Star-shaped π-conjugated oligomers and their applications in organic electronics and photonics

Abstract

Strategies for the design and construction of non-linear, 2D and 3D conjugated macromolecules are presented in this critical review. The materials, termed here as star-shaped structures, feature a core unit which may or may not provide conjugated links between arms that radiate like spokes from a central axle. The arms of the macromolecules consist of linear oligomers or irregular conjugated chains lacking a formal repeat unit. The cores range from simple atoms to single or fused aromatic units and can provide a high level of symmetry to the overall structure. The physical properties of the star-shaped materials can be markedly different to their simple, linear conjugated analogues. These differences are highlighted and we report on anomalies in absorption/emission characteristics, electronic energy levels, thermal properties and morphology of thin films. We provide numerous examples for the application of star-shaped conjugated macromolecules in organic semiconductor devices; a comparison of their device performance with those comprising analogous linear systems provides clear evidence that the star-shaped compounds are an important class of material in organic electronics. Moreover, these structures are monodisperse, well-defined, discrete molecules with 100% synthetic reproducibility, and possess high purity and excellent solubility in common organic solvents. They feature many of the attributes of plastic materials (good film-forming properties, thermal stability, flexibility) and are therefore extremely attractive alternatives to conjugated polymers (210 references).

Location, Location, Location ‐ Strategic Positioning of 2,1,3‐Benzothiadiazole Units within Trigonal Quaterfluorene‐Truxene Star‐Shaped Structures

“…The development of these compounds represents the introduction of an additional degree of freedom into the design of star-shaped molecules. [ 9 ] The BT unit is a fascinating fused heterocycle that was fi rst introduced into fl uorene-based copolymer light emitting diode material systems by E. P. Woo and colleagues at the Dow Chemical Company. [ 10 ] It has been used since to great effect in the design of new organic semiconductors for light emission and energy harvesting applications.…”

Supramolecular polymerization of hydrogen-bonded rosettes with anthracene chromophores: regioisomeric effect on nanostructures

“…19,20 In addition to disc-shaped molecules, multi-arm π-conjugated molecules where three or more π-conjugated units are linked to a central core unit are useful building blocks for constructing one-dimensional supramolecular nanomaterials. 21,22 Although this molecular design has merits, such as its applicability to known functional π-conjugated molecules, it is challenging to introduce many arms onto a central unit because the synthesis and purification of the desired multi-arm products from incomplete side products are demanding. 23 An alternative approach towards such multi-arm π-conjugated structures would be supramolecular macrocyclization (supermacrocyclization) of π-conjugated building blocks using directional noncovalent interactions such as hydrogen-bonding.…”

Solvent effects on the properties of hyperbranched polythiophenes

“…24 4 -Conjugated dendrimers are considered attractive candidates for organic-electronic applications due to their solution processability, redox properties, band gap ( g ) and isotropic charge-transport ability. 25 In the particular, all-Th dendrons and dendrimers, hereafter denoted nT (where n is the number of Th rings), behave as p-type semiconductors, being proposed as components of photovoltaic devices and organic solar cells. 24,26,27 Therefore, understanding of the electronic properties of nT is a key stage not only in the ongoing evolution of these systems for their promising applications but also in the development of new alternatives to conventional oligothiophenes and polythiophenes in the organic semiconductor field.…”