Condensed Derivatives of Thiadiazoloquinoxaline as Strong Acceptors

Three novel thiadiazoloquinoxaline (TQ) derivatives, <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, were synthesized by introducing two triisopropylsilylethynyl groups and alternating the aromatic ring units in the condensed moiety of TQ. The synthetic route is very efficient, providing high yields. Cyclic voltammetry suggests high electron affinity values of −3.82, −3.95, and −3.99 eV for <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, respectively. Single-crystal X-ray diffraction reveals that three molecules form corresponding dimers by intermolecular S–N interaction and have very similar two-dimensional π-stacking. The π-stacking distances between them are as close as 3.34–3.46 Å

Condensed Derivatives of Thiadiazoloquinoxaline as Strong Acceptors

Three novel thiadiazoloquinoxaline (TQ) derivatives, <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, were synthesized by introducing two triisopropylsilylethynyl groups and alternating the aromatic ring units in the condensed moiety of TQ. The synthetic route is very efficient, providing high yields. Cyclic voltammetry suggests high electron affinity values of −3.82, −3.95, and −3.99 eV for <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, respectively. Single-crystal X-ray diffraction reveals that three molecules form corresponding dimers by intermolecular S–N interaction and have very similar two-dimensional π-stacking. The π-stacking distances between them are as close as 3.34–3.46 Å

Highly Ordered Phenanthroline-Fused Azaacene

A new synthetic route to prepare a centrosymmetric phenanthroline-fused azaacene derivative, <b>TIPS-BisPhNPQ</b>, is described. Another axialsymmetric analogue, <b>TIPS-PhNTQ</b>, is also synthesized for comparison. Cyclic voltammetry measurements indicate high electron affinity values of −4.03 and −4.01 eV for <b>TIPS-PhNTQ</b> and <b>TIPS-BisPhNPQ</b>, respectively. Single-crystal X-ray diffraction reveals that <b>TIPS-PhNTQ</b> forms dimers by intermolecular S–N and N–N interaction, while <b>TIPS-BisPhNPQ</b> shows a highly ordered arrangement via two-dimensional brickwork packing and intermolecular hydrogen bonding. The synthetic protocol established in this paper should be highly applicable to the preparation of more azaacene derivatives with extended π-conjugations

Condensed Derivatives of Thiadiazoloquinoxaline as Strong Acceptors

Three novel thiadiazoloquinoxaline (TQ) derivatives, <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, were synthesized by introducing two triisopropylsilylethynyl groups and alternating the aromatic ring units in the condensed moiety of TQ. The synthetic route is very efficient, providing high yields. Cyclic voltammetry suggests high electron affinity values of −3.82, −3.95, and −3.99 eV for <b>TIPS-APhTQ</b>, <b>TIPS-PhTQ</b>, and <b>TIPS-BDTTQ</b>, respectively. Single-crystal X-ray diffraction reveals that three molecules form corresponding dimers by intermolecular S–N interaction and have very similar two-dimensional π-stacking. The π-stacking distances between them are as close as 3.34–3.46 Å

Three-Dimensional Pyrene-Fused <i>N</i>‑Heteroacenes

Four three-dimensional (3D) pyrene-fused N-heteroacenes (P1–P4) are designed and synthesized. From P1 to P4, their lengths are extended in an iterative way, where the thiadiazole unit can be reduced to diamine and the obtained diamines can be further condensed with the diketones with a thiadiazole unit. Compared to their two-dimensional counterparts, the solubility of these 3D pyrene-fused N-heteroacenes is improved by this 3D covalent linkage with two-dimensional units. The diameters of P1–P4 are 3.66, 6.06, 8.48 and 10.88 nm, respectively, and these 3D molecules are characterized by 1H, 13C and 2D NMR, MS, UV–vis, PL and CV spectra. Our strategy shows a promising way to large 3D pyrene-fused N-heteroacenes

Efficient Exciton Dissociation Enabled by the End Group Modification in Non-Fullerene Acceptors

For organic photovoltaic (OPV) cells, in order to overcome the larger Coulombic binding energy between holes and electrons, an extra driving force is required for efficient exciton dissociation. Here, we report two nonfullerene acceptors named IO-4H and IO-4F for OPV cells. By employing the polymer PBDB-TF as a donor, the PBDB-TF:IO-4H-based device only shows a power conversion efficiency (PCE) of 0.30% with a charge dissociation probability (Pdiss) of 13.3%. On the contrary, the PBDB-TF:IO-4F-based device demonstrates a PCE of 7.85% with a Pdiss of 81.3%. The photoelectric processes demonstrate that both devices have similar charge transport and charge recombination properties. The limitation of photovoltaic performance is the low exciton dissociation efficiency in the PBDB-TF:IO-4H-based device. The theoretical studies show the electrostatic potential (ESP) of IO-4H is negative in the end groups and similar to the ESP of PBDB-TF, whereas ESP of IO-4F is positive. PBDB-TF and the IO-4F may form a strong intermolecular electric field to assist the exciton dissociation. Our results suggest that increasing the ESP difference between donor and acceptor may be beneficial to promote exciton dissociation, thus improving photovoltaic performance

