Baomin Zhao

Donor–acceptor conjugated polymers based on thieno[3,2-b]indole (TI) and 2,1,3-benzothiadiazole (BT) for high efficiency polymer solar cells

A universal synthetic strategy toward thieno[3,2-b]indole (TI) derivatives was developed. Three conjugated polymers (PTIBT, PTITBT and PTIDTBT) containing N-alkyl-TI as the donor units, 2,1,3-benzodiathiazole (BT) as the acceptor units and thiophene as the spacers were synthesized. The thiophene spacers have a dramatic impact on the physical and electrochemical properties of these copolymers. These polymer donors were used for the fabrication of bulk heterojunction polymer solar cells (PSCs). Preliminarily, power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al exhibit a large distinction (1.61% for PTIBT, 5.83% for PTITBT and 1.79% for PTIDTBT) at optimal device fabrication conditions. The device based on PTITBT : PC71BM (1 : 3, w/w) shows the best PCE of 5.83% (Voc = 0.69 V, Jsc = 13.92 mA cm−2, FF = 61.8%), which represents one of the best performances among PCDTBT analogues. In addition, the Jsc of 13.92 mA cm−2 is also among the highest Jsc values of all PCDTBT analogues. On the basis of our results, one can conclude that incorporating TI and its derivatives into donor–acceptor conjugated polymers is a feasible and effective way to develop novel donor materials for high efficiency PSC applications.

Thermally Activated Delayed Fluorescence Organic Dots (TADF Odots) for Time‐Resolved and Confocal Fluorescence Imaging in Living Cells and In Vivo

The fluorophores with long‐lived fluorescent emission are highly desirable for time‐resolved fluorescence imaging (TRFI) in monitoring target fluorescence. By embedding the aggregates of a thermally activated delayed fluorescence (TADF) dye, 2,3,5,6‐tetracarbazole‐4‐cyano‐pyridine (CPy), in distearoyl‐sn‐glycero‐3‐phosphoethanolamine‐poly(ethylene glycol) (DSPE‐PEG2000) matrix, CPy‐based organic dots (CPy‐Odots) with a long fluorescence lifetime of 9.3 μs (in water at ambient condition) and high brightness (with an absolute fluorescence quantum efficiency of 38.3%) are fabricated. CPy‐Odots are employed in time‐resolved and confocal fluorescence imaging in living Hela cells and in vivo. The green emission from the CPy‐Odots is readily differentiated from the cellular autofluorescence background because of their stronger emission intensities and longer lifetimes. Unlike other widely studied DSPE‐PEG2000 encapsulated Odots which are always distributed in cytoplasm, CPy‐Odots are located mainly in plasma membrane. In addition, the application of CPy‐Odots as a bright microangiography agent for TRFI in zebrafish is also demonstrated. Much broader application of CPy‐Odots is also prospected after further surface functionalization. Given its simplicity, high fluorescence intensity, and wide availability of TADF materials, the method can be extended to develop more excellent TADF Odots for accomplishing the challenges in future bioimaging applications.

D–A conjugated polymers based on thieno[3,2-b]indole (TI) and 2,1,3-benzodiathiazole (BT) derivatives: synthesis, characterization and side-chain influence on photovoltaic properties

A facile synthetic strategy toward thieno[3,2-b]indole (TI) derivatives was developed by the Cadogan annulation method. Three donor–acceptor (D–A) conjugated polymers P1, P2 and P3 containing N-alkyl-TI derivatives and 4,7-dithien-5-yl-2,1,3-benzodiathiazole (DTBT) derivatives were successfully synthesized and applied to bulk heterojunction (BHJ) polymer solar cells (PSCs). Different side chains were introduced to TI units (for P2) or DTBT units (for P3), the results indicate that the bandgaps, energy levels and photovoltaic performance were finely tuned by the side chains in the TI-DTBT copolymer. Power conversion efficiencies (PCEs) based on the device structure of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al exhibit a large distinction (1.61% for P1, 0.53% for P2 and 2.73% for P3) under optimal device fabrication conditions. The optimized devices based on P3:PC71BM blends with a relatively higher mobility (2.84 × 10−5 cm2 V−1 s−1) show the best PCE under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm−2, which is in good agreement with its high current density and light absorption property. Accordingly, the TI unit can be used as the efficient donor units for D–A conjugated donor materials for PSCs application. In addition, this work suggests that the side chains on low bandgap polymers significantly impact their molecular energy levels and the observed PCEs of the corresponding BHJ solar cells.

