Jean-François Eckert

Photoinduced processes in fullerenopyrrolidine and fullerenopyrazoline derivatives substituted with an oligophenylenevinylene moietyElectronic supplementary information (ESI) available: synthetic procedures and full characterization of all new compounds. See http://www.rsc.org/suppdata/jm/b2/b200432a/

Fullerene derivatives A-3PV and B-3PV in which an oligophenylenevinylene trimeric subunit (3PV) is attached to C60 through, respectively, a pyrrolidine or a pyrazoline ring have been prepared. The electrochemical and excited-state properties of the multicomponent arrays A-3PV and B-3PV have been investigated in solution using the related oligophenylenevinylene derivative 3PV, fullerenopyrrolidine A and fullerenopyrazoline B as reference compounds. In A-3PV quantitative OPV → C60 photoinduced singlet–singlet energy transfer has been observed. Population of the lowest fullerene singlet excited state is followed by nearly quantitative intersystem crossing to the lowest fullerene triplet excited state in CH2Cl2 and toluene, whereas OPV → C60 electron transfer is able to compete significantly in the more polar solvent benzonitrile. In the case of B-3PV, the excited-state properties are more complex due to the electron donating ability of the pyrazoline ring. As observed for A-3PV, quantitative OPV → C60 photoinduced singlet–singlet energy transfer occurs in B-3PV. However, in this case, the population of the lowest fullerene singlet excited state is followed by an efficient electron transfer from the pyrazoline ring in CH2Cl2 and benzonitrile. In B-3PV, studies of the dependence of photoinduced processes on solvent polarity, addition of acid, and temperature also reveal that this compound can be considered as a fullerene-based molecular switch, the switchable parameters being the photoinduced processes. Finally, A-3PV and B-3PV have been tested as active materials in photovoltaic devices and the differences of light to energy conversion efficiencies found for the two compounds have been rationalised on the basis of their photophysical properties.

Synthesis of Amphiphilic Fullerene Derivatives and Their Incorporation in Langmuir and Langmuir-Blodgett Films

Various amphiphilic fullerene derivatives were prepared by functionalization of [5,6]fullerene-C60-Ih (C60) with malonate or bis-malonate derivatives obtained by esterification of the malonic acid mono-esters 5–7. Cyclopropafullerene 10 was obtained by protection of the carboxylic acid function of 6 as a tert-butyl ester, followed by Bingel addition to C60 and a deprotection step (Scheme 2). The preparation of 10 was also attempted directly from the malonic acid mono-ester 6 under Bingel conditions. Surprisingly, the corresponding 3′-iodo-3′H-cyclopropa[1,9][5,6]fullerene-C60-Ih-3′-carboxylate 11 was formed instead of 10 (Scheme 3). The general character of this new reaction was confirmed by the preparation of 15 and 16 from the malonic acid mono-esters 13 and 14, respectively (Scheme 4). All the other amphiphilic fullerene derivatives were prepared by taking advantage of the versatile regioselective reaction developed by Diederich and co-workers which led to macrocyclic bis-adducts of C60 by a cyclization reaction at the C-sphere with bis-malonate derivatives in a double Bingel cyclopropanation. The bis-adducts 37–39 with a carboxylic acid polar head group and four pendant long alkyl chains of different length were prepared from diol 22 and acids 5–7, respectively (Scheme 9). In addition, the amphiphilic fullerene derivatives 45, 46, 49, 54, and 55 bearing different polar head groups and compound 19 with no polar head group were synthesized (Schemes 11–13, 15, and 5, resp.). The ability of all these compounds to form Langmuir monolayers at the air-water interface was investigated in a systematic study. The films at the water surface were characterized by their surface pressure vs. molecular area isotherms, compression and expansion cycles, and Brewster-angle microscopy. The spreading behavior of compound 10 was not good, the two long alkyl chains in 10 being insufficient to prevent aggregation resulting from the strong fullerene-fullerene interactions. While no films could be obtained from compound 19 with no polar head group, all the corresponding amphiphilic fullerene bis-adducts showed good spreading characteristics and reversible behavior upon successive compression/expansion cycles. The encapsulation of the fullerene in a cyclic addend surrounded by four long alkyl chains is, therefore, an efficient strategy to prevent the irreversible aggregation resulting from strong fullerene-fullerene interactions usually observed for amphiphilic C60 derivatives at the air-water interface. The balance of hydrophobicity to hydrophilicity was modulated by changing the length of the surrounding alkyl chains or the nature of the polar head group. The best results in terms of film formation and stability were obtained with the compounds having the largest polar head group, i.e.45 and 46, and dodecyl chains. Finally, the Langmuir films obtained from the amphiphilic fullerene bis-adducts were transferred onto solid substrates, yielding high-quality Langmuir-Blodgett films.

