Jinsheng Song

Simultaneous enhancement of the molecular planarity and the solubility of non-fullerene acceptors: effect of aliphatic side-chain substitution on the photovoltaic performance

Three planar nonfullerene acceptors (FTIC-C8C6, FTIC-C6C6 and FTIC-C6C8) comprising a central fluorenedicyclopentathiophene (FT) core and two 2-methylene-(3-(1,1-dicyanomethylene)-indanone) terminal groups are designed and synthesized. The coplanarity of the molecular backbone can be maintained through a locked conformation via intramolecular noncovalent interactions. The solubility of these nonfullerene acceptors is very good because the FT core can bear enough flexible aliphatic side-chain substitutions. Thus, the dilemma of the planarity–solubility tradeoff can be minimized. Through changing the length of the six flexible aliphatic side chains at the central FT core, we can easily adjust the π–π interactions of nonfullerene acceptors and optimize the nanoscale morphology of the photoactive layers. Among these three small molecular acceptors, FTIC-C6C8 based active layers show the best morphology together with the highest electron and hole mobility. These inherent advantages of FTIC-C6C8 guarantee it a high power conversion efficiency of 11.12% when used in non-fullerene polymer solar cells with a wide-bandgap polymer donor PBDB-T. Our results provide an appropriate molecular design strategy for building high-performance nonfullerene acceptors and show that optimizing alkyl-side chains is a very effective way to further improve the photovoltaic performance of devices.

Synthesis of dendrimers based on tetrakis(thiophene-2-yl)ethene as new dendron.

Two novel dendrimers, 16T and 20T, based on 1,1,2,2-tetra(thiophen-2-yl)ethene (4T) as a new dendron, were efficiently synthesized via carbonylation, Suzuki, and McMurry reactions. All intermediates and title compounds were fully characterized by (1)H NMR, (13)C NMR, and HRMS. 4T and 16T were confirmed by X-ray single crystal analyses. In addition, the absorption behaviors of two titled dendrimers are also described.

Thiophene-Based Double Helices: Syntheses, X-ray Structures, and Chiroptical Properties

We demonstrate facile and efficient construction of conjugated double helical ladder oligomers from the saddle-shaped cyclooctatetrathiophene (COTh) building blocks. The key step involves deprotonation of tetra[3,4]thienylene (β,β-COTh) with n-BuLi which displays remarkably high ipsilateral selectivity. Three racemic double helical ladder oligomers, rac-DH-1, rac-DH-2, and rac-DH-3, containing two, three, and five COTh annelated moieties are efficiently synthesized by diastereoselective coupling of the racemic precursors. The X-ray crystallographic studies of rac-DH-1, rac-DH-2 and rac-DH-3 unambiguously revealed that each double helical scaffold has two single helices intertwined with each other via the C-C single bonds. Following removal of TMS groups, double helical ladder oligomer rac-DH-1-D had sufficient solubility to be resolved via chiral HPLC, thus enabling determination of its chirooptical properties such as CD spectra and optical rotation. (+)-DH-1-D has a large barrier for racemization, with lower limit of ΔG(‡) > 48 kcal mol(-1), which may be compared to DFT-computed barrier of 51 kcal mol(-1). The enantiomers of DH-1-D show 1 order of magnitude stronger chirooptical properties than the carbon-sulfur [7]helicene, as determined by the anisotropy factor g = Δε/ε = -0.039, based on Δεmax = -11 and ε = 2.8 × 10(2) L mol(-1) cm(-1) in cyclohexane at 327 nm.

Novel dithienosilole-based conjugated copolymers and their application in bulk heterojunction solar cells

Three asymmetrical dithienosilole monomers with different electron withdrawing groups (nonanoyl group, octyl cyanoacetate or malononitrile) were synthesized and a series of silicon containing conjugated polymers (PBDTDTSi-1, PBDTDTSi-2 to PBDTDTSi-3) were prepared from these asymmetrical dithienosilole building blocks via microwave assisted polymerization. Density functional theory (DFT) quantum chemistry calculations were employed for the optimization of molecular structures, deep understanding of the electronic structures and their photophysical properties. When these polymers were utilized as the donor materials for polymer solar cells (PSCs), the influence of side chains on the photovoltaic performance was investigated and all the polymers presented high open-circuit voltage above 1.0 V. PSCs with a blend of PBDTDTSi-1:PC71BM (1 : 4, by weight) as the active layer showed the highest power conversion efficiency of 3.29%, with an open-circuit voltage of 1.07 V, a short-circuit current density of 7.53 mA cm−2, and a fill factor of 0.41. Our research revealed that the variation of substituents on the dithienosilole moieties had a great influence on the morphology of blend films and charge carrier mobilities, which are crucial to the performance of PSCs.

Naphthotetrathiophene-Based Helicene-Like Molecules: Synthesis and Photophysical Properties

Two novel helicene-like molecules based on naphthotetrathiophene are successfully synthesized. All target molecules and intermediates are characterized by (1)H NMR, (13)C NMR, IR, and HRMS. Their electrochemical and photophysical properties are studied. The configurations of the molecules are optimized by DFT quantum calculations and UV-vis behaviors are also predicted to further understand the origin of different absorption bands. We believe the current work illustrated an efficient way for the design and synthesis of sophisticated structures with naphthotetrathiophene as building blocks.

Facile Synthesis of the O-Functionalized Ladder-Type Dipyran Building Block and Its Application in Polymer Solar Cells.

A new centrosymmetrical dipyran unit (DTDP) is successfully prepared by means of an efficient and universal way, and a series of PDTDP polymers have been prepared so as to assess their potential application in organic photovoltaic. The function of pyran moiety is not merely limited to tune the electron-donating roles and energy levels but it also contributes to solubility improvement. Interestingly, all pyran-based polymers displayed wide absorption ranging from 350 to 780 nm, but varied aggregation phenomena are observed. Furthermore, the quantum chemistry calculations for dimers, morphology study and grazing-incidence wide-angle X-ray scattering analysis for blend films have been utilized to understand the variations at photovoltaic performances. Finally, PDTDP-4 achieved the highest power conversion efficiency of 7.26% ( Voc = 0.72 V, FF = 0.66, and Jsc = 15.30 mA/cm2), demonstrating promising usage for high-efficiency polymer donors in polymer solar cells. In all, not only a promising dipyran building block is provided by this study, more dipyran derivatives and polymers could be prepared via this facile synthetic route.

Bright red fluorescent conjugated polymer nanoparticles with dibenzopyran as electron donor for cell imaging

Fluorescent conjugated polymers (CPs) have been successfully used to make conjugated polymer nanoparticles (CPNs) for cellular imaging, bio-orthogonal labeling, and in vivo tumor targeting, since CPNs have superior bright fluorescent emission and photostability. However, the preparation of red fluorescent CPNs with reasonably high quantum yield (QY) is still very challenging. We have synthesized bright red fluorescence CPNs based on a conjugated polymer that contains an annulated pyran ring and branched alkoxy chains, which have helped to reduce close packing in the solid phase. We examined the impact of the molecular weight of CPs on the QYs of CPNs. QY as high as 51.8–36.8% was observed in all CPNs with normally used CPs, with a surfactant mass ratio of 1 : 2. Our CPNs provided intense and stable fluorescence which could be traced through several generations in cell imaging, indicating the considerable photostability and biocompatibility of our CPNs.