Fluorination Enhances NIR-II Emission and Photothermal Conversion Efficiency of Phototheranostic Agents for Imaging-Guided Cancer Therapy.

Phototheranostics with second near-infrared (NIR-II) imaging and photothermal effect have become a burgeoning biotechnology for tumor diagnosis and precise treatment. As important parameters of phototheranostic agents (PTAs), fluorescence quantum yield (QY) and photothermal conversion efficiency (PCE) are usually considered as a pair of contradictions that is difficult to be simultaneously enhanced. Herein, a fluorination strategy for designing A-D-A type PTAs with synchronously improved QY and PCE is proposed. Experimental results show that the molar extinction coefficient (ε), NIR-II QY, and PCE of all fluorinated PTAs nanoparticles (NPs) are definitely improved compared with the chlorinated counterparts. Theoretical calculation results demonstrate that fluorination can maximize the electrostatic potential difference by virtue of the high electronegativity of fluorine, which may increase intra/intermolecular D-A interactions, tighten molecule packing, and further promote the increase of ε, ultimately leading to simultaneously enhanced QY and PCE. In these PTA NPs, FY6-NPs display NIR-II emission extended to 1400 nm with the highest NIR-II QY (4.2%) and PCE (80%). These features make FY6-NPs perform well in high-resolution imaging of vasculature and NIR-II imaging-guided photothermal therapy (PTT) of tumors. This study develops a valuable guideline for constructing NIR-II organic PTAs with high performance.

Visible-light induced activation of persulfate by self-assembled EHPDI/TiO2 photocatalyst toward efficient degradation of carbamazepine.

Removal of pharmaceutical and personal care products from wastewater is very important in water treatment process. Combining photocatalysis with persulfate (PS) could be a good solvent for this problem. Novel perylene diimide derivative (EHPDI) was designed and synthesized. Furthermore, self-assembled EHPDI/TiO2 composite photocatalyst (EPT) was prepared and applied in activating persulfate (PS) under visible light to enhance the photodegradation of pollutants. The presence of the alkyl side chain 2-ethylhexyl optimizes the self-assembly process, enabling the composite material to achieve high performance under low EHPDI loading. Various methods were used to detect the physical and chemical characteristics of EPT. Carbamazepine (CBZ) was chosen to be the model pollutant to study the removal efficiency of EPT/PS system under visible light. Within 30 min, 5.0 mg/L CBZ could be almost completely degraded, and the removal ratio of TOC was 75.2% within 60 min. The SO4-, OH, O2-, 1O2, and h+ were proved to be involved in the removal of CBZ by EPR and quenching experiments. Then, other typical pollutants were degraded by this EPT/PS system, demonstrating this system is suitable for degrading different pollutants. Besides, the degradation paths of CBZ were proposed by HPLC/MS. Finally, the EPT showed excellent recyclability and stability.

Structural Cutting of Non-fullerene Acceptors by Chlorination: Effects of Substituent Number on Device Performance.

Effects of chlorination on photovoltaic performance of organic solar cells are yet largely unclear though it is emerging as a special yet effective strategy to design highly efficient non-fullerene acceptors (NFAs). Herein, a bi-chlorine-substituted NFA with regioregularity, namely, bichlorinated dithienothiophen[3.2-b]- pyrrolobenzothiadiazole (BTP-2Cl-δ), is synthesized and compared to the non-chlorinated BTP and tetra-chlorine-substituted BTP-4Cl to study the effects of Cl number on the photovoltaic performance. From BTP to BTP-2Cl-δ and BTP-4Cl, the three molecules show gradually red-shifted absorption peaks, narrowed band gaps, and lowered highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). Polymer solar cells are fabricated using PM6 as the donor and the three small molecules as the acceptors. From BTP to BTP-2Cl-δ, efficiencies (8.8 vs 15.4%) are significantly enhanced due to the better film morphology and strong crystallization of the BTP-2Cl-δ-based device, giving rise to boosted fill factors (FFs) and short-circuit current densities (JSC's). From BTP-2Cl-δ to BTP-4Cl, although JSC's (24.3 vs 25.0 mA cm-2) are slightly elevated due to the higher crystallinity of BTP-4Cl, leading to improved exciton dissociation and collection efficiencies, FFs (71.1 vs 68.0%) are obviously decreased owing to the unfavorable film morphology, unbalanced hole-electron mobilities, and higher charge recombination in BTP-4Cl-based devices. As such, the efficiency of the BTP-2Cl-δ-based device (15.4%) is superior to that of the BTP-4Cl-based device (14.5%). This work elucidates a design strategy by cutting the numbers of substituent chlorine to obtain desired energy levels and crystallization with optimal performance.

