Hierarchical Self-Assembly of Semiconductor Functionalized Peptide α-Helices and Optoelectronic Properties

Abstract

To determine the ability of semiconductors templated by α-helical polypeptides to form higher order structures and the charge carrier properties of the supramolecular assemblies, L-lysine was functionalized with a sexithiophene organic semiconductor unit via iterative Suzuki coupling and the click reaction. The resultant amino acid was incorporated into a homopolypeptide by ring-opening polymerization of an amino acid N-carboxyanhydride. Spectroscopic investigation of the polypeptide revealed that it adopted an α-helical secondary structure in organic solvents that underwent hierarchical self-assembly to form higher order structures. In cyclohexane, the polymer formed organogels at 2% (w/v). Organic photovoltaic and organic field effect transistor devices were fabricated by deposition of the PCBM blended active layer from chlorobenzene at concentrations shown to induce self-assembly of the polymer. Compared with control compounds, these devices showed significantly greater hole mobility, short circuit current, and efficiency. This work establishes the potential of this previously unreported bioinspired motif to increase device performance.

Self‐Assembled Gelators for Organic Electronics

“…Conducting gel-liquid crystal composites (26,27) are shown to have insulator character (26: s rt < 3 10 À10 S cm À1 ), however, the conductivity significantly increased after exposure to I 2 for 2 minutes (s rt = 2 10 À7 S cm À1 ). [68] Interestingly, the conductivity value additionally improved to 1 10 À5 S cm À1 after doping with tetracyanoquinodimethane (TCNQ).…”

“…This enhancement could be attributed to the significantly high J sc value obtained through the helical arrangement of chromophores, which resulted in favorable charge transport domains. [26] A self-sorting approach to organogels of D-A systems is useful to the design of heterojunction organic semiconductors. For example, the two-component gel of thiophene 6 and perylenebisimide 7 (Scheme 2), composed of entangled fibrous aggregates is useful for the fabrication of photovoltaic devices.…”

“…[38] The OFET device of the ahelical polypeptide functionalized thiophene gelator 5 and PCBM (1:2; Scheme 1) exhibited an enhanced hole mobility of 1.9 10 À7 cm 2 V À1 s À1 when compared to that of the corresponding nongelaters. [26] Lutsyk et al have carried out a comparative study of OFETs fabricated from 1 by spin-and spray-coating techniques using fresh and aged solutions. [39] In all the cases, irrespective of the deposition technique, charge-carrier mobilities in samples fabricated using fresh solutions exhibited values on the order of 10 À4 cm 2 V À1 s À1 .…”

Useful synthetic method of polypeptides with well‐defined structure by polymerization of activated urethane derivatives of α‐amino acids

“…Therefore, its polymerization system could allow to construct various kinds of polypeptides-based functional materials, including drug delivery, [6][7][8] tissue engineering, 9 surface modification, [10][11][12] and organic electronics. 13,14 Although living polymerization of NCA affords an important advantage in synthesis of well-defined polypeptide, the susceptive nature of NCA for moisture and heating is major drawbacks for its production toward practical use. Thus, development of alternative procedure for polypeptide synthesis is a great challenge in this research area.…”

Peptide π-Electron Conjugates: Organic Electronics for Biology?

“…In addition to targeting beta-sheet motifs, Holmes and co-workers 53 reported sexithiophenes attached to alpha-helical poly-L-lysine which forms organogels at 2 wt% in cyclohexane. Organic photovoltaic and field-effect transistors (FET) were fabricated out of these materials, wherein the semiconductor peptide was blended with phenyl-C60-butyric acid methyl ester (PCBM) to form a donoracceptor system that was used for the photovoltaic device and as an active semiconducting unit for the FET.…”