Synthesis of Low Band Gap [1,2,5]-Thiadiazolo[3,4-g]quinoxaline and Pyrazino[2,3-g]quinoxaline Derivatives by Selective Reduction of Benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole

Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers

Conjugated polymers are promising materials for thermoelectrics as they offer good performances at near ambient temperatures. The current focus on polymer thermoelectric research mainly targets a higher power factor (PF; a product of the conductivity and square of the Seebeck coefficient) through improving the charge mobility. This is usually accomplished via structural modification in conjugated polymers using different processing techniques and doping. As a result, the structure-charge transport relationship in conjugated polymers is generally well-established. In contrast, the relationship between the structure and the Seebeck coefficient is poorly understood due to its complex nature. A theoretical framework by David Emin (Phys. Rev. B, 1999, 59, 6205-6210) suggests that the Seebeck coefficient can be enhanced via carrier-induced vibrational softening, whose magnitude is governed by the size of the polaron. In this work, we seek to unravel this relationship in conjugated polymers using a series of highly identical pro-quinoid polymers. These polymers are ideal to test Emin's framework experimentally as the quinoid character and polaron delocalization in these polymers can be well controlled even by small atomic differences (<10 at. % per repeating unit). By increasing the polaron delocalization, that is, the polaron size, we demonstrate that both the conductivity and the Seebeck coefficient (and hence PF) can be increased simultaneously, and the latter is due to the increase in the polaron's vibrational entropy. By using literature data, we also show that this phenomenon can be observed in two closely related diketopyrrolopyrrole-conjugated polymers as well as in p-doped P3HT and PANI systems with an increasing molecular order.

I2-Catalyzed Carbonylation of α-Methylene Ketones to Synthesize 1,2-Diaryl Diketones and Antiviral Quinoxalines in One Pot

An efficient approach for the synthesis of 1,2-diaryl diketones was developed from readily available α-methylene ketones by catalysis of I2. In the same oxidation system, a novel one-pot procedure was established for the construction of antiviral and anticancer quinoxalines. The reactions proceeded well with a wide variety of substrates and good functional group tolerance, affording desired compounds in moderate to excellent yields. Quinoxalines 4ca and 4ad inhibited viral entry of SARS-CoV-2 spike pseudoviruses into HEK-293T-ACE2h host cells as dual blockers of both human ACE2 receptor and viral spike RBD with IC50 values of 19.70 and 21.28 μM, respectively. In addition, cytotoxic evaluation revealed that 4aa, 4ba, 4ia, and 4ab suppressed four cancer cells with IC50 values ranging from 6.25 to 28.55 μM.

Narrow-energy gap conjugated polymers based on benzobisthiadiazole and thiadiazoloquinoxaline: DFT and TDDFT study

Herein, the HOMO-LUMO energy gaps (Eg) and UV spectra of benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole (BBT) and [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ)-based donor-acceptor-donor type-conjugated polymers were computed by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at B3LYP/6-31G(d,p) level. The donor groups consist of thiophene (TH), 3,4-ethylenedioxythiophene (EDOT), and 3,4-propylene dioxythiophene (ProDOT) units and the bisthiadiazole and thiadiazoloquinoxaline were chosen as electron acceptor groups. To examine the effects of the alkyl side chain on the molecular structure and Eg of the polymer, methyl groups were added at the 3,4-, 2,3-, and 3,3-positions of TH, EDOT, and ProDOT donor groups, respectively. Our calculated HOMO-LUMO energy gaps are in the range of 0.05 to 1.37 eV. The calculation results show that the energy gaps are in line with the available experimental values. The novel BBT and TQ derivatives with improved optical and electronic properties may find use in electronic applications. Graphical abstract.

A fluorescent probe based on novel fused four ring quinoxalinamine for palladium detection and bio-imaging

An “off–on” fluorescent probe was designed to detect palladium of all the typical oxidation states (0, +2, +4) without additional additives.

