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π-Stacked dendrimers consisting of cofacially aligned donors and acceptors are developed by introducing three dendritic teracridan donors with orthogonal configuration and three triazine acceptors in periphery of hexaphenylbenzene skeleton. The dendritic structure and orthogonal configuration of teracridan not only make their outer acridan segments approaching to acceptor in close distance, but also fix donor and acceptor in face-to-face alignment, leading to through-space charge transfer emission with thermally activated delayed fluorescence (TADF) effect. By regulating charge transfer strength via substituent effect of acceptor, emission color of the dendrimers can be tuned from blue to yellow/red region. Solution-processed two-color white organic light-emitting diodes (OLEDs) based on blue and yellow π-stacked donor-acceptor dendrimers exhibit the maximum external quantum efficiency of 20.6 % and maximum power efficiency of 58.9 lm W-1 , representing the state-of-the-art efficiency for all-TADF white OLEDs by solution process.

Based on a donor-acceptor (D-A) structure, small molecules with thermally activated delayed fluorescence (TADF) have been widely applied in cost-effective and high-performance organic light-emitting diodes (OLEDs). As an analogue, however, D-A conjugated polymers often possess a significant frontier molecular orbital overlap because of the conjugation elongation to some degree, leading to no TADF caused by a large singlet-triplet energy splitting (∆ E ST ). To solve this problem, herein a novel steric locking strategy is proposed by incorporating methyl groups into D-A conjugated polymers. Benefitting from the methyl hindrance, the torsion between the donor and acceptor can be well tuned to form a sterically-locked conformation, so that the unwanted relaxation toward planarity and thus conjugation elongation is prevented to boost hole-electron separation. Consequently, the resultant sterically-locked D-A conjugated polymer achieves an extremely low ∆ E ST of 0.09 eV to enable efficient TADF. The corresponding doped and non-doped devices are fabricated via a solution process, revealing a record-high external quantum efficiency (EQE) of 24.0% (79.4 cd/A, 75.0 lm/W) and 15.3% (50.9 cd/A, 47.3 lm/W), respectively, together with a gentle efficiency roll-off at high luminance.

Boron (B)- and sulfur (S)-doped polycyclic aromatic hydrocarbons (PAHs) are developed as a novel kind of multiple resonance emitters for ultrapure blue thermally activated delayed fluorescence (TADF) polymers with narrowband electroluminescence. The combination of electron-deficient B atom and electron-rich S atom in PAH can form an intramolecular push-pull electronic system in a rigid aromatic framework, leading to reduced singlet-triplet energy splitting and limited structure relaxation of excited states. The critical roles of S atom in determining emission properties with respect to the oxygen analogues are in two aspects: (i) reducing energy bandgap to shift emission from human-eye-insensitive ultraviolet zone to blue region, and (ii) promoting reverse intersystem crossing process by heavy-atom effect to activate TADF effect. The resulting polymer containing B,S-doped PAH as emitter and acridan as host exhibits efficient blue electroluminescence at 458 nm with small full-width at half-maximum of 31 nm, representing the first example for ultrapure TADF polymer with narrowband electroluminescence.

Thermally activated delayed fluorescent (TADF) materials based tetracoordinate boron acceptors hold great potential for organic light emitting diode (OLED) applications; however, these emitters suffer from a low luminescent efficiency (ΦPL) and a large device efficiency roll-off. Herein, we design and synthesize two D–A-type emitters based on two fused boron ketoiminate (FBKI and aza-FBKI) acceptors and a 9,9-dimethylacridine (DMAC) donor. Through changing the carbon atom to a nitrogen atom in the fused boron ketoiminate units, a conventional fluorescent molecule (DMAC-FBKI) can be transformed into a highly efficient TADF molecule (DMAC-aza-FBKI) due to the dramatically reduced ΔEST (0.46–0.04 eV). DMAC-aza-FBKI exhibits a short delay lifetime of 2.2 μs and a large reverse intersystem crossing rate constant (kRISC ≈ 1.5 × 106 s−1), which is attributed to the rather close energy levels of its 3LE, 3CT and 1CT states based on theoretical calculations. Furthermore, compared with DMAC-FBKI (ΦPL ≈ 44%), DMAC-aza-FBKI has a higher ΦPL of 82% due to the existence of intramolecular hydrogen bonding. Consequently, the corresponding electroluminescent device achieves the highest external quantum efficiency (EQE) of 16.2% and an efficiency roll-off of only 9.3% at 1000 cd m−2, which are much better than those of the device based on the TADF-inactive DMAC-FBKI.

Organic compounds with selective near-infrared absorption and visible transparency are very desirable for fabrication of transparent/semitransparent optoelectronic devices. Herein, we develop a molecule with selective near-infrared absorption property, QBNA-O, in which four B←N units are incorporated to the core and two benzodioxin groups are introduced at the termini of the dibenzo-azaacene skeleton. QBNA-O exhibits a small optical gap of 1.39 eV due to the strong electron-donating benzodioxin groups and the strong electron-withdrawing B←N units. In toluene solution, QBNA-O shows a strong absorption peak at 856 nm with the full width at half maximum (FWHM) of only 41 nm as well as very weak absorption in the visible range from 380 nm to 760 nm. Thin films of QBNA-O exhibit the average visible transparency (AVT) of 78 % at the thickness of 205 nm and 90 % at the thickness of 45 nm. Solution-processed organic field-effect transistors (OFETs) of QBNA-O display ambipolar transporting behavior with the electron mobility of 0.52 cm2 V-1 s-1 and the hole mobility of 0.013 cm2 V-1 s-1 together with excellent air-stability. The selective NIR absorbing property and excellent charge transporting property imply that QBNA-O can be used to fabricate transparent organic optoelectronic devices.

