Georges Hadziioannou

Fullerene derivatives in which an oligophenylenevinylene (OPV) group is attached to C60 through a pyrrolidine ring have been prepared by 1,3-dipolar cycloaddition of the azomethine ylides generated in situ from the corresponding aldehydes and sarcosine. Electrochemical and photophysical studies have revealed that ground-state electronic interactions between the covalently bonded OPV moiety and the fullerene sphere are small. The photophysical investigations have also shown that both in dichloromethane and benzonitrile solution an efficient singlet−singlet OPV → C60 photoinduced energy-transfer process takes place, and occurrence of electron transfer, if any, is by far negligible relative to energy transfer. The C60−OPV derivatives have been incorporated in photovoltaic devices, and a photocurrent could be observed showing that photoinduced electron transfer does take place under these conditions. However, the efficiency of the devices is limited by the fact that photoinduced electron transfer from the OPV moiety to the C60 sphere must compete with an efficient energy transfer. The latter process, as studied in solution, leads to the population of the fullerene lowest singlet excited state, found to lie slightly lower in energy than the charge-separated state expected to yield electron/hole pairs. Thus, only a small part of the absorbed light is able to contribute effectively to the photocurrent.

We performed a series of molecular dynamics simulations investigating the static and dynamic properties of polymer melts confined between planar solid surfaces. The solid–melt interface was found to be very narrow (approximately two segment diameters) and independent of chain length. Inside the interface the segment density profile was oscillatory, the bond orientation altered between directions parallel and normal to the solid surface, and the chain ends accumulated very close to the wall (in the absence of strong wall–segment attraction). The oscillations of the segment density profile were weaker and were dampened faster than those of a simple fluid density profile next to the same solid surface. This reflected the reduced ability of sequences of connected segments (chains) to layer themselves against a solid surface because of restrictions on their configurations imposed by the chain connectivity requirement. This effect made the solid–melt interface even narrower than that of a simple fluid. Only the chain portions lying inside the interface had their shape affected by the wall. Chain statistical segments inside the interface assumed orientations parallel to the wall. In the absence of wall–segment attraction, the size of the statistical segments inside the interface was unaffected. This situation resulted in an apparent decrease of the radius of gyration normal to the wall an apparent increase of the radius of gyration parallel to the wall and spatial independence of the total radius of gyration. The wall effect was gradually diminished and chains assumed their bulk dimensions when their center-of-mass was so far from the solid surface that no portions of the chain could reach the interface (i.e., at a distance comparable to the bulk radius of gyration). The microscopic dynamics of chain portions inside the interface were strongly anisotropic. The mobility increased in the direction parallel to the wall and decreased normal to the wall. This fact was caused by the angular asymmetry of the segment–segment collisions inside the interface, i.e., by the same mechanism that induces the segment layering. The total mobility inside the neutral wall–melt interface was identical with that in the bulk reflecting the fact that the average segment density inside the interface had essentially the bulk value. The presence of strong wall–segment attraction increased the average interfacial density above the bulk value and lowered the mobility of the interfacial chain portions in all directions. The mean-square displacement of the chain center-of-mass during a certain time interval was affected by the solid only if the chain had a portion of itself inside the interface for a fraction of this time interval. The longest relaxation time of the chains, a property that cannnot be localized properly on a length scale smaller than the interfacial width, exhibited a weak and strongly diminishing with chain length spatial dependence.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTForces between surfaces of block copolymers adsorbed on micaGeorges. Hadziioannou, Sanjay. Patel, Steve. Granick, and Matthew. TirrellCite this: J. Am. Chem. Soc. 1986, 108, 11, 2869–2876Publication Date (Print):May 1, 1986Publication History Published online1 May 2002Published inissue 1 May 1986https://pubs.acs.org/doi/10.1021/ja00271a014https://doi.org/10.1021/ja00271a014research-articleACS PublicationsRequest reuse permissionsArticle Views783Altmetric-Citations301LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

A donor−acceptor, rod−coil diblock copolymer has been synthesized with the objective of enhancing the photovoltaic efficiency of the PPV−C60 (PPV = poly(p-phenylenevinylene)) system by the incorporation of both components in a molecular architecture that is self-structuring through microphase separation. Diblock copolymers were obtained by using an end-functionalized rigid-rod block of poly(2,5-dioctyloxy-1,4-phenylenevinylene) as a macroinitiator for the nitroxide-mediated controlled radical polymerization of a flexible poly(styrene-stat-chloromethylstyrene) block. The latter block was subsequently functionalized with C60 through atom-transfer radical addition. In a spin-cast film of the final diblock copolymer, the luminescence from PPV is strongly quenched, indicating efficient electron transfer to C60. Under suitable conditions, solution-cast films of these diblock copolymers exhibit micrometer-scale, honeycomb-like patterns of holes.