Perylene diimide self-assembly: From electronic structural modulation to photocatalytic applications

As an emerging organic semiconductor,perylene diimide(PDI)self-assembly has attracted tremendous attention in the aspects of solar cells,sensors,fluorescence probes and n-transistors,etc.In term of photocatalysis,various photocatalysts based on PDI self-assembly exhibit some unique properties,such as intrinsicΠ-Πstacking structure,fast internal charge transfer,band-like electronic structure,flexible structural modifiability,well-defined morphological adjustability and excellent light absorption.This paper mainly presents recent progress on PDI self-assembly regarding how to regulate the electronic structure of PDI self-assembly.In addition,the photocatalytic applications of PDI self-assembly and its complexes were reviewed,such as environmental remedy,energy productions,organic synthesis and photodynamic/photothermal therapy,further highlighting related photocatalytic mechanisms.Finally,the review contents and some perspectives on photocatalytic research of PDI selfassembly were summarized,and some key scientific problems were put forward to direct related photocatalytic research in future.

All-organic covalent organic frameworks/perylene diimide urea polymer S-scheme photocatalyst for boosted H_(2) generation

Conjugated covalent organic frameworks(COFs)hold great promise in photocatalytic hydrogen evolution owing to their high crystallinity,large surface area,and distinct structure.However,COFs exhibit poor charge separation.Therefore,investigating highly effective COF-based photocatalysts is crucial.For the first time,conjugated COF/perylene diimide urea polymer(PUP)all-organic heterostructure with S-scheme interfacial charge-transfer channels was successfully developed and manufactured via in situ coupling of the two-dimensional triazine-based imine-linked COF(denoted as TATF-COF)with PUP.The optimal photocatalytic hydrogen-evolution rate of 94.5 mmol h^(-1) g^(-1) for TATF-COF/PUP is 3.5 times that of pure TATF-COF and is comparable to or even higher than that of the previously reported COF-based photocatalysts,resulting in an apparent quantum efficiency of up to 19.7%at 420 nm.The improved directional S-scheme charge transfer driven by the tuned built-in electric field and enhanced oxidation and reduction reaction rates of the photogenerated carriers contribute synergistically to the boosted photocatalytic H_(2) evolution.Experiments and theoretical studies reveal plausible H_(2) evolution and spatial S-scheme charge-separation mechanisms under visible-light irradiation.This study provides advanced methods for constructing all-organic S-scheme high-efficiency photocatalysts by the modulation of band structures.

Hydrochloric acid‐mediated synthesis of ZnFe_(2)O_(4) small particle decorated one‐dimensional Perylene Diimide S‐scheme heterojunction with excellent photocatalytic ability

The recyclable and stable ZnFe_(2)O_(4) small particle decorated one‐dimensional perylene diimide(PDI)S‐scheme heterojunction(1D PDI/ZnFe_(2)O_(4))is prepared by the hydrochloric acid‐mediated(HCl‐mediated)strategy,interestingly,the morphology of the 1D PDI/ZnFe_(2)O_(4) can also be effectively regulated by HCl‐mediated process,the existence of HCl can regulate PDI into a uniform rod structure,while the co‐existence of HCl and PDI can limit ZnFe_(2)O_(4) to become the uniform small particles.More importantly,based on the 1D rod structure of PDI and the small size effect of ZnFe_(2)O_(4),carriers can migrate to the surface more easily,which can improve the photocatalytic activity.Meanwhile,due to the appropriate energy level structure,the S‐scheme heterojunction structure is formed between PDI and ZnFe_(2)O_(4),which eliminates meaningless photo‐generated charge carriers through recombination and introduces strong redox to further enhance the photodegradation effect,thereby,1D PDI/ZnFe_(2)O_(4) exhibits excellent photocatalytic ability,under the visible light irradiation,the degradation rate of tetracycline(TC)with 1D PDI/ZnFe_(2)O_(4)(66.67%)is 9.18 times that with PDI(7.26%)and 9.73 times that with ZnFe_(2)O_(4)(6.85%).This work proposes new ideas for the assembly of magnetic organic‐inorganic S‐scheme heterojunction photocatalysts.

Synthesis,characterization,and activity of a covalently anchored heterogeneous perylene diimide photocatalyst

The consecutive two‐photon photocatalytic behavior of perylene diimide(PDI)enables it to catalyze photoreduction reactions that are thermodynamically unfavorable via single‐photon processes.In this work,we developed a heterogeneous PDI photocatalyst by covalently binding PDI molecules on the surface of nanosilica.This photocatalyst structure overcomes the intrinsic limitation of the low solubility of PDI,but retains its consecutive two‐photon photocatalytic property.Detailed characterization of the photocatalyst by techniques such as thermogravimetric analysis,solid‐state nuclear magnetic resonance spectroscopy,and Fourier transform infrared spectroscopy indicated that the PDI molecules were anchored covalently on the surface of nanosilica.The obtained photocatalyst reduced aryl halides under visible‐light irradiation in polar organic solvent and in water.The present study provides a promising strategy to realize two‐photon activity of PDI in common solvents for photocatalytic applications.

