The development of nanotechnology using organic materials is one of the most intellectually and commercially exciting stories of our times. Advances in synthetic chemistry and in methods for the investigation and manipulation of individual molecules and small ensembles of molecules have produced major advances in the field of organic nanomaterials. The new insights into the optical and electronic properties of molecules obtained by means of single-molecule spectroscopy and scanning probe microscopy have spurred chemists to conceive and make novel molecular and supramolecular designs. Methods have also been sought to exploit the properties of these materials in optoelectronic devices, and prototypes and models for new nanoscale devices have been demonstrated. This Review aims to show how the interaction between synthetic chemistry and spectroscopy has driven the field of organic nanomaterials forward towards the ultimate goal of new technology.

The Chemistry of Organic Nanomaterials

This paper reviews the tools to manipulate and minimize the band gap of conjugated (co)polymers. The effects of minimization of the bond length alternation and of the incorporation of donor-π-acceptor units are discussed in particular. A systematic study of a series of alternating donor–acceptor oligomers has revealed the achievable limits and allowed for a prognosis of the performance of corresponding copolymers. The decisive influence of the LUMO eigenvectors of the acceptors on the band gap is highlighted. A new synthesis of benzo[1,2-c:4,5-c]bis[1,2,5]thiadiazole containing donor–acceptor monomers and their acid-catalyzed polymerization are described. Finally, band gap tuning by appropriate substitution, conformational adjustment and mesoscopic ordering is discussed.

Developments in the chemistry and band gap engineering of donor-acceptor substituted conjugated polymers

The photophysical, electrochemical, and optoelectronic properties of conjugated systems incorporating dibenzophosphole or phosphole moieties are described. Dibenzophosphole derivatives are not suitable materials for OLEDs due to their weak photoluminescence (PL) in the solid state and the instability of the devices. Variation of the substitution pattern of phospholes and chemical modification of their P atoms afford thermally stable derivatives, which are photo- and electroluminescent. Comparison of the optical properties of solution and thin film of thioxophospholes shows that these compounds do not form aggregates in the solid state. This property, which is also supported by an X-ray diffraction study of three novel derivatives, results in an enhancement of the fluorescence quantum yields in the solid state. In contrast, (phosphole)gold(I) complexes exhibit a broad emission in thin film, which is due to the formation of aggregates. Single- and multilayer OLEDs using these P derivatives as the emissive layer have been fabricated. The emission color of these devices and their performances vary with the nature of the P material. Interestingly, di(2-thienyl)thiooxophosphole is an efficient host for the red dopant DCJTB, and devices using the gold complexes have broad emission spectra.

Toward Functional π-Conjugated Organophosphorus Materials: Design of Phosphole-Based Oligomers for Electroluminescent Devices

Fur das Ermitteln von Struktur-Funktions-Beziehungen, deren Kenntnis zum Verstandnis der Eigenschaften hochmolekularer linear π-konjugierter Polymere beitragt, haben sich monodisperse Oligomere als auserst nutzlich erwiesen. Eine grose Vielfalt spektakularer molekularer Architekturen wurde entwickelt, wobei derzeit ein Hohepunkt mit der Herstellung von uber 10 nm langen molekularen Drahten wie 1 als potentiellen Bausteinen fur die molekulare Elektronik erreicht ist.

Lineare monodisperse π-konjugierte Oligomere: mehr als nur Modellverbindungen für Polymere

Die Chemie organischer Nanomaterialien

Cyclodehydrogenation of soluble polyperylenes gives polymers containing predominantly quaterrylene units by spectral analysis. Evidence for larger rylene units is also seen. These polymers represent important intermediates toward a poly(peri-naphthalene) (PPN). Reactions on model compounds suggest that the insolubility of polymers with larger rylene units is predominantly due to the rigidity of the polymer backbone.

Cyclodehydrogenation of Poly(perylene) to Poly(quaterrylene): Toward Poly(peri-naphthalene)

Donor/acceptor‐substituted phenylenevinylenes

A carbon−carbon bond formation through cation−anion coupling allows the synthesis of poly(p-phenylenevinylene)s (PPV) 1 and 2a−f, which contain donor and acceptor groups in each vinylene unit. The crucial step in the double bond formation is the quantitative elimination of methanethiol at room temperature. In this work we describe the optimization of the molecular weight of polymers of structure types 1 and 2a−f with regard to (i) solubility of the monomers and polymers and (ii) the reactivity and side reactions of the monomers. The simultaneous donor and acceptor substitution on the central double bond in PPV-analogous structures raises the question of the additivity of dipoles in each repeat unit of a conjugated polymer chain from the viewpoint of potential use in electrooptical applications. The sequence of donor and acceptor groups along the π-conjugated chain can be controlled by the choice of suitable monomers and is crucial for the alignment of the dipole components. The aggregation of polymers 1 a...

Connective CC Double Bond Formation for the Synthesis of Donor- and Acceptor-Substituted Poly(p-phenylenevinylene)s

We have investigated the orientational behavior of a series of novel oligophenylenevinylenes which carry a sequence of hyperpolarizable and dipolar donor−acceptor (DA) pairs, designed to allow for a free rotation of the DA orientation in a plane perpendicular to the long molecular axis. The studies include both the measurement of effective dipole moments, which are relevant for the degree of polar ordering required for second-harmonic generation, and the assessment of the time scales involved in the orientational motion of the effective dipole moment. The comparison between calculated dipole moments and those measured for different oligomers in toluene solution and in a polystyrene matrix confirm that a DA-pair separation of ≈10 A along the oligomer leads to a high chromophore concentration in the sample, yet without the unfavorable effect of aggregation or antiparallel alignment of neighboring dipole pairs. Both the bulkiness of the oligomer molecules and the electrostatic coupling of adjacent dipoles gi...

Orientation and Dynamics of Chainlike Dipole Arrays: Donor-Acceptor-Substituted Oligophenylenevinylenes in a Polymer Matrix

Ortho-, meta- and para-xylenes 1, 13a, 13b and 13c, with donor and acceptor substituents at the α- and α′ positions, lead to a remarkable variety of intermediates and reaction products after deprotonation of the benzylic proton. Thus, the reaction of para-(cyanomethyl)dialkyl[(methylthio)phenylmethylene]ammonium tetrafluoroborates 13a and 13b with sodium hydride affords the para-quinodimethanes 14a and 14b. Poly(meta-phenylenevinylene) 14c can be obtained when starting from 13c. We report the synthesis of para-quinodimethanes 14a and 14b and poly(meta-phenylenevinylene) 14c and describe a successive approach towards meta-phenylenevinylenes of definite length 16b and 17b starting from 12d. Moreover, we compare the stability and reactivity of para-quinodimethane 14a and 14b with those of the ortho-quinodimethane 2 and we focus on the characterization of the resulting donor and acceptor substituted compounds.

Carsten Former

Papers

Cyclodehydrogenation of Poly(perylene) to Poly(quaterrylene): Toward Poly(peri-naphthalene)

Donor/acceptor‐substituted phenylenevinylenes

Connective CC Double Bond Formation for the Synthesis of Donor- and Acceptor-Substituted Poly(p-phenylenevinylene)s

Orientation and Dynamics of Chainlike Dipole Arrays: Donor-Acceptor-Substituted Oligophenylenevinylenes in a Polymer Matrix

From donor and acceptor substituted meta- and para-xylenes to para-Quinodimethanes and Poly(meta-phenylenevinylene)s†