Design strategies for organic semiconductors beyond the molecular formula

Abstract

Organic semiconducting materials based on polymers and molecular systems containing an electronically delocalized structure are the basis of emerging optoelectronic technologies such as plastic solar cells and flexible transistors. For isolated molecules, guidelines exist that rely on the molecular formula to tailor the frontier (highest occupied or lowest unoccupied) molecular orbital energy levels and optical absorption profiles. Much less control can be achieved over relevant properties, however, as one makes the transition to the ensemble behaviour characteristic of the solid state. Polymeric materials are also challenging owing to the statistical description of the average number of repeat units. Here we draw attention to the limitations of molecular formulae as predictive tools for achieving properties relevant to device performances. Illustrative examples highlight the relevance of organization across multiple length scales, and how device performances--although relevant for practical applications--poorly reflect the success of molecular design.

Controlling the crystalline three-dimensional order in bulk materials by single-wall carbon nanotubes

“…They are in the same way red shifted as seen for the absorption features-vide supra. For example, the corresponding maxima appear for SDBS/SWCNT at 958, 1,028, 1,125 and 1,250 nm, which are attributed to (6,5), (7,5), (7,6) and (8,7) SWCNTs. When comparing the fluorescence intensity of 1a/SWCNT with that of SDBS/SWCNT exhibiting both equal absorbances at the excitation wavelength, a significant quenching is noted.…”

“…The well-known correlation between order of materials across different length scales, on one hand, and efficiency of device performance, on the other hand, has fuelled the development of self-organizing small molecules at the nanoscale, the macroscale and so on [5][6][7] . Despite numerous efforts regarding the construction of wellordered architectures, the macroscopic control over the threedimensional (3D) order of bulk materials still remains a key challenge.…”

Pathway Diversity in the Self-Assembly of DNA-Derived Bioconjugates

“…[8][9][10][11][12] In addition, the proper choice of assembly protocols helps in tuning the properties of biomaterials 13 or improves the performance of organic semiconductors. 14 Thus, the chemical composition alone is often insufficient to achieve the best performance of complex supramolecular assemblies, among which DNA-based materials take a prominent role. 15 DNA-assembled objects are of interest in the design and development of drug carriers, nanomachines, and other types of sophisticated nanomaterials.…”

Harnessing self-assembly strategies for the rational design of conjugated polymer based materials

“…Advances in synthetic design mean that conjugated polymers are no longer restricted to the propagation of a single repeat unit and as demonstrated above, a variety of structural arrangements, such as block copolymer, dendrimers and star-burst polymers, are now readily accessible. 26 Similarly, structural modications of individual fragments of the polymer chain may provide a mechanism by which the self-assembly of multiple chains can be directed. This may be at a fundamental level, for example the strategic introduction of functional groups that promote weak physical interactions such as hydrogen bonding or van der Waals forces.…”

“…through the introduction of charged, hydrophilic, hydrophobic segments etc.). 26 In this Highlight, recent examples towards the development of integrated conjugated polymer systems, exhibiting controlled orientation and/or organisation of the polymer chains through virtue of self-assembly are described. We rst consider how the nature of the solvent can be exploited to either induce or inhibit interchain interactions in solution, thereby modulating the aggregation state of the polymer.…”