Effects of 1,7-Bromine Substitution at Bay Area on Self-assembly Behavior and Photo Physical Properties of Perylene Diimide

N,N'-bis( n-dodecyl)-3,4: 9,10-tetracarboxyl-diimide( 1,7-H-PDI-C12) and its bay position 1,7-Br substituted derivative have been synthesized and characterized by1H-NMR,13C-NMR,FT-IR,and X-ray diffraction( XRD). A comparison of the two samples by measuring their photo physical properties using UV visible absorption and fluorescence emission spectra revealed that bay substitutions of bromine do not have significant effect on the perylene diimide( PDI) photo physical properties in solution. However,the solid state fluorescence properties were enhanced by brominating at bay areas. The solid fluorescence quantum yield of 1,7-Br-PDI-C12 was 2. 83%( Фf= 2. 83%) and 1,7-H-PDI-C12 was only 0. 02%( Фf= 0. 02%). This behavior was also reflected in the steady-state fluorescence spectra. This work shows that solid state photo physical properties of PDI could be improved without changing the other properties by simply using bromine substitution at bay areas. These types of materials are useful intermediate for further synthesis of PDI with tunnable optoelectronic properties.

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.

Effect of Fluorination on Aggregate Structure of Perylene Diimide

The effect of fluorination on the aggregate structure of a novel fluorinated perylene diimide, N, N'-diperfluorophenyl-3, 4, 9, 10-perylenetetracarboxylic diimide 1, was investigated by UV-Vis absorptions and the conformation simulations from AM1 semi-empirical quantum mechanics modeling. The results showed that in the solid film 1 molecules stacked with the perfluorinated phenyl groups straightly over or below the perylene cores of the adjacent 1 molecules.

Self-assembled helical nanostructures from an asymmetrical perylene diimide

An asymmetrical perylene diimide 3, N-（4-methoxyphenyl）-N＇-（4-nitrophenyl）-perylene-3,4,9,10-tetracarboxylic diimide, was synthesized, and its self-assembly and dissociation behaviors in chloroform was studied in detail by UV-vis and fluorescence spectroscopies. The resulting unique helical nanostructures from 3 were proposed to be self-assembled via the cooperative actions of π-π stacking, steric hindrance and electrophile-nucleophile type pairing.

Synthesis and Fluorescence Quenching of Copolymer Containing3, 4, 9, 10-Perylenetetracarboxyl Diimide Side Chains

A photoluminescence material, copolymer of N-vinylcarbazole (VCz) and N,N'- bisallyl-3, 4. 9, 10-ferylenetetracarboxyl diimide (APTC) chromophores P(VCz-APTC) was synthesized. The fluorescence quenching of P(VCz-APTC) by fullerene (C-60) and triethylamine was also studied.

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.

Synthesis and Crystal Structure of N,N′-4-aminomethyl-pyromellitic diimide

The title compound N,N′-4-aminomethyl-pyromellitic diimide （4-pmpmd） crystallizes in monoclinic, space group P21/c with a = 4.785（1）, b = 6.200（1）, c = 29.907（2） A, β = 93.583（11）°, V= 885.5（2） A^3, Dc = 1.494 g/cm^3, Z= 2, C22H14N4O4, Mr = 398.37,/t（MoKα） = 0.106 mm^-1 and F（000） = 412, and its structure was refined to R = 0.0469 and wR = 0.1017 for 1194 observed reflections （F0 〉 4σ（F0））. The X-ray diffraction shows the existence of the staggered strong intermolecular C-H…O （DA） hydrogen bonds between adjacent molecules, the intermo- lecular C-H…π hydrogen bonds and the weak π…π stacking interactions, leading to the formation of multi-dimensional supramolecular network based on the Z-mode conformation of the title compound.

