Prato Reaction Research Articles

Diarylfluorene-Modified Fulleropyrrolidine Acceptors to Tune Aggregate Morphology for Solution-Processable Polymer/Fullerene Bulk-Heterojunction Solar Cells

A series of n-type fulleropyrrolidine derivatives as the acceptors, including Th-C60, PFTh-C60, and OPFTh-C60, have been synthesized via the key step of the typical Prato reaction to investigate the steric hindrance effect of various phenylfluorenyl moieties on the electronic structures, aggregate morphologies, and device performances of solar cells. Conjugation-interrupted linkage obviously does not change the energy bandgaps and lowest unoccupied molecular orbital (LUMO) energy levels in PFTh-C60 and OPFTh-C60 models with respect to that of precursor Th-C60 according to UV–vis spectra and cyclic voltammetry. In contrast, dramatically different phase separation behaviors in the bulk heterojunction (BHJ) film blending with poly(3-hexylthiophene) (P3HT) were observed by atomic force microscopy. A prototype OPFTh-C60-based BHJ polymer solar cell (PSC) with the configuration of ITO/PEDOT:PSS/P3HT:OPFTh-C60 (1:1) (200 nm)/Ca/Al has the performance with the short-circuit current (Isc) of 8.68 mA/cm2, open-circ...

Product formation in the Prato reaction on Sc3N@D5h-C80: preference for [5,6]-bonds, and not pyracylenic bonds

We report here reaction energies and NMR data for the N-tritylpyrrolidino mono-adducts of Sc(3)N@D(5h)-C(80). The pyracylene adduct that was previously suggested to be important for the Prato reaction is ruled out both from energetic and NMR points of view.

Organosulfur-Based Fullerene Materials

Chemical functionalizations of an endohedral metallofullerene, La2@Ih-C80, and an empty fullerene, C60, are demonstrated using organosulfur compounds. A novel donor–acceptor system of La2@Ih–C80-exTTF (3) synthesized using the Prato reaction shows photo-induced intramolecular charge separation. On the other hand, the photoreaction of C60 with N-p-toluenesulfonyl sulfilimine affords N-tosyl-1,2-aziridinofullerene (5). The first reversible interconversion of 1,2-aziridinofullerene and 1,6-azafulleroid was found for mono-substituted fullerenes by thermal rearrangement of 5 to 6. S,S-Diphenylsulfilimines (7) with an electron-donating group on the N atom reacts with C60 to afford corresponding aziridinofullerenes (8–10) regioselectively. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Synthesis of a Broadly Absorbing Modified PCBM and Application As Electron Acceptor with Poly(3-Hexylthiophene) As Electron Donor in Efficient Bulk Heterojunction Solar Cells

A simple and effective modification of PCBM was carried out by a two-step reaction. The modified PCBM, i.e., A was obtained as a mixture of monoadduct and multiadducts arising from the Prato reaction and was soluble in THF. It showed broader and stronger absorption in the visible region of the solar spectrum than PCBM due to the presence of a cyanovinylene 4-nitrophenyl segment. The lowest occupied molecular energy level (LUMO) of A was measured and found that it is higher than that of PCBM by 0.15 eV. The polymer solar cell (PSC) based on the P3HT as the electron donor with A as the electron acceptor shows an open circuit voltage (Voc) of 0.80 V, a short-circuit current (Jsc) of 9.0 mA/cm2, and a power conversion efficiency (PCE) of 3.88%, which are higher than those for the PSC based on P3HT:PCBM. The higher PCE for the PSC based on P3HT:A accounts for the increase in both Jsc and Voc, due to the increased absorption of A in the visible region and its higher LUMO level. The PCE of the PSC has been furth...

Synthesis, Properties, and Potential Applications of Porphyrin-Fullerenes

The review focuses current research in the rapidly developing chemistry of porphyrin-fullerene complexes, and highlights recent advances in the synthesis, properties, and potential applications of this family. An overview of the most popular methods to prepare porphyrin complexes with C 60 fullerene exhibiting various types of linkage is given with the main focus on the Prato reaction and its modifications. The discussion of porphyrin-fullerene complexes will include the structures of noncovalently linked porphyrin-fullerenes along with the covalently linked complexes; the chemistry and design of supramolecular ensembles will be covered rather comprehensively. Finally, the potential applications for porphyrin-fullerene conjugates will be discussed.

