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. 2019 May 29:30:10-16.
doi: 10.1016/j.mattod.2019.04.002. Epub 2019 Apr 22.

Stable and optoelectronic dipeptide assemblies for power harvesting

Affiliations

Stable and optoelectronic dipeptide assemblies for power harvesting

Kai Tao et al. Mater Today (Kidlington). .

Abstract

Low biocompatibility or engineerability of conventional inorganic materials limits their extensive application for power harvesting in biological systems or at bio-machine interfaces. In contrast, intrinsically biocompatible peptide self-assemblies have shown promising potential as a new type of ideal components for eco-friendly optoelectronic energy-harvesting devices. However, the structural instability, weak mechanical strength, and inefficient optical or electrical properties severely impede their extensive application. Here, we demonstrate tryptophan-based aromatic dipeptide supramolecular structures to be direct wide-gap semiconductors. The molecular packings can be effectively modulated by changing the peptide sequence. The extensive and directional hydrogen bonding and aromatic interactions endow the structures with unique rigidity and thermal stability, as well as a wide-spectrum photoluminescence covering nearly the entire visible region, optical waveguiding, temperature/irradiation-dependent conductivity, and the ability to sustain quite high external electric fields. Furthermore, the assemblies display high piezoelectric properties, with a measured open-circuit voltage of up to 1.4 V. Our work provides insights into using aromatic short peptide self-assemblies for the fabrication of biocompatible, miniaturized electronics for power generation with tailored semiconducting optoelectronic properties and improved structural stability.

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Conflict of interest statement

Competing interests The authors declare no competing interests.

Figures

Figure 1
Figure 1. Crystal structures of the aromatic dipeptide packings.
(a) Molecular structures and the corresponding crystal morphologies of cyclo-FW (left) and cyclo-WW (right). (b) Crystallographic structure of cyclo-FW. The hydrogen bonding between backbone diketopiperazine rings, the water bridge, and the hydrophobic zone composed of side-chain aromatic moieties are magnified in the right panels and marked as “1”, “2”, and “3”, respectively. (c) Crystallographic structure of cyclo-WW. The hydrogen bonding between backbone diketopiperazines, the hydrophobic zone composed of side-chain aromatic moieties, and the water bridged hydrophilic channels are magnified in the right panels and marked as “1”, “2”, and “3”, respectively. (d) Monomeric crystal structures of W-containing dipeptides: cyclo-FW, linear-GW, cyclo-WW, and linear-W(d)W. The monomers incorporate a different number of water molecules, ranging from one to four, respectively. Note that in (b–d) the hydrogen bonds are labeled between the donor and acceptor atoms.
Figure 2
Figure 2. Mechanical properties of the aromatic cyclo-dipeptide crystals.
(a) TGA curves of the dipeptide crystals. Note that at 170 °C (marked by arrow), linear-dipeptides transform into the cyclic counterparts due to intramolecular concentration following the removal of a water molecule. (b–d) Statistical distributions of (b) Young’s modulus, (c) Point stiffness, and (d) Shear modulus of the cyclo-FW crystals.
Figure 3
Figure 3. Photoluminescent properties of the cyclo-dipeptide crystals.
(a) Calculated bandgaps of cyclo-FW crystals. (b) Close-ups of the electronic band structures of cyclo-FW crystals near their main band gaps. Direct electron transitions occur at the G point. (c) Fluorescent emission spectra under different excitation wavelengths: i, cyclo-FW; ii, cyclo-WW; iii, cyclo-W(d)W. (d) Fluorescent lifetime and (e) fluorescent emission photostability of the crystals shown in (c). (f) Optical waveguiding of cyclo-FW crystals. Bright-field optical image (upper panel) and photoluminescent images (lower panels) of a single peptide platelet showing the waveguide upon laser excitation at different positions. The blue circles indicate the laser excitation; the red circles at the two edges show the outcoupled light. The width of the circles indicates the light intensity.
Figure 4
Figure 4. Electrical properties of the cyclo-FW crystals.
(a) Voltage–current curves of cyclo-FW crystals at different temperatures. (b) Statistical distribution of cyclo-FW crystals resistance at the temperatures shown in (a). (c) Conductivity characterization of cyclo-FW crystals in the dark or under UV light irradiation (256 nm). (d) Conductivity characterization of cyclo-FW crystals in different external electric fields. (e) Photograph of the generator utilized as a direct power source using cyclo-FW crystals as active components. (f) Schematic configuration of the peptide-based generator shown in (e). (g) Open-circuit voltage and (h) short-circuit current from the generator shown in (e). (i) Linear dependence of the open-circuit voltage on the applied forces. The insets in (a) and (c) show photographic pictures of the experimental measuring setups for (a, b) and (c, d), respectively.

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