Molecular electronic structure plays a vital role in the photovoltaic performances in polymer solar cells (PSCs) due to their influences on light-harvesting, charge carrier transfer, π–π stacking, etc. Indacenodithiophene as a star unit has been well studied in PSCs; various structural derivation methods have been tried, but they are still not efficient in improvement of power conversion efficiencies (PCE) due to the narrow optical absorptions. In this contribution, a novel planar DMIDT with extended lateral π-electron delocalization is efficiently synthesized via introduction of sp2 hybrid carbons as the bridge atoms. Based on this novel building block, a two-dimensional conjugated polymer PDMIDT-TPD is prepared, and the unique structure improves the conjugation at the lateral direction, enlarges the electron delocalization area, and greatly broadens the absorption spectrum with a full coverage from 350 to 700 nm. Finally, a PCE of 8.26% is achieved when blended with PC71BM, which is the highest result among the IDT-based polymer donors. Meanwhile, PDMIDT-TPD also presents good compatibility with the non-fullerene acceptor, and a preliminary PCE of 6.88% is obtained. In all, this work not only provides an excellent donor material but also offers a general and simple derivation strategy for fused aromatic building blocks.

New building blocks, 2,5-di(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]selenophene ((TMS)2-DSS) and 2,5-di(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]thiophene ((TMS)2-DST), for helicenes were obtained from selenophene with total yields of 54 and 61%. From (TMS)2-DSS and (TMS)2-DST, selenophene-based hetero[7]helicenes, 5,5′-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]thiophene) (rac-1), and 5,5′-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]selenophene) (rac-2) were prepared. The overall yields from selenophene were approximately 6.5 and 6.1%, respectively. Intermolecular interactions such as C–Se, C–S, and Se–Se were observed in the crystal packings of rac-1 and rac-2. In addition, the absorption behaviors of rac-1 and rac-2 were investigated.

The sequential lithiation mechanism for the selective deprotonation of tetra[3,4]thienylene (1) to form Li4-1 in the present of n-BuLi in THF is investigated. The specific contralateral and ipsilateral selectivities of the lithiation sites in the different steps are explored. A series of tetra-substituted 1 are obtained, viaLi4-1 with electrophiles, in good yields.

A series of thiophene-based conjugated microporous polymers (ThPOPs) have been synthesized on the basis of ferric chloride-catalyzed oxidative coupling polymerization of multi-thienyl monomers. The structures of ThPOPs were confirmed via solid-state 13C CP/MAS NMR spectroscopy and Fourier-transform infrared spectroscopy. The ThPOPs possess high porosities and their high Brunauer-Emmett-Teller specific surface area results vary between 350 and 1320 m2 g−1. The presence of abundant ultra-micropores at 0.50–0.63 nm allows ThPOPs efficient gas (carbon dioxide, methane, and hydrogen) adsorption.

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 × 102 L mol–1 cm–1 in cyclohexane at 327 nm.

In this research, with the assistance of scanning tunneling microscopy (STM), we observed the two-dimensional (2D) self-assembly transition of a star-shaped oligofluorene derivative (StOF) from disordered structure to honeycomb network by adjusting StOF concentration in solution. By introducing guest molecules coronene (COR), we for the first time achieved novel triangle-shaped COR trimers on liquid/highly oriented pyrolytic graphite (HOPG) interface in both honeycomb network and the disordered structure. In thermal tests, the COR/StOF–disorder system underwent a structural conformation to form well-ordered ladder structures, while the COR/StOF–honeycomb system remained the perfect hexagonal network with COR trimers included in the cavities. Density functional theory (DFT) calculations have been employed to investigate the forming mechanism of the molecular nanoarrays. These studies are expected to enhance controlling on 2D self-assembly and provide a facial approach toward constructing on-surface molecular clusters.Keywords: concentration regulation; coronene cluster; honeycomb network; scanning tunneling microscopy; temperature regulation