Fulleropyrrolidine End-Capped Molecular Wires for Molecular Electronics—Synthesis, Spectroscopic, Electrochemical, and Theoretical Characterization

In continuation of previous studies showing promising metal-molecule contact properties a variety of C(60) end-capped "molecular wires" for molecular electronics were prepared by variants of the Prato 1,3-dipolar cycloaddition reaction. Either benzene or fluorene was chosen as the central wire, and synthetic protocols for derivatives terminated with one or two fullero[c]pyrrolidine "electrode anchoring" groups were developed. An aryl-substituted aziridine could in some cases be employed directly as the azomethine ylide precursor for the Prato reaction without the need of having an electron-withdrawing ester group present. The effect of extending the π-system of the central wire from 1,4-phenylenediamine to 2,7-fluorenediamine was investigated by absorption, fluorescence, and electrochemical methods. The central wire and the C(60) end-groups were found not to electronically communicate in the ground state. However, the fluorescence of C(60) was quenched by charge transfer from the wire to C(60). Quantum chemical calculations predict and explain the collapse of coherent electronic transmission through one of the fulleropyrrolidine-terminated molecular wires.

The Prato reaction on nanodiamond: Surface functionalization by formation of pyrrolidine rings

The Prato reaction is a highly valued reaction for the functionalization of fullerenes and carbon nanotubes. It uses the generation of pyrrolidine rings from azomethine ylides in the formation of a covalent grafting of functional moieties. Here we present the first application of this reaction on thermally annealed nanodiamond as a way for the grafting of a multitude of functional moieties. We used two types of azomethine ylides (aliphatic and pyridine derived) to show the broad applicability of the reaction for the surface modification of nanodiamond. The possibility to attach glycol units or alkyl chains, both with or without reactive terminal groups opens the way to tune the surface properties of such “Prato-functionalized” diamond in a very flexible way.

Synthesis and characteristics of a solution-processable fullerene derivative for n-type organic field-effect transistors

A fullerene molecule, C60TH2-DcB, was prepared by Prato reaction which provides better product yields and purity compared with the reaction for the synthesis of [60]methanofullerene analogues. The C60TH2-DcB is readily soluble in common organic solvents and shows good thermal properties. Field-effect transistors fabricated by solution processing exhibit good n-channel characteristics with a maximum mobility of 1.5 × 10 −3 cm 2 V −1 s −1 with a threshold voltage of 11 V and on/off current ratio of 1.0 × 10 5.

Close Proximity Dibenzo[a,c]phenazine–Fullerene Dyad: Synthesis and Photoinduced Singlet Energy Transfer

AbstractA dibenzo[a,c]phenazine–fullerene (DBPZ‐C60) dyad in which two chromophores are linked in close proximity to each other has been synthesized and studied in detail by optical spectroscopy to explore a new energy donor–acceptor system. The dyad was prepared by Prato reaction between 11‐formyldibenzo[a,c]phenazine and fullerene. 3,5‐Di‐tert‐butylbenzyl group was introduced onto the fulleropyrrolidine unit to achieve adequate solubility of the dyad. A thorough study of the photophysical properties of the dyad and relevant reference compounds, performed by means of steady state and time resolved spectroscopic measurements, has revealed the presence of highly efficient (ca. 98 %) and extremely fast (ken = 5 × 1011 s–1) intramolecular photoinduced singlet–singlet energy‐transfer process from singlet excited state of the DBPZ moiety to fullerene. In both polar and nonpolar environment transduction of singlet excited state energy governs the excited state deactivation, but the efficiency and rate of energy transfer were found to be higher in nonpolar solvents in comparison to polar. The DBPZ singlet excited state decays within 2 and 4.7 ps in toluene andbenzonitrile, respectively, via singlet–singlet energy transfer to produce a fullerene singlet excited state which decays with a life time of 1.5 ns to give a very long‐lived fullerene triplet state as final populated excited state.

N‐pyrrolidine functionalized C60‐fullerenes/epoxy nanocomposites

AbstractA series of functionalized C60‐fullerene/epoxy nanocomposites were prepared, and their respective ultimate tensile strengths were determined. The functionalization route of the fullerenes was performed using the Prato reaction, with modified amino acids, resulting in the formation of N‐pyrrolidine rings across the [6,6] junctions. Characterization of the functionalized fullerenes was done using Laser Desorption Ionization Time‐of‐Flight (LDI‐TOF) mass spectrometry. The mechanical properties of the nanocomposites were affected by the type of modified amino acid, the degree of functional group attachment, and the consequent degree of dispersion into the epoxy matrix. A specially blended diglycidyl ether of bisphenol A (DGEBA) epoxy, having a low viscosity and high strain‐to‐failure was prepared by adding 1,4‐butanediol diglycidyl ether to DGEBA. The lower viscosity blended epoxy allowed for easier mixing of the fullerenes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Spin Divergence Induced by Exohedral Modification: ESR Study of Sc3C2@C80 Fulleropyrrolidine

The paramagnetic properties of the endohedral fullerene Sc3C2@C80 are adjustable by exohedral modification by the Prato reaction (see picture). Analysis of spin densities and endocluster dynamics reveal unique paramagnetic properties of the Sc3C2@C80 fulleropyrrolidine and provide general insight into the addend-dependent paramagnetic behavior of endohedral fullerenes.

