Sn and Ge Complexes with Redox-Active Ligands as Efficient Interfacial Membrane-like Buffer Layers for p-i-n Perovskite Solar Cells.

Inverted perovskite solar cells with a p-i-n configuration have attracted considerable attention from the research community because of their simple design, insignificant hysteresis, improved operational stability, and low-temperature fabrication technology. However, this type of device is still lagging behind the classical n-i-p perovskite solar cells in terms of its power conversion efficiency. The performance of p-i-n perovskite solar cells can be increased using appropriate charge transport and buffer interlayers inserted between the main electron transport layer and top metal electrode. In this study, we addressed this challenge by designing a series of tin and germanium coordination complexes with redox-active ligands as promising interlayers for perovskite solar cells. The obtained compounds were characterized by X-ray single-crystal diffraction and/or NMR spectroscopy, and their optical and electrochemical properties were thoroughly studied. The efficiency of perovskite solar cells was improved from a reference value of 16.4% to 18.0-18.6%, using optimized interlayers of the tin complexes with salicylimine (1) or 2,3-dihydroxynaphthalene (2) ligands, and the germanium complex with the 2,3-dihydroxyphenazine ligand (4). The IR s-SNOM mapping revealed that the best-performing interlayers form uniform and pinhole-free coatings atop the PC61BM electron-transport layer, which improves the charge extraction to the top metal electrode. The obtained results feature the potential of using tin and germanium complexes as prospective materials for improving the performance of perovskite solar cells.

The Novel Gallium Aminobisphenolate Initiator of the Ring-Opening Copolymerization of L-Lactide and ε-Caprolactone: A Computational Study.

Density functional theory (DFT) simulations of ring-opening copolymerization of ε-caprolactone (CL) and L-lactide (LA) in presence of novel gallium complex on aminobis (phenolate) ligand are conducted. The initial steps of polymerization of CL and LA as well as the first steps of propagation which led to LGa-LA-LA-OMe, LGa-LA-CL-OMe, LGa-CL-LA-OMe, or LGa-CL-CL-OMe derivatives have been analyzed in detail. According to these data, the studied catalyst is a rare example of a catalyst in which, during copolymerization, the polymerization of CL should proceed faster than LA. Thus, we predict the formation of a mainly block copolymer poly(CL-block-LA) using this catalyst.

Gallium (III) Complexes Based on Aminobisphenolate Ligands: Extremely High Active ROP-Initiators from Well-Known and Easily Accessible Compounds.

We report herein the synthesis and full characterizations of the first examples of gallium complexes based on "privileged" aminobisphenolate ligands which are easily available. These complexes turned out to be extremely active in the ring-opening polymerization of ε-caprolactone even at room temperature and highly active in the ROP of L-lactide. The combination of factors such as the easy availability of these compounds and the supposedly low toxicity, together with the extremely high activity in ROP, allows us to consider these compounds as suitable for use on an industrial scale for the synthesis of biodegradable polymers for biomedical applications.

Remote Stereoelectronic Effects in Pyrrolidone- and Caprolactam-Substituted Phenols: Discrepancies in Antioxidant Properties Evaluated by Electrochemical Oxidation and H-Atom Transfer Reactivity.

New antioxidants are commonly evaluated via two main approaches, i.e., the ability to donate an electron and the ability to intercept free radicals. We compared these approaches by evaluating the properties of 11 compounds containing both antioxidant moieties (mono- and polyphenols) and auxiliary pharmacophores (pyrrolidone and caprolactam). Several common antioxidants, such as butylated hydroxytoluene (BHT), 2,3,5-trimethylphenol (TMP), quercetin, and dihydroquercetin, were added for comparison. The antioxidant properties of these compounds were determined by their rates of reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and their oxidation potentials from cyclic voltammetry. Although these methods test different chemical properties, their results correlate reasonably well. However, several exceptions exist where the two methods give opposite predictions! One of them is the different behavior of mono- and polyphenols: polyphenols can react with DPPH more than an order of magnitude faster than monophenols of a similar oxidation potential. The second exception stems from the size of a "bystander" lactam ring at the benzylic position. Although the phenols with a seven-membered lactam ring are harder to oxidize, the sterically nonhindered compounds react with DPPH about 2× faster than the analogous five-membered lactams. The limitations of computational methods, especially those based on a single parameter, are also evaluated and discussed.