Highly Contorted 1,2,5-Thiadiazole-Fused Aromatics for Solution-Processed Field-Effect Transistors: Synthesis and Properties.

A straightforward strategy has been used to construct 1,2,5-thiadiazole-fused 12-ring π systems through twofold Stille coupling and subsequent cyclodehydrogenation by utilizing the building blocks of naphthodithiophene and 5,6-substituted benzo[b]-2,1,3-thiadidazole. Molecules 1 a and 1 b, which exhibit highly contorted π surfaces, show a butterfly-shaped conformation according to DFT calculations. Within the molecules, a plane-to-plane angle of 44.8° was found. UV/Vis absorption, thermogravimetric analysis, differential scanning calorimetry, and cyclic voltammetry (CV) were used to study their physical properties. Strong intermolecular interactions of the nonplanar molecules were also observed by concentration-dependent (1) H NMR spectroscopy measurements and thin-film XRD characterization. The low-lying LUMO and high-lying HOMO levels of the molecules are -3.73 and -5.48 eV, respectively, as estimated from CV measurements; this indicates their potential as semiconducting materials for solution-processed organic field-effect transistors (OFETS). A field-effect hole mobility of up to 0.035 cm(2)  V(-1)  s(-1) , a threshold voltage of 6.98 V, and a current on/off ratio of 8.65×10(5) in air for 1 a have been demonstrated with the top-contact bottom-gate field-effect transistor device structures; this represents an important step toward the solution-processed OFET application of contorted aromatics.

Unprecedented side reactions in Stille coupling: desired ones for Stille polycondensation

Two types of unprecedented side reactions were identified in the Stille coupling reaction, including the direct C-H stannylation of the α-hydrogen of thiophene and the stannylation of arylbromides with trialkylstannane bromide. These results reveal the major source of enhancements for Stille polycondensation efficiency.

Ladder-type nonacyclic indacenodithieno[3,2-b]indole for highly efficient organic field-effect transistors and organic photovoltaics

Developing electron-donating building blocks for organic semiconductors is still one big chemical challenge to achieve high performance active materials for organic photovoltaics (OPVs). In this work, we have successfully designed and synthesized a novel ladder-type nonacyclic indacenodithieno[3,2-b]indole (IDTI) unit via intramolecular annulation with rigid and coplanar features. Two donor–acceptor copolymers of PIDTI-BT and PIDTI-DTBT were synthesized by utilizing the Suzuki and Stille coupling polymerization method with IDTI units. Both copolymers displayed excellent solubility, high thermal stability, broad absorption and a low band gap. The FET hole mobility reaches 2.1 × 10−2 and 1.4 × 10−2 cm2 V−1 s−1 for PIDTI-BT and PIDTI-DTBT, respectively. The conventional bulk-heterojunction (BHJ) polymer solar cell (PSC) devices based on the PIDTI-BT : PC71BM (1 : 2 in wt%) blend exhibit a moderate PCE of 4.02% with a Voc of 0.82 V, a Jsc of 8.99 mA cm−2 and a FF of 54.6% under AM 1.5G, 100 mW cm−2 illumination, which is among the highest values for polymer donor materials based on multifused TI units. The improved performance may be associated with the extended conjugation length, which optimizes the interchain interactions and improves molecular organization for accelerating charge transport. Our results demonstrate that the multifused nonacyclic TIBDP as the donor unit is very promising for application in PSCs and FETs.