Thiadizoloquinoxaline-Based Low-Bandgap Conjugated Polymers as Ambipolar Semiconductors for Organic Field Effect Transistors

Two novel conjugated polymers with high molecular weight, <b>PBDTTQ-3</b> and <b>PAPhTQ</b>, were synthesized by tuning alkyl chains and alternating the electron-donating ability of the thiadiazoloquinoxaline (TQ) moiety. Both polymers have excellent solubility in common organic solvents. UV–vis–NIR absorption and cyclic voltammetry indicate a bandgap of (0.76 eV) and high electron affinity level (−4.08 eV) for <b>PBDTTQ-3</b>. Two dimensional wide-angle X-ray scattering shows that both polymers are only poorly ordered in the bulk but possess a close π-stacking distance of 0.36 nm. Despite the disorder in thin film observed by grazing incidence wide-angle X-ray scattering, <b>PBDTTQ-3</b> exhibits good ambipolar transport, with a maximum hole mobility of 0.22 cm² V^–1 s^–1 and comparable electron mobility of 0.21 cm² V^–1 s^–1

Benzodithiophene–Thiadiazoloquinoxaline as an Acceptor for Ambipolar Copolymers with Deep LUMO Level and Distinct Linkage Pattern

Two new conjugated copolymers, <b>PBDTTQ-1</b> and <b>PBDTTQ-2</b>, with a distinct linked pattern between benzodithiophene–thiadiazoloquinoxaline (<b>BDTTQ</b>) as acceptor and bithiophene as donor were synthesized and characterized. The difference in the linkage between donor and acceptor exerts great influence on the optoelectronic properties of the two polymers. The optical band gap decreases from 1.18 eV for <b>PBDTTQ-1</b> to 1.03 eV for <b>PBDTTQ-2</b>, due to the lower LUMO energy level (−4.01 eV) of the latter. Moreover, density functional theory calculations demonstrate that the electron density is mainly confined on the acceptor unit in both HOMO and LUMO of <b>PBDTTQ-1</b>, while the electronic densities almost delocalize along the entire backbone of <b>PBDTTQ-2</b>, which facilitates the charge transport within the polymer chain. In contrast to <b>PBDTTQ-1</b> missing any field-effect characteristics, <b>PBDTTQ-2</b> exhibits ambipolar charge transporting behavior with mobilities of 1.2 × 10^–3 cm²/(V s) for holes and 6.0 × 10^–4 cm²/(V s) for electrons

Photochemical Reaction Enabling the Engineering of Photonic Spin–Orbit Coupling in Organic-Crystal Optical Microcavities

The control and active manipulation of spin–orbit coupling (SOC) in photonic systems are fundamental in the development of modern spin optics and topological photonic devices. Here, we demonstrate the control of an artificial Rashba–Dresselhaus (RD) SOC mediated by photochemical reactions in a microcavity filled with an organic single crystal of photochromic phase-change character. Splitting of the circular polarization components of the optical modes induced by photonic RD SOC is observed experimentally in momentum space. By applying an ultraviolet light beam, we control the spatial molecular orientation through a photochemical reaction, and with that we control the energies of the photonic modes. This way, we realize a reversible conversion of spin splitting of the optical modes with different energies, leading to an optically controlled switching between circularly and linearly polarized optical modes in our device. Our strategy of in situ and reversible engineering of SOC induced by a light field provides a promising approach to actively design and manipulate synthetic gauge fields toward future on-chip integration in photonics and topological photonic devices

Molecular Ordering of Dithieno[2,3‑<i>d</i>;2′,3′‑<i>d</i>]benzo[2,1‑<i>b</i>:3,4‑<i>b</i>′]dithiophenes for Field-Effect Transistors

Four derivatives of dithieno­[2,3-<i>d</i>;2′,3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;3,4-<i>b</i>′]­dithiophene (<b>DT<i>m</i>BDT</b>) have been synthesized to investigate the correlation between molecular structure, thin-film organization, and charge-carrier transport. Phenyl or thiophene end-capped derivatives at alpha positions of the outer thiophenes of <b>DT<i>m</i>BDT</b> present vastly different optoelectronic properties in comparison with bay-position alkyl-chain-substituted <b>DT<i>m</i>BDT</b>, which was additionally confirmed by density functional theory simulations. The film morphology of the derivatives strongly depends on alkyl substituents, aromatic end-caps, and substrate temperature. Field-effect transistors based on <b>DT<i>m</i>BDT</b> derivatives with bay-substituted alkyl chains show the best performance within this studied series with a hole mobility up to 0.75 cm²/V s. Attachment of aromatic end-caps disturbs the ordering, limiting the charge-carrier transport. Higher substrate temperature during deposition of the <b>DT<i>m</i>BDT</b> derivatives with aromatic end-caps results in larger domains and improved the transistor mobilities but not beyond the alkylated <b>DT<i>m</i>BDT</b>