High-Performance Ternary Polymer Solar Cells Enabled by a New Narrow Bandgap Nonfullerene Small Molecule Acceptor with a Higher LUMO Level.

Obtaining a large open-circuit voltage (VOC ) and high short-circuit current density (JSC ) simultaneously is important in improving power conversion efficiency (PCE) of organic photovoltaics. The ternary strategy with using a higher lowest unoccupied molecular orbital (LUMO) level nonfullerene acceptor (NFA) guest can achieve increased VOC , yet JSC is decreased or maintained, so it's still a challenge to offer increased VOC and JSC values concurrently via the newly presented VOC -increased ternary strategy. To overcome this issue, a new narrow bandgap NFA TT-S-4F is reported by introducing 3,6-dimethoxylthieno[3,2-b]thiophene (TT) as π-spacers to connect electron-rich core with terminal groups, so as to upshift the LUMO level and extend π-system. When adding 10% TT-S-4F into binary system based on PTB7-Th:IEICO-4F, the higher-LUMO-level of TT-S-4F, the increased charge mobilities, the reduced trap-assisted combination loss, and a finer nanofiber structure and increased phase separation size are obtained, which simultaneously promotes JSC , VOC , and fill factor (FF), thus obtaining an optimal PCE (12.5% vs 11.5%). This work illustrates that an extending conjugated backbone with large π-spacers and inclusion of alkylthiophenyl side-chains is a concept to synthesize NFA guests for use on the VOC -increased ternary strategy that enables to realize simultaneously increased JSC , VOC , and FF.

Ion Exchange/Insertion Reactions for Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

The low toxicity, narrow bandgaps, and high charge-carrier mobilities make tin perovskites the most promising light absorbers for low-cost perovskite solar cells (PSCs). However, the development of the Sn-based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn2+ to Sn4+ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI3) film via ion exchange/insertion reactions between solid-state SnF2 and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI3 can be well controlled, and a highly uniform pinhole-free MASnI3 perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI3 film due to the presence of a large amount of remaining SnF2. This high-quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI3-based solar cells. Moreover, the MASnI3 solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low-cost and lead-free tin-based halide perovskite solar cells.

Lanthanide MOFs for inducing molecular chirality of achiral stilbazolium with strong circularly polarized luminescence and efficient energy transfer for color tuning.

We present herein an innovative host-guest method to achieve induced molecular chirality from an achiral stilbazolium dye (DSM). The host-guest system is exquisitely designed by encapsulating the dye molecule in the molecule-sized chiral channel of homochiral lanthanide metal-organic frameworks (P-(+)/M-(-)-TbBTC), in which the P- or M-configuration of the dye is unidirectionally generated via a spatial confinement effect of the MOF and solidified by the dangling water molecules in the channel. Induced chirality of DSM is characterized by solid-state circularly polarized luminescence (CPL) and micro-area polarized emission of DSM@TbTBC, both excited with 514 nm light. A luminescence dissymmetry factor of 10-3 is obtained and the photoluminescence quantum yield (PLQY) of the encapsulated DSM in DSM@TbTBC is ∼10%, which is close to the PLQY value of DSM in dilute dichloromethane. Color-tuning from green to red is achieved, owing to efficient energy transfer (up to 56%) from Ln3+ to the dye. Therefore, this study for the first time exhibits an elegant host-guest system that shows induced strong CPL emission and enables efficient energy transfer from the host chiral Ln-MOF to the achiral guest DSM with the emission color tuned from green to red.

Improving ternary blend morphology by adding a conjugated molecule into non-fullerene polymer solar cells.