The copper(i) arylacetylide polymers reported previously are almost insoluble and infusible so as to restrain their applications. Herein, an unusual design strategy for stable and soluble copper(i) arylacetylide polymers is reported.

A series of blue-emitting poly(2,8-indenofluorene-co-2,7-carbazole)s, namely P(IF-Cz10), P(IF-Cz25), and P(IF-Cz50), has been designed and synthesized for use in polymer light-emitting diodes (PLEDs). With increasing carbazole content, the resultant copolymers are found to show blue-shifted emission and reduced photoluminescence quantum yields (PLQYs) in films. Consequently, P(IF-Cz25) represents the best trade-off between PLQY and blue light of these materials. The corresponding device reveals a peak external quantum efficiency of 4.12% (3.19 cd A−1, 2.78 lm W−1) and Commission Internationale de L’Eclairage coordinates of (0.150, 0.081). The results clearly indicate that the copolymerization of indenofluorene and carbazole is a promising strategy for developing blue PLEDs with simultaneous high efficiency and good color purity, with a CIEy value of

The electronic properties of quinoidal compounds can be modulated both by their central quinoidal cores and by their end groups. However, there have only been a few studies of the effects of end-groups on the electronic properties of quinoidal compounds, due to synthetic challenges. In this study, we have prepared four quinoidal compounds, IDOTT, 2FIDOTT, 4FIDOTT, and 6FIDOTT, with different numbers of fluorine (F) atoms on the terminal isatin units, and the effects of terminal fluorination on their optical properties, energy levels, molecular packing (as single crystals and thin-films), and electron transport properties have been evaluated. The incorporation of F atoms decreased the HOMO/LUMO levels and blue-shifted the absorption spectra. All four quinoidal compounds showed n-type transport behavior in organic thin-film transistor (OTFT) devices, but their electron mobilities strongly depended on the number of F atoms. Among these compounds, 4FIDOTT exhibited the highest electron mobility (0.16 cm2 V−1 s−1), due to its two-dimensional electron transport, highly ordered thin-film, and appropriate morphology.

Room-temperature phosphorescence of most purely organic compounds can hardly be observed in their solutions. Here, we report a tetraphenylmethane derivative with four aldehyde groups, which exhibits clear blue phosphorescence in its solution at room temperature. Furthermore, its crystal displays a nearly 7-fold higher phosphorescence quantum yield as compared to the solution.

Four wide bandgap donor-acceptor (D-A) conjugated polymers, i.e. P-diF2T, P-TT, P-BDT and P-NDT, with bis(5-(2-decyltetradecyl)-[2,3′-bithiophen]-2′-yl)arylenes as D-units and 2-propyl-5,6-difluorobenzo[d][1,2,3]triazole (ffTAZ) as A unit were synthesized for photovoltaic applications. In P-diF2T, P-TT, P-BDT and P-NDT, 3,3′-difluoro-2,2′-bithiophene (diF2T), thieno[3,2-b]thiophene (TT), benzo[1,2-b:4,5-b']dithiophene (BDT) and naphtho[1,2-b:5,6-b']dithiophene (NDT) were used as aryl central units, respectively, to adjust the properties of the polymers. The optical bandgap is 1.83 eV for P-diF2T, 1.85 eV for P-TT, 1.90 eV for P-BDT and 2.04 eV for P-NDT. All four polymers show temperature-dependent aggregation behavior in solution, and their absorption spectra are complementary with that of non-fullerene acceptor (NFA) 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(5-hexylthiophen-2-yl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC-Th). Polymer solar cells (PSCs) based on these polymers and ITIC-Th were fabricated and characterized. Power conversion efficiencies (PCEs) higher than 7% were demonstrated for all polymers. The devices based on P-diF2T exhibited the highest PCE up to 10.08% with a high fill factor (FF) of 0.741. The good photovoltaic performance of P-diF2T is attributed to the synergies of the low-lying highest occupied molecular orbital (HOMO) energy level of the polymer and the favorable microstructures and morphology and thereby high and balanced charge carrier mobilities of the blend films. This study suggested that adjusting aromatic D units together with using alkylthiophene as side chains is an effective approach to design donor polymers for high performance PSCs based on NFA.

The preparation of micron- to nanometer-sized functional materials with well-defined shapes and packing is a key process to their applications. There are many ways to control the crystal growth of organic semiconductors. Adding polymer additives has been proven a robust strategy to optimize semiconductor crystal structure and the corresponding optoelectronic properties. We have found that poly(3-hexylthiophene) (P3HT) can effectively regulate the crystallization behavior of N,N′-dioctyl perylene diimide (C8PDI). In this study, we combined P3HT and polyethylene glycol (PEG) to amphiphilic block copolymers and studied the crystallization modification effect of these block copolymers. It is found that the crystallization modification effect of the block copolymers is retained and gradually enhanced with P3HT content. The length of C8PDI crystals were well controlled from 2 to 0.4 μm, and the width from 210 to 35 nm. On the other hand, due to the water solubility of PEG block, crystalline PEG-b-P3HT/C8PDI micelles in water were successfully prepared, and this water phase colloid could be stable for more than 2 weeks, which provides a new way to prepare pollution-free aqueous organic semiconductor inks for printing electronic devices.

