Perylene Diimide Units Research Articles

DNA-Templated Synthesis of Perylenediimide Stacks Utilizing Abasic Sites as Binding Pockets and Reactive Sites.

DNA is considered to be a promising biomolecule as a template and scaffold for arranging and organizing functional molecules on the nanoscale. The construction and evaluation of DNAs containing multiple functional molecules that are useful for optoelectronic devices and sensors has been studied. In this paper we report the efficient incorporation of perylenediimide (PDI) units into DNA by using abasic sites both as binding sites and as reactive sites and the construction of PDI stacks within the DNA structure, accomplished through the preorganization of the PDI units in the hydrophobic pocket within the DNA. Our approach could become a valuable method for construction of DNA/chromophore hybrid structures potentially useful for the design of DNA-based devices and biosensors.

Electron Delocalization in Perylene Diimide Helicenes

AbstractWe report two new helicenes derived from the double fusion of an acene with two perylene diimide (PDI) subunits. These PDI‐helicene homologs exhibit very different structural and electronic properties, despite differing by only a single ring in the link between the PDI units. The shorter inter‐PDI link brings the two PDI subunits closer together, and this results in the collision of their respective π‐electron clouds. This collision facilitates intramolecular through‐space electronic delocalization when the PDI‐helicene is reduced.

Electron Delocalization in Perylene Diimide Helicenes.

We report two new helicenes derived from the double fusion of an acene with two perylene diimide (PDI) subunits. These PDI-helicene homologs exhibit very different structural and electronic properties, despite differing by only a single ring in the link between the PDI units. The shorter inter-PDI link brings the two PDI subunits closer together, and this results in the collision of their respective π-electron clouds. This collision facilitates intramolecular through-space electronic delocalization when the PDI-helicene is reduced.

ESA-CF Synthesis of Linear and Cyclic Polymers Having Densely Appended Perylene Units and Topology Effects on Their Thin-Film Electron Mobility

A pair of topologically contrastive, linear and cyclic polymers having densely appended perylene diimide (PDI) units have been prepared by means of an electrostatic self-assembly and covalent fixation (ESA-CF) process, using an assembly composed of either linear or cyclic polyacrylate anions of different segment lengths (DPn = 50, 93, and 128) accompanying countercations of a perylene diimide (PDI) derivative having a cyclic ammonium salt group (IIL/III and IIC/III, respectively). The subsequent heating treatment at 180 °C produced the covalently converted product, i.e., the linear IVL and the cyclic IVC, respectively, in which the PDI unit was introduced nearly quantitatively to the backbone acrylate units. The obtained linear and cyclic polymers having pendant PDI units were observed to form commonly spherical self-assemblies both in bulk and in solution states, while the solution viscosity was noticeably higher with the linear products than with the cyclic counterparts. The electron-only device (EOD) m...

A twisted monomeric perylenediimide electron acceptor for efficient organic solar cells

Perylenediimide (PDI)-based materials exhibit great potential as non-fullerene acceptors in bulk-heterojunction (BHJ) organic solar cells (OSCs). Recent investigations have revealed that PDI molecules with a twisted structure could disrupt aggregation of perylene unit. Here, we present a PDI monomer via bay-substitutions with four fused naphthalene units by three-step reactions, named TN-PDI. The introduction of four fused naphthalene rings into the bay positions of PDI unit leads to a strong steric hindrance with a twist angle of 33° between the two PDI subplanes. Blended with a wide-band gap polymer donor (PDBT-T1), the TN-PDI based non-fullerene solar cells show power conversion efficiency (PCE) of 3.0%. Our results indicate that the bay-substitutions with fused aromatic substitutions could be an efficient approach to develop monomeric PDI acceptors.

Electronic energy and electron transfer processes in photoexcited donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units.

We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.

Supramolecular aggregates with distinct optical properties from PDI oligomers of similar structures.

The self-assembly behaviors of two series of monodispersed oligomers consisting of perylenediimide (PDI) linked by ethynylene and butadiynylene spacers are investigated in solutions. In spite of the very similar chemical structures, the two sets of oligomers manifest completely different optical properties upon self-aggregation, implying differed aggregate structures. While the oligomers containing butadiynylene spacers form H-aggregates, those featuring ethynylene linkers display J-aggregation characteristics. Thermodynamic analysis revealed that the self-association constants of both series of oligomers increase with the number of PDI units in the backbones. Oligomers containing the same number of PDI units but different spacers display nearly identical enthalpy changes. According to the molecular exciton theory, the observed H- and J-aggregates are suggested to comprise similar packing motifs with slightly varied slipping angles, giving rise to greatly disparate optical properties.