Iodine-Promoted Domino Oxidative Cyclization for the One-Pot Synthesis of Novel Fused Four-Ring Quinoxaline Fluorophores by sp3 C-H Functionalization

A method for the synthesis of novel fused four-ring quinoxaline skeleton has been described by an I₂ promoted sp³ C-H functionalization between 1,2,3,3-tetramethyl-3H-indolium iodides and 1,2-diamines. This transformation proceeds smoothly under metal- and peroxide-free conditions through a sequential iodination, oxidation, annulation and rearrangement. Moreover, 8,9-dichloro-5,12,12-trimethyl-2-(trifluoromethyl)-5,12-dihydroquinolino[2,3-b]quinoxaline showed good photophysical properties and was used in live cell imaging, indicating the potential value of this skeleton as a fluorophore in probes.

Iodine-Mediated Oxidative Rearrangement of α,β-Unsaturated Diaryl Ketones: A Facile Access to 1,2-Diaryl Diketones

A metal-free oxidative rearrangement was explored for the synthesis of 1,2-diaryl diketones by utilizing α,β-unsaturated diaryl ketones and I2/TBHP in good to high yields. The reaction proceeds via oxidative aryl migration, followed by C-C bond cleavage. A simple and high-yielding protocol was developed for the synthesis of a wide range of 1,2-diaryl diketones, which are the backbone for a variety of medicinally important molecules.

Synthesis and photophysical properties of pyridyl conjugated triazole appended naphthalenediimide derivatives

Pyridyl substituted triazole appended NDI-derivatives displayed two reduction potentials corresponding to the formation of stable anionic radicals. NDI-PyTzs have promising fluorescence and electrochemical properties.

Tuning the electronic and optical properties of NDT-based conjugated polymers by adopting fused heterocycles as acceptor units: a theoretical study

Donor-acceptor conjugated polymers have been successfully applied in bulk heterojunction solar cell devices. Tuning their donor and acceptor units allows the design of new polymers with desired electronic and optical properties. Here, to screen new candidate polymers based on a newly synthesized donor unit, dithieo[2,3-d:2',3'-d']naphtho[1,2-b:3,4-b']dithiophene (NDT), a series of model polymers with different acceptor units were designed and denoted NDT-A₀ to NDT-A₁₂, and the structures and optical properties of those polymers were investigated using DFT and TDDFT calculations. The results of the calculations revealed that the electronic and optical properties of these polymers depend on the acceptor unit present; specifically, their HOMO energies ranged from -4.89 to -5.38 eV, their HOMO-LUMO gaps ranged from 1.30 to 2.80 eV, and their wavelengths of maximum absorption ranged from 538 to 1212 nm. The absorption spectra of NDT-A₁ to NDT-A₆, NDT-A₈, NDT-A₉, and NDT-A₁₂ occur within the visible region (<900 nm), indicating that these polymers are potential candidates for use in solar cells. On the other hand, the absorption spectra of NDT-A₇, NDT-A₁₀, and NDT-A₁₁ extend much further into the near-infrared region, implying that they absorb near-infrared light. These polymers could meet the requirements of donor units for use in tandem and ternary solar cells. Graphical abstract Theoretical calculations by TD-DFT reveal that the optical properties of NDT-based conjugated polymers can be well tuned by adopting different acceptor units, and these ploymers are potential donor materials for tandem and ternary solar cells.

Tetraalkoxyphenanthrene-Fused Thiadiazoloquinoxalines: Synthesis, Electronic, Optical, and Electrochemical Properties, and Self-Assembly

π-Extended thiadiazoloquinoxaline (TQ) derivatives 1a,b-3a,b, in which a tetraalkoxyphenanthrene moiety is annulated with the TQ core and benzene rings are incorporated via the ethynylene spacer, were synthesized. They display absorption bands reaching into 750 nm and possess the electron-affinity comparable to [60]fullerene. The CF₃- and OMe-substituents on the benzene rings have moderate effects on modulation of the HOMO and LUMO levels. Tetraalkoxyphenanthrene-fused TQs 1a,b-3a,b aggregate in the solid state and assemble in solution through π-π stacking interactions. The self-assembly of 1a,b-3a,b into 1D superstructures was confirmed, and the difference in the alkoxy groups and the solvents for self-assembly proved to change their morphology. Comparison of the properties of 1a and those of reference compounds 4 and 5 clarified the effects of both the fusion of the phenanthrene moiety and the introduction of ethynylene spacers on the properties.