The B←N unit has a large dipole and it is isoelectronic to C-C moiety with no dipole. Incorporating B←N units into π-conjugated system is a powerful strategy to design organic small molecules and polymers with intriguing opto-electronic properties and excellent opto-electronic device performance. However, it is unclear how the B←N unit affects electronic structures and opto-electronic properties of large π-conjugated molecules. In this work, to address this question, we developed three dibenzo-azaacene molecules in which two B←N units were introduced at different positions. Although the dibenzo-azaacene skeleton is fully π-conjugated, the effect of B←N unit on the electronic structures of the adjacent rings is much stronger than that of the distant rings. As a result, the three molecules with isomerized B←N incorporation patterns possess different electronic structures and exhibit tunable opto-electronic properties. Among the three molecules, the centrosymmetrical molecule exhibits higher LUMO/HOMO energy levels than those of the two axisymmetrical molecules. When used as the active layer in organic field-effect transistors (OFETs), while the two axisymmetrical molecules show unipolar electron transporting property, the centrosymmetrical molecule exhibits ambipolar hole and electron transporting behavior. This work not only deepens our understanding on organoboron π-conjugated molecules, but also indicates a new strategy to tune opto-electronic properties of organic semiconductors for excellent device performance.

In this work, two thermally activated delayed fluorescence (TADF) fluorophores (TAT-BP and TAT-2BP) based on triazatruxene (TAT) and benzophenone (BP) have been successfully prepared. While both compounds show similar green emission and typical AIE behaviors, TAT-2BP with two BP units exhibits a shorter delay fluorescence lifetime (0.54 μs) than TAT-BP with one BP unit (0.79 μs) in neat films. In solution-processable non-doped organic light-emitting diodes (OLEDs), TAT-2BP shows a better EL performance with a turn-on voltage of 2.5 V, a maximum current efficiency of 32.3 cd A−1, a maximum power efficiency of 33.0 lm W−1, and a maximum external quantum efficiency of 9.8%. Remarkably, very small efficiency roll-offs of 1.0% at 1000 cd m−2 and 2.0% at 2000 cd m−2 are realized for TAT-2BP based devices, which are also much lower than those of TAT-BP (10.9% at 1000 cd m−2 and 28.0% at 2000 cd m−2), indicating that the utilization of TAT-2BP with a shorter delay fluorescence lifetime can efficiently retard the efficiency decline.

Two isomeric 2-hexyl substituted five-ring-fused asymmetric thienoacenes, i.e., thieno[1]benzothieno[3,2-b][1]benzothiophene (BTBTT6), in which the S atom in the terminal thiophene ring is located at different positions relative to the BTBT core, were synthesized and characterized. The syn-isomer forms bilayer “head-to-head” structures with herringbone packing modes within the layers in crystals, while the anti-isomer shows “head-to-tail” single-layer structures and sandwich-herringbone packing within the layers. The difference in packing structures involved the fact that the syn-isomer has stronger intermolecular interactions than the anti-isomer. Importantly, organic thin-film transistors (OTFTs) with near-ideal transfer and output characteristics were fabricated. Mobilities in the saturation and the linear regime (μsat and μlin) of up to 11.7 and 10.6 cm2 V−1 s−1, respectively, were achieved for the syn-isomer. This is the first report on OTFTs with both μsat and μlin above 10 cm2 V−1 s−1.

Three novel water-soluble and pH neutral small molecules based on a triazatruxene (TAT) core containing sodium propanylsulfonate, sodium butanylsulfonate and sodium butanyl-2-sulfonate as the side chains, respectively, have been designed and used as hole injection materials in solution-processable organic light-emitting diodes. These molecules show a high transmittance of nearly 100% in the visible and near infrared region (400–1000 nm). Relative to PEDOT:PSS, the comparable HOMO levels and higher LUMO levels of TAT-based materials favor the efficient injection of holes to the emitting layer and the efficient blocking of electrons and excitons. Among the TAT-based materials, the device based on TAT-4C with the sodium butanylsulfonate side chains exhibits the best performance with a maximum EQE of 11.0%, a maximal current efficiency (LE) of 38.8 cd A−1 and a power efficiency (PE) of 39.2 lm W−1, which are also higher than those of the PEDOT:PSS-based device (an EQE of 10.6%, a LE of 37.6 cd A−1 and a PE of 35.1 lm W−1). In additon, all the devices based on the TAT-based molecules show better performance than PEDOT:PSS-based device at 10 000 cd m−2, owing to their wider bandgaps and higher LUMO levels than PEDOT:PSS, indicating that the utilization of these TAT-based molecules as hole injection materials retards the efficiency decline.

Seven diketopyrrolopyrrole (DPP)-based donor–acceptor (D–A) conjugated polymers, i.e., poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-3,3′,4,4′-tetrafluoro-2,2′-bithiophene] (P4F2T-C40), poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-1,2-bis(3,4-difluorothiophen-2-yl)ethyne] (P4FTAT-C40), poly[2,5-bis(4-octadecyldocosyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C40), poly[2,5-bis(4-tetradecyloctadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C32), poly[2,5-bis(4-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)ethene] (P4FTVT-C24), poly[2,5-bis(2-decyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-1,2-bis(3,4-difluorothien-2-yl)et...

Four bisisoindigo (bis-IID) derivatives containing different numbers of electron withdrawing fluorine (F) or nitrogen (N) atoms and eight alternating copolymers of them with 2,2′-bithophene (BT) or 3,3′,4,4′-tetrafluoro-2,2′-bithiophene (4FBT) were synthesized. Depending on the numbers of F and N atoms incorporated, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the polymers were feasibly tuned in the ranges of −5.51 to −6.06 eV and −3.64 to −4.01 eV, respectively. Top gate and bottom contact (TGBC) organic thin-film transistors (OTFTs) were fabricated to study the semiconducting properties of the polymers. Five polymers, i.e., P0F-BT, P2F-BT, P4F-BT, P2N2F-BT, and P0F-4FBT that contain 0–4 F and N atoms in the repeating unit, with HOMO and LUMO energy levels above −5.90 and −3.80 eV, respectively, all showed ambipolar OTFT characteristics. Three other polymers P2F-4FBT, P4F-4FBT, and P2N2F-4FBT that contain 6 or 8 F and N atoms with HOMO ...