Investigations into the structure-activity relationship in gemini QACs based on biphenyl and oxydiphenyl linker.

Eighteen novel gemini quaternary ammonium compounds were synthesized to examine the effect of linker nature, aliphatic chain length and their relative position on antibacterial and antifungal activity. The synthesized compounds showed strong bacteriostatic activity against a panel of both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and two fungi. Some of these compounds exhibited a wider and more potent antimicrobial spectrum than commonly-used antiseptics, such as benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), chlorhexidine digluconate (CHG) and octenidine dihydrochloride (OCT).

Supramolecular D⋯A-layered structures based on germanium complexes with 2,3-dihydroxynaphthalene and N,N'-bidentate ligands.

The concept of using redox-active ligands, which has become extremely widespread in organometallic chemistry, is often considered from 'their effect on the metal center properties' point of view and 'how to modify the ligands'. In this paper, we present the reverse side of this effective approach - a dramatic change of redox properties of ligands under the influence of a redox-inert metal. Germanium derivatives based on 2,3-dihydroxynaphthalene (1) and N,N'-bidentate ligands, namely 2,2'-bipyridine (2) and 1,10-phenanthroline (3), were obtained and characterized by CV, UV-vis spectroscopy, DFT calculations and in the case of 3 X-ray diffraction. It was shown that the HOMO of the complexes is almost completely located on the naphthalene fragment while the LUMO is on the N,N-ligands. At the same time, there are no boundary molecular orbitals on the germanium atom, but it forms the axial part of the molecule holding two opposite motifs together. Moreover, it sharply affects the level of HOMO and LUMO. Derivatives 2 and 3 are more easily oxidized compared to 2,3-dihydroxynaphthalene by 0.31-0.34 V (7-8 kcal mol-1) and are more easily reduced compared to N,N-donors by 1.08-1.15 V (25-26.5 kcal mol-1). All this together makes it possible to form a system with a narrow HOMO/LUMO gap (∼2 eV). The crystal structure of 3 consists of alternating monomolecular easily oxidizing and easily reducing layers formed due to intermolecular interactions, in particular π-stacking. In addition, in contrast to 1 that starts to decompose noticeably at the temperatures from 200 °C, 2 and 3 have an extremely high thermal stability. They remain stable with no signs of decomposition and melting up to 400 °Ð¡. We believe that this approach to the formation of the supramolecular structure may present prospects for obtaining new functional materials.

Catalyst-Solvent System for PASE Approach to Hydroxyquinolinone-Substituted Chromeno[2,3-b]pyridines Its Quantum Chemical Study and Investigation of Reaction Mechanism.

The Pot, Atom, and Step Economy (PASE) approach is based on the Pot economy principle and unites it with the Atom and Step Economy strategies; it ensures high efficiency, simplicity and low waste formation. The PASE approach is widely used in multicomponent chemistry. This approach was adopted for the synthesis of previously unknown hydroxyquinolinone substituted chromeno[2,3-b]pyridines via reaction of salicylaldehydes, malononitrile dimer and hydroxyquinolinone. It was shown that an ethanol-pyridine combination is more beneficial than other inorganic or organic catalysts. Quantum chemical studies showed that chromeno[2,3-b]pyridines has potential for corrosion inhibition. Real time 1H NMR monitoring was used for the investigation of reaction mechanism and 2-((2H-chromen-3-yl)methylene)malononitrile was defined as a key intermediate in the reaction.

2-Carboxyethylgermanium Sesquioxide as A Promising Anode Material for Li-Ion Batteries.

