Photoactive Naphthalene Diimide Functionalized Titanium-Oxo Clusters with High Photoelectrochemical Responses

Photoactive functionalized titanium-oxo clusters(TOCs)are regarded as an important model compound for dye-sensitized titanium dioxide solar cells.However,the dyes used for sensitizing TOCs are still limited.Herein,two cyclic TOCs are reported,namely,[Ti_(6)(μ_(3)-O)_(2)(Oi-Pr)_(8))(LA)_(2)]·i-PrOH(S1)and[Ti_(6)(μ_(3)-O)2(Oi-Pr)_(8))(LV)_(2)]·i-PrOH(S2),which are functionalized by photoactive naphthalene diimide(NDI)chromophores.Their molecular structures and photophysical and photochemical properties were systematically studied.As shown by ultraviolet-visible(UV-vis)spectra and photocurrent study results,the band gap and the photocurrent response of S1 and S2 were derived from NDI ligands which extend the absorption edge of S1 and S2 approaching 500 nm and afford high photocurrent densities of 2.12μA/cm^(2)and 1.95μA/cm^(2)for S1 and S2,respectively,demonstrating the significance of the photoactive ligand in modulating photoresponse of TOCs.This work is expected to enrich the structural library of photoactive TOCs and provide insights into understanding the structure-property relationships of sensitized clusters.

The marriage of dual-acceptor strategy and C-H activation polymerization:naphthalene diimide-based n-type polymers with adjustable molar mass and decent performance

The development of readily accessible high-mobility n-type semiconducting polymers is in great demand for realizing highperformance p-n junction-based organic electronics.In this study,we demonstrate that with the combination of dual-acceptor strategy and C-H direct arylation polymerization(DAr P),unipolar n-type semiconducting polymers can be conveniently synthesized.By tuning the monomer concentration,three dual-acceptor polymers,namely,poly(naphthalene diimide-alt-dithiophenyl pyrrolopyrrole-dione)(PNDI-DPP),poly(naphthalene diimide-alt-dithiophenyl isoindigo)(PNDI-IID),and poly(naphthalene diimide-alt-dithiophenyl bezothiadiazole)(PNDI-BT)can be obtained via C-H activation with decent number average molecular weight of~10 to 30 kg mol^(-1)and relatively narrow polydispersity index of~2.In addition,these polymers are defect-free in nature as evidenced by the nuclear magnetic resonance.Moreover,we attribute the different molar masses of the three copolymers under the same DAr P condition to the differentα-C-H acidity,which may stem from different electronwithdrawing capability of the hydrogenated acceptor units.Furthermore,the influence of the hydrogenated acceptor monomers on the optical,electrochemical and charge transporting properties is comprehensively studied.Among the three dual-acceptor polymers,PNDI-BT demonstrates the highest electron mobilities of up to 0.6 cm^(2)V^(-1)s^(-1)in unipolar n-type organic transistors because of its relatively planar backbone,larger overlaps of the lowest unoccupied molecular orbital and strong H-aggregation.Note that the transistor performance of PNDI-BT synthesized via C-H activation in this study is at least comparable to the one made by conventional C(sp^(2))-C(sp^(2))Stille or Suzuki cross-coupling polymerization.This study demonstrates the presented protocol can be a useful platform for sustainable and convenient synthesis of high-performance n-type semiconducting polymers.

Naphthalene diimide based near-infrared luminogens with aggregation-induced emission characteristics for biological imaging and high mobility ambipolar transistors

Organic conjugated materials combining high conductivity with strong solid-state emission are highly desired for organic electronic applications,yet still rather rare.Herein,a novel luminogen(TEN)comprised by linking naphthalene diimides and triphenyl ethylene with vinyl bridges is reported.TEN exhibits aggregation-induced emission(AIE)behavior of a strong nearinfrared fluorescence over 700 nm and the efficiency above 60.5%in the solid state,while also shows promising application in vivo bio-imaging with good permeability and extremely low background.Single crystal of TEN reveals intra-and intermolecular C–H…O hydrogen bonds,contributing to an inclined molecular stacking along the a-axis of the cell,creating a 1 D charge carrier transporting channel under a shortπ-πinteraction distance of 3.42?,which might benefit the solid emission and charge transport ability simultaneously.Solution processed bottom contact,top gate organic field effect transistors based on TEN reveal a high ambipolar charge transport ability with the hole mobility up to 0.13 cm2 V-1 s-1 and electron mobility up to0.010 cm2 V-1 s-1.Further atomic force microscopy and X-ray diffraction analysis on TEN thin film confirm the existence of the1 Dπ-πstacking channel,suggesting the stacking geometry revealed in crystal crucial for facilitating high charge carrier mobility while preserving the strong solid emission at the same time.