We herein report the synthesis and characterization of four asymmetric conjugated oligomers based on polycyclic aromatics, i.e. , 2-(5-hexylselenophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-S6), 2-(5-hexylfuryl-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-F6), 2-(5-hexylselenophen-2-yl)[1]benzoselenopheno[3,2-b][1]benzoselenophene (BSBS-S6) and 2-(5-hexylfuryl-2-yl)[1]benzofuro[3,2-b][1]benzofuran (BFBF-F6), for elucidating the influence of chalcogens on molecular geometries, electronic structures, thin film microstructures and the performance of organic thin-film transistors (OTFTs). Compared to the previously reported analogue 2-(5-hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-T6), all four molecules have higher-lying highest occupied molecular orbital (HOMO) energy levels. BTBT-S6 and BSBS-S6 (S replaced by Se atoms) display similar mesomorphic behavior and packing motif in solid state. However, BSBS-S6 shows much poorer crystallinity. Only crystal phase was observed for BTBT-F6 and BFBF-F6 (S replaced by O atoms). These two molecules also adopt the molecular arrangements, film growth modes and film morphology distinct from BTBT-S6 and BSBS-S6. Thus, the four molecules exhibited very different OTFT performance. BTBT-S6 showed the highest mobility of 4.68 cm 2 V −1 s −1 and all other three compounds exhibited mobilites lower than 1 cm 2 V −1 s −1 .

Two polythiophenes with carboxylate side chains and vinylene linkers in conjugated backbones, i.e., poly[5,5′-(E)-bis(2-hexyldecyl)-2,2′-(ethene-1,2-diyl)bis(thiophene-3-carboxylate)-alt-5,5′- 2,2′-bithiophene] (PBT) and poly[5,5′-(E)-bis(2-hexyldecyl)-2,2′-(ethene-1,2-diyl) bis(thiophene-3-carboxylate)-alt-5,5′-thieno[3,2-b]thiophene] (PTT), were synthesized and characterized. Compared to poly(3-hexylthiophene) (P3HT), both polymers displayed deeper HOMO energy levels caused by the introduction of the electron-withdrawing carboxylate group and lower band gaps and shorter π-π stacking distances (ca. 3.5 A) due to the incorporation of vinylene linkers in the conjugated backbones. Polymer PBT possesses greater self-organization ability and thereby more ordered intermolecular packing in solid state. Consequently, organic field-effect transistors (OFETs) based on PBT showed a hole mobility of 0.24 cm2 V−1s−1, much higher than that (0.073 cm2 V−1s−1) of PTT. Polymer solar cells (PSCs) with the two polymers as donor materials and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor material were fabricated, and both PBT- and PTT-based PSCs showed open circuit voltage (Voc) above 0.8 V. Owing to the better hole transport property and more ordered nano-fibrillar film morphology, PBT-based PSCs exhibited a superior photovoltaic performance with power conversion efficiency (PCE) of 6.25%, higher than that of PTT-based PSCs (PCE = 5.53%). This study indicates that simultaneously introducing electron-withdrawing carboxylate in side chains and vinylene linkers in conjugated backbones could efficiently tune the energy levels and enhance the π-π interactions between conjugated backbones.

We disclose a novel strategy to design n-type acenes through the introduction of boron-nitrogen coordination bonds (B←N). We synthesized two azaacenes composed of two B←N units and six/eight linearly annelated rings. The B←N unit significantly perturbed the electronic structures of the azaacenes: Unique LUMOs delocalized over the entire acene skeletons and decreased aromaticity of the B←N-adjacent rings. Most importantly, these B←N-containing azaacenes exhibited low-lying LUMO energy levels and high electron affinities, thus leading to n-type character. The solution-processed organic field-effect transistor based on one such azaacene exhibited unipolar n-type characteristics with an electron mobility of 0.21 cm2 V-1 s-1 .

Herein, we report the synthesis and characterization of a series of [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based asymmetric conjugated molecules, that is, 2-(5-alkylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-Tn, in which T and n represent thiophene and the number of carbons in the alkyl group, respectively). All of the molecules with n ≥ 4 show mesomorphism and display smectic A, smectic B (n = 4), or smectic E (n > 4) phases and then crystalline phases in succession upon cooling from the isotropic state. Alkyl chain length has a noticeable influence on the microstructures of vacuum-deposited films and therefore on the performance of the organic thin-film transistors (OTFTs). All molecules except for 2-(thiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-ethylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene showed OTFT mobilities above 5 cm2 V–1 s–1. 2-(5-Hexylthiophen-2-yl)[1]benzothieno[3,2-b][1]benzothiophene and 2-(5-heptylthiophen-2-yl)[1]benzothieno[3,2-b][1]benz...

Two indacenodithiophene derivative bridged diketopyrrolopyrroles (DPP), i.e., 2,7-bis(2,5-bis(2-decyltetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-dione (DDPP-PhCO) and 2,2′-(2,7-bis(2,5-bis(2-decyltetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-s-indaceno[1,2-b:5,6-b′]dithiophene-4,9-diylidene)dimalononitrile (DDPP-PhCN), were developed via intramolecular Friedel–Crafts acylation and Knoevenagel condensation. A series of donor–acceptor (D–A) conjugated polymers were synthesized by Stille or direct arylation polycondensation with these two novel units as acceptors and vinyl or thiophene derivatives as donors. The polymers with DDPP-PhCO as acceptor unit exhibited optical bandgaps (Egopt) of ca. 1.2 eV and the highest occupied molecular orbital (HOMO) energy levels of ∼−5.3 eV with the difference less than 0.1 eV, and their lowest unoccupied molecular orbital (LUMO) levels were in the range o...