N-Annulated perylene diimide derivatives as non-fullerene acceptors for solution-processed solar cells with an open-circuit voltage of up to 1.14 V

Three different non-fullerene small molecular acceptors containing N-annulated perylene diimide, named di-PNR, TPA-PNR and EDOT-PNR, were successfully designed and synthesized for photovoltaic applications. Introducing an electron donating unit such as triphenylamine (TPA) or 2,3-dihydrothieno[3,4-b][1,4]dioxine (EDOT) into the N-annulated PDI derivatives significantly influences the light-harvesting capabilities, energy level, morphology as well as the photovoltaic performance. Preliminarily, TPA-PNR and EDOT-PNR possessed lower band gaps and higher HOMO/LUMO energy levels. Power conversion efficiencies (PCEs) of 5.29% and 4.54% were obtained for the inverted solar cells based on the blends of PTB7-Th/di-PNR and PTB7-Th/TPA-PNR, respectively, resulting from the smooth morphology of the blend films and the intense light absorption that increases the Jsc and FF. Under the same optimization conditions, EDOT-PNR exhibited a low PCE of 1.6% with a remarkably high Voc of 1.14 V because of its higher LUMO energy level, which was one of the highest Voc values reported for organic solar cells using N-annulated PDI derivatives as electron acceptors. Our work offers effective guidelines for the design of non-fullerene acceptors using N-annulated PDI derivatives.

Poly(sodium 4-styrenseulfonate)-modified monolayer graphene for anode applications of organic photovoltaic cells

An insulated poly(sodium 4-styrenseulfonate) (PSS) was used to modify monolayer graphene for anode applications of organic photovoltaics (OPVs). With this PSS interfacial modification layer, the OPVs showed a significant increase of 56.4% in efficiency due to an improved work function and hydrophilic feature of graphene and an enlarged recombination resistance of carriers/excitons. Doping a highly contorted 1,2,5-thiadiazole-fused 12-ring polyaromatic hydrocarbon into the active layer to form ternary blended OPVs further enlarged the recombination resistance of carriers/excitons and improved light absorption of the active layer, with which a high power conversion efficiency of 6.29% was acquired.

A selenophene substituted diketopyrrolopyrrole nanotheranostic agent for highly efficient photoacoustic/infrared-thermal imaging-guided phototherapy

Phototherapy, a light-induced cancer therapy, has presented great promise for multimodal cancer treatment. Herein, a selenophene substituted diketopyrrolopyrrole based nanotheranostic photosensitizer (SeDPP-TPA) has been designed and synthesized. The introduction of selenophene enables SeDPP-TPA to produce a high yield of singlet oxygen (1O2) (ΦΔ = 40.2%), and show a bathochromic shift in absorbance (λmax at 648 nm), enhanced charge transfer and biocompatibility. After nanoprecipitation, SeDPP-TPA nanoparticles (NPs) are prepared with excellent water dispersibility and passive tumor-targeting properties based on the enhanced permeability and retention effect. Besides, SeDPP-TPA NPs present a high photothermal conversion efficiency (η = 37.9%). An in vitro cytotoxicity test shows that the half-maximal inhibitory concentration (IC50) of SeDPP-TPA NPs on tumor cells is ∼12 μg mL−1, indicating their excellent phototherapy efficiency. What is more, because of the thermal expansion and tumor-targeting properties, SeDPP-TPA NPs can also act as a contrast agent for photoacoustic imaging to visualize the therapy in vivo. Coupled with the infrared thermal imaging properties of the photothermal agent, SeDPP-TPA NPs are proved to be a multifunctional theranostic agent for dual-modal imaging-guided phototherapy.

Plasmonic Heterodimers with Binding Site‐Dependent Hot Spot for Surface‐Enhanced Raman Scattering

A novel plasmonic heterodimer nanostructure with a controllable self-assembled hot spot is fabricated by the conjugation of individual Au@Ag core-shell nanocubes (Au@Ag NCs) and varisized gold nanospheres (GNSs) via the biotin-streptavidin interaction from the ensemble to the single-assembly level. Due to their featured configurations, three types of heterogeneous nanostructures referred to as Vertice, Vicinity, and Middle are proposed and a single hot spot forms between the nanocube and nanosphere, which exhibits distinct diversity in surface plasmon resonance effect. Herein, the calculated surface-enhanced Raman scattering enhancement factors of the three types of heterodimers show a narrow distribution and can be tuned in orders of magnitude by controlling the size of GNSs onto individual Au@Ag NCs. Particularly, the Vertice heterodimer with unique configuration can provide extraordinary enhancement of the electric field for the single hot spot region due to the collaborative interaction of lightning rod effect and interparticle plasmon coupling effect. This established relationship between the architecture and the corresponding optical properties of the heterodimers provides the basis for creating controllable platforms which can be exploited in the applications of plasmonic devices, electronics, and biodetection.