Effect of Hyperconjugation on Photovoltaic Performance in Pseduo-2D Perylene Diimide Derivatives

Theπ-πinteraction is acknowledged as the predominant factor to determine the molecular packing in organic photovoltaic materials,while other non-covalent intermolecular interactions especially theσ-πhyperconjugation are often ignored.Herein,a perylene diimide(PDI)derivative named FIDT-PDI is designed and synthesized to shed light into the effect of hyperconjugation on the molecular packing and further the photovoltaic performance.Dynamic NMR and 2D NOE NMR demonstrate the formation of intermolecularσ-πhyperconjugation between the C—H bond of the PDI moiety in one molecule and the phenyl sidechain in another molecule of FIDT-PDI.Benefiting from theσ-πhyperconjugation,FIDT-PDI with twisted backbone reversely exhibits more ordered packing and stronger crystallinity compared with another PDI derivative FIDTT-PDI which has better planarity,consequently achieving superior PCE and higher carrier mobility.This contribution is the first paradigm to unravel the structure-property relationship betweenσ-πhyper-conjugation of conjugated materials and corresponding photovoltaic performance.

Lighting up aggregate emission of perylene diimide by leveraging polymerization-mediated through-space charge transfer and π-π stacking

The molecular engineering of fluorescent organic/polymeric materials,specifically those emitting in the deep red to near-infrared spectrum,is vital for advancements in optoelectronics and biomedicine.Perylene diimide(PDI),a well-known fluorescent scaffold,offers high thermal and photophysical stability but suffers from fluorescence quenching in solid or aggregate states due to intenseπ-πinteractions.To mitigate this,simple and versatile methods for strong PDI aggregate emission without extensive synthetic demands are highly desirable but still lacking.Here,we report a straightforward strategy to enhance the solid-state emission of PDI by introducing certain degree of through-space charge transfer(TSCT)via controlled radical polymerization,which can efficiently distort the typical face-to-face PDI stacking,enabling greatly enhanced deep red emission.This is achieved by growing electron-donating star-shape styrenic(co)polymers from a multidirectional electron-accepting PDI initiator.The incorporation of polycyclic aromatic monomers further shifted the emission into the near-infrared region,albeit with a reduced intensity.Overall,the emission of the PDI-based TSCT polymers can be systematically manipulated by leveraging the balance between PDI stacking and the TSCT degree,as confirmed by both experimental study and theoretical calculations.Our approach circumvents complex synthetic procedures,offering highly emissive materials with large Stokes shifts and showing broad potential for optoelectronic technology.

Surface doping effect on the optoelectronic performance of 2D organic crystals based on cyano-substituted perylene diimides

Compared to organic thin films,organic single crystals offer significant potential in organic phototransistors(OPTs)due to their enhanced charge transport,large surface area,and defect-free nature.However,the development of n-type semiconductors has lagged behind p-type semiconductors.To enhance semiconductor device performance,a doping process can be employed,which typically involves the introduction of charged impurities into the crystalline semiconducting material.Its aim is to reduce the Ohmic losses,increase carrier density,improve transport capabilities,and facilitate effective carrier injection,ultimately enhancing the electrical properties of the material.Traditional doping processes,however,often pose a risk of damaging the structure of single crystals.In this study,we have synthesized novel cyanosubstituted chiral perylene diimides,which self-assemble into two-dimensional single crystals that can be used for n-type semiconductor devices.We have employed a surface doping strategy using diethylamine vapor without disrupting the crystal structure.The fabricated devices exhibit significantly higher charge transport properties after doping,achieving a maximum electron mobility of 0.14 cm^(2)V^(-1)s^(-1),representing an improvement of over threefold.Furthermore,the optoelectronic performance of the doped devices has significantly improved,with the external quantum efficiency increased by over 9 times and the significantly improved response time.These results suggest that our surface doping technology is a promising way for enhancing the performance of 2D organic single-crystal OPTs.

Sn-fused perylene diimides: Synthesis, mechanism, and properties

The first example of metal Sn-fused perylene diimides(PDI)derivative(Sn-PDI)was designed,synthesized,and investigated.To obtain this type compound,a simple one-pot synthesis,named stannylative cycloaddition reaction,has been successfully developed via a palladium-based catalyst system.The novel mechanism exhibits that the reaction experiences oxidative addition,Pd-cyclization,stannylation,Pd-Sn-cyclization,and reductive elimination processes successively.This stannylative cycloaddition does realize uniqueσ-πhyperconjugation effect and therefore significantly influencing on the photophysical,electrochemical and excited state properties.Compared with those of PDI,both of the absorption and fluorescence spectra of Sn-PDI display large red-shifts over 20 nm.The electron energy levels of Sn-PDI have changed with an uncommon regulation.And Sn-PDI gives a considerably raised highest occupied molecular orbital(HOMO)level of-6.00 eV More importantly,the singlet excitons of Sn-PDI could efficiently intersystem cross(ISC)into triplet state with a long lifetime of 17.8μs,which is far longer than that(4.4 ns)of PDI.