•Different dithienosilole building blocks are prepared with different alkyl side chains.•A series of dithienosilole based conjugated copolymers are prepared.•Side chain plays an important role in morphology and photovoltaic performance.A series of dithienosilole copolymers are designed and prepared from dithienosilole monomers with different acyl groups and benzodithiophene as the comonomer. Microwave assisted Stille coupling method is employed for the polymerization. The photophysical, thermal, electrochemical and photovoltaic properties of the new polymers were characterized. The series of the polymers presented similar absorption behavior, but slight differences could be observed. Finally, the polymers were evaluated as the donor materials for polymer solar cells, which all presented high open-circuit voltage around 1.0 V, and the branched 3,7-dimethyloctane modified polymer displayed the best performance with a PCE of 2.66% (Voc = 1.01 V, Jsc = 6.71 mA/cm2 and FF = 0.39). This photovoltaic variation might be attributed to the morphology difference raised by the substituted alkyl chains.

Two novel helicene-like molecules based on naphthotetrathiophene are successfully synthesized. All target molecules and intermediates are characterized by 1H NMR, 13C 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.

The unsymmetric dithieno[3,2-b:3′,4′-d]thiophene (ts-DTT) was efficiently synthesized, and two novel heptathienoacenes with linear and bull’s horn shapes were designed and prepared via different ring cyclization connection manners. All intermediates and aimed heptathienoacenes were fully characterized by 1H NMR, 13C NMR, and HRMS. Their UV–vis absorption behavior, fluorescence, and electrochemical properties are characterized. In addition, DFT quantum calculation was employed to further understand the electron distribution and the origin of the absorption bands.

2,5-Distyryl-dithieno[2,3-b:2′,3′-d]thiophene (DEP-bt-DTT), an isomer of 2,5-distyryl-dithieno [2,3-b:3′,2′-d]thiophene (DEP-bb-DTT) and 2,5-distyryl-dithieno[3,2-b:2′,3′-d]thiophene (DEP-tt-DTT), was synthesized. Organic field-effect transistors (OFETs) based on these three isomers were fabricated. The structure cell parameters and the formation of intermolecular interactions in their single crystals show regular change when the positions of sulphur atoms vary from top–bottom–top in DEP-tt-DTT to bottom–bottom–top in DEP-bt-DTT, then to bottom–bottom–bottom in DEP-bb-DTT. Combining the results of theoretical calculations and OFET performances, it reveals that: (1) the positions of sulphur atoms determine the contribution extent of sulphur atoms to the molecular conjugation and the formation of intermolecular interactions; (2) the existence of the intermolecular interactions, especially for S–π, benefits for the charge transport; (3) the field-effect mobility (μ) increases with increasing of the sulphur atom contribution to the molecular conjugation.

The novel propeller type compound, 2,4,6-tri(anthracen-9-yl)-1,3,5-triazine (TAT) with C3 symmetry was synthesized by using 9-anthryl lithium with 1,3,5-trichlorotriazine or 2-chloro-4,6-dimethoxy-1,3,5-triazine in the presence of palladium catalyst in 22–48% yield. Another two propeller-like compounds, 2-(anthracen-9-yl)-4,6-dimethoxy-1,3,5-triazine (3) and 2,4-di(anthracen-9-yl)-6-methoxy-1,3,5-triazine (4) were obtained at the same time. The propeller type structures of TAT, 3 and 4 were confirmed by crystal analysis and theoretical calculations. The intramolecular C–C bond rotations between the anthryl groups and the triazine units in molecules TAT, 3 and 4 were regarded as the key factor to understand their spectroscopic behaviors in fluid medium and rigid solution.

Four cross-conjugated butterfly-shaped molecules were designed and synthesized with the branched tetrakis(thiophene-2-yl)ethene or the planar naphthotetrathiophene as the donors and dicyanovinylene as the acceptor. Owing to the donor–acceptor conjugated structures, these molecules exhibited broad and strong absorbance in the UV–vis region. Their electrochemical and photophysical properties were studied; in addition, the UV–vis behaviors were also described by virtue of DFT calculations to further understand the origins of different absorption bands and efficient charge transfer was observed for given optical transitions from the ground states to the excited states in natural transition orbitals. Finally, these butterfly-shaped molecules were applied to fabricate organic photovoltaic devices and we believe the current work illustrated an efficient way for the design and synthesis of sophisticated structures with the tetrathiophene building blocks.