Synthesis, Characterization of Star-Shaped Analogue with Benzene Core and Three Naphthalene Diimide Side-Arms

Two star-shaped molecules with benzene core and three naphthalene diimide （NDI） side arms were facilely prepared by two-step imidization reaction from the 1,4,5,8-naphthalenetetracarboxylic dianhydride. Two com- pounds showed the similar UV-Vis absorption band as well as NDI. It was found that they displayed bathochromic shift of their UV-Vis absorption and emission spectra in film compared with that in solution, ascribing to the aggregation between molecules in the solid state. Reversible reduction process was observed by cyclic voltammetry and low lying LUMO energy levels （-3.83 eV for la, -3.87 eV for lb） were deduced, which suggest that these two compounds possessed good electron-acceptor property and can be used as potential n-type materials.

Fine-tuning the molecular energy levels by incorporating thiophene units onto the π-backbone of core-expanded naphthalene diimides

A series of core-expanded naphthalene diimides（NDI-DTYM） and thiophene-based derivatives（1a-c）were designed and synthesized to investigate the relationship between molecular structures and the highest occupied molecular orbital（HOMO） energy levels but has little impact on the lowest unoccupied molecular orbital（LUMO） energy levels.The results demonstrated that increasing the number of thiophene units can gradually elevate the HOMO energy levels but had little impact on the LUMO energy levels.The n-channel organic field-effect transistors（OFETs） based on 1b and 1c have demonstrated that these almost unchanged LUMO energy levels are proper to transport electrons.

Selenium-containing core-expanded naphthalene diimides for high performance n-type organic semiconductors

The incorporation of heavy atoms into molecular backbone is an extremely straightforward strategy for fine-tuning the optoelectronic properties of organic semiconductors.However,it is rarely studied in n-type small molecules.Herein,by selenium substitution of NDI3 HU-DTYM2,two Se-decorated core-expanded naphthalene diimides(NDI)derivatives DTYM-NDI3 HUDSYM(1)and NDI3 HU-DSYM2(2)were synthesized.In comparison with the reference S-containing compound NDI3 HUDTYM2,the highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)energy levels of 1 and 2 were fine-tuned with?HOMO of about 0.2 e V,?LUMO of 0.1 e V and the narrowed HOMO-LUMO gaps.More surprisingly,the as-spun organic thin film transistors(OTFTs)based on 1 and 2 both showedμe,satvalues as high as1.0 cm2 V-1 s-1,which are 2-fold higher than that of NDI3 HU-DTYM2 with the same device structure and measurement conditions.In addition,the single crystal OFET devices based on Se-containing compound NDI2 BO-DSYM2 showed a highμe,satvalue of 1.30 cm2 V-1 s-1.The molecular packing of NDI2 BO-DSYM2 in single crystals(two-dimensional supramolecular structure formed by intermolecular Se···Se interactions)is quite different from that of a S-containing compound NDI-DTYM2(one dimensional supramolecular structure formed by intermolecularπ-πstacking).Therefore,the Se substitution can cause dramatic change about molecular stacking model,giving rise to high n-type OTFT performance.Our results demonstrated an effective strategy of the heavy atom effect for designing novel organic semiconductors.

Tuning the Charge Transport Property of Naphthalene Diimide Derivatives by Changing the Substituted Position of Fluorine Atom on Molecular Backbone

Three naphthalene diimides(2,3 and 4)fused with 2-(1,3-dithiol-2-ylidene)-2-fluorophenylacetonitrile moieties were designed and synthesized.Due to the different substituted positions of fluorine atom on the phenyl group,the solution-processed thin films of 2 and 3 operated in air as n-channel transistors,while the films of 4 performed as ambipolar transistors,indicating that the variation of substituted position of fluorine atom on molecular backbone may tune the material’s charge transport behavior.

Synthesis and Characterization of Donor-Acceptor-Donor Triads Containing Tetrathiafulvalene and Naphthalene Diimide Units: Towards Regulation of the Intermolecular Charge-Transfer Interaction by Varying the Attached Side Groups

A series of donor-acceptor-donor triads 16 consisting of tetrathiafulvalene and naphthalene diimide units were synthesized and characterized. UV/Vis spectroscopic and cyclic voltammetric studies indicate that these triads show negligible intramolecular charge transfer interaction in the ground state. In contrast to that of the reference compound 36, their fluorescence intensities were reduced in the following sequences: 3≈4≈5≈6<1≈2, which is probably due to photoinduced electron transfer in triads 16. Two solid forms (yellow and green) of triads 15 were obtained, while only green form for triad 6 was obtained under the same conditions. Studies of the yellow and green forms with UV, XRD and DSC were performed. It was suggested that varying the attached side groups may regulate intermolecular charge transfer interactions in the solid state.

n-Type Conjugated Polymer Based on Dicyanodistyrylbenzene and Naphthalene Diimide Units for All-Polymer Solar Cells