Enhancing the deep-red/near-infrared fluorescence of higher rylene diimides via the chalcogen-annulation strategy

Deep-red/near-infrared fluorescence is highly suitable for bioimaging owing to its ability to deeply penetrate tissues,organs,and live animals.However,developing organic fluorophores with high deep-red/near-infrared fluorescence quantum yield(Φ_(FL))and fluorescent brightness remain a significant challenge owing to the energy gap law.Herein,we developed a straightforward and effective chalcogen-annulation strategy by introducing O,S and Se into the bay region of TDI and QDI fluorophores,realizing the increase ofΦFLand fluorescent brightness up to 10 times.To our best knowledge,this study potentially stands as the pioneering instance showcasing the anti-heavy-atom effect of chalcogens,and the absoluteΦFL(93%)and fluorescent brightness(128,200 cm^(-1)mol^(-1)L)of Se-TDI is among top deep-red/near-infrared organic fluorophores currently available.The femtosecond transient absorption(fs-TA)measurements show the absence of obvious changes of the excited state lifetime after the introduction of chalcogens in TDI and QDI fluorophores,indicating that intersystem crossing(ISC)can be neglected in TDI and QDI fluorophores.Theoretical calculations further reveal the chalcogen-annulation strategy increase the radiative rates and reduce the reorganization energy of several accepting modes at the ground state in TDI fluorophores,leading to the suppression of internal conversion(IC)processes.Our chalcogen-annulation strategy,which effectively increases the Φ_(FL)and restricts the IC processes,while remaining unaffected by the heavy-atom effect,offers novel insights and theoretical support for the design and synthesis of deep-red/near-infrared organic fluorophores with high Φ_(FL)and fluorescent brightness.

Side-chain engineering for regulating structure and properties of a novel visible-light-driven perylene diimide-based supramolecular photocatalyst

Systematic and in-depth explorations of the effects of side-chain modulation on the molecular assembly,optoelectronic properties,and photocatalytic properties of supramolecular systems,as well as the kinetics of charge separation and migration in these systems,are rare.In this study,a novel supramolecular photocatalyst with an alkoxy side chain(S-EPDI)was successfully developed through subtle design of the short and linear alkoxyl side chains,affording a phenol degradation efficiency approximately four times that of the counterpart with an alkyl side chain(S-APDI).Notably,combined density functional theory(DFT)calculations,absorption spectroscopy,and other characterizations revealed that the perylene diimide(PDI)molecular units,throughπ-πstacking,formed a unique rotationally offset stacked supramolecular structure,exhibiting a significant dipole moment.This gave rise to the formation of a larger inherent electric field within S-EPDI compared to S-APDI.Moreover,the study quantitatively demonstrated that a stronger inherent electric field and lower rate of surface charge recombination facilitate efficient separation of the photogenerated carriers.Therefore,the side-chain molecular engineering method employed in this study offers an effective approach for modulating the kinetics of charge migration.

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%.

Responsive Gels with the Polymer Containing Alternating Naphthalene Diimide and Fluorinated Alkyl Chains： Gel Formation and Responsiveness as Well as Electrical Conductivity of Polymer Thin Films

A new electroactive polymer 1 with alternating NDI （naphthalene diimide） moieties and fluorinated alkyl chains was prepared and characterized. Gels of polymer 1 were formed in several solvents. Interestingly, gels of polymer 1 exhibited responsiveness toward N2H4, F and CN . Absorption and ESR spectroscopic studies revealed that such responsiveness is owing to the reduction of NDI moieties into the respective NDI＇-. In addition, thin films of polymer 1 were easily prepared with spin-coating technique and the electrical conductivity of thin films reached 52.4 S/m after exposure to NeH4 vapor.

A new perylene diimide-based colorimetric and fluorescent sensor for selective detection of Cu^(2+) cation

A new perylene diimide (PDI) ligand (1) functionalized with a dipicolylethylenediamine (DPEN) moiety was synthesized and first used as a colorimetric and fluorometric dual-channel sensor to specifically detect the presence of Cu2+ over a wide range of other cations. The solution of 1 (10 μmol/L) upon ad-dition of Cu2+ displayed distinguishing pink color compared with other cations including K+,Ni2+,Ca2+,Mn2+,Na+,Sr2+,Zn2+,Co2+,Cd2+,Mg2+,Cr3+,Ag+,and Ba2+,indicating the sensitivity and selectivity of 1 to Cu2+. Thus,the advantage of this assay is that naked-eye detection of Cu2+ becomes possible. More-over,among these metal ions investigated,only Cu2+ quenched more than half fluorescent intensity of 1. The ESI-TOF spectrum of a mixture of 1 and CuCl2 in combination of the fluorescence titration spectra of 1 (10 μmol/L) upon addition of various amounts of Cu2+ revealed the formation of a 2︰1 metal-ligand complex through the metal coordination interaction.