Publications

Completely understanding the working mechanisms of sophisticated supramolecular self-assembly exhibiting competing paths is very important for chemists en route to acquiring the ability of constructing supramolecular systems with controlled structures and designed functions. Here, the self-aggregation behaviors of an N-heterocyclic aromatic dicarboximide molecule 1, boasting two competing paths that give rise to different supramolecular structures and exhibit distinct thermodynamic features, are carefully examined. First, a group of H-aggregates are observed when providing a medium driving force for aromatic stacking, and their formation is manifested as an anticooperative process. When exposed to enhanced strength of aromatic interactions, these H-aggregates are found to transform into J-aggregates via a cooperative assembly mechanism. With the assistance of a mathematic model accommodating two competing polymerization pathways, calculations are conducted to simulate and explain the thermodynamic equilibria of such a unique supramolecular system. The calculation results are highly consistent with the experimental observations, and some important properties are elucidated. Specifically, the anticooperative assembly mechanism generally promotes the formation of low to medium oligomers, whereas the cooperative path is more competent at producing high polymers. If the anticooperative and cooperative routes coexist and compete for the same molecule, the cooperative formations of high polymers are significantly suppressed unless a very high degree of polymerization can be achieved. Such a unique feature of concurring anticooperative and cooperative paths emerges to the H- and J-aggregates of molecule 1 and thus brings about the interesting sequential appearances of the two types of aggregates under conditions of continuously enlarged driving force for self-aggregation. Finally, based on the knowledge acquired from this study and by analyzing the steric features of 1 that influence its supramolecular packing motifs, a slightly modified molecular structure is designed, with which the intermediate H-aggregation state was successfully suppressed, and a single cooperative J-aggregation path is manifested.

A pair of uranyl complexes incorporating tetrahydrosalen and N,N-dimethyltetrahydrosalen ligands are synthesized and studied. These new ligands, with saturated secondary and tertiary amines, exhibit higher chemostability than the prototype Schiff base (salen) structure, especially under acidic conditions. As shown by X-ray diffraction crystallography, the coordination geometry of uranium in these new complexes is a distorted pentagonal bipyramid. Interestingly, UO2([H-4]-salen), comprising the tetrahydrosalen ligand, forms a dimeric structure in the crystals, with two subunits held together by sharing one of the two phenoxy oxygen atoms from each subunit, whereas UO2([H2Me2]-salen) with the N,N-dimethyltetrahydrosalen ligand is in the monomer state, with a solvent molecule coordinated to uranium to complete the penta-coordination configuration. Moreover, as revealed by UV/Vis spectroscopy using the colorimetry method, these hydrogenated salen ligands exhibit comparable, or even higher, binding affinities toward uranyl than the prototype Schiff base salen ligand in weakly basic solution.

Attaining control on charge injection properties is significant for meaningful applications of organic field-effect transistors (OFETs). Here, molecular electron-doping is applied with an air-stable dimer dopant for n-type OFETs based on (naphthalene diimide-diketopyrrolopyrrole) polymer hosts. Through investigating the doping effect on contact and transport properties, it is found that the electron transport increases in n-doped OFETs at low doping regime with remaining large on/off ratios. These favorable meliorations are reconciled by the mitigated impacts of contact resistance and interfacial traps, as well as the surface morphology exhibiting features of increased ordering. The occurrence of doping in the presence of dimer dopants is evidenced by the observed shift of Fermi level toward vacuum level coupled with compositional analysis. Without applying vacuum-deposition-based contact doping, charge injection efficiencies are gained without losing OFET characteristics using the solution-based methodology.

As indispensable molecular components, photosensitizers play a crucial role in determining the quantum efficiency of triplet-triplet annihilation upconversion (TTA UC). This emergent technology has attracted great attention in recent years for realizing large anti-Stokes shifts with noncoherent excitation sources. In a typical TTA UC, low-energy photons are first harvested by the photosensitizers, which upon intersystem crossing (ISC) undergo triplet-triplet energy transfer (TTET) to emitters (i.e., annihilators). Following the bimolecular TTA among the emitters, high-energy photons are given off by the singlet excited state of the emitters. Apparently, the efficiencies of photon absorption, ISC, and TTET are all dependent on the sensitizers. With a Dexter-type ET mechanism requiring collisional interactions, a long triplet lifetime of the energy donor (photosensitizer) is evidently favorable for enhancing the efficiency of TTET. This progress report summarizes the recent developments of photosensitizers used for TTA UC, many of which feature a bichromophoric molecular scaffold. Among the various consequences and functions entailed by such bichromophoric designs, the extended triplet lifetime is a particularly advantageous property for TTA UC. Additionally, these new potent photosensitizers with long triplet lifetimes are also useful for other applications such as singlet oxygen sensitization and oxygen sensing.