Silicon spiro carbon–sulfur double helicene-like compounds 1 and rac-2 were synthesized from 2,5-bis-trimethylsilanyldithieno[2,3-b:3′,2′-d]thiophene, with total yields of 17% and 7%, respectively. 1H and 13C NMR spectra and X-ray crystallographic analysis showed the predicted 4-fold symmetry for 1 and rac-2 and confirmed their spiro double helicene-like spatial configurations. The absorption behavior of compounds 1 and rac-2 was also investigated.

Based on the selectivity of deprotonation of 5,5′-bistrimethylsilyl-2,3′-bithiophene (4) in the presence of n-BuLi, three new cyclooctatetrathiophenes (COThs), COTh-1, COTh-2, and COTh-3 have been efficiently developed via intermolecular or intramolecular cyclizations. Their crystal structures clearly show that the different connectivity sequence of the thiophene rings in the molecules. The CV data and UV–vis absorbance spectra of COThs are also described. In addition, the time-dependent density functional theory (TDDFT) calculations accurately reproduce experimental observations and afford band assignment.

Thiophene-based organic semiconductors used as the active components have received much attention. Their photoelectric properties can be easily tuned with various substitutions at different positions on molecular structures. Here, we synthesized series cyclopentadithiophene (CDT) derivatives with sulfur atoms at ortho- (o-CDT), meta- (m-CDT), and para-positions (p-CDT) of the bridge carbon. These CDT derivatives were substituted by carbonyl/dicyanomethylene at the bridge position and/or by phenyl groups at the α position, respectively. Due to the different conjugation extent and the variation of donor–acceptor (D–A) interaction originating from the change of sulfur atom position, diverse absorption spectra were observed. Especially for dicyanomethylene substituted o-CDT with phenyl as substitution group (DPCN-o-CDT), its absorption spectrum covers the whole region of visible light. Combining with the electrochemical behaviors and theoretical calculations, it was found that the sulfur atoms mainly contribute to the molecular conjugation in these CDT derivatives, especially for o-CDT derivatives. For phenyl groups, they primarily act as electron donor in m-CDT derivatives, and chiefly contribute to molecular conjugation in p-CDT derivatives, and simultaneously work as electron donor and conjugation component in o-CDT derivatives, respectively.

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 1H NMR, 13C 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.

A series of derivatives based on annelated β-oligothiophenes were synthesized and characterized as active layer in organic field-effect transistors (OFETs). Highest field-effect mobility of 0.52 V−1 s−1 for 2,5-dibiphenyl-dithieno[2,3-b:3′,2′-d]thiophene (DBP-DTT), 2.2 cm2 V−1 s−1 for 2,5-distyryl-dithieno[2,3-b:3′,2′-d]thiophene (DEP-DTT), and 0.16 cm2 V−1 s−1 for 1,4-di[2-dithieno[2,3-b:3′,2′-d] thiophen-2-yl-vinyl]benzene (DDTT-EP) were obtained, while 2,5-diphenyl-dithieno [2,3-b:3′,2′-d]thiophene (DP-DTT) presents no field-effect behaviors. Their thermal, optical and electrochemical properties, topographical and X-ray diffraction patterns of films, and the single crystal structures were also investigated. With the end-capping groups changing in these materials, the intermolecular interactions could transform from S–S in DP-DTT to S–C in DBP-DTT, to S–π in DEP-DTT, and to the coexisting of S–S and S–π in DDTT-EP. According to the device performances and the results of transfer integral calculations, it was revealed that S–π intermolecular interaction benefits not only improving the mobility but also reducing the threshold voltage (VT), while S–S intermolecular interaction is not favorable for promoting the mobility.Graphical abstractIntermolecular interaction in the single crystals of DTT derivatives.Highlights► The intermolecular interaction can transfer from S–S to S–C, to S–π, and to the coexisting of S–S and S–π. ► The molecules adopt a condensed arrangement as the S–C intermolecular interaction existing. ► S–π intermolecular interaction benefits not only improving the mobility but also reducing the threshold voltage.