Synthesis by Prato Reaction and In Situ Ultraviolet Characterization of Several Fulleropyrrolidine Derivatives

ABSTRACT 1-Methyl-2-phenylfulleropyrrolidine (1), 1-methyl-2-(4-(1-piperidyl)-phenyl)fulleropyrrolidine (2), 1-methyl-2-(4-fluorophenyl)-fulleropyrrolidine (3), and 1-methyl-2-(3-hydroxy-2-naphtyl)-3,4-fulleropyrrolidine (4) were synthesized by Prato reaction and characterized in situ in the reaction mixture by ultraviolet-visible (UV-vis) spectroscopy, high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption ionization (MALDI). A comparison of theoretical and experimental UV spectra was carried out.

Zinc Porphyrins Covalently Bound to the Side Walls of Single-Walled Carbon Nanotubes via Flexible Bonds: Photoinduced Electron Transfer in Polar Solvent

Single-walled carbon nanotubes (SWCNTs) tethering zinc porphyrins (ZnP) with flexible aliphatic bonds, ZnP−(spacer)−SWCNT, were prepared with applying the Prato reaction. Under illumination by visible light (>500 nm), ZnP−(spacer)−SWCNT effectively catalyzed the reduction of the benzylviologen dication (BV2+) by 1-benzyl-1,4-dihydronicotinamide in dimethylformamide (DMF). The H2 evolution was also confirmed when the ZnP−(spacer)−SWCNT aqueous solution was illuminated by visible light in the presence of Pt particles. Furthermore, the photocurrent and photovoltage were observed to respond to the on−off cycles of the visible light irradiation in a solar cell consisting of a transparent glass electrode modified with ZnP−(spacer)−SWCNT. The time-resolved fluorescence and absorption spectral measurements revealed the photoinduced electron-transfer mechanism.

Unexpected formation of N-methylfulleropyrrolidines by the reaction of fullerene and gossypol and their bioactivity

Reaction of fullerene, sarcosine and gossypol through the Prato reaction resulted in some unexpected N-methylfulleropyrrolidines. These fulleropyrrolidines were fully characterized via rigorous structure determination through multiple spectral experiments, which included 1D, 2D NMR, FT-IR, MS and X-ray crystallography. During the reaction, gossypol decomposed into benzaldehyde which was successfully detected as a new intermediate through GC–MS. In an in vitro assay of NO radical induced apoptosis in 3T3L1 cells, N-methylfulleropyrrolidine ( 2) and N-methyl-2,2-dimethylfulleropyrrolidine ( 3) showed dose dependent and stronger radical scavenging activities than the parent fullerene.

New pyrrolidine and pyrroline derivatives of fullerenes: from the synthesis to the use in light-converting systems

The results of the authors’ studies on the [2+3] cycloaddition of azomethine and nitrile ylides generated from picolylamine and benzylamine derivatives to fullerenes are systematized and new experimental data are considered. Catalysts and microwave radiation promoting the formation of ylides and their addition to fullerenes were successfully used for the first time. A large series of new pyrrolidine and pyrroline derivatives of fullerenes C60 and C70 were synthesized and characterized. The proposed procedures afford the reaction products in yields twice as high (80–85%) as those attained by the classical Prato reaction. The reactions proceed with virtually complete regio- (in the case of C70) and stereoselectivity to afford only cis-2′,5′-disubstituted and trans-1′,2′,5′-trisubstituted pyrrolidinofullerenes. Pyridyl-substituted pyrrolidinofullerenes react with metalloporphyrins and phthalocyanines to form self-ordered coordination complexes. The latter are analogs of natural photosynthetic antenna systems due to photoinduced charge separation that occurs in these complexes upon exposure to light.