The use of ternary polymer solar cells (PSCs) is a promising strategy to enhance photovoltaic performance while improving the fill factor (FF) of a device, but is still a challenge due to the complicated morphology. Herein, ternary PSCs are fabricated via adding the conjugated small molecule p-DTS(FBTTh2)2 into a well-known blended film, PTB7-Th:IEICO-4F. The ternary blend morphology and device characterization reveal that the addition of p-DTS(FBTTh2)2 can improve crystallinity and optimize morphology, leading to the FF of the optimized device increasing to 73.69%. In combination with the advantages of an ultra-narrow bandgap material, IEICO-4F, with a broad optical absorption spectrum, the optimized ternary solar cell exhibits a high short-circuit current-density (J SC) of 25.22 mA cm-2. The best power conversion efficiency (PCE) is 12.84% for this optimized ternary device with 10 wt% p-DTS(FBTTh2)2 in the donors. This work indicates that incorporating a small molecule with high crystallinity into host binary non-fullerene PSCs would give an active layer with high crystallinity, thus greatly enhancing the FFs and PCEs of PSCs.

Effects of Halogenation in B ← N Embedded Polymer Acceptors on Performance of All-Polymer Solar Cells.

Halogenation, for example, fluorination and chlorination, is an effective strategy to regulate the performance of organic photovoltaic materials. Although fluorination has been widely applied to polymer acceptors, systematic studies on the comparison of nonhalogenated, fluorinated, and chlorinated polymer acceptors have been a blank to now. Herein, a B ← N embedded electron-deficient unit (A), namely, BNIDT was copolymerized with three electron-rich units (D), that is, benzodithiophene (BDT), fluorinated BDT, and chlorinated BDT to obtain three D-A polymers of BN-BDT, BN-BDT-F, and BN-BDT-Cl, respectively. The three polymers exhibit similar LUMOs of ca. -3.77 eV, whereas the HOMOs are remarkably decreased from BN-BDT (-5.46 eV) to BN-BDT-F (-5.71 eV) and further slightly lowered to BN-BDT-Cl (-5.74 eV). All-polymer solar cells (all-PSCs) were fabricated using PBDB-T as the donor and the three B ← N-based polymers as the acceptors. The efficiencies of all-PSCs were significantly promoted from nonhalogenated BN-BDT (1.60%) to fluorinated BN-BDT-F (3.71%) and further elevated to chlorinated BN-BDT-Cl (4.23%). Device characterizations revealed that halogenation on the polymer acceptors leads to enhanced hole-transfer driving forces and better donor/acceptor miscibility, for example, smaller domain sizes and root-mean-square roughness (rms) values, which further gives rise to higher and more balanced hole/electron mobilities and efficient physical processes, for example, efficient exciton dissociation and collection and weaker recombination losses in halogenated devices. This work demonstrates that the photovoltaic performance of nonhalogenated polymer acceptors can be remarkably boosted by fluorination and further enhanced by chlorination. This is the first systematic study on the halogenated polymer acceptors by comprehensively comparing nonhalogenated, fluorinated, and chlorinated ones.

Quaternary Solar Cells with 12.5% Efficiency Enabled with Non-Fullerene and Fullerene Acceptor Guests to Improve Open Circuit Voltage and Film Morphology.

Designing the bulk-heterojunction structure (binary, ternary and quaternary) is of great fundamental interest for relaxing the trade-off between open circuit voltage (Voc ) and short circuit current density (   Jsc ). Herein, a new quaternary blended material system is reported with a nonfullerene and PC71 BM as the third and fourth component of PBDB-T:ITCT, leading to simultaneously increased Voc and Jsc and maintained fill factor (FF). The guest IT-T-IC has upshifted LUMO energy level helping to obtain a higher Voc . The further addition of 0.2 PC71 BM as the fourth component yields an even higher Voc because the LUMO of PC71 BM is higher than that of ITCT. Interestingly, the blend of PC71 BM leads to the formation of an unprecedented neuron-like morphology, which acts as new centers not only performing light absorption and charge separation but also charge transport through their surrounding donor and acceptor fibers. The increased hole and electron mobilities and the reduced bimolecular loss results in an even larger Jsc and FF. These results indicate that a combination using a structurally similar higher-LUMO-level non-fullerene acceptor and PCBM is a simple yet effective quaternary material approach to simultaneously increase Voc and Jsc while maintaining FF, improving final device performance.