In this work, room-temperature-operated ultrasensitive solution-processed perovskite photodetectors (PDs) with near infrared (NIR) photoresponse are reported. In order to enable perovskite PDs possessing extended NIR photoresponse, novel n-type low bandgap conjugated polymer, poly[(N, N'bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl) (2,5-dioctyl-3,6-di(thiophen-2-yl) pyrrolo[3,4-c] pyrrole-1,4-dione-5,5'-diyl)] (NDI-DPP), which has strong absorption in the NIR region, is developed and then employed in perovskite PDs. By the formation of type II band alignment between NDI-DPP with single-wall carbon nanotubes (SWCNTs), the NIR absorption of NDI-DPP is exploited, which contributes to the NIR photoresponse for the perovskite PDs, where perovskite is incorporated with NDI-DPP and SWCNTs as well. In addition, SWCNTs incorporated with perovskite active layer can offer the percolation pathways for high charge-carrier mobility, which tremendously boosts the charge transfer in the photoactive layer, and consequently improves the photocurrent in the visible region. As a result, the perovskite PDs exhibit the responsivities of approximate to 400 and approximate to 150 mA W-1 and the detectivities of over 6 x 10(12) Jones (1 Jones = 1 cm Hz(1/2) W-1) and over 2 x 10(12) Jones in the visible and NIR regions, respectively. This work reports the development of perovskite PDs with NIR photoresponse, which is terrifically beneficial for the practical applications of perovskite PDs.

A heavy-atom-free triplet sensitizer suitable for triplet-triplet annihilation-based photon upconversion was developed from the thermally activated delayed fluorescence (TADF) molecule 4CzPN by covalently tethering a pyrene derivative (DBP) as a triplet acceptor. The triplet exciton produced by 4CzPN is captured by the intramolecular pyrenyl acceptor and subsequently transferred via intermolecular triplet triplet energy transfer (TTET) to freely diffusing pyrenyl acceptors in toluene. Transient absorption and time-resolved photoluminescence spectroscopy were employed to examine the dynamics of both the intra- and intermolecular TTET processes, and the results indicate that the intramolecular energy transfer from 4CzPN to DBP is swift, quantitative, and nearly irreversible. The reverse intersystem crossing is suppressed while intersystem crossing remains efficient, achieving high triplet yield and long triplet lifetime simultaneously. The ultralong excited state lifetime characteristic of the DBP triplet was shown to be crucial for enhancing the intermolecular TTET efficiency and the subsequent triplet-triplet annihilation photochemistry. It was also demonstrated that with the long triplet lifetime of the tethered DBP, TTET was enabled under low free acceptor concentrations and/or with sluggish molecular diffusion in polymer matrixes.

The activation of C-H bonds in terminal alkynyl groups at room temperature was achieved in the reaction of 2,5-diethynyl-1,4-bis(4-bromophenylethynyl) benzene on Ag(111). Scanning tunneling microscopy studies showed the formation of organometallic species, whose stabilization was confirmed by density functional theory calculations, at room temperature as the product of C-H bond activation. The partial conversion of organometallic structures into covalent products of the homocoupling between the terminal alkynes was achieved by further annealing the sample at 420 K. Detached Br adatoms were suggested to play a key role in promoting the C-H bond activation. This proposal was supported by the theoretical study based on a simplified model of the system, showing the weakening of the C-H bond in the alkynyl group by an approaching Br atom. The results provide a new strategy for on-surface C-H bond activation under mild conditions, which register great potential applications in on-surface synthesis and bottom-up preparation of functional nanomaterials.