Various forms of germanium and germanium-containing compounds and materials are actively investigated as energy-intensive alternatives to graphite as the anode of lithium-ion batteries. The most accessible form-germanium dioxide-has the structure of a 3D polymer, which accounts for its rapid destruction during cycling, and requires the development of further approaches to the production of nanomaterials and various composites based on it. For the first time, we propose here the strategy of using 2-carboxyethylgermanium sesquioxide ([O1.5 GeCH2 CH2 CO2 H]n , 2-CEGS), in lieu of GeO2 , as a promising, energy-intensive, and stable new source system for building lithium-ion anodes. Due to the presence of the organic substituent, the formed polymer has a 1D or a 2D space organization, which facilitates the reversible penetration of lithium into its structure. 2-CEGS is common and commercially available, completely safe and non-toxic, insoluble in organic solvents (which is important for battery use) but soluble in water (which is convenient for manufacturing diverse materials from it). This paper reports the preparation of micro- (flower-shaped agglomerates of ≈1 µm thick plates) and nanoformed (needle-shaped nanoparticles of ≈500×(50-80) nm) 2-CEGS using methods commonly available in laboratories and industry such as vacuum and freeze-drying of aqueous solutions of 2-CEGS. Lithium half-cell anodes based on 2-CEGS show a capacity of ≈400 mAh g-1 for microforms and up to ≈700 mAh g-1 for nanoforms, which is almost two times higher than the maximal theoretical capacity of graphite. These anodes are stable during the cycling at various rates. The results of DFT simulations suggest that Li atoms form the stable Li2 O with the oxygen atoms of 2-CEGS, and actual charge-discharge cycles involve deoxygenated GeC3 H5 molecules. Thus, C3 chains loosen the anode structure compared to pure Ge, improving its ability to accommodate Li ions.

Pot, atom and step economic (PASE) assembly of salicylaldehydes, malononitrile dimer and 4-hydroxypyridine-2(1H)-ones into medicinally relevant 5H-chromeno[2,3-b]pyridine scaffold.

The new multicomponent reaction (MCR) has been found: one-pot selective and efficient formation of the new 5-(4-hydroxy-2-oxo-1,2-dihydropyridin-3-yl)-substituted 5H-chromeno[2,3-b]pyridines in 61-97% yields directly from simple and easily available salicylaldehydes, malononitrile dimer and 4-hydroxypyridine-2(1H)-ones in small amount of pyridine-ethanol catalyst/solvent system. This complex "domino" transformation includes Knoevenagel condensation of salicylaldehyde with malononitrile dimer, Michael addition of 4-hydroxypyridine-2(1H)-one, double Pinner-type reaction cyclization and isomerization with following protonation. This facile multicomponent process opens a new way to 5-(4-hydroxy-2-oxo-1,2-dihydropyridin-3-yl)-substituted 5H-chromeno[2,3-b]pyridine systems, which are promising compounds for the treatment for human inflammatory TNFα-mediated diseases and different biomedical applications.

One-pot five-component high diastereoselective synthesis of polysubstituted 2-piperidinones from aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate.

A novel five-component diastereoselective synthesis of polysubstituted 2-piperidinones is reported. The Knoevenagel condensation-Michael addition-Mannich cascade of two equivalents of aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate or aqueous ammonia in alcohols provides convenient access to alkyl (3SR,4RS,6SR)-5,5-dicyano-2-oxo-4,6-diarylpiperidine-3-carboxylates with three stereocenters in 52-90% or dialkyl (2SR,3RS,4RS,5SR)-2,4-diaryl-3-cyano-6-oxopiperidine-3,5-dicarboxylates with four stereocenters in 38-88%. The formation of products was highly stereoselective, with only one diastereomer formed. Ammonium acetate or aqueous ammonia plays a role both as a catalyst and as a nitrogen source. 2,4,6-triaryl-3,3,5,5-tetracyanopiperidines were obtained as a side products in the reactions with nitro-substituted aldehydes or with ethyl and n-propyl cyanoacetates. A series of 14 2-piperidinones and piperidines was assessed for antimicrobial activity against a panel of five bacteria and two fungi; no significant activity was observed. Two side piperidines with nitro substituents in aromatic ring possess bacteriostatic action against S. aureus ATCC 43300 and A. baumannii ATCC 19606 at 32 ug/mL.

Infrared-Spectroscopic Study of (4-Methylpent-3-en-1-ynyl)methylthiocarbene, Its Photochemical Transformations, and Reactions in an Argon Matrix.

