Organic semiconductors are usually polycyclic aromatic hydrocarbons and their analogs containing heteroatom substitution. Bioinspired materials chemistry of organic electronics promises new charge transport mechanism and specific molecular recognition with biomolecules. We discover organic semiconductors from deoxyribonucleic acid topoisomerase inhibitors, featuring conjugated backbone decorated with hydrogen-bonding moieties distinct from common organic semiconductors. Using ellipticine as a model compound, we find that hydrogen bonds not only guide polymorph assembly, but are also critical to forming efficient charge transport pathways along π−conjugated planes when at a low dihedral angle by shortening the end-to-end distance of adjacent π planes. In the π−π stacking and hydrogen-bonding directions, the intrinsic, short-range hole mobilities reach as high as 6.5 cm2V−1s−1and 4.2 cm2V−1s−1measured by microwave conductivity, and the long-range apparent hole mobilities are up to 1.3 × 10–3cm2V−1s−1and 0.4 × 10–3cm2V−1s−1measured in field-effect transistors. We further demonstrate printed transistor devices and chemical sensors as potential applications.
Theobromine and direct arylation: a sustainable and scalable solution to minimize aggregation caused quenching
A green and scalable method to synthesize organic luminophores with minimal aggregation caused quenching (ACQ) is reported where direct arylation is used to attach alkylated theobromine moieties onto luminophores. The resulting compounds demonstrated high photoluminescence quantum yields (PLQYs) in solution and as aggregates. The minimized ACQ can be ascribed to the large dihedral angles that theobromine moieties introduce into these molecules, preventing π–π interactions between the luminophores. Furthermore, the large dihedral angles promote the formation of hybridized local and charge-transfer states in these molecules. Finally, amplified spontaneous emission measurements were performed to explore their potential in lasers.
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- NSF-PAR ID:
- 10170970
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 21
- Issue:
- 24
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 6600 to 6605
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Thermal Transport in Poly(p-phenylene): Anomalous Dimensionality Dependence and Role of π–π StackingFor heat conduction along polymer chains, a decrease in the axial thermal conductivity often occurs when the polymer structure changes from one-dimensional (1D) to three-dimensional (3D). For example, a single extended aliphatic chain (e.g., polyethylene or poly(dimethylsiloxane)) usually has a higher axial thermal conductivity than its double-chain or crystal counterparts because coupling between chains induces strong interchain anharmonic scatterings. Intuitively, for chains with an aromatic backbone, the even stronger π–π stacking, once formed between chains, should enhance thermal transport across chains and suppress the thermal conductivity along the chains. However, we show that this trend is the opposite in poly(p-phenylene) (PPP), a typical chain with an aromatic backbone. Using molecular dynamics simulations, we found that the axial thermal conductivity of PPP chains shows an anomalous dimensionality dependence where the thermal conductivity of double-chain and 3D crystal structures is higher than that of a 1D single chain. We analyzed the probability distribution of dihedral angles and found that π–π stacking between phenyl rings restricts the free rotation of phenyl rings and forms a long-range order along the chain, thus enhancing thermal transport along the chain direction. Though possessing a stronger bonding strength and stabilizing the multiple-chain structure, π–π stacking does not lead to a higher interchain thermal conductance between phenyl rings compared with that between aliphatic chains. Our simulation results on the effects of π–π stacking provide insights to engineer thermal transport in polymers at the molecular level.more » « less
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Electron transfer (ET) in donor–bridge–acceptor (DBA) compounds depends strongly on the structural and electronic properties of the bridge. Among the bridges that support donor–acceptor conjugation, alkyne bridges have attractive and unique properties: they are compact, possess linear structure permitting access to high symmetry DBA molecules, and allow torsional motion of D and A, especially for longer bridges. We report conformation dependent electron transfer dynamics in a set of novel DBA compounds featuring butadiyne (C4) bridge, N -isopropyl-1,8-napthalimide (NAP) acceptors, and donors that span a range of reduction potentials (trimethyl silane (Si-C4-NAP), phenyl (Ph-C4-NAP), and dimethyl aniline (D-C4-NAP)). Transient mid-IR absorption spectra of the CC bridge stretching modes, transient spectra in the visible range, and TD-DFT calculations were used to decipher the ET mechanisms. We found that the electronic excited state energies and, especially, the transition dipoles (S 0 → S n ) depend strongly on the dihedral angle ( θ ) between D and A and the frontier orbital symmetry, offering an opportunity to photo-select particular excited states with specific ranges of dihedral angles by exciting at chosen wavelengths. For example, excitation of D-C4-NAP at 400 nm predominantly prepares an S 1 excited state in the planar conformations ( θ ∼ 0) but selects an S 2 state with θ ∼ 90°, indicating the dominant role of the molecular symmetry in the photophysics. Moreover, the symmetry of the frontier orbitals of such DBA compounds not only defines the photo-selection outcome, but also determines the rate of the S 2 → S 1 charge separation reaction. Unprecedented variation of the S 2 –S 1 electronic coupling with θ by over four orders of magnitude results in slow ET at θ ca. 0° and 90° but extremely fast ET at θ of 20–60°. The unique features of high-symmetry alkyne bridged DBA structures enable frequency dependent ET rate selection and make this family of compounds promising targets for the vibrational excitation control of ET kinetics.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9GC03391B