Despite the rapid progress that has been made in increasing the power conversion efficiency (PCE) of organic solar cells (OSCs) over the past decade, it is a challenge to realize efficient and environment-friendly OSCs. In this contribution, all polymer solar cells were fabricated with a blend of poly[4,8-bis(5-(2ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate](PTB7Th) donor and vinylene-bridged perylenediimide-based polymer (PDI-V) acceptor, in which non-halogenated tetrahydrofuran (THF) was used as the host solvent. A conventional ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/PTB7-Th:PDI-V/zirconium device structure of ITO/poly(3,4acetylacetonate(ZrAcac)/Al was employed, where PEDOT:PSS functioned as the hole transporting layer (HTL) and ZrAcac functioned as the electron transporting layer (ETL). The mixed solution of PTB7-Th and PDI-V was spin cast on the top of PEDOT:PSS layer to form the active layer. After that, ZrAcac solution was spin cast on the top of PTB7-Th:PDI-V layer. Different thermal annealing temperatures were used to optimize the active layer morphology. In details, OSCs without thermal annealing showed a PCE of 7.1%, with a short-circuit current (JSC) of 14.9 mA/cm2, an open-circuit voltage (VOC) of 0.74 V, and a fill factor (FF) of 64%. The devices annealed at 120 °C showed a high PCE of 8.1% with a JSC of 15.5 mA/cm2, a VOC of 0.74 V, and a FF of 70%. Further increasing the annealing temperature to 150 °C led to decreased FF and thereby a relatively lower PCE (7.4%). To the best of our knowledge, the PCE of ~ 8.1% is one of the highest PCE values reported in the literature so far for all polymer solar cells. The high and balanced hole and electron mobility partially contributed to such a high performance. These results suggest that THF as good non-halogenated solvent can be used to fabricate high-performance all polymer solar cells. Higher efficiency can be achieved for OSCs with THF solvent when better polymer acceptors are employed. 以聚合物PTB7-Th为给体、聚合物PDI-V为受体和四氢呋喃为溶剂，构筑了全聚合物太阳能电池.PTB7-Th与PDI-V光谱互补，有效地拓宽了活性层在可见光区的吸收范围，这有利于提高光电流.在器件优化过程中，发现热退火的方法可以有效地提高器件的光伏性能.尽管热退火处理对器件的开路电压影响不大，但是可以一定程度上提高器件的短路电流和填充因子，从而将电池的效率从7.1%提高到8.1%.8.1%的效率也是目前采用非卤素溶剂加工的基于苝酰亚胺类聚合物受体电池效率的最高值.该实验结果表明，四氢呋喃作为一种低毒性的有机非卤素溶剂，可以用来制备高性能有机光伏器件.

Bulk-heterojunction (BHJ) polymer solar cells (PSCs) have attracted attention over the past decades due to their distinct advantages of low cost, light weight, and the suitability for flexible-device fabrications. Despite the remarkable success in improving the efficiency of PSCs, fullerene-based acceptors have shown evident limitations. Accordingly, increased research efforts have been invested in developing non-fullerene acceptors, and great development has been witnessed in this field in recent years. Among all different kinds of BHJ PSCs, all polymer solar cells (all-PSCs) potentially possess the most stable donor-acceptor phase separation morphology, and all-polymer films are expected to boast superior mechanical properties. Yet, the bottle neck of enhancing the power conversion efficiency (PCE) of all-PSCs currently lies in the performance of the polymer acceptors. In the past years, we have been focusing on designing new polymer acceptors using perylenediimide (PDI) as the main building block and studing their performance in all-PSCs. A series of PDI-based polymer acceptors have been synthesized and studied since 2013. Due to the steric hindrance induced by the bay-region substitution, the PDI polymers mostly manifest low crystallinity. Accordingly, by enhancing the conjugation and rigidity of the polymer backbone, and thereby improving the aggregation and crystallization ability of the polymers, increased PCE has been achieved with all-PSC devices. Consistently, experimental evidence has also been collected showing improved morphology of the active layer. As a result of the continued and systematic studies on designing and synthesizing new polymer acceptors, along with the optimization of device fabrication conditions, the best PCE of all-PSC incorporating a PDI polymer acceptor has now been boosted to 8.59%. Very similar PCE values can be obtained from devices fabricated under ambient conditions, proving the high chemo-stability of the active-layer materials. The synthetic methods of these PDI-based polmers and the device fabrication conditions are much more convenient and economical. All these properties are friendly to the large-scale material preparation and device production. 二元或多元聚合物组成的本体异质结具备高度稳定的微相分离形貌，带来潜在的器件寿命和稳定性方面的巨大优势，全聚合物活性层器件因而成为有机太阳能电池的重要发展方向和研究内容.本文系统介绍近年来苝二酰亚胺类聚合物受体的研究进展，以及将这类聚合物受体应用于全聚合物太阳能电池所取得的重要成果.通过多种不同共聚单元结构的设计和筛选、主链和侧链化学结构的调控和优化，获得了一系列性能优越的苝二酰亚胺聚合物受体，这些材料的运用大幅度地提升了全聚合物太阳能电池的能量转化效率.相关的研究数据和结果也为后续酰亚胺类聚合物受体的设计开发、全聚合物本体异质结活性层的形貌特征和光电转化机制的分析和研究，以及全聚合物太阳能电池器件性能的优化和提升提供了良好的实验基础.