In this work, the racemate and mesomer of the thiophene-based naphthalene-cored double helicenes (1) were obtained efficiently by one-pot photocyclization of 1,1,2,2-tetrakis(dithieno[2,3-b:3′,2′-d]thiophen-2-yl)ethene in the presence of iodine in dry benzene. The structure of meso-1a was confirmed by single crystal X-ray analysis. The chiral resolution of the racemate was carried out by chiral HPLC, and the chiral properties, such as CD spectra, optical rotations, and half-life of enantiomers were characterized.

A novel bull’s horn-shaped oligothienoacene with seven fused thiophene rings (1) based on dithieno[2,3-b:2′,3′-d]thiophene (2) was efficiently synthesized. X-ray diffraction data indicate that 1 possesses an extraordinary compressed sandwich-herringbone arrangement and shows strong intermolecular S···C and S···S interactions. In addition, the UV/vis properties, theoretical calculations, and cyclic voltammetry behaviors of 1 are also described.

The novel selective synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings (DTHAs) has been developed via intramolecular cyclization of 4,4′-dibromo-3,3′-bithiophene (3). Four reaction conditions including n-BuLi/Et2O, n-BuLi/THF, s-BuLi/Et2O, and t-BuLi/Et2O were employed to react with 3 for selective formation of two types of dicarbanions, which generate the symmetrical and unsymmetrical DTHAs after quenching with three electrophilic reagents (4a–c). The possible mechanism of formation of DTHAs was proposed. In addition, two unsymmetrical DTHAs were confirmed by X-ray single-crystal analyses.

With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV–vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino–imino tautomerization emission in excited state.Highlights► A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. ► Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. ► Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. ► Amino–imino tautomerization emission in excited state are proposed.

The efficient synthesis of novel unsymmetrical dithienosiloles, 7,7-dimethyl-4,6-di(trimethylsilyl)-dithieno[2,3-b:4′,3′-d]silole (1) and 7,7-dimethyl-2,4,6-tri(trimethylsilyl)-dithieno[2,3-b:4′,3′-d]silole (2) has been developed by intramolecular silole formation with 4,4′-dibromo-2,2′,5,5′-tetrakis(trimethylsilyl)-[3,3′]bithienyl (3) as the starting material in the presence of t-BuLi. Upon treatment with N-bromosuccinimide (NBS) under controlled conditions, dithieno[2,3-b:4′,3′-d]silole was selectively brominated to produce mono-, di-, and tribrominated dithieno[2,3-b:4′,3′-d]siloles in good yields. The crystal structures of the title compounds are described.

Organic field-effect transistors based on two derivatives of annelated β-oligothiophenes are fabricated. High mobility of 2.2 cm2 V−1 s−1 is obtained for 2,5-distyryl-dithieno[2,3-b:3′,2′-d]thiophene (DEP-DTT) while 2,5-diphenyl-dithieno[2,3-b:3′,2′-d]thiophene (DP-DTT) presents no field-effect characteristics. The existence of S–π intermolecular interaction in DEP-DTT, which is introduced by CC double bonds, plays an important role in the molecular arrangement both in single crystal and thin film structures, and the charge transport of organic field-effect transistors.

Bis(trimethylsilyl)benzohexathia[7]helicene 1, naphthalene cored double helicene 2 (the fused dimer of 1), and a novel ten-membered cyclic diketone with four moieties of dithieno[2,3-b:3′,2′-d]thiophene (3) were efficiently synthesized. Their crystal structures were determined with single-crystal X-ray analysis. In their crystal packings, they all show mutiple short contacts including intermolecular π···π, π···S, and S···S interactions. UV/vis spectra indicate that significant π-electron delocalization existed in 1, 2, and 3.