In this manuscript, we report a disk-type polyarene consisting of an all-hexagon π-framework and four B←N units. It exhibits intriguing electronic structures and opto-electronic properties, such as locally modulated (anti)aromaticity, strong red fluorescence and n-type semiconductor characteristics, thus representing a new kind of π-molecule containing B←N units.

Two donor–acceptor (D–A) conjugated polymers with alkylthiophene as side chains, i.e., poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′-di(2-(2-decyltetradecyl)thiophene-5-yl)-2,2′;5′,2′′;5′′,2′′′-quaterthiophene-5,5′′′-diyl)] (P-2T) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(2,5-bis(3-(2-decyltetradecyl)thiophene-5-yl)thiophen-2-yl)thieno[3,2-b]thiophene] (P-TT), are designed and synthesized. Both polymers exhibit temperature-sensitive aggregation in solution. Polymer solar cells (PSCs) based on them are fabricated with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor material. The devices based on P-TT deliver power conversion efficiency (PCE) up to 9.96% while no additive is used. Moreover, the photovoltaic performance of P-TT is insensitive to the polymer:PC71BM ratio and active layer thickness, and PCEs are all above 9% with the donor : acceptor (D : A) weight ratio of 1 : 1–1 : 1.8 (wt/wt) and film thickness of 200–360 nm. The high photovoltaic performance of P-TT is ascribed to its high and balanced charge carrier mobilities (4.51 × 10−3 and 3.44 × 10−3 cm2 V−1 s−1 for holes and electrons, respectively), owing to the favorable face-on packing of the conjugated backbones as well as the desired morphology of the blend films. Our study demonstrates that alkylthiophenes are one kind of promising synthon of oligothiophene based D–A conjugated polymers, which can serve as side chains for tuning the aggregation of the polymer in solution and the packing mode of the conjugated backbones in the film state.

In this communication, we report a series of polymer semiconductors based on a novel electron-deficient building block, double B←N bridged bipyridine (BNBP). These polymers show ambipolar or unipolar n-channel charge-transporting characteristics with electron mobilities in the range of 0.02–0.32 cm2 V−1 s−1 in organic thin film transistors.

Four donor–acceptor (D–A) conjugated polymers (CPs), i.e., poly[(E)-1,2-bis(5-(2-hexyldecyl)-[2,3′-bithiophen]-2′-yl)ethene-alt-5,6-difluorobenzo[c][1,2,5]thiadiazole] (PTVT-T8), poly[(E)-1,2-bis(5-(2-octyldodecyl)-[2,3′-bithiophen]-2′-yl)ethene-alt-5,6-difluorobenzo[c][1,2,5]thiadiazole] (PTVT-T10), poly[(E)-1,2-bis(3-(2-hexyldecyl)thiophen-2-yl)ethene-alt-5,6-difluorobenzo[c][1,2,5]thiadiazole] (PTVT-C8) and poly[(E)-1,2-bis(3-(2-octyldodecyl)thiophen-2-yl)ethene-alt-5,6-difluorobenzo[c][1,2,5]thiadiazole] (PTVT-C10) were synthesized and characterized. Compared to PTVT-C8 and PTVT-C10, PTVT-T8 and PTVT-T10 that comprise two-dimensional (2D) conjugated D units displayed lower bandgaps, more rigid backbones, higher self-organization ability and shorter π–π stacking distances (∼3.5 A). As a result, the hole mobility of PTVT-T8 and PTVT-T10 (up to 0.42 cm2 (V s)−1) was one magnitude higher than that of PTVT-C8 and PTVT-C10 (up to 0.039 cm2 (V s)−1), as measured with organic field-effect transistors (OFETs). Polymer solar cells (PSCs) of these polymers were prepared with PC71BM as an acceptor and o-xylene as a processing solvent, and power conversion efficiencies (PCEs) up to 6.79%, 5.65%, 3.94% and 1.70% were achieved for PTVT-T8, PTVT-T10, PTVT-C8 and PTVT-C10, respectively. PTVT-T8 and PTVT-T10 exhibited photovoltaic properties superior to PTVT-C8 and PTVT-C10 owing to their high hole-mobility and the formation of ordered nano-fibrillar structures in which polymer backbones preferred face-on arrangement.

Four donor (D)–acceptor (A) conjugated polymers with isoindigo[7,6-g]isoindigo ([3E,8E]-3,8-bis(2-oxoindolin-3-ylidene)-6,8-dihydroindolo[7,6-g]indole-2,7(1H,3H)-dione, DIID) as A-unit and thiophene derivatives as D-units were synthesized by Stille polycondensation. Optical and electrochemical properties of the polymers were studied by UV–vis–NIR absorption spectrometer and cyclic voltammetry. Compared with isoindigo-based analogues, the polymers display much broader absorption spectra (covering 400–950 nm) and remarkably lower bandgaps (ca. 1.3 eV). All polymers showed ambipolar transport properties as evaluated by bottom-gate/top-contact (BGTC) and top-gate/bottom-contact (TGBC) organic thin film transistors (OTFTs) in air. Gate-voltage-dependent hole mobility (μh) was observed for BGTC devices, while the mobility of TGBC devices exhibited weak gate-voltage dependence. P3 delivered the best device performance. At the optimized thermal annealing temperature (200 °C), a μh of 1.79 cm2/(V s) and an electro...

