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.

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.

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.

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.

Highly emissive perylene diimide-based bowtie-shaped metallacycles

Metallacycles hold great promise for fluorescence-based sensing due to their synthetic advantages and unique physicochemical properties. However, it remains highly challenging to develop a versatile methodology for constructing highly emissive metallacycles with targeted functionalities and therefore soughtafter properties. Herein, we report a general strategy to construct a series of highly emissive perylene diimide-based metallacycles via the self-assembly of perylene diimide-based tetrapyridyl ligand with different dicarboxylic ligands featuring fixed angles and cis-Pt(PEt_(3))_(2)(OTf)_(2). Single crystal X-ray diffraction analyses verify the formation of bowtie-like metallacycles with two triangular cavities. Notably, the fluorescence quantum yields of most assemblies exceed 98%, amongst the highest values for metallacycles.Additionally, such metallacycles exhibit sensitive fluorescence responses toward picric acid with a detection limit of 2.8 × 10^(-6)mol/L. This study not only provides a rational strategy for preparing highly emissive bowtie-shaped metallacycles, but also sheds light on their usage in the detection of picric acid and associated compounds.

Interface Engineering of Inverted Perovskite Solar Cells Using a Self-doped Perylene Diimide Ionene Terpolymer as a Thickness-Independent Cathode Interlayer

Inverted perovskite solar cells(PerSCs)are a highly promising candidate in the photovoltaic field due to their low-temperature fabrication process,negligible hysteresis,and easy integration with Si-based solar cells.A cathode interlayer(CIL)is necessary in the development of inverted devices to reduce the trap density and energy barrier between the electron transport layer(ETL)and the electrode.However,most CILs are highly thickness-sensitive due to low conductivity and poor film-forming.In this study,we report on a self-doping perylene imide-based ionene polymer(PNPDIN)used as CIL material to modify electrode in inverted PerSCs.PNPDIN exhibits high conductivity and a good solubility in polar solvent,which results in an improved power conversion efficiency(PCE)from 10.05%(device without a CIL)to 16.97%.When the blend of PNPDIN and Bphen was used as a mixed CIL,the PCE of PerSCs can be further increased to 21.28%owing to the excellent morphology and matched energy level.More importantly,the PCE of the device is highly tolerant to the thickness of the mixed CIL,which benefited from the high conductivity of PNPDIN.This development is expected to provide an excellent mixed CIL material for roll-to-roll processing efficient and stable inverted PerSCs.

Electronic Characteristics of Perylene Diimide Anion Radical and Dianion Films by Quantitative Doping

Due to their unique physicochemical properties,the anion radical and dianion of perylene diimide derivatives(PDIs)recently attracted significant attention for organic semiconductors.However,the impact of packing structure and the radical content for carrier transport in the solid state still need to be determined.Bringing the electron-withdrawing groups is an effective strategy for enablingπ−πstacking distance.Here,bay-tetrachloro-substituted PDI(B-4Cl-PDI)anion radical and dianion films were fabricated quantitatively doped with N_(2)H_(4)·H_(2)O.The radical contents were quantitatively calculated by absorption spectra in different doping ratios.The X-ray powder diffraction patterns showed that the anion radical presented a crystalline structure,and dianion aggregates exhibited an amorphous structure.With precise manipulation of the radical content,the anion radical aggregates and dianion aggregates showed the maximum electrical conductivity value of 0.024 and 0.0018 S/cm,respectively.The experiment results show that doping level and aggregate structure play a crucial role in electronic transport properties.

Photoinduced excimer generation in perylene diimide dimer:effects of solvent polarity[Invited]

The aggregation and photoinduced excited state dynamics of organic π-conjugated molecules play a vital role in solar energy conversion and applications.This work investigates how solvent polarity affects the aggregation behavior and the photophysical process of perylene diimide dimer(PDI-II).The results show that the conjugations between PDI intramolecular chromophores are more likely to generate excimer,and the conjugations between PDI intermolecular chromophores are more likely to experience symmetry-breaking charge separation.Our study can provide a reference for the design of high-efficiency solar energy conversion materials.

A Red-Emissive Sextuple Hydrogen-Bonding Self-Assembly Molecular Duplex Bearing Perylene Diimide Fluorophores for Warm-White Organic Light-Emitting Diode Application