8.78% Efficient All-Polymer Solar Cells Enabled by Polymer Acceptors Based on a B←N Embedded Electron-Deficient Unit.

In the field of all-polymer solar cells (all-PSCs), all efficient polymer acceptors that exhibit efficiencies beyond 8% are based on either imide or dicyanoethylene. To boost the development of this promising solar cell type, creating novel electron-deficient units to build high-performance polymer acceptors is critical. A novel electron-deficient unit containing B←N bonds, namely, BNIDT, is synthesized. Systematic investigation of BNIDT reveals desirable properties including good coplanarity, favorable single-crystal structure, narrowed bandgap and downshifted energy levels, and extended absorption profiles. By copolymerizing BNIDT with thiophene and 3,4-difluorothiophene, two novel conjugated polymers named BN-T and BN-2fT are developed, respectively. It is shown that these polymers possess wide absorption spectra covering 350-800 nm, low-lying energy levels, and ambipolar film-transistor characteristics. Using PBDB-T as the donor and BN-2fT as the acceptor, all-PSCs afford an encouraging efficiency of 8.78%, which is the highest for all-PSCs excluding the devices based on imide and dicyanoethylene-type acceptors. Considering that the structure of BNIDT is totally different from these classical units, this work opens up a new class of electron-deficient unit for constructing efficient polymer acceptors that can realize efficiencies beyond 8% for the first time.

A Cation-Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn2+ to Sn4+ . Now a chemical route is developed for fabrication of high-quality methylammonium tin iodide perovskite (MASnI3 ) films: hydrazinium tin iodide (HASnI3 ) perovskite film is first solution-deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI2 ), and then transformed into MASnI3 via a cation displacement approach. With the two-step process, a dense and uniform MASnI3 film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI3 as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.

13%-Efficiency Quaternary Polymer Solar Cell with Nonfullerene and Fullerene as Mixed Electron Acceptor Materials.

In this article, we report 13%-efficiency quaternary polymer solar cell. By introducing bis-PC71BM:PC71BM into a known nonfullerene system-poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl))benzo[1,2- b:4,5- b']dithiophene)- co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2- c:4,5- c']dithiophene-4,8-dione):3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone-methyl))-5,5,11,11-tetrakis(4- n-hexylphenyl)-dithieno[2,3 d:2',3' d']- s-indaceno[1,2 b:5,6 b']dithiophene (PBDB-T:IT-M), the quaternary solar cell significantly outperforms the nonfullerene binary and the ternary (PBDB-T:IT-M:fullerene) devices with a significant increase in the short-circuit current-density (18.2 vs 16.5 and 16.8-17.5 mA/cm2) and the fill factor (0.73 vs 0.67 and 0.707-0.726), and hence, large power conversion efficiency (13% for quaternary vs 11% for the binary and 12% for the ternary). Grazing incidence wide-angle X-ray scattering data indicate that both the polymer and IT-M phase crystallinity becomes greater upon introduction of PC71BM as the forth additive into the host ternary PBDB-T:IT-M:bis-PC71BM, which results in an increase in both the electron and hole mobilities, contributing to the Jsc enhancement. Our results indicate that the use of the forth fullerene component provides more choices and more mechanisms than the ternary systems for tuning the photon-to-electron conversion; therefore, sheds light on the realization of high-efficiency polymer solar cells by designing the multiacceptor components with aligned energy levels, complementary absorption spectra, and improved film morphologies.

Molecular Quadripod as a Noncovalent Interfacial Coupling Reagent for Forming Immobilized Coordination Assemblies.

A pyrene-cored molecular quadripod 1,3,6,8-tetra(di( p-pyrid-4-ylphenyl)amino)pyrene (TAPyr) is presented as a noncovalent interfacial coupling reagent for the immobilization of coordination assemblies. This bench-stable molecule is readily available and has a quadripod shape with four pyridine legs and four pyridine handles on the top exterior. By a simple and short dipping procedure under ambient conditions, TAPyr is firmly immobilized on electrode surfaces in an upright fashion as probed by electrochemical, absorption spectral, atomic force microscopy, and scanning tunneling microscopy analysis. Using Pd(PhCN)2Cl2 as a metallolinker, 4-ferrocenylpyridine, a pyridine-terminated monoruthenium complex 1, and a diruthenium complex 2 with two pyridine ends have been grafted onto the ITO/TAPyr surface. The obtained thin films exhibit good electrochemical stability that is comparable or superior to those prepared by the state-of-the-art Si-O-Sn covalent functionalization. Appealing electrochromism is demonstrated with the thin films of ruthenium complexes on ITO.