Asymmetric enaminone difluoroboron complexes (BFs) exhibit highly solid emission and appropriated electron-accepting properties, whereas the position of the substituents has a significant influence on their optical properties due to the structural asymmetry. In this work, we employed BF as acceptor and 9,9-dimethylacridine (DMAC) as donor to construct two thermally activated delay fluorescence (TADF) molecules DMAC-BF and BF-DMAC, in which DMAC unit was set on the B-O and B-N sides of BF, respectively. DMAC-BF and BF-DMAC exhibited the broad orange-red emission bands in toluene, while they emitted yellow and red fluorescence in solid state, respectively. The photoluminescence quantum yield (PLQY) of DMAC-BF (52%) is higher than that of BF-DMAC (29%), owing to its lower nonradiative decay rate. Solution-processed organic light-emitting diode (OLED) devices based on both of DMAC-BF and BF-DMAC exhibited orange-red electroluminicence spectra. Owing to its higher photoluminescence quantum yield, DMAC-BF-based OLED exhibited better electroluminicence performance with a maximum current efficiency of 24.9 cd/A, a maximum power efficiency of 23.0 lm/W, and a maximum EQE of 11.3%.

Photothermal conversion nanoagents based on conjugated polymers (CPs) are attracting increasing attention for in vivo disease theranostics and high-performing ones are in urgent pursuit. Herein, we report a new and non-donor-acceptor approach to photothermal conversion CPs that combine several merits including low bandgaps, strong near-infrared absorption, low intersystem crossing rate and non-emissive nature. Three CPs based on 6,7; 6′,7′-fused isoindigos (nIIDs), i.e., P2IIDV, P3IIDV and P4IIDV that have optical bandgaps of 1.30, 1.22 and 1.17 eV, respectively, are synthesized. The nanoparticles (NPs) of the CPs in water are prepared via nanocoprecipitation, which are non-fluorescent due to the rapid intramolecular twisting in the CP backbone within NPs, enabling most of the excitation energy flow to generate heat. The photothermal conversion efficiencies of the NPs as measured under irradiation at 808, 880 and 980 nm are 62.4%, 40.5% and 15.8% for P2IIDV, 65.1%, 41.0% and 38.9% for P3IIDV and 71.5%, 48.9% and 41.7% for P4IIDV, which are significantly higher than indocyanine green and many popularly reported photothermal conversion materials. In vivo studies using xenograft 4T1 tumor-bearing mouse model demonstrate that the P4IIDV NPs can serve as a rather effective photothermal conversion nanoagent for enhanced photoacoustic imaging and photothermal therapy of tumors.

A polycyclic aromatic unit comprising six rings, i.e., 5,11-bis(2-octyldodecyl)dithieno[3,2-b:3′,2′-b′]naphtho[1,2-b:5,6-b′]dithiophene (DTNDT), was developed. Four donor–acceptor (D–A) conjugated polymers, which are named P-BT, P-2FBT, P-IID, and P-DPP, were synthesized with DTNDT as the D-unit and 2,1,3-benzothiadiazole (BT), 5,6-difluorobenzo[c][1,2,5]thiadiazole (2FBT), isoindigo (IID), and diketopyrrolopyrrole (DPP) as the A-unit, respectively. All four polymers are thermally stable with decomposition temperature above 390 °C and show pseudo-straight-shaped backbones. Their ordered thin films were prepared via solution spin-casting, in which conjugated backbones mainly adopted edge-on alignment on the substrate. The semiconducting properties of the polymers were characterized with bottom gate and top contact (BGTC) organic thin film transistors (OTFTs). All four polymers showed p-type transport behavior, and the hole mobilities were 0.023, 0.078, 0.50, and 1.80 cm2/(V s) for P-BT, P-2FBT, P-IID, and ...

A diketopyrrolopyrrole-based conjugated polymer, PDPP-4FTVT, which exhibits ambipolar transport behavior in air with hole and electron mobilities up to 3.40 and 5.86 cm(2) V(-1) s(-1), respectively, is synthesized via direct arylation polycondensation. Incorporation of F-atoms in β-positions of thiophene rings dramatically improves the efficiency of direct arylation polycondensation.

Solution processible organic semiconductors have attracted great attention in recent years due to their applications in printable electronics, such as organic thin-film transistor (OTFT). This type of device requires semiconductors characterized by low reorganization energies and strong intermolecular electronic interaction. Phthalocyanines are 18 π -electron disc-like aromatic macrocycles with two-dimensional (2D) π -electron delocalization over the whole molecule, and are featured with low reorganization energies and close π - π stacking. Moreover, tight 2D cofacial π - π stacking, which is beneficial for charge transport in the channel of OTFTs, can be realized by incorporating axially substituted metals or large metals in the core of phthalocyanines. Introducing alkyl substituents can endow phthalocyanines good solubility in organic solvents. However, the number and positions of alkyl substituents have great influence on the packing structures thereby OTFT performance of phthalocyanines. In the current paper, four dioctyl substituted vanadyl phthalocyanines, i.e. 2,3-dioctyl vanadyl phthalocyanine (2,3-C8OVPc), 2,16(17)-dioctyl vanadyl phthalocyanine ( dp - C8OVPc), 1,15-dioctyl vanadyl phthalocyanine (1,15-C8OVPc) and 1,18-dioctyl vanadyl phthalocyanine ( dp -C8OVPc), were synthesized, and the effect of the positions of octyl groups on their photophysical properties, OTFT performance was studied in detail. All four compounds are soluble in organic solvents such as chloroform and exhibit excellent thermal stability with the decomposition temperature ( T d) beyond 400°C. In dilute solution, the positions of octyl groups have negligible influence on their absorption spectra and frontier molecular orbital energy levels. Their absorption maxima ( λ max) are all at ca. 700 nm and the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels are - 5.2 and - 3.8 eV, respectively. From solution to film, their absorption spectra exhibited a remarkable bathochromic shift. In film state, four compounds all can form ordered thin films, in which they arrange in an edge-on way. Bottom gate and top contact OTFTs based on thermally annealed films of these four compounds were fabricated via solution spin-casting. All compounds showed p-type transport behavior with field-effect mobility above 0.1 cm2/(V s) 2,3-C8OVPc displayed the best OTFT device performance. A mobility of 0.19 cm2/(V s) has been demonstrated when the films were annealed at 150°C.

