁻¹⁵ M) of fullerene C₆₀ on uniformly assembled Au nanoparticles. It was found that resonant excitation at 785 nm is a powerful tool to probe SM‐SERS in this system. The appearance of additional bands and splitting of some vibrational modes were observed because of the symmetry reduction of the adsorbed molecule and a relaxation in the surface selection rules. Time‐evolved spectral fluctuation and ‘hot spot’ dependence in the SM‐SERS spectra were demonstrated to result from the single‐molecule Raman behavior of the spherical C₆₀ on Au nanoparticles. Copyright © 2010 John Wiley & Sons, Ltd.     

Templating a face-centered cubic (110) termination of C60

Scanning tunneling microscopy has been used to study C₆₀ overlayers on TiO₂(100)-(1 × 3). Initial adsorption preferentially occurs on O vacancies (Ti³⁺), evidencing a site-specific interaction dominated by substrate-adsorbate charge transfer. At saturation coverage the molecules are incommensurate with Ti³⁺ sites along [001], suggesting a delicate balance between intermolecular and substrate interactions. The unit cell of the C₆₀ overlayer is 13.8Å× 10.0 ± 0.5Å, consistent with the first layer of fcc C₆₀(110); molecules also adopt sites in the troughs of the (1 × 3) structure to form the second layer.     

Solution‐Based Phototransformation of C60 Nanorods: Towards Improved Electronic Devices

A modified liquid–liquid interface precipitation synthesis of C₆₀ nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field‐effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of ≈10³ and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm² V^?1 s^?1, as measured in a FET geometry, is reported for as‐grown nanorods, with the peak value being an impressive 1.0 cm² V^?1 s^?1. A photoexposure using green laser light (λ = 532 nm) is demonstrated to result in the formation of a polymer‐C₆₀ shell encapsulating a monomer‐C₆₀ bulk; such photo‐transformed nanorods exhibit an electron mobility of 4.7 × 10^?3 cm² V^?1 s^?1. It is notable that the utilized FET geometry only probes the polymer‐C₆₀ nanorod surface shell, and that the monomer‐C₆₀ bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer‐C₆₀ shell.     

Hartree–Fock and density functional theory study of remote substituent effects on heterolytic Fe–N bond energies of p‐G‐C6H4NHFe(CO)2(η5‐C5H5) and p‐G‐C6H4N(COMe)Fe(CO)2(η5‐C5H5)

The nature and strength of metal–ligand bonds in organotransition‐metal complexes are crucial to the understanding of organometallic reactions and catalysis. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–N bond energies of para‐substituted anilinyldicarbonyl(η⁵‐cyclopentadienyl)iron [p‐G‐C₆H₄NH(η⁵‐C₅H₅)Fe(CO)₂, abbreviated as p‐G‐C₆H₄NHFp (1), where G = NO₂, CN, COMe, CO₂Me, CF₃, Br, Cl, F, H, Me, MeO, and NMe₂] and para‐substituted α‐acetylanilinyldicarbonyl(η⁵‐cyclopentadienyl)iron [p‐G‐C₆H₄N(COMe)(η⁵‐C₅H₅)Fe(CO)₂, abbreviated as p‐G‐C₆H₄N(COMe)Fp (2)] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔH_het(Fe–N)'s. The linear correlations [r = 0.98 (g, 1a), 0.93 (g, 2b)] between the substituent effects of heterolytic Fe–N bond energies [ΔΔH_het(Fe–N)'s] of series 1 and 2 and the differences of acidic dissociation constants (ΔpK_a) of N–H bonds of p‐G‐C₆H₄NH₂ and p‐G‐C₆H₄NH(COMe) imply that the governing structural factors for these bond scissions are similar. And the linear correlations [r = ?0.99 (g, 1c), ?0.92 (g, 2d)] between ΔΔH_het(Fe–N)'s and the substituent σ_p^? constants show that these correlations are in accordance with Hammett linear free energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔH_het(Fe–N)'s. ΔΔH_het(Fe–N)'s(1, 2) follow the captodative principle. ME_{α‐COMe, para‐G}s include the influences of the whole molecules. The correlation of ME_{α‐COMe, para‐G}s with σ_p^? is excellent. ME_{α‐COMe, para‐G}s rather than ΔΔH_het(Fe–N)'s in series 2 are more suitable indexes for the overall substituent effects on ΔH_het(Fe–N)'s(2). Insight from this work may help the design of more effective catalytic processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Reactivities of acridine compounds in hydride transfer reactions