All polymer solar cells （all-PSCs）, possessing superior mechanical strength and flexibility, offer the commercialization opportunity of the PSCs for flexible and portable devices. In this work, we designed and synthesized two copolymer acceptors based on dicyanodistyrylbenzene （DCB） and naph-thalene diimide （NDI） units. The corresponding copolymer acceptors are denoted as PDCB-NDI812 and PDCB-NDI1014. The medium band gap copolymer PBDB-T was selected as donor material for investigation of the photovoltaic performance. Two alI-PSCs devices showed power conversion efficiencies （PCE） of 4.26% and 3.43% for PDCB-NDI812 and PDCB-NDI1014, respectively. The improved PCE was ascribed to the higher short-circuit current （Jsc）, greater charge carrier mobility and higher exciton dissociation probability of the PBDB-T：PDCB-NDI812 blend film. These results suggest that DCB unit and NDI unit based copolymer acceptors are promising candidates for high performance alI-PSCs.

Naphthalene Diimide Templated Synthesis of Pillar[6]arenes

A facile method for the selective synthesis of pillar[6]arenes has been developed.Due to a strong electron do-nor-acceptor interaction between the electron-deficient naphthalene diimide and a precursor for the pillararene,1,4-diisobutoxy-2,5-bis(methoxymethyl)benzene,naphthalene diimide has been demonstrated to act as a template for selective synthesis of pillar[6]arene in a modest yield(30%).

Recent advances in rylene diimide polymer acceptors for all-polymer solar cells

In recent years, a large library of n-type polymers have been developed and widely used as acceptor materi- als to replace fullerene derivatives in polymer solar cells （PSCs）, stimulating the rapid expansion of research on so-called all-polymer solar cells （aPSCs）. In particular, rylene diimide-based n-type polymer acceptors have attracted broad research interest due to their high electron mobility, suitable energy levels, and strong light-harvesting ability in the visible region. Among various polymer acceptors, rylene diimide-based poly- mers presented best performances when served as the acceptor materials in aPSCs. Typically, a record power conversion efficiency （PCE） of 7.7% was very recently achieved from an aPSC with a rylene diimide polymer derivative as the acceptor component. In this review, we highlight recent progress of n-type polymers orig- inated from two significant classes of rylene diimide units, namely naphthalene diimide （NDI） and perylene diimide （PDI）, as well as their derivatives for aPSC applications.

The role of halogen bonding in improving OFET performance of a naphthalenediimide derivative

Controlling microstructure and thin film morphology of organic semiconductors by supramolecular arrangement is critical to improving their device performance. To realize well-controlling supramolecular assembly, a core-expanded naphthalene diimides derivative （1） was designed and synthesized as an n-type organic semiconductor and also as a halogen bonding （XB） donor that could form complementary XBs with 2,2-dipyridine or 2,2-bipyrimidine acceptor. The XB interactions in the solid state of 1/2,2- dipyridine and 1/2,2-bipyrimidine were confirmed by a series of characterization methods, such as thermal gravimetric analysis （TGA）, X-ray photoelectron spectroscopy （XPS）, nuclear magnetic resonance （NMR） involving 13F NMR and solid-state 13C NMR. Organic field-effect transistors （OFETs） based on XB complexes 1/2,2-dipyridine or 1/2,2-bipyrimidine showed better device performance than that of devices based on pure 1, with the average electron mobility increased more than doubled （from 0.027cm2V-1 s-1 to 0.070cm2V-1 s-1）.

Rylene Diimide and Dithienocyanovinylene Copolymers for Polymer Solar Cells

Two polymers containing （E）-2,3-bis（thiophen-2-yl）acrylonitrile （CNTVT） as a donor unit, perylene diimide （PDI） or naphthalene diimide （NDI） as an acceptor unit, are synthesized by the Stille coupling copolymerization, and used as the electron acceptors in the solution-processed organic solar cells （OSCs）. Both polymers exhibit broad absorption in the region of 300-850 nm. The LUMO energy levels of the resulted polymers are ca. -3.93 eV and the HOMO energy levels are -5.97 and -5.83 eV. In the binary blend OSCs with PTB7-Th as a donor, PDI polymer yields the power conversion efficiency （PCE） of up to 1.74%, while NDI polymer yields PCE of up to 3.80%.

NDI-induced Topological Conversion of Human Telomeric G-Quadruplexes from Hybrid-2 to Parallel Form

G-Quadruplexes(GQs),which are formed by G-rich DNA sequences in human telomeres,have become an attractive target for cancer treatment.The ligands to stabilize the conformation of human telomeric GQs in vivo are particularly important for structure-based ligand design and drug development targeting the noncanonical DNA structure.Here we report the conformational conversion of Tel26 induced by a naphthalene diimide(NDI)ligand in K^(+)buffer,even at cellular physiological temperature(37℃)and under mimetic cellular crowding conditions created by Ficoll 70.We provide an insight into the dynamic conversion from initial hybrid-2 GQ topology to final parallel GQ topology.These results are helpful for the design of ligands with GQ conformation regulation.