The challenge of continuous printing in high-efficiency large-area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large-area, solution-coated all-polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small-scale solution shearing coater to a large-scale continuous roll-to-roll (R2R) printer. Large-area all-polymer solar cells are continuously roll-to-roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm2. This is among the highest efficiencies realized with R2R-coated active layer organic materials on flexible substrate.

The self-assemblies of polycyclic aromatic diimide (PAI) compounds on solid surfaces have attracted great interest because of the versatile and attractive properties for application in organic electronics. Here, a planar guest species (coronene) selectively adsorbs on the helicene-typed PAI1 monolayer strongly, depending on the conjugated cores of these PAIs. PAI1 molecule displays evidently a bowl structure lying on the highly oriented pyrolytic graphite surface due to the torsion of the "C"-shaped fused benzene rings. In combination with density functional theory calculation, the selective inclusion of coronene atop the backbone of the PAI1 array might be attributed to the bowl structure, which provides a groove for immobilizing coronene molecules. On the other planar densely packed arrays, it is difficult to observe the unstable adsorption of coronene. The selective addition of coronene molecules would be a strategic step toward the controllable multicomponent supramolecular architectures.

A large triangular arylene-ethynylene macrocycle featuring unique circularly arranged -[D-pi-A](3)- electronic characteristics is designed and synthesized. The shape-persistent pi-conjugated backbone is composed of alternating electron-rich dialkoxyphenanthrene and electron-deficient dicyanodibenzo[f, h] quinoxaline units, connected by ethynylene linkers. The synthesis of such a special macrocyclic molecule is realized by employing a post-cyclization functional group installation strategy. The absorption and emission spectra of the macrocycle are found sensitively dependent on the solvent polarity. By virtue of a conjugated pi-scaffold and a cyclic -[D-pi-A](3)- motif, evident two-photon absorption (2PA) and two-photon excitation fluorescence properties are exhibited, with a 2PA cross section maximum of 3 x 10(3) GM determined by the Z-scan method.

A new polymer acceptor, naphthodiperylenetetraimide-vinylene (NDP-V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all-polymer solar cells (all-PSCs). With this polymer acceptor, a new record power-conversion efficiencies (PCE) of 8.59% has been achieved for all-PSCs. The design principle of NDP-V is to reduce the conformational disorder in the backbone of a previously developed high-performance acceptor, PDI-V, a perylenediimide-vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor-acceptor (PTB7-Th: NDP-V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP-V in the shorter-wavelength range offers a better complement to the donor. All these factors contribute to a short-circuit current density (J(sc)) of 17.07 mA cm(-2). With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all-PSCs.

The side-chain structures of conjugated molecules are well recognized to sensitively influence the crystallinity, morphology and thus carrier transport properties of organic semiconductors. Here, by varying the alkyl side-chain length in the polymer acceptors, the effect of side-chain engineering on the photovoltaic performance is systematically studied in all-polymer solar cells. Clear trends of first an increase and then a decrease in the J(sc) and FF values are observed as the branched alkyl groups are extended from 4 to 8 carbons. Correspondingly, the maximum average PCE (ca. 7.40%) is attained with an acceptor bearing a branched side-chain length of seven carbon atoms.

Four polymers based on perylenediimide co-polymerized with thiophene, bithiophene, selenophone and thieno[3,2-b]thiophene were investigated as the acceptor materials in all-polymer solar cells. Two different donor polymers, poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2,6-diyl] (PTB7-Th) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3aEuro '-di(2-dodecyltetradecyl)-2,2';5',2aEuro(3);5aEuro(3),2aEuro '-quaterthiophen-5,5aEuro '-diyl)] (PffBT4T-2DT), with suitably complementary absorption spectra and energy levels were applied and examined. Among all different donor-acceptor pairs studied here, the combination of PTB7-Th:poly[N,N'-bis(1-hexylheptyl)-3,4,9,10-perylenediimide-1,6/1,7-diyl-alt-2,5-thiophene] (PDI-Th) exhibited the best power conversion efficiency (PCE) of 5.13%, with open-circuit voltage (Voc) = 0.79 V, short-circuit current density (J (sc) = 12.35 mA center dot cm(-2) and fill-factor (FF) = 0.52. The polymer of PDI-Th acceptor used here had a regio-irregular backbone, conveniently prepared from a mixture of 1,6- and 1,7-dibromo-PDI. It is also noteworthy that neither additive nor post-treatment is required for obtaining such a cell performance.