Reactivities of acridine derivatives (10‐benzylacridinium ion, 1a ⁺, 10‐methylacridinium ion, 1b ⁺, and 10‐methyl‐9‐phenylacridinium ion, 1c ⁺) have been compared quantitatively for hydride transfer reactions with 1,3‐dimethyl‐2‐substituted phenylbenzimidazoline compounds, 2Ha–h . Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2‐propanol to one part of water by volume at 25 ± 0.1 °C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a ⁺ –c ⁺ by 2Hb would be the same in aqueous solution and accepting ?361 mV as the reduction potential of the 1‐benzyl‐3‐carbamoylpyridinium ion. The resulting reduction potentials, E, are ?47 mV for 1a ⁺, ?79 mV for 1b ⁺, and ?86 mV for 1c ⁺. Each of acridine derivatives gives a linear Brønsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one‐step mechanism involving no high‐energy intermediates. Copyright © 2007 John Wiley & Sons, Ltd.     

Gas‐phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativities

Rate constants for the reactions of Cl atoms with CH₃OCHCl₂ and CH₃OCH₂CH₂Cl were determined at (296 ± 2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH₂ClCH₂Cl and n‐C₅H₁₂. Using rate constants of 1.33 × 10^?12 and 2.52 × 10^?10 cm³ molecule^?1 sec^?1 for the reaction of Cl atoms with CH₂ClCH₂Cl and n‐C₅H₁₂, respectively, the following rate coefficients were derived: k(Cl + CH₃OCHCl₂) = (1.05 ± 0.11) × 10^?12 and k(Cl + CH₃OCH₂CH₂Cl) = (1.14 ± 0.10) × 10^?10, in units of cm³ molecule^?1 s^?1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH₃OCHR¹R² + Cl reactions and ΔElectronegativity of ? CHR¹R². Copyright © 2008 John Wiley & Sons, Ltd.     

Hidden chemistry in phenoxyl radical (C6H5O•) coupling reaction mechanism revealed

A novel hidden reaction of the phenoxyl radical (C₆H₅O^?) with a specific daughter is found to significantly alter its hitherto accepted coupling reactions' scheme. Transient characterizations and mechanistic evaluations in highly acidic to strongly alkaline aqueous medium reveal this concurrent reaction competing favorably in nanosecond–microsecond time‐scale with the five distinct C₆H₅O^? + C₆H₅O^? reactions, which produce various phenolic end‐products as reported earlier (M. Ye and R. H. Schuler, J. Phys. Chem. 1989, 93, 1898). Presently, only the symmetric 4,4′‐dioxo transient precursor, O?C₆H₅? H₅C₆?O that leads to the stable 4,4′‐biphenol product, gets partially oxidized by a fraction of remaining C₆H₅O^?. The resulting secondary transient ^?C₁₂H₉O₂ radical is generated at diffusion‐controlled rate, k > 5.0 × 10⁹ M^?1 s^?1, and follows an independent chemistry. Consequently, when the previously reported five coupled end product distribution ratios were appropriately updated, the respective fractional values revealed a closer match for the symmetric 2,2′‐ and 4,4′‐biphenols with their suggested coupling reaction branching probabilities based on the atomic spin‐density distributions in the C₆H₅O^? radical (P. Neta, R. W. Fessenden, J. Phys. Chem., 1974, 78, 523). Results also suggest that in the remaining fraction, differential solvation in aqueous medium of various orientation‐related encounter complexes (C₆H₅O…C₆H₅O) formed during coupling favors rearrangement only toward 2,4′‐biphenolic product, at the cost of 2‐ and 4‐phenoxyphenolic species. Copyright © 2009 John Wiley & Sons, Ltd.     

Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions

The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C₂? C₇ cyclization and more exothermic (Δ_RE = ?69.38 kcal/mol). For R₁ = CH₃ and t‐Bu, the increasing barrier of the C₂? C₇ cyclization is higher than that for the C₂? C₆ cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R₁ = t‐Bu would shift the C₂? C₇ cyclization to the [4 + 2] cycloaddition. On the other hand, for R₁ = Ph, NH₂, O^?, NO₂, and CN substituents, the barrier of the C₂? C₆ cyclization would be more diminished than the C₂? C₇ cyclization due to strong mesomeric effect; the reaction path of C₂? C₇ cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.     

Cycloaddition of 2′-azidoethyl glycosides to fullerene[C60] under ultrasonic irradiation

The reactions of fullerene[C₆₀] with 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2a) and 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (2b) under ultrasonic irradiation cause the cycloaddition of 2′-azidoethyl glycosides to fullerene[C₆₀] and lead to d-glycosyl fullerene[C₆₀] derivatives 3a and 3b, respectively. The glycosyl fullerene[C₆₀] derivatives were characterized by ¹H and ¹³C NMR, UV–vis, FAB-MS, FT-IR spectra and were a 1:1 glycoside fullerene [C₆₀]-adduct.     

Hartree–Fock and density functional theory study of remote substituent effects on gas‐phase heterolytic Fe–O and Fe–S bond energies of p‐G‐C6H4OFe(CO)2(η5‐C5H5) and p‐G‐C6H4SFe(CO)2(η5‐C5H5)

The knowledge of accurate bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S bond energies of para‐substituted phenoxydicarbonyl(η⁵‐cyclopentadienyl) iron [p‐G‐C₆H₄O(η⁵‐C₅H₅)Fe(CO)₂, abbreviated as p‐G‐C₆H₄OFp ( 1 ), where G = NO₂, CN, COMe, CO₂Me, CF₃, Br, Cl, F, H, Me, MeO, and NMe₂] and para‐substituted benzenethiolatodicarbonyl(η⁵‐cyclopentadienyl) iron [p‐G‐C₆H₄S(η⁵‐C₅H₅)Fe(CO)₂, abbreviated as p‐G‐C₆H₄SFp ( 2 )] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔH_het(Fe–O)'s and ΔH_het(Fe–S)'s. The excellent linear free‐energy relations [r = 0.99 (g, 1a), 1.00 (g, 2b)] among the ΔΔH_het (Fe–O)'s and Δpk_a's of O–H bonds of p‐G‐C₆H₄OH or ΔΔH_het(Fe‐S)'s and Δpk_a's of S–H bonds of p‐G‐C₆H₄SH imply that the governing structural factors for these bond scissions are similar. And the linear correlations [r = ?0.99 (g, 1g), ?0.98 (g, 2h)] among the ΔΔH_het (Fe‐O)'s or ΔΔH_het(Fe‐S)'s and the substituent σ_p^? constants show that these correlations are in accordance with Hammett linear free‐energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔH_het(Fe–O)'s or ΔH_het(Fe–S)'s. ΔΔH_het(Fe–O)'s(g) ( 1 ) and ΔΔH_het(Fe–S)'s(g)( 2 ) follow the Capto‐dative principle. The substituent effects on the Fe–O bonds are much stronger than those on the less polar Fe–S bonds. Insight from this work may help the design of more effective catalytic processes. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative charge transfer studies in nonmetallated and metallated porphyrin fullerene dyads

Single 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 (?ΔG^o_ET) 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 V_oc, J_sc, and fill factor in single material organic solar cell using H2P‐C60 compared to previous reports.     

Pressure-induced dimerization kinetics of fullerene C60

Dimerization kinetics was studied for fullerene C₆₀ by IR spectroscopy at a pressure of 1.5 GPa in the temperature range 373–473 K. The kinetic curves for the formation of a dimer (C₆₀)₂ were obtained using its analytical IR band at 796 cm^?1. Under the assumption that pressure-induced C₆₀ dimerization is a second-order irreversible reaction, the reaction rate constants were determined at different temperatures. The corresponding activation energy and preexponential factor were found to be 134±6 kJ/mol and (1.74± 0.24)×10¹⁴ s^?1, respectively. The specific features of the solid-phase C₆₀ dimerization in simple cubic and face-centered cubic fullerite phases are discussed.