The first representative of singlet carbenes bearing both ethynyl and methylthio groups at the carbene center, (4-methylpent-3-en-1-ynyl)methylthiocarbene, has been generated in a low-temperature Ar matrix upon UV photolysis of 3,3-dimethyl-5-methylthioethynyl-3H-pyrazole and detected by FTIR spectroscopy. The generation of the carbene proceeds via intermediate (3-diazo-5-methylhex-4-en-1-ynyl)methylsulfane. The comparison of FTIR spectroscopy data with the results of quantum chemical calculations (B3LYP/aug-cc-pVTZ) and NRT analysis shows that (4-methylpent-3-en-1-ynyl)methylthiocarbene has a singlet ground state with the localization of the unpaired spins on the carbon atom in the α-position to methylthio moiety. Two major pathways of further phototransformation of the studied carbene have been found. One of them produces photochemically stable thioketone (S═CMe-C≡C-CH═CMe2) as a result of methyl group migration from sulfur to the neighboring carbon atom, and the other one leads to the formation of labile thioketene (S═C═C(Me)-CH═CH-CMe═CH2). Ability of (4-methylpent-3-en-1-ynyl)methylthiocarbene to insert into the H-Cl bond was established, which additionally confirms the singlet nature of this intermediate.

Upconversion of Reductants.

The many applications of photon upconversion-conversion of low-energy photons into high-energy photons-raises the question of the possibility of "electron upconversion". In this Review, we illustrate how the reduction potential can be increased by using the free energy of exergonic chemical reactions. Electron (reductant) upconversion can produce up to 20-25 kcal mol-1 of additional redox potential, thus creating powerful reductants under mild conditions. We will present the two common types of electron-upconverting systems-dissociative (based on unimolecular fragmentations) and associative (based on the bimolecular formation of three-electron bonds). The possible utility of reductant upconversion encompasses redox chain reactions in electrocatalytic processes, photoredox cascades, design of peroxide-based medicines, firefly luminescence, and reductive repair of DNA photodamage.

Halogen-free GeO2 conversion: electrochemical reduction vs. complexation in (DTBC)2Ge[Py(CN)n] (n = 0 2) complexes.

3,5-di-tert-Butylcatecholate (DTBC) germanium complexes (DTBC)2Ge[Py(CN)n]2 (n = 0…2) have been synthesized from GeO2, 3,5-di-tert-butylcatechol and cyano-substituted pyridines Py(CN)n and characterized by elemental analysis, NMR, IR and UV-VIS spectroscopy. The structure of 1 (with 4-cyanopyridine) has been determined by X-ray single crystal analysis. UV-VIS spectra have shown that these complexes are stable in CH3CN, toluene and CH2Cl2 solutions; in contrast, they are rapidly decomposed by dimethylformamide and tetrahydrofuran. Complexes 1 and 2 (with 4-cyano and 3-cyanopyridine) are electrochemically reducible in toluene/1 M Bu4NPF6 at E = -1.3…-1.7 V vs. AgCl. The quantum-chemical study of these complexes is in accordance with the unsuccessful attempts to obtain analogous derivatives with 2-cyanopyridine and 2,6-dicyanopyridine.

High diastereoselective amine-catalyzed Knoevenagel-Michael-cyclization-ring-opening cascade between aldehydes, 3-arylisoxazol-5(4H)-ones and 3-aminocyclohex-2-en-1-ones.

A highly diastereoselective three-component cascade reaction among aromatic aldehydes, 3-arylisoxazol-5(4H)-ones and 3-aminocyclohex-2-en-1-ones takes place under the catalysis of triethylamine, providing (3SR,4SR)-4-aryl-3-[(E)-(hydroxyimino)(aryl)methyl]-4,6,7,8-tetrahydroquinoline-2,5(1H,3H)-diones in 45-85% yields. The transformation presumably proceeds through a sequential cascade of Knoevenagel/Michael-addition/cyclization/ring-opening reactions. This process was carried out in green media (EtOH/water, 1:1-1:3) at reflux. Products are crystallized directly from the reaction mixture and their isolation includes only filtration. The structure of (3SR,4SR)-3-[(E)-(hydroxyimino)(phenyl)methyl]-7,7-dimethyl-4-phenyl-4,6,7,8-tetrahydroquinoline-2,5(1H,3H)-dione was confirmed by X-ray diffraction analysis.

Crystal structure of 4,8-di-tert-butyl-6,6-di-chloro-13-ethyl-2,10-dimethyl-13,14-di-hydro-12H-dibenzo[d,i][1,3,7,2]dioxaza-silecine toluene 0.25-solvate.