Syntheses and Chiroptical Properties of Optically Active Helical Poly(phenylacetylene)s Bearing [60]Fullerene Pendants

Two novel C60-bound chiral (3) and achiral (2) phenylacetylenes were synthesized by the treatment of C60 with (R)-N-[1-(4-ethynylphenyl)ethyl]glycine and N-(4-ethynylbenzyl)glycine by the Prato reaction in the presence of paraformaldehyde and dipentadecyl ketone, respectively. The homopolymerization of the achiral 2 bearing long alkyl chains and copolymerization with optically active phenylacetylenes including 3 using a rhodium catalyst in chloroform homogeneously occurred, giving the C60-containing helical poly(phenylacetylene)s soluble in chloroform, while the homopolymers of the analogous achiral C60-bound phenylacetylenes with no alkyl chain (1) and 3 were totally insoluble in common organic solvents. The obtained copolymers exhibited an induced circular dichroism (ICD) both in the main-chain region and in the fullerene chromophoric region, indicating that the optically active copolymers possess a preferred-handed helical conformation and that the pendant fullerene groups are arranged in helical arrays with a predominant screw-sense along the polymer backbones. The formation of a hierarchical supramolecular assembly of the homopolymers of 1 and 3 bearing fullerene pendants on each repeating unit was also studied by electron microscopy.

Synthesis and characterization of star polyfluorenes with a C60 core

AbstractC60‐cored star polyfluorenes were synthesized and fully characterized. A high yield (81%) hexakisaddition of C60 was developed by using Prato reaction and bulky fluorene addends. Suzuki polycondensation of the hexakisadducts of C60 carrying six 2‐bromofluorene addends and AB‐type monomer (2‐bromo‐9,9‐dioctylfluorenyl‐4,4,5,5‐tetramethyl‐ [1,3,2]‐dioxaborane) with Pd(PPh3)4 as the catalyst precursor afforded the desired C60‐cored star polyfluorenes. Their three‐dimensional structure can effectively reduce the aggregation of the polyfluorene chains. Annealing studies indicated that the C60‐cored star polyfluorenes are of good color stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4696–4706, 2007

Novel fluorene-containing fullerenes C60: synthesis and structures

Reactions of fullerene C60 with fluorene-2-carbaldehyde or 2,7-diacetylfluorene in toluene gave novel spiromethanofullerenes containing a reactive free formyl group. A novel fluorene-containing fullerenopyrrolidine was obtained by the Prato reaction. The purity and compositions of the compounds obtained were confirmed by MALDI TOF mass spectrometry and HPLC. Their structures were confirmed by 2D homo-and heterocorrelation NMR techniques.

Single-Wall Carbon Nanotubes Bearing Covalently Linked Phthalocyanines − Photoinduced Electron Transfer

HiPco single-walled carbon nanotubes (SWNTs) have been sidewall-functionalized with phthalocyanine addends following two different approaches: a straightforward Prato reaction with N-octylglycine and a formyl-containing phthalocyanine, and a stepwise approach that involves a former Prato cycloaddition to the double bonds of SWNTs using p-formyl benzoic acid followed by esterification of the derivatized nanotubes with an appropriate phthalocyanine molecule. The two materials obtained by these routes comprise different carbon/Pc-addenda ratios, as evidenced by Raman, TGA, and photophysical studies. The occurrence of electron transfer from photoexcited phthalocyanines to the nanotube framework in these ZnPc-SWNT ensembles is observed in transient absorption experiments, which confirm the absorption of the one-electron oxidized ZnPc cation and the concomitant bleaching of the van Hove singularities typical from SWNTs. Charge-separation (i.e., 2.0 x 1010 s(-1)) and charge-recombination (i.e., 1.5 x 106 s(-1)) dynamics reveal a notable stabilization of the radical ion pair product in dimethylformamide.

Synthesis and characterization of polyethylene chains grafted onto the sidewalls of single-walled carbon nanotubes via copolymerization

Polyethylene (PE) chains grafted onto the sidewalls of SWCNTs (SWCNT-g-PE) were successfully synthesized via ethylene copolymerization with functionalized single-walled carbon nanotubes (f-SWCNTs) catalyzed by rac-(en)(THInd)(2)ZrCl2/ MAO. Here f-SWCNTs, in which alpha-alkene groups were chemically linked on the sidewalls of SWCNTs, were synthesized by Prato reaction. The composition and microstructure of SWCNT-g-PE were characterized by means of H-1 NMR, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyses (TGA), field-emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Nanosized cable-like structure was formed in the SWCNT-g-PE, in which the PE formed a tubular shell and several SWCNTs bundles existed as core. The formation of the above morphology in the SWCNT-g-PE resulted from successfully grafting of PE chains onto the surface of SWCNTs via copolymerization. The grown PE chains grafted onto the sidewall of the f-SWCNTs promoted the exfoliation of the mass nanotubes. Comparing with pure PE, the physical mixture of PE/f-SWCNTs and in situ PE/SWCNTs mixture, thermal stability, and mechanical properties of SWCNT-g-PE were higher because of the chemical bonding between the f-SWCNTs and PE chains.