Self-organized dithieno [3,2-b:2’,3’-d] thiophene-2,5-dicarboxylic acid (A) and dithieno [2,3-b:3’,2’-d] thiophene-2,5-dicarboxylic acid (B) films were prepared through solvent-induced order-disorder transition method. The arrangement of the two molecules on substrates were observed by atomic force microscopy (AFM), which demonstrated that A was arranged orderly in a certain angle on mica, while B was flat-flying on mica. The optical and conductance properties in micro region of these two compound films were characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy and conductive atomic force microscopy (C-AFM). The results revealed that the fluorescence and absorption peaks of A had a large red shift in comparison with those of B. The conductance of the J-aggregates for A is three orders magnitude higher than that of B. It is concluded that the large conductance difference mainly comes from different aggregation structures and orientations of these two molecules on substrate.

With 4,4′-dibromo-2,2′,5,5′-tetrakis(trimethylsilyl)[3,3′]bithienyl (4) as substrate in the presence of t-BuLi (4 equiv)/CuCl2, a compound with a novel structure, a D2-symmetric derivative of thienosilole (1), is prepared in 55−64% yield. Three steps of bond breaking and bond forming are involved in the “one-pot” reaction to form 1: (1) a C−Si bond forms in the ring formation of silole; (2) a C−S bond breaks in thiophene ring-opening alkynylation; (3) a S−S bond forms in the CuCl2-promoted coupling. On the other hand, if a short time for Br/Li exchange was used in the process, the intramolecular coupling compound tetrakis(trimethylsilyl)cyclobuta[1,2-c:3,4-c′]dithiophene (2) was obtained instead. 2 could be obtained in 11−20% yield. None of the intermolecular coupling compound octakis(trimethylsilyl)tetrathienylene (5) was observed.

The sequential lithiation mechanism for the selective deprotonation of tetra[3,4]thienylene (1) to form Li4-1 in the present of n-BuLi in THF is investigated. The specific contralateral and ipsilateral selectivities of the lithiation sites in the different steps are explored. A series of tetra-substituted 1 are obtained, viaLi4-1 with electrophiles, in good yields.

Organic field-effect transistors based on two derivatives of annelated β-oligothiophenes are fabricated. High mobility of 2.2 cm2 V−1 s−1 is obtained for 2,5-distyryl-dithieno[2,3-b:3′,2′-d]thiophene (DEP-DTT) while 2,5-diphenyl-dithieno[2,3-b:3′,2′-d]thiophene (DP-DTT) presents no field-effect characteristics. The existence of S–π intermolecular interaction in DEP-DTT, which is introduced by CC double bonds, plays an important role in the molecular arrangement both in single crystal and thin film structures, and the charge transport of organic field-effect transistors.

2,5-Distyryl-dithieno[2,3-b:2′,3′-d]thiophene (DEP-bt-DTT), an isomer of 2,5-distyryl-dithieno [2,3-b:3′,2′-d]thiophene (DEP-bb-DTT) and 2,5-distyryl-dithieno[3,2-b:2′,3′-d]thiophene (DEP-tt-DTT), was synthesized. Organic field-effect transistors (OFETs) based on these three isomers were fabricated. The structure cell parameters and the formation of intermolecular interactions in their single crystals show regular change when the positions of sulphur atoms vary from top–bottom–top in DEP-tt-DTT to bottom–bottom–top in DEP-bt-DTT, then to bottom–bottom–bottom in DEP-bb-DTT. Combining the results of theoretical calculations and OFET performances, it reveals that: (1) the positions of sulphur atoms determine the contribution extent of sulphur atoms to the molecular conjugation and the formation of intermolecular interactions; (2) the existence of the intermolecular interactions, especially for S–π, benefits for the charge transport; (3) the field-effect mobility (μ) increases with increasing of the sulphur atom contribution to the molecular conjugation.