In this investigation, the two-dimensional (2D) self-assembly nanostructures of a series of cyclic oligo(phenylene-ethynylene) (OPE) molecules (L1, L2-6 and L2-12) at the 1-phenyloctane/highly oriented pyrolytic graphite (HOPG) interface were thoroughly studied using scanning tunneling microscopy (STM). Comparative STM studies with their triangular Pt(II) diimine complexes (C1, C2-6 and C2-12) were also carried out. Based on careful measurements on single molecule level STM images and density functional theory (DFT) calculations, the formation mechanisms of the nanoarrays formed were revealed.

All-polymer solar cells with 7.57% power conversion efficiency are achieved via a new perylenediimide-based polymeric acceptor. Furthermore, the device processed in ambient air without encapsulation can still reach a high power conversion efficiency (PCE) of 7.49%, which is a significant economic advantage from an industrial processing perspective. These results represent the highest PCE achieved from perylenediimide-based polymers.

Efficient visible-to-UV photon upconversion via triplet triplet annihilation (TTA) is accomplished in polyurethane (PU) films by developing new, powerful photo sensitizers fully functional in the solid-state matrix. These rationally designed triplet sensitizers feature a bichromophoric scaffold comprising a tris-cyclometalated indium(111) complex covalently tethered to a suitable organic small molecule. The very rapid intramolecular triplet energy transfer from the former to the latter is pivotal for achieving the potent sensitizing ability, because this process out-competes the radiative and nonradiative decays inherent to the metal complex and produces long-lived triplet excitons localized with the acceptor moiety readily available for intermolecular transfer and TTA. Nonetheless, compared to the solution state, the molecular diffusion is greatly limited in solid matrices, which even creates difficulty for the Dexter-type intramolecular energy transfer. This is proven by the experimental results showing that the sensitizing performance of the bichromophoric molecules strongly depends on the spatial distance separating the donor (D) and acceptor (A) units and that incorporating a longer linker between the D and A evidently curbs the TTA upconversion efficiency in PU films. Using a rationally optimized sensitizer structure in combination-with 2,7-di-teit-butylpyrene as the annihilator/emitter, the doped poly-urethane (PU) films demonstrate effective visible-to-UV upconverted.emission signal under noncoherentlight irradiation, attaining an upconversion quantum yield of 2.6%. Such quantum efficiency is the highest value so far reported for the visible-to-UV TTA systems in solid matrices.

Herein, we report an all-polymer solar cell with a PCE of over 5% fabricated with non-halogenated solvent. Our method of polymer side-chain engineering using polystyrene enhanced the solubility of polymers in toluene. The phase separation size of the polymer-polymer blend was controlled by tuning the additive concentration. Three different additives were employed and studied. To the best of our knowledge, this is the highest performing all-polymer solar cell fabricated with both non halogenated solvent and non-halogenated additive, which highlights its potential toward environmentally friendly manufacturing of all polymer organic solar cells.

The folding and aggregation behavior of a pair of oligo(phenylene ethynylene) (OPE) foldamers are investigated by means of UV/Vis absorption and circular dichroism spectroscopy. With identical OPE backbones, two foldamers, 1 with alkyl side groups and 2 with triethylene glycol side chains, manifest similar helical conformations in solutions in n-hexane and methanol, respectively. However, disparate and competing folding and aggregation processes are observed in alternative solvents. In cyclohexane, oligomer 1 initially adopts the helical conformation, but the self-aggregation of unfolded chains, as a minor component, gradually drives the folding-unfolding transition eventually to the unfolded aggregate state completely. In contrast, in aqueous solution (CH3OH/H2O) both folded and unfolded oligomer 2 appear to undergo self-association; aggregates of the folded chains are thermodynamically more stable. In solutions with a high H2O content, self-aggregation among unfolded oligomers is kinetically favored; these oligomers very slowly transform into aggregates of helical structures with greater thermodynamic stability. The folded-unfolded conformational switch thus takes place with the free (nonaggregated) molecules, and the very slow folding transition is due to the low concentration of molecularly dispersed oligomers.