A novel sextuple hydrogen-bonding （HB） self-assembly molecular duplex bearing red-emitting perylene diimide （PDI） fluorophores, namely PDIHB, was synthesized, and its molecular structure was confirmed by IH NMR, 13C NMR, TOF-MS and 2D NMR. Compared with the small molecular reference compound PDI, PDIItB shows one time enhanced fluorescence efficiency in solid state （4.1% vs. 2.1%）. More importantly, the presence of bulky HB oli- goamide strands in PDIHB could trigger effective spatial separation between guest and host fluorophores in thin solid film state, hence inefficient energy transfer occurs between the blue-emitting host 2TPhNII/B and red guest PDIHB in the 2 wt% guest/host blending film. As a result, a solution-processed organic light-emitting diode （OLED） with quite simple device structure of ITO/PEDOT：PSS （40 nm）/PVK （40 nm）/PDIHB （2 wt%）： 2TPhNII-IB （50 nm）/LiF （0.8 nm）/A1 （100 nm） could emit bias-independent warm-white electroluminescence with stable Commission Intemationale de L＇Eclairage coordinates of （0.42, 0.33）, and the maximum brightness and current efficiency of this device are 260 cdom-2 and 0.49 cd·A-1, respectively. All these results indicated that HB self-assembly supramolecular fluorophores could act as prospective materials for white OLED application.

Crystal Growth and Characterization of Fluorinated Perylene Diimides

One-dimensional crystals of fluorinated perylene diimides were achieved by the self-assembly of them via solvent-nonsolvent exchanging.The π-conjugated fluorinated perylene diimides were assembled into highly-ordered nanostructures of well-defined morphologies in organic solvents due to the π-π interaction between the aromatic cores.It was found that with more introduced F atoms,perylene diimides showed remarkably improved solubility and thus were much easier to grow into crystals,due to the increased polarity induced by the strong electron-withdrawing F group.More importantly,single crystal of N,N＇-diperfluorophenyl-3,4,9,10-perylenetetracarboxylic diimide（DPFPP）was obtained,and the unit cell-dimensions of triclinic structure were determined by the selected area electron diffraction（SAED） pattems to be a=0.712 nm,b=1.072 nm,c=2.914 nm,a=97.0°,β=89.6°,γ=93.4°.Owing to most of the longest c-axis orienting nearly vertically to the long axis of the needle crystal,the molecular planes are expected to be vertical to the needle axis.

Recent development of perylene diimide-based small molecular non-fullerene acceptors in organic solar cells

Recently, perylene diimide （PDI） derivatives were attractive as the electron-deficient acceptor materials in non-fullerene organic solar cells since Tang first used a single PDI compound as the n-type semiconductor to fabricate photovoltaic devices in 1986, which achieved a power conversion efficiency of 1%. Beside the monomeric PDIs, the linear and three dimensional （3D） PDl-based small molecular acceptors have also made great achievements with the power conversion efficiencies over 9.0% in single- junction polymer solar cells, and over 10.0% in tandem solar cells. The excellent device performance can be realized by forming suitable twisted structure, developing suitable donor materials and optimizing device technologies. In this review, we summarize the recent development of PDl-based small molecular non-fullerene acceptors in non-fullerene organic solar cells, including molecular design strategies and structure-property relationships.

Cationic conjugated polymers as signal reporter for label-free assay based on targets-mediated aggregation of perylene diimide quencher

Herein, we reported a new label-free and fluorescence turn-on biosensor based on cationic conjugated poly（9,9-bis（6＇-N,N,N-trimethylammonium）hexyl）fluorine phenylene）（PFP） and perylene diimide derivatives（PDI）. Cationic PFP, single-stranded nucleic acid and PDI were used as signal reporter, probe and fluorescence quencher, respectively. In the presence of nucleic acids, they form complexes with PFP and PDI through strong electrostatic attraction interactions, resulting in PDI aggregating on nucleic acids and fluorescence of PFP being quenched. When nucleic acids are hydrolyzed by enzymes or their conformation is changed via recognizing targets, the effective aggregation of PDI is disrupted and the quenching ability is decreased. Thus the fluorescence of PFP recovers significantly. By taking advantage of the mechanism, we construct a new biosensor for endonuclease and small molecules detection. Here, S1 nuclease and bisphenol A are used as model systems. The detection limit of the SI nuclease and BPA are1.0×10^-6U/mL and 0.05 ng/mL, respectively. Our method is sensitive, cost-effective and simple, and provides a new platform for bioanalysis.

1,1’-Binaphthol annulated perylene diimides: Aggregation-induced emission enhancement and chirality inversion

Aggregation-induced emission enhancement and aggregation-induced chirality inversion are two individ-ual phenomena for the enantiomerically pure organic dyes in the aggregates.Herein we reported for the first time that these two interesting phenomena could be observed simultaneously in the aggregated states of enantiomerically pure S/R-1,1?-binaphthol annulated perylene diimides,in which two perylene diimides moieties were bridged by S/R-1,1?-binaphthol(BINOL)at the bay positions.Owing to the rotat-able C2 axes between two naphthol annulated perylene diimides moieties,both of them display intrinsic behaviors of aggregation-induced emission enhancements.At the same time,due to the steric hindrances in the imide and methoxy positions,the neighboring twoπ-systems of these two unique polycyclic aro-matic imides in poor solvents are preferable to adopt a cross-stacking mode and thus form helical X-aggregates of opposite chirality(M/P)with chirality inversion characteristics in their circular dichroism and circularly polarized luminescence spectroscopic studies.

