No abstract

A novel nonfullerene small molecular acceptor (BZIC) based on a ladder-type thieno[3,2-b]pyrrolo-fused pentacyclic benzotriazole core (dithieno[3,2-b]pyrrolobenzotriazole, BZTP) and end-capped with 1,1-dicyanomethylene-3-indanone (INCN) has been first reported in this work. Through introducing multifused benzotriazole and INCN, BZIC could maintain a high-lying lowest unoccupied molecular orbital (LUMO) energy level of -3.88 eV. Moreover, BZIC shows a low optical bandgap of 1.45 eV with broad and efficient absorption band from 600 to 850 nm due to increased π-π interactions by the covalently locking thiophene and benzotriazole units. A power conversion efficiency of 6.30% is delivered using BZIC as nonfullerene acceptor and our recently synthesized hexafluoroquinoxaline-based polymer HFQx-T as donor. This is the first time to synthesize mutifused benzotriazole-based molecules as nonfullerene electron acceptor up to date. The preliminary results demonstrate that the mutifused benzotriazole derivatives hold great potential for efficient photovoltaics.

A straightforward strategy has been used to construct large BN-embedded π-systems simply from azaacenes. BN heterosuperbenzene derivatives, the largest BN heteroaromatics to date, have been synthesized in three steps. The molecules exhibit curved π-surfaces, showing two different conformations which are self-organized into a sandwich structure and further packed into a π-stacking column. The assembled microribbons exhibit good charge transport properties and photoconductivity, representing an important step toward the optoelectronic applications of BN-embedded aromatics.

Great progress in organic solar cells (OSCs) has been recently achieved owing to the advent of non-fullerene acceptors (NFAs). Indeed, low-bandgap NFAs ranging from 1.3 to 1.6 eV with broad absorption and easily tunable energy levels can utilize more solar radiation and maintain a small voltage loss when paired with suitable donors. Efficient OSCs are dependent on the good compatibility between donor and acceptor materials, active layer morphology control, and device engineering. In this review, we summarize some design and synthesis strategies for NFAs, achieving low bandgap and high power conversion efficiency. We also propose solutions toward innovative materials and device engineering to advance the development and applications of OSCs.

A benzo-fused double [7]carbohelicene (D7H) was synthesized through a regioselective cyclodehydrogenation of a tetranaphthyl-p-terphenyl-based precursor. The twisted (D7H-1) and anti-folded (D7H-2) conformers of D7H were separated by recrystallization, and their double helicene structures with overlapping terminal benzene rings were unambiguously elucidated by X-ray crystallography. A record-high isomerization barrier (46.0 kcal mol ) in double helicenes was estimated based on density functional theory (DFT) calculation, which resulted in the excellent conformational stability of D7H. The physicochemical properties of D7H-1 and D7H-2 were investigated by UV/Vis absorption spectroscopy and cyclic voltammetry, displaying the variation of electronic structure upon conformational changes. The optical resolution of the racemic D7H-1 was carried out by chiral HPLC, offering enantiopure D7H-1-(P,P) and D7H-1-(M,M), which were further characterized by circular dichroism spectroscopy.

The development of helicene molecules with significant chiroptical responses covering a broad range of the visible spectrum is highly desirable for chiral optoelectronic applications; however, their absorption dissymmetry factors (g abs ) have been mostly lower than 0.01. In this work, we report unprecedented B,N-embedded double hetero[7]helicenes with nonbonded B and N atoms, which exhibit excellent chiroptical properties, such as strong chiroptical activities from 300 to 700 nm, record high g abs up to 0.033 in the visible spectral range, and tunable circularly polarized luminescence (CPL) from red to near-infrared regions (600−800 nm) with high photoluminescence quantum yields (PLQYs) up to 100%. As revealed by theoretical analyses, the high g abs values are related to the separate molecular orbital distributions owing to the incorporation of nonbonded B and N atoms. The new type of B,N-embedded double heterohelicenes opens up an appealing avenue to the future exploitation of high-performance chiroptical materials.

Solution-processable n-doped graphene-containing cathode interfacial material with a low work function demonstrates 16.52% power conversion efficiency in organic solar cells.

The synthesis of 11a,25a-dibora-11,12,25,26-tetraoxatetranaphtho[1,2-a:2',1'-f:1″,2″-j:2‴,1‴-o]perylene, a double [7]heterohelicene containing OBO units, has been achieved via tandem demethylation-borylation, representing the highest double helicene reported thus far with all six-membered rings. Single-crystal X-ray analysis clearly demonstrated a significantly twisted structure with the terminal aromatic rings overlapping at both ends, giving the first example of a double helicene with intramolecular π-layers. Such structural features resulted in a high theoretical isomerization barrier of 45.1 kcal/mol, which is the highest value for all the double helicenes ever reported, rendering the achieved molecule with high chiral stability. The (P,P)- and (M,M)-isomers were separated by chiral HPLC and the chiroptical properties were investigated, revealing opposite circular dichroism responses.