Richard Charvet

Challenges and breakthroughs in recent research on self-assembly

Abstract The controlled fabrication of nanometer-scale objects is without doubt one of the central issues in current science and technology. However, existing fabrication techniques suffer from several disadvantages including size-restrictions and a general paucity of applicable materials. Because of this, the development of alternative approaches based on supramolecular self-assembly processes is anticipated as a breakthrough methodology. This review article aims to comprehensively summarize the salient aspects of self-assembly through the introduction of the recent challenges and breakthroughs in three categories: (i) types of self-assembly in bulk media; (ii) types of components for self-assembly in bulk media; and (iii) self-assembly at interfaces.

Chiroselective Assembly of a Chiral Porphyrin−Fullerene Dyad: Photoconductive Nanofiber with a Top-Class Ambipolar Charge-Carrier Mobility

Upon slow admission of MeOH, the enantiomerically pure form of chiral amphiphilic porphyrin-fullerene dyad 1 in CH(2)Cl(2) self-assembles at 25 degrees C into nanofibers with a built-in donor/acceptor heterojunction, while its racemic form, under identical conditions, self-assembles into submicrometer-sized spheres with a donor/acceptor arrangement essentially different from that in the nanofiber assembly. Although a cast film of the latter hardly shows a photoconducting profile on micrometer-gap electrodes, the former sample clearly displays photoconduction with an ambipolar charge-transporting character. The electron and hole mobilities under zero electric field, as estimated from time-of-flight profiles, are 0.14 and 0.10 cm(2) V(-1) s(-1), respectively, which are comparable to or even better than those reported for top-class organic materials with a donor/acceptor heterojunction.

Segregated and alternately stacked donor/acceptor nanodomains in tubular morphology tailored with zinc porphyrin-C60 amphiphilic dyads: clear geometrical effects on photoconduction.

Amphiphilic zinc porphyrin (P(Zn); electron donor, D)-fullerene (C(60); electron acceptor, A) dyads 2 and 3, bearing an identical hydrophilic wedge with triethylene glycol chains but different linkers between the P(Zn) and C(60) units, self-assemble into nanotubes with essentially different dimensional and geometrical features from one another. The nanotube from dyad 2 with an ester linker consists of a bilayer wall formed with coaxially segregated D and A nanodomains along the tube axis (coaxial D-A heterojunction), thereby displaying explicit photoconductivity with ambipolar carrier transport properties. In contrast, the nanotube from dyad 3 with a rigid arylacetylene linker consists of a monolayer wall with an alternate geometry of D/A stacking, resulting in poor photoconducting outputs. Such a geometrical difference also significantly affects the photovoltaic properties.

Block-copolymer-nanowires with nanosized domain segregation and high charge mobilities as stacked p/n heterojunction arrays for repeatable photocurrent switching.

Development of materials for efficient photoenergy conversion is a subject of critical importance in current science and technology. Efficient performance requires well-controlled segregation of electron donor and acceptor moieties, which we have achieved using block copolymers of tetraphenylporphinatozinc(II) (donor) and C(60) fullerene (acceptor) using living ring-opening metathesis polymerization (ROMP). The resulting amphiphilic ROMP block copolymers undergo self-assembly into nanostructured phase-segregated 1-dimensional nanowires with an approximately 5.5 nm periodicity zebra-stripe-like morphology simply by drop-casting solutions of the polymers onto a substrate such as mica or highly oriented pyrolytic graphite (HOPG). Thin films of the self-assembled nanophase-segregated copolymers exhibit high charge carrier mobilities (approximately 0.26 cm(2) V(-1) s(-1)) and electrical conductivities (up to 6.4 x 10(-4) cm(2) V(-1) s(-1)) as well as highly repeatable photocurrent switching with rapid ON/OFF responses upon white light irradiation.

Self-assembly of a π-electronic amphiphile consisting of a zinc porphyrin–fullerene dyad: formation of micro-vesicles with a high stability

An amphiphilic zinc porphyrin-fullerene dyad appended with triethyleneglycol chains in aqueous media forms uniformly-sized multilamellar vesicles with a mean diameter of 100 nm that are thermally stable and robust against membrane lysis with surfactants.

Polyethylenes bearing a terminal porphyrin group

An α-[Cu(II)-porphyrin]-polyethylene was synthesized for the first time using copper catalyzed 1,3-dipolar azide-alkyne Huisgen cycloaddition yielding highly colored moiety-substituted polyethylene.

RECENT DEVELOPMENTS ON PORPHYRIN ASSEMBLIES

The porphyrin macrocycle is one of the most frequently investigated functional molecular entities and can be incorporated into advanced functional nanomaterials upon formation of organized nanostructures. Thus, study of the science and technology of porphyrin assemblies has attracted many organic, biological and supramolecular chemists. A wide variety of nanostructures can be obtained by supramolecular self-assembly because the porphyrin moiety is amenable to chemical modifications through thoughtful synthetic design and moderate preparative effort. Some recent developments in porphyrin assembly, obtained through various supramolecular approaches, are briefly summarized. Topics described in this review are classified into four categories: (i) non-specific assemblies; (ii) specific assemblies; (iii) assemblies in organized films; (iv) molecular-level arrangement. We present examples in the order of structural precision of assemblies.