Complexation of fullerenes with dendritic cyclotriveratrylene derivatives

Dendritic derivatives containing a cyclotriveratrylene core for the complexation of fullerenes have been prepared. The association constants for the binding of fullerene derivatives determined by UV-vis titrations in CH2Cl2 and C6H6 are significantly increased as the generation number of the dendritic substituents is increased.

Polybenzyl ether dendrimers for the complexation of [60]fullerenes

The formation of host-guest complexes between C60 and polybenzyl ether dendrimers with different central cores (phloroglucinol, meso-tetraphenylporphyrin, cyclotriveratrylene) has been investigated in organic solvents by means of 13C-NMR and UV-Vis spectroscopy. The interior of the dendrimers with a phloroglucinol core provides the correctly sized space for the inclusion of [60]fullerene and 13C-NMR studies suggest that the guest resides near the central core. In the dendrimers containing a meso-tetraphenylporphyrin (TPP) core, the absorbance of the porphyrin Soret band is substantially reduced in the presence of [60]fullerene, thus providing evidence for close vicinity of the fullerene guest to the central core. In solution, the cyclotriveratrylene (CTV) unit alone is a poor receptor for fullerene, but its functionalization with polybenzyl ether dendrons affords an internal cavity with a more appropriate shape and dimension, thus allowing complexation. Indeed, the Ka values (order of magnitude 101–102 L mol−1) increase significantly with the generation number of the surrounding dendritic substituents.

Functionalization of [60]fullerene with new light-collecting oligophenylenevinylene-terminated dendritic wedges

Abstract New oligophenylenevinylene-terminated phenylenevinylene dendrons have been prepared and attached to C 60 by a 1,3-dipolar cycloaddition of the azomethine ylides generated in situ from the dendritic aldehydes and N -methylglycine. Preliminary photophysical investigations of the resulting fullerodendrimers have revealed interesting light-harvesting properties.

Synthesis of a C60-oligophenylenevinylene hybrid and its incorporation in a photovoltaic device

A fulleropyrrolidine derivative bearing an oligophenylenevinylene substituent has been prepared by 1,3-dipolar cycloaddition of an azomethine ylide to C60 and incorporated in a photovoltaic device.

Columnar order in thermotropic mesophases of oligophenylenevinylene derivatives

Abstract Oligophenylenevinylene derivatives substituted with long alkyl chains on one end and a carboxylic acid function on the other end have been prepared and the dimeric polycatenar calamitic supramolecules resulting from hydrogen bonding of their acid functions show columnar liquid crystalline phases.

Copper(I) complexes of 1,10-phenanthroline–oligophenylenevinylene conjugates

Copper(I) complexes obtained from 2,9-diphenyl-1,10-phenanthroline derivatives substituted with an oligophenylenevinylene (OPV) unit have been prepared. Very strong intramolecular quenching of the lowest OPV excited state by the copper(I) complex has been evidenced in these multicomponent systems. The mechanism of the photoinduced process depends on the length of the conjugated OPV backbone. Upon irradiation of the OPV unit, quantitative sensitization of the Cu(I) complex has been evidenced for the system substituted with trimeric OPV units, but not for those with tetrameric OPV units. Therefore, energy transfer is the sole quenching mechanism for the former complex, whereas electron transfer might play a role in the latter case. This different behaviour is ascribed to the slightly increased electron-accepting character of the OPV tetrameric unit when compared to the corresponding trimer. As far as excited state deactivation in the copper(I) complex is concerned, the hybrid compounds exhibit the characteristic luminescence band attributable to the deactivation of low-lying metal-to-ligand charge transfer (MLCT) excited state(s). As shown by the comparison with a model copper(I) complex, the OPV units have no influence on the MLCT excited state(s) deactivation at room temperature in fluid solutions. In contrast, they are capable of acting as “hooks” when the measurements are performed at low temperature in a rigid matrix, thus reducing the excited state distortion of the copper(I) complex. As a result, at 77 K the MLCT emission spectral shapes and band maxima of the hybrid compounds are no longer identical to those of the corresponding model complex.

Controlling the energy-transfer direction: an oligophenylenevinylene– phenanthroline dyad acting as a proton triggered molecular switch

In a two-component system combining an oligophenylenevinylene (OPV) group with a protonable phenanthroline unit, the direction of intercomponent photoinduced energy transfer can be tuned by proton input, thus allowing on/off switching of the luminescence of the OPV moiety.

Liquid-crystalline fullerene–oligophenylenevinylene conjugates

Functionalization of C60-oligophenylenevinylene derivatives with a cyanobiphenyl-terminated dendromesogen leads to new donor-acceptor systems with liquid-crystalline properties.