The coordination polyhedron at the silicon atom in the title compound, C26H37Cl2NO2Si·0.25C7H8, is typical for penta-coordinated silicon derivatives and represents a slightly distorted trigonal bipyramid with an N atom and a Cl atom in the apical positions and the two O atoms and the other Cl atom occupying the equatorial sites. There are two independent mol-ecules in the asymmetric unit. The N-Si-Cl fragment in each is close to linear [178.24 (5) and 178.71 (5)°], in good agreement with 4e-3c theory, as is the elongation of the apical bond lengths [Si-Cl = 2.1663 (7) and 2.1797 (7) Å] in comparison with the equatorial bonds [Si-Cl = 2.0784 (7) and 2.0748 (7) Å]. Orthogonal least-squares fitting of the two independent mol-ecules resulted in r.m.s. deviation of 0.017 Å. The conformations of the two mol-ecules are almost the same, with corresponding torsion angles differing by less than 5.5°. The toluene solvent mol-ecule is disordered about an inversion centre.

Crystal structure of 2,6-bis-(2-hy-droxy-5-methyl-phen-yl)-4-phenyl-pyridinium bromide di-chloro-methane hemisolvate hemihydrate.

The asymmetric unit in the structure of the title compound, C25H22NO2 (+)·Br (-)·0.5CH2Cl2·0.5H2O, comprises two pseudosymmetry-related cations, two bromide anions, a di-chloro-methane molecule and a water mol-ecule of solvation. The two independent cations are conformationally similar with the comparative dihedral angles between the central pyridine ring and the three benzene substituent rings being 3.0 (2), 36.4 (1) and 24.2 (1)°, and 3.7 (2), 36.5 (1) and 24.8 (1)°, respectively. In the crystal, the cations, anions and water mol-ecules are linked through O-H⋯O and O-H⋯Br hydrogen bonds, forming an insular unit. Within the cations there are also intra-molecular N-H⋯O hydrogen bonds. Adjacent centrosymmetrically related aggregates are linked by π-π stacking inter-actions between the pyridine ring and a benzene ring in both cations [ring-centroid separations = 3.525 (3) and 3.668 (3) Å], forming chains extending across the ac diagonal. Voids between these chains are filled by dichloromethane molecules.

Crystal structure of a mixed-valence µ-oxide Sn12 cluster.

The mixed-valence µ-oxide Sn12 cluster, deca-carbonyl-tetra-µ4-oxido-hexa-µ3-oxido-tetra-kis-[µ-2,2'-(pyridine-2,6-di-yl)bis(1,1-di-phenyl-ethano-lato)]deca-tin(II)ditin(IV)dimolyb-denum(O)(2 Mo-Sn) toluene hepta-solvate, [Mo2Sn12(C33H27NO2)4O10(CO)10]·7C7H8, has a crystallographically imposed inversion centre. The asymmetric unit also contains three and a half toluene solvent mol-ecules, one of which is disordered about a centre of symmetry. The complex mol-ecule comprises six distinct Sn atom species with four different coordination numbers, namely 3, 4, 5, and 6. The Sn(II) atoms forming the central Sn10O10 core adopt distorted trigonal-pyramidal, square-pyramidal and octa-hedral coordination geometries provided by the µ-oxide atoms and by the O- and N-donor atoms of two pyridinedi-ethano-late ligands. The terminal Sn(IV) atoms have distorted trigonal-bipyramidal coordination geometries, with a µ4-oxide atom and the N atom of a pyridinedi-ethano-late ligand occupying the axial positions, and the Mo atom of a Mo(CO)5 group and the alk-oxy O atoms of a ligand forming the equatorial plane. In the crystal, weak intra- and inter-molecular C-H⋯O hydrogen bonds are observed.

Unusual isotope effect in the reaction of chlorosilylene with trimethylsilane-1-d. Absolute rate studies and quantum chemical and Rice-Ramsperger-Kassel-Marcus calculations provide strong evidence for the involvement of an intermediate complex.