Symmetry-Induced Orderly Assembly Achieving High-Performance Perylene Diimide-Based Nonfullerene Organic Solar Cells

Controllable assembly of organic semiconductors has opened an avenue for an in-depth perception of their structure–property relationships;however,a detailed investigation of their molecular controllability remains challenging.Discerning the assembly of organic semiconductors could enable the attainment of a significant improvement of performance.

Synthesis,characterization,photophysical and electrochemical properties of oxygen bridged twisted heptatomic biphenyl substituted perylene diimides

The perylene diimide derivatives（s-THBPDI and d-THBPDI） bearing oxygen bridged twisty heptatomic biphenyl in the bay positions of the perylene core through acetylene bond were designed and synthesized.The photophysical properties of the functionalized dyes were investigated in solution and solid state by UV-vis and photoluminescence（PL） spectra.Their UV-vis and PL spectrum both exhibited the different concentration-dependent behaviors due to the difference of chemical structure.Moreover,cyclic voltammetry results indicated that the introduction of oxygen bridged twisted heptatomic biphenyl could decrease the LUMO energy level of the perylene diimide effectively and made it promising material in photoelectric devices.

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.

Molecular design towards two-dimensional electron acceptors for efficient non-fullerene solar cells

Non-fullerene polymer solar cells(NF-PSCs) have gained wide attention recently. Molecular design of non-fullerene electron acceptors effectively promotes the photovoltaic performance of NF-PSCs. However,molecular electron acceptors with 2-dimensional(2 D) configuration and conjugation are seldom reported.Herein, we designed and synthesized a series of novel 2 D electron acceptors for efficient NF-PSCs. With rational optimization on the conjugated moieties in both vertical and horizontal direction, these 2 D electron acceptors showed appealing properties, such as good planarity, full-spectrum absorption, high absorption extinction coefficient, and proper blend morphology with donor polymer. A high PCE of 9.76%was achieved for photovoltaic devices with PBDB-T as the donor and these 2 D electron acceptors. It was also found the charge transfer between the conjugated moieties in two directions of these 2 D molecules contributes to the utilization of absorbed photos, resulting in an exceptional EQE of 87% at 730 nm. This work presents rational design guidelines of 2 D electron acceptors, which showed great promise to achieve high-performance non-fullerene polymer solar cells.

Regulating the dimensionality of diphosphaperylenediimide-based polymers by coordinating the out-of-plane anisotropic π-framework toward Ag^(+)

The development of hetero-π-conjugated molecules is of significance for constructing diverse assembling superstructures based on heteroatom-related bonded or nonbonded interactions.Herein,we developed one-pot P-heteroannulation via palladiumcatalyzed dual P-C bonds formation and subsequent sulfidation to construct two isomeric diphosphaperylenediimides(cis-5 and trans-5).The unique out-of-plane anisotropic π-framework induced a cumulative anisotropy with a dipole moment of up to 8.82 D for cis-5,leading to distinct supramolecular packing arrangements.Optical and electrochemical characterizations demonstrated that they showed the largest redshifts extending to 574 nm and rather low-lying LUMO levels of −4.41 eV.Furthermore,the introduced P=S moieties endowed these diphosphaperylenediimides with prominent coordination ability towards Ag^(+),and thus the first example of perylene diimide(PDI)core-involved metal-organic coordination polymers(MOCPs)with tunable dimensionality varying from 1D,2D,to 3D was tactfully achieved.In view of easy accessibility and 2D layered porous structure,thus 2D(trans-5)·(AgOTf)based MOCP showed high crystallinity and good CO_(2) adsorption capacity with surface area of 112 m^(2)/g.The result opens a span-new avenue for exploring rylene imide-based MOCPs and related properties by integrating P functionality.

A Highly Selective and Turn-on Fluorescent Probe for Fe^(3+) Ion Based on Perylene Tetracarboxylic Diimide

We have demonstrated a turn-on fluorescent sensor 6 for detection of Fe^(3+) based on photo-induced electron transfer(PET)mechanism.The probe comprises a perylene tetracarboxylic diimide(PDI)fluorophore and two bis((1,2,3-triazol-4-yl)methyl)amine(DTA)moieties as the metal ion receptors.It exhibits high selectivity toward Fe^(3+) over various other metal ions in CH_(3)CN/H_(2)O(1∶1,V/V).The binding stoichiometry for 6-Fe^(3+) complexes has been determined to be 1∶2 by a Job plot of fluorescence.The association constant between 6 and Fe^(3+) was estimated to be 1.04×10^(10)(mol/L)^(−2) by Benesi-Hildebrand equation.

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%.