Rubrene single-crystal transistors have achieved one of the highest carrier mobilities in organic semiconductors. However its thin film transistor usually shows inferior performance due to the poor film quality. Therefore how to obtain large-area and high quality rubrene thin film has become a prominent challenge. This work utilized weak epitaxy growth method with new inducing layer 1,3-di(terphenyl) benzene (m-7P), and lager-area highly ordered terrace rubrene film was obtained. Based on this high quality film, the hole mobility of rubrene polycrystalline thin film transistor has been enhanced to 11.6 cm 2 V −1 s −1 with VOPc as buffer layer between semiconductor layer and electrodes. This high device performance was attributed to the flat inducing layer and the single orientation of rubrene domains on m-7P layer, which may reduce grain boundaries and improve the film quality. This easy process to prepare large-area high performance rubrene device supplies a good opportunity for large-area electronic device manufacture.

Large-area continuous α phase thin films of monodisperse poly(9,9-dioctylfluorene) (PFO), with 32 or 64 fluorene repeating units, named as F32 or F64, respectively, are prepared by melt crystallization. A spherulite-like structure, composing of crystalline nanofibrils, is formed via radial growth after sufficient isothermal treatment. In these nanofibrils, the polymer chains remain extended conformation, which is demonstrated by the similarity between nanofibril widths and extended chain lengths. Comparing this discovery on F32/F64 with our previous observations on F16 (monodisperse PFO consisting of 16 repeating units) leads us conclude that the melt-crystallized phases change from β′ phase (F16) to α phase (F32 and F64) as the molecular weight increases. It is speculated that as the number of repeating unit goes up, the backbone planarity of PFO decreases, leading to the formation of different melt-crystallized phases at different molecular weights.

Two π-conjugation expanded isoindigo derivatives (DIID-PhCO and TIID-PhCO) composed of up to 18 rings and two donor–acceptor conjugated polymers based on DIID-PhCO were synthesized. Both polymers are ambipolar semiconductors with balanced hole and electron mobilities up to 0.10 and 0.14 cm2 V−1 s−1, respectively, under ambient conditions.

Three low bandgap conjugated polymers based on 7-fluorinated isoindigo (IID1F) and dithieno[3,2-b;6,7-b]carbazole (DTC), i.e., poly[N-dodecyldithieno[3,2-b;6,7-b]carbazole-alt-7-fluoro-N,N-di(2-octyldodecyl)isoindigo] (P1), poly[N-dodecyldithieno[3,2-b;6,7-b]carbazole-alt-7-fluoro-N,N-di(3-octyltridecyl)isoindigo] (P2) and poly[N-dodecyldithieno[3,2-b;6,7-b]carbazole-alt-7-fluoro-N,N-di(4-octyltetradecyl)isoindigo] (P3), were synthesized. All three polymers are soluble in non-chlorinated solvent o-xylene owing to regio-random distribution of F-atoms along the conjugated backbone. The position of the alkyl-branching point has a negligible influence on energy levels and absorption spectra of the polymers, but has a small effect on their charge transport properties. Bulk heterojunction (BHJ) polymer solar cells (PSCs) of the polymers were fabricated with phenyl-C61-butyric acid methyl ester (PC61BM) as an electron acceptor. When o-xylene was used as a solvent, all three polymers delivered power conversion efficiencies (PCEs) above 7%. P2 exhibited the best device performance with a PCE of 7.5%. The devices processed with o-xylene showed higher device efficiency than those fabricated with o-dichlorobenzene (o-DCB) since the films of polymer:PC61BM blends prepared with o-xylene exhibited better morphology and higher and more balanced charge-carrier mobilities, leading to less recombination loss and higher fill factor (FF).

Three donor–acceptor–donor (D–A–D) conjugated oligomers, i.e., 2ATT-IID-C8C10, 2ATT-IID-C6C8 and 2ATT-IID-C4C6, have been synthesized using anthra[1,2-b]thieno[2,3-d]thiophene (ATT) as an electron-donor unit and isoindigo (IID) as an electron-acceptor unit by combining the planar and rigid structure of fused aromatics and the strong intramolecular interaction of D–A conjugated molecules, and their semiconducting properties were studied via organic thin-film transistors (OTFTs). The alkyl chains, which are 2-octyldodecyl (C8C10), 2-hexyldecyl (C6C8) and 2-butyloctyl (C4C6), respectively, were employed in the IID unit in order to study the effect of alkyl bulkiness on the properties of the oligomers. All three oligomers adopted an edge-on alignment in thin films. Decreasing the bulkiness or length of the alkyls caused a noticeable improvement of the packing order of the oligomers, leading to a remarkably enhanced charge carrier mobility. 2ATT-IID-C8C10 could only form the film featured with one-dimensional order. Consequently, it exhibited the lowest OTFT mobility (