Organophosphorus Derivatives as Cathode Interfacial-Layer Materials for Highly Efficient Fullerene-Free Polymer Solar Cells.

Roles of cathode interfacial layer (CIL) for low work function metal cathode, which influences significantly the electron extraction and transport processes, are in current trends for improvement in the organic solar cell (OSC) performance. Two organophosphorus derivatives tetraphenylphosphonium bromide (QPhPBr) and ((2-(1,3-dioxan-2-yl)ethyl)triphenylphosphonium bromide) (TPhPEtBr) as CILs individually and with mixed binary layer with N719 were demonstrated. Tremendous improvement in photovoltaic performance with QPhPBr with an average power conversion efficiency, PCE, of 11.08% and TPhPEtBr with PCE of 10.20% as well as their binary layers with 11.61 and 10.74%, respectively, has been achieved using the PBDBT:ITIC blend active layer, in comparison to that of the bare Al cathode (7.37%). The maximum PCE of 12.0% is achieved with QPhPBr:N719 as the CIL, which is the highest value reported in the literature to date for PBDB-T:ITIC-based single junction binary fullerene-free OSCs, suggesting the potential of ionic organophosphorus derivatives and their binary blended mixtures with an ionic n-type organic semiconductor such as N719 used as CILs for realizing high-efficiency fullerene-free OSCs. Their efficient performance would be helpful for potential selection of CILs in OSCs.

Tetraphenylphosphonium Bromide as a Cathode Buffer Layer Material for Highly Efficient Polymer Solar Cells.

Here, we introduced the role of small organic molecule tetraphenylphosphonium bromide (QPhPBr) as an electron-transporting layer (ETL) material for fabricating high-efficiency bulk heterojunction polymer solar cells (PSCs). Their significantly higher power conversion efficiency (PCE) in well-known active layer devices (PTB7-Th:PC71BM, PBDTTT-CT:PC71BM, and P3HT:PC71BM) was observed compared to that of the bare Al cathode. The use of N719 as an ETL was also demonstrated. Observed data reveal that QPhPBr-based devices exhibit high PCEs up to 9.18, 8.42, and 4.81% from PTB7-Th, PBDTTT-CT, and P3HT, respectively. For comparisons, the bare Al devices show PCEs of 5.37, 4.75, and 3.01%, respectively. Moreover, further enhancement of PSC efficiency (9.83, 8.69, and 5.35%) is achieved from mixed binary solution of N719:QPhPBr because of modulated adjustment of the work function of the Al electrode. Our results indicate the excellent function of tetraphenylphosphonium bromide and its binary blend as effective small-molecule organic materials to regulate the metal surface properties and the potential used as excellent cathode buffer layer materials for realizing high-efficiency PSCs.

Comparison Study of Wide Bandgap Polymer (PBDB-T) and Narrow Bandgap Polymer (PBDTTT-EFT) as Donor for Perylene Diimide Based Polymer Solar Cells.

Perylene diimide (PDI) derivatives as a kind of promising non-fullerene-based acceptor (NFA) have got rapid development. However, most of the relevant developmental work has focused on synthesizing novel PDI-based structures, and few paid attentions to the selection of the polymer donor in PDI-based solar cells. Wide bandgap polymer (PBDB-T) and narrow bandgap polymer (PBDTTT-EFT) are known as the most efficient polymer donors in polymer solar cells (PSCs). While PBDB-T is in favor with non-fullerene acceptors achieving power conversion efficiency (PCE) more than 12%, PBDTTT-EFT is one of the best electron donors with fullerene acceptors with PCE up to 10%. Despite the different absorption profiles, the working principle of these benchmark polymer donors with a same electron acceptor, specially PDI-based acceptors, was rarely compared. To this end, we used PBDB-T and PBDTTT-EFT as the electron donors, and 1,1'-bis(2-methoxyethoxyl)-7,7'-(2,5-thienyl) bis-PDI (Bis-PDI-T-EG) as the electron acceptor to fabricate PSCs, and systematically compared their differences in device performance, carrier mobility, recombination mechanism, and film morphology.

