Organic electronics offer a route toward electronically active biocompatible soft materials capable of interfacing with biological and living systems. One class of promising organic electronic materials are π-conjugated peptides, synthetic molecules comprising an aromatic core flanked by oligopeptides, that can be engineered to self-assemble into elongated nanostructures with emergent optoelectronic functionality. In this work, we combine molecular dynamics simulations with electronic structure and charge transport calculations to computationally screen for high charge mobility π-conjugated peptides and to elucidate design rules linking aromatic core character with charge mobility. We consider within our screening library variations in the aromatic core chemistry and length of the alkyl chains connecting the oligopeptide wings to the core. After completing our computational screen we identify particular π-conjugated peptides capable of producing self-assembled biocompatible nanoaggregates with predicted hole mobilities of 0.224 cm^2/(Vs) and electron mobilities of 0.143 cm^2/(Vs), and uncover design rules that enhance understanding of the molecular determinants of charge mobility within π-conjugated peptide assemblies.
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Hybrid computational–experimental data-driven design of self-assembling π-conjugated peptides
Biocompatible molecules with electronic functionality provide a promising substrate for biocompatible electronic devices and electronic interfacing with biological systems. Synthetic oligopeptides composed of an aromatic π-core flanked by oligopeptide wings are a class of molecules that can self-assemble in aqueous environments into supramolecular nanoaggregates with emergent optical and electronic activity. We present an integrated computational–experimental pipeline employing all-atom molecular dynamics simulations and experimental UV-visible spectroscopy within an active learning workflow using deep representational learning and multi-objective and multi-fidelity Bayesian optimization to design π-conjugated peptides programmed to self-assemble into elongated pseudo-1D nanoaggregates with a high degree of H-type co-facial stacking of the π-cores. We consider as our design space the 694 982 unique π-conjugated peptides comprising a quaterthiophene π-core flanked by symmetric oligopeptide wings up to five amino acids in length. After sampling only 1181 molecules (∼0.17% of the design space) by computation and 28 (∼0.004%) by experiment, we identify and experimentally validate a diversity of previously unknown high-performing molecules and extract interpretable design rules linking peptide sequence to emergent supramolecular structure and properties.
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- Award ID(s):
- 1841807
- NSF-PAR ID:
- 10332535
- Date Published:
- Journal Name:
- Digital Discovery
- ISSN:
- 2635-098X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Peptides naturally have stimuli‐adaptive structural conformations that are advantageous for endowing synthetic materials with dynamic functionalities. Here, we report a carbodiimide‐based approach, combined with electrostatic modulation, to instruct π‐conjugated peptides to self‐assemble and be responsive to thermal disassembly cues upon consumption of the assembly trigger. Quaterthiophene‐functionalized peptides are utilized as a model system herein to study the formation of nanostructures at non‐equilibrium states. Peptides were designed to have aspartic acid at the termini to allow intramolecular anhydride formation upon adding carbodiimide, which consequentially reduces the electrostatic repulsion and facilitates assembly. We show that the carbodiimide‐fueled assembly and subsequent thermally assisted disassembly can be modulated by the net charge of the peptidic monomers, suggesting an assembly mechanism that can be encoded by sequence design. This carbodiimide‐based approach for the assembly of designer π‐conjugated systems offers a unique opportunity to develop bioelectronic supramolecular materials with controllable formation of dynamic and stimuli‐responsive structures.
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Conjugated copolymers containing electron donor and acceptor units in their main chain have emerged as promising materials for organic electronic devices due to their tunable optoelectronic properties. Herein, we describe the use of direct arylation polymerization to create a series of fully π-conjugated copolymers containing the highly tailorable purine scaffold as a key design element. To create efficient coupling sites, dihalopurines are flanked by alkylthiophenes to create a monomer that is readily copolymerized with a variety of conjugated comonomers, ranging from electron-donating 3,4-dihydro-2 H -thieno[3,4- b ][1,4]dioxepine to electron-accepting 4,7-bis(5-bromo-3-hexylthiophen-2-yl)benzo[ c ][1,2,5]thiadiazole. The comonomer choice and electronic nature of the purine scaffold allow the photophysical properties of the purine-containing copolymers to be widely varied, with optical bandgaps ranging from 1.96–2.46 eV, and photoluminescent quantum yields as high as ϕ = 0.61. Frontier orbital energy levels determined for the various copolymers using density functional theory tight binding calculations track with experimental results, and the geometric structures of the alkylthiophene-flanked purine monomer and its copolymer are found to be nearly planar. The utility of direct arylation polymerization and intrinsic tailorability of the purine scaffold highlight the potential of these fully conjugated polymers to establish structure–property relationships based on connectivity pattern and comonomer type, which may broadly inform efforts to advance purine-containing conjugated copolymers for various applications.more » « less
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Accelerating the development of π-conjugated molecules for applications such as energy generation and storage, catalysis, sensing, pharmaceuticals, and (semi)conducting technologies requires rapid and accurate evaluation of the electronic, redox, or optical properties. While high-throughput computational screening has proven to be a tremendous aid in this regard, machine learning (ML) and other data-driven methods can further enable orders of magnitude reduction in time while at the same time providing dramatic increases in the chemical space that is explored. However, the lack of benchmark datasets containing the electronic, redox, and optical properties that characterize the diverse, known chemical space of organic π-conjugated molecules limits ML model development. Here, we present a curated dataset containing 25k molecules with density functional theory (DFT) and time-dependent DFT (TDDFT) evaluated properties that include frontier molecular orbitals, ionization energies, relaxation energies, and low-lying optical excitation energies. Using the dataset, we train a hierarchy of ML models, ranging from classical models such as ridge regression to sophisticated graph neural networks, with molecular SMILES representation as input. We observe that graph neural networks augmented with contextual information allow for significantly better predictions across a wide array of properties. Our best-performing models also provide an uncertainty quantification for the predictions. To democratize access to the data and trained models, an interactive web platform has been developed and deployed.more » « less
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Abstract Like other discotic molecules, self‐assembled supramolecular structures of perylene bisimides (PBIs) are commonly limited to columnar or lamellar structures due to their distinct π‐conjugated scaffolds and unique rectangular shape of perylene cores. The discovery of PBIs with supramolecular structures beyond layers and columns may expand the scope of PBI‐based materials. A series of unconventional spherical packing phases in PBIs, including A15 phase, σ phase, dodecagonal quasicrystalline (DQC) phase, and body‐centered cubic (BCC) phase, is reported. A strategy involving functionalization of perylene core with several polyhedral oligomeric silsesquioxane (POSS) cages achieved spherical assemblies of PBIs, instead of columnar assemblies, due to the significantly increased steric hindrance at the periphery. This strategy may also be employed for the discovery of unconventional spherical assemblies in other related discotic molecules by the introduction of similar bulky functional groups at their periphery. An unusual inverse phase transition sequence from a BCC phase to a σ phase was observed by increasing annealing temperature.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1dd00047k