Time-resolved studies of chlorosilylene, ClSiH, generated by the 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with trimethylsilane-1-d, Me(3)SiD, in the gas phase. The reaction was studied at total pressures up to 100 Torr (with and without added SF(6)) over the temperature range of 295-407 K. The rate constants were found to be pressure independent and gave the following Arrhenius equation: log[(k/(cm(3) molecule(-1) s(-1))] = (-13.22 ± 0.15) + [(13.20 ± 1.00) kJ mol(-1)]/(RT ln 10). When compared with previously published kinetic data for the reaction of ClSiH with Me(3)SiH, kinetic isotope effects, k(D)/k(H), in the range from 7.4 (297 K) to 6.4 (407 K) were obtained. These far exceed values of 0.4-0.5 estimated for a single-step insertion process. Quantum chemical calculations (G3MP2B3 level) confirm not only the involvement of an intermediate complex, but also the existence of a low-energy internal isomerization pathway which can scramble the D and H atom labels. By means of Rice-Ramsperger-Kassel-Marcus modeling and a necessary (but small) refinement of the energy surface, we have shown that this mechanism can reproduce closely the experimental isotope effects. These findings provide the first experimental evidence for the isomerization pathway and thereby offer the most concrete evidence to date for the existence of intermediate complexes in the insertion reactions of silylenes.

Gas-phase kinetics of chlorosilylene reactions II. ClSiH + C2H4: absolute rate measurements and quantum chemical and RRKM calculations for the prototype pi addition reaction.

Time-resolved studies of chlorosilylene, ClSiH, generated by the 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene, are carried out to obtain rate constants for its bimolecular reaction with ethene, C(2)H(4), in the gas-phase. The reaction is studied over the pressure range 0.13-13.3 kPa (with added SF(6)) at five temperatures in the range 296-562 K. The second order rate constants, obtained by extrapolation to the high pressure limits at each temperature, fitted the Arrhenius equation: log(k(infinity)/cm(3) molecule(-1) s(-1)) = (-10.55+/-0.10) + (3.86 +/- 0.70) kJ mol(-1)/RT ln10. The Arrhenius parameters correspond to a loose transition state and the rate constant at room temperature is 43% of that for SiH(2) + C(2)H(4), showing that the deactivating effect of Cl-for-H substitution in the silylene is not large. Quantum chemical calculations of the potential energy surface for this reaction at the G3MP2//B3LYP level show that, as well as 1-chlorosilirane, ethylchlorosilylene is a viable product. The calculations reveal how the added effect of the Cl atom on the divalent state stabilisation of ClSiH influences the course of this reaction. RRKM calculations of the reaction pressure dependence suggest that ethylchlorosilylene should be the main product. The results are compared and contrasted with those of SiH(2) and SiCl(2) with C(2)H(4).

A highly delocalized triplet carbene, 5-Methylhexa-1,2,4-triene-1,3-diyl: matrix IR identification, structure, and reactions.

The first representative of highly delocalized triplet carbenes bearing both vinyl and ethynyl groups at the formal carbene center, 5-methylhexa-1,2,4-triene-1,3-diyl, has been generated in a low-temperature Ar matrix upon UV photolysis of 5-ethynyl-3,3-dimethyl-3H-pyrazole and detected by FTIR spectroscopy. The transformation of 3H-pyrazole into the carbene proceeds in two stages via intermediate 3-diazo-5-methylhex-4-en-1-yne. According to DFT PBE/TZ2P calculations, 5-methylhexa-1,2,4-triene-1,3-diyl possesses an effective conjugation along the five-carbon chain and shows the same type of the bond length alternation as the HC(4m+1)H-type polyacetylenic carbenes. The carbene readily reacts with molecular oxygen, producing carbonyl oxides, which undergo further transformations typical of this type of compound upon irradiation in the UV-visible region. Two major photolytic rearrangements of 5-methylhexa-1,2,4-triene-1,3-diyl represent reactions characteristic of vinyl carbenes and resulting in the formation of 1-ethynyl-3,3-dimethylcyclopropene and 3E-2-methylhexa-1,3-dien-5-yne. A minor reaction is that typical of ethynylcarbenes; this leads to the formation of singlet 2-(2-methylpropenyl)cyclopropenylidene. Fragments of singlet and triplet potential energy surfaces of the C(7)H(8) system have been explored in DFT PBE/TZ2P calculations.