An STM/STS study of site-selective adsorption of C70 molecules onto arc-shaped BODIPY molecular-networks.

In this article, a donor-acceptor H-T-BO/C70 system was studied by a STM/STS method on the molecular level. STM results revealed that H-T-BO, a BODIPY-based derivative, can form a semi-closed molecular network at the 1-phenyloctane/HOPG interface. After introducing C70 fullerene molecules into the network, two kinds of self-assembled nanoarrays were observed by STM. Density functional theory has been utilized to reveal the formation mechanism of the molecular nanoarrays. Scanning Tunneling Spectroscopy (STS) measurements were performed to investigate the electronic properties of H-T-BO/C70 systems. I-V spectra combined with theoretical analyses showed that the introduction of C70 into the H-T-BO system induced a great drop of the band gap, which should be a result of electrons transferring from the donor H-T-BO to the acceptor C70 molecules.

High-Performance Solution-Processed Single-Junction Polymer Solar Cell Achievable by Post-Treatment of PEDOT:PSS Layer with Water-Containing Methanol.

PEDOT: PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)) is widely used as the hole-transporting layer for fabrication of new-generation solar cells. Herein, we utilize water-containing methanol to post-treat the PEDOT:PSS surface, by which the insulating PSS component is partially washed out with the PEDOT-to-PSS weight ratio increasing from 1:6.79 to 1:2.93. As a result, the surface becomes more covered with the electrically conductive PEDOT nanodomains, and again the mean current of the conductive nanodomains increases slightly from 6.68 to 7.28 pA, as demonstrated with conductive atomic force microscopy images. The electrical conductivity of the bulk PEDOT:PSS layer increases from 5.51 × 10-4 to 4.04 × 10-2 S/cm. The improvement in the surface conductivity allows for more efficient collection of mobile holes with a bit higher value of the hole mobility (5.56 vs 6.78 × 10-4 cm2 V-1 s-1). The solution-processed single-junction polymer solar cell fabricated on the treated PEDOT:PSS surface shows a higher mean short-circuit current-density (14.46 vs 16.48 mA cm-2) and, hence, a higher mean power conversion efficiency (8.23% vs 9.28%) than that on the untreated surface, as calculated from over 200 cells.

Design of Diketopyrrolopyrrole (DPP)-Based Small Molecules for Organic-Solar-Cell Applications.

After the first report in 2008, diketopyrrolopyrrole (DPP)-based small-molecule photovoltaic materials have been intensively explored. The power conversion efficiencies (PCEs) for the DPP-based small-molecule donors have been improved up to 8%. Furthermore, through judicious structure modification, DPP-based small molecules can also be converted into electron-acceptor materials, and, recently, some exciting progress has been achieved. The development of DPP-based photovoltaic small molecules is summarized here, and the photovoltaic performance is discussed in relation to structural modifications, such as the variations of donor-acceptor building blocks, alkyl substitutions, and the type of conjugated bridges, as well as end-capped groups. It is expected that the discussion will provide a guideline in the exploration of novel and promising DPP-containing photovoltaic small molecules.

Tunable Self-Assembly and Morphology-Dependent Photoconductivity of a Donor-Acceptor-Structured Diruthenium Complex.

A donor-acceptor-structured diruthenium complex, 1(PF6)4, that contains an electron-deficient bridging ligand and electron-rich distal diarylamines modified with long aliphatic chains has been synthesized. By varying the solvent environments and assembly conditions, we obtained three different self-assembled nanostructures of 1(PF6)4, including zero-dimensional nanospheres, one-dimensional nanofibers, and thin films with interconnected nanowire networks. These structures were investigated by scanning electron microscopy, transmission electron microscopy, dynamic light scattering, X-ray diffraction, and atomic force microscopy (AFM) analysis. Conductive AFM analysis shows that the nanowire networks exhibit a high conductivity of 0.023 S/cm and an enhanced photoconductivity of 0.59 S/cm under visible light irradiation.