Low Band Gap Donor⁻Acceptor Type Polymers Containing 2,3-Bis(4-(decyloxy)phenyl)pyrido[4,3-b]pyrazine as Acceptor and Different Thiophene Derivatives as Donors

Four donor–acceptor type conducting polymers, namely poly(2,3-bis(4-decyloxy)phenyl)-5,8-bis(4-thiophen-2-yl)pyrido[4,3-b]pyrazine) (P1), poly(2,3-bis(4-decyloxy)phenyl)-5,8-bis(4-butylthiophen-2-yl)pyrido[4,3-b]pyrazine) (P2), poly(2,3-bis(4-(decyloxy)phenyl)-5,8-bis(4-hexyloxythiophen-2-yl)pyrido[4,3-b]pyrazine) (P3) and poly(2,3-bis(4-(decyloxy)phenyl)-5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)pyrido[4,3-b]pyrazine) (P4), containing thiophene or its derivative as the donor and pyrido[4,3-b]pyrazine as the acceptor were prepared and characterized by cyclic voltammetry, scanning electron microscopy, and UV-Vis spectroscopy to detect the influence of the donor units’ strength on the electrochromic performances. The results demonstrated that all of the polymers could be reversibly reduced and oxidized by p-type doping and n-type doping, and showed near-infrared activities and different color changes in p-type doping process. Especially, P3 and P4 showed lower optical band gap than P1 and P2 due to the strong electron-donating hexyloxythiophen group of P3 and ethylenedioxythiophene group of P4. Besides, P3 and P4 displayed the saturated green color at the neutral state and the desirable transparency at the oxidized state. All the polymers displayed desirable optical contrasts, satisfactory coloration efficiency, excellent stability and short switching time, which made the polymers fascinating candidates in the electrochromic device applications.

Bi-diketopyrrolopyrrole (Bi-DPP) as a novel electron accepting compound in low band gap π-conjugated donor-acceptor copolymers/oligomers

The synthesis and characterization of a novel 2,5-diketopyrrolo[3,4-c]pyrrole(DPP)-based accepting building block with the scheme DPP-neutral small linker-DPP (Bi-DPP) is presented, which was utilized as electron accepting moiety for low band gap π-conjugated donor–acceptor copolymers as well as for a donor–acceptor small molecule. The electron accepting moiety Bi-DPP was prepared via a novel synthetic pathway by building up two DPP moieties step by step simultaneously starting from a neutral phenyl core unit. Characterization of the synthesized oligomeric and polymeric materials via cyclic voltammetry afford LUMO energy levels from −3.49 to −3.59 eV as well as HOMO energy levels from −5.07 to −5.34 eV resulting in low energy band gaps from 1.52 to 1.81 eV. Spin coating of the prepared donor–acceptor oligomers/polymers resulted in well-defined films. Moreover, UV–vis measurements of the investigated donor–acceptor systems showed a broad absorption over the whole visible region. It is demonstrated that Bi-DPP as an electron accepting moiety in donor–acceptor systems offer potential properties for organic solar cell devices.

Strengthening the acceptor properties of thiadiazoloquinoxalines via planarization

Fused aromatic ring extension strongly enhances the acceptor strength.

Novel donor–acceptor polymers based on 7-perfluorophenyl-6H-[1,2,5]thiadiazole[3,4-g]benzoimidazole for bulk heterojunction solar cells

Three polymers with 7-perfluorophenyl-6H-[1,2,5]thiadiazole[3,4-g]benzoimidazole as a building unit were synthesized for BHJ solar cells, and a PCE of 1.92% was obtained.

Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages

D–A copolymers incorporating new pyrrolo[3,4-g]quinoxaline-6,8-dione (PQD) building blocks were synthesized for bulk heterojunction solar cells with high photovoltages.

New low band gap 2-(4-(trifluoromethyl)phenyl)-1H-benzo[d]imidazole and benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole based conjugated polymers for organic photovoltaics

Novel low band gap conjugated polymers (PBDTTBIandPBDTBBT) are designed and synthesized for polymer solar cell applications.