A low bandgap conjugated polymer, i.e., poly[2,2′-bithiophene-alt-7-fluoro-N,N′-bis(2-octyldodecyl)isoindigo] (P(1FIID-BT)), was synthesized. The polymer was soluble in non-chlorinated solvents such as o-xylene and mesitylene, and exhibited a film optical bandgap of 1.61 eV as calculated from the absorption onset and a deep highest occupied molecular orbital (HOMO) energy level of −5.46 eV as measured by an electrochemical method. Remarkably high mobilities of 0.33 and 0.42 cm2 V−1 s−1 were obtained for organic field-effect transistors (OFETs) based on pristine and annealed films, respectively. Inverted polymer solar cells (PSCs) were fabricated with phenyl-C61-butyric acid methyl ester (PC61BM) as the acceptor material and o-xylene as the processing solvent. The device efficiency was insensitive to the thickness of the active layer, and all devices with film thickness in the range of 105–340 nm showed a power conversion efficiency (PCE) higher than 6.5%. The devices based on 270 nm thick films displayed the highest performance with a VOC of 0.89 V, a JSC of 14.50 mA cm−2 and a FF of 0.58, leading to a PCE of 7.46%. This is the first low bandgap conjugated polymer for PSCs which combine three features: non-chlorinated solvent processability, high efficiency and insensitivity of efficiency to the active layer thickness.

Oligo(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene)s Tn and Tn-2CN (n = 4, 8, 12, 20, n represents the number of thiophene rings), which have H and CN end-groups, respectively, were synthesized, and the effect of chain-length and end-groups on their properties was studied. For both Tn and Tn-2CN, a red-shift of absorption spectra was observed as the chain length increased. Introduction of electron-withdrawing CN end-groups resulted in a remarkable red-shift of absorption spectra in both solution and film states for shorter oligomers (n = 4 and 8). However, for oligomers with n = 12 and 20, obvious red-shift of absorption spectra was only observed in the film state. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were both lowered by introducing CN end-groups, and the level of reduction decreased with an increase of the chain length. Both the chain length and end-groups influenced the thin film microstructures of the oligomers as revealed by two-dimensional grazing incidence X-ray diffraction (2D-GIXD) and atomic force microscopy (AFM) studies. The oligomers with n = 4 and 8 stood on the substrates with a tilt angle, and the films of T4-2CN and T8-2CN were characterized with 3D crystal structures. In contrast, the oligomers with n = 12 and 20 adopted an edge-on arrangement with the long axes of the molecules parallel to the substrates, like polymeric counterparts. Compared to the films of T12 and T20, those of T12-2CN and T20-2CN comprised larger and more oriented crystal-domains to the substrates along with shorter lamellar distances. Charge-transport properties of the oligomers were influenced by both the chain length and end-groups due to their remarkable effect on the film morphology and packing structures. The film of T8-2CN combined three features: large domain sizes, low surface-roughness and diminished grain boundaries, and therefore exhibited the highest field-effect mobility.

Pi-extended thienoacenes that comprise alternatively arranged anthracene and thieno[3,2-b]thiophene moieties and have 8 or 13 aromatic rings were synthesized. the delocalization of their homo and lumo orbitals is over the entire molecules, and low-lying homo levels endow them good stability. (c) 2014 elsevier ltd. all rights reserved.

Controlled Suzuki–Miyaura catalyst-transfer polycondensations (SCTPs) of fluorene- and thiophene-based AB-type monomers have been demonstrated with a N-heterocyclic carbene (NHC)-based Pd complex, Pd(IPr)(OAc)2, as the catalyst. The number average molecular weights (Mns) of the resulting poly(9,9-dioctyl-9H-fluorene)s (PF8s) were linear to the conversions of the monomer. PF8s with Mns in the range of 10.5–69.2 kDa and polydispersity indices (PDIs) of ∼1.60 were successfully synthesized by tuning the feed ratios ([monomer]0/[Pd]). The protocol is also applicable to the controlled synthesis of poly(3-hexylthiophene) (P3HT). Polymers with Mns of 9.5–63.8 kDa, which were linearly correlated to feed ratios, were obtained when the catalyst loading was tuned to 5–0.5 mol%. The “living” characteristics of the polymerization were also confirmed by monomer-addition and block copolymerization experiments. In addition, PF8 with a moderate molecular weight (MW) was mainly end-capped with Br/H end groups as evidenced by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass and 1H NMR spectra, indicating that this polymerization involves a catalyst-transfer mechanism. The mechanism was further confirmed by the fact that the cross-coupling of dibromofluorene (1 equiv.) and biphenylboronic acid ester (1 equiv.) with Pd(IPr)(OAc)2 as the catalyst preferentially gave a di-substituted product.

Two benzothienobenzothiophene (BTBT)-based conjugated oligomers, i.e., 2,2'-bi[1]benzothieno[3,2-b][1]benzothiophene (1) and 5,5'-bis([1]benzothieno[3,2-b][1]benzothiophen-2-yl)-2,2'-bithiophene (2), were prepared and characterized. Both oligomers exhibit excellent thermal stability, with 5% weight-loss temperatures (T(L)) above 370 °C; no phase transition was observed before decomposition. The highest occupied molecular orbital (HOMO) levels of 1 and 2 are -5.3 and -4.9 eV, respectively, as measured by ultraviolet photoelectron spectroscopy. Thin-film X-ray diffraction and atomic force microscopy characterizations indicate that both oligomers form highly crystalline films with large domain sizes on octadecyltrimethoxysilane-modified substrates. Organic thin-film transistors with top-contact and bottom-gate geometry based on 1 and 2 exhibited mobilities up to 2.12 cm(2)/V·s for 1 and 1.39 cm(2)/V·s for 2 in an ambient atmosphere. 1-based devices exhibited great air and thermal stabilities, as evidenced by the slight performance degradation after 2 months of storage under ambient conditions and after thermal annealing at temperatures below 250 °C.