Synthesis and photovoltaic properties of low bandgap dimeric perylene diimide based non-fullerene acceptors

Non-fullerene organic acceptors have attracted increasing attention in recent years. One of the challenges in the synthesis of non-fullerene organic acceptors is to tune the absorption spectrum and molecular frontier orbitals, affording low bandgap molecules with improved absorption of the near-infrared solar photons. In this paper, we present the synthesis, optoelectronic and photovoltaic properties of a series of dimeric perylene diimide (PDI) based non-fullerene acceptors. These PDI dimers are bridged by oligothiophene (T) from 1T to 6T. With the increase of the oligothienyl size, the highest occupied molecular orbital (HOMO) energy is raised from −5.65 to −5.10 eV, while that of the lowest unoccupied molecular orbit (LUMO) is kept constant at −3.84 eV, affording narrow bandgap from 1.81 to 1.26 eV. The absorption from the oligothiophene occurs between 350 and 500 nm, which is complementary to that from its bridged PDI units, leading to a wide spectral coverage from 350 to 850 nm. The optimal dihedral angle between the bridged two perylene planes is dependent on the oligothienyl size, varying from 5° to 30°. The solubility of the dimers depends on the oligothienyl size and can be tuned by the alkyl chains on the bridged thienyl units. The possible applications as the solution-processable non-fullerene organic acceptor is primarily studied using commercial P3HT as the blend donor. The photovoltaic results indicate that 1T, 4T and 6T all yield a higher efficiency of ∼1.2%, whereas 2T, 3T and 5T all give a lower efficiency of <0.5%. The difference in the cell performance is related with the tradeoff between the differences of absorption, HOMO level and film-morphology between these dimers.

High‐Performance n‐Type Electrical Memory and Morphology‐Induced Memory‐Mode Tuning of a Well‐Defined Brush Polymer Bearing Perylene Diimide Moieties

Poly(N‐(1‐hexylheptyl)‐N′‐(12‐oxydodecyl)perylene‐3,4,9,10‐tetracarboxyldiimide acrylate) (PAcPDI), a perylene diimide (PDI) containing brush polymer, is synthesized, revealing good solubility in organic solvents, excellent thermal stability up to around 340 °C, and two melting transitions over 130−220 °C. The self‐assembly and n‐type memory characteristics of PAcPDI in nanoscale thin films are quantitatively investigated. As‐cast films of PAcPDI are completely amorphous and the PDI units nevertheless formed π–π stacks favorably. However, the PAcPDI molecules can self‐assemble via thermal annealing, developing a well‐ordered horizontal lamellar structure with monomorphic or polymorphic monoclinic PDI crystals. The formation of monomorphic or polymorphic monoclinic crystals is attributed to various π–π stack modes of the PDI units, and is shown to be dependent on the film thickness. The differences in the thin film morphologies are directly reflected into the electrical memory behavior. The thermally annealed films demonstrate high‐performance n‐type unipolar volatile memory behavior within the thickness range of 12−31 nm. The as‐cast films show n‐type unipolar nonvolatile or volatile memory behavior in the range of 12−53 nm. The memory mode of PAcPDI films can be tuned by changing either the morphology or the film thickness.

Intramolecular Interactions of Highly π-Conjugated Perylenediimide Oligomers Probed by Single-Molecule Spectroscopy.

Highly π-conjugated perylenediimide (PDI) oligomers are promising low band gap organic materials for various applications in optoelectronics. In this work, individual fluorescence dynamics of ethynylene- and butadiynylene-bridged dimeric and trimeric PDIs (PEP, PBP, and PEPEP) were monitored and analyzed by single-molecule fluorescence spectroscopy to gain information on the degree of extension of π-conjugation through the acetylene bridge in PDI multichromophores. The simultaneous measurements of fluorescence intensity, lifetime, and spectrum indicate a sequential decrease in π-conjugation upon photobleaching of PDI monomer units. Furthermore, Huang-Rhys (HR) factors, S, are obtained to evaluate the degree of electronic coupling in view of π-conjugation and overall rigidity between the PDI units in PDI oligomers at the single-molecule level. In addition, butadiynylene-bridged dimeric PDI (PBP) reveals conformational heterogeneity due to the long butadiynylene linker. These results suggest a new way to control the photophysical properties of the PDI multichromophoric system by expansion of π-conjugation and modification with different linker groups.

Helical ribbons for molecular electronics.

We describe the design and synthesis of a new graphene ribbon architecture that consists of perylenediimide (PDI) subunits fused together by ethylene bridges. We created a prototype series of oligomers consisting of the dimer, trimer, and tetramer. The steric congestion at the fusion point between the PDI units creates helical junctions, and longer oligomers form helical ribbons. Thin films of these oligomers form the active layer in n-type field effect transistors. UV-vis spectroscopy reveals the emergence of an intense long-wavelength transition in the tetramer. From DFT calculations, we find that the HOMO-2 to LUMO transition is isoenergetic with the HOMO to LUMO transition in the tetramer. We probe these transitions directly using femtosecond transient absorption spectroscopy. The HOMO-2 to LUMO transition electronically connects the PDI subunits with the ethylene bridges, and its energy depends on the length of the oligomer.

Perylene diimides: a thickness-insensitive cathode interlayer for high performance polymer solar cells

With the power conversion efficiency of polymer solar cells (PSCs) approaching the milestone value of 10%, their instability associated with a low work function metal cathode, particularly in the presence of oxygen and moisture, becomes a critical issue for real applications. To alleviate the air-sensitive problem, two easy-accessible solution-processed, environmentally friendly organic small-molecule cathode interlayers, with perylene diimides (PDI) as the core and amino (PDIN) or amino N-oxide (PDINO) as the terminal substituent, are explored. Benefitting from the extended planar structure of the PDI units, the two interlayer materials show high conductivities of ∼10−5 S cm−1, which make them capable of functioning efficiently in a wide thickness range of 6 to 25 nm. This is the first time that thickness-insensitive small-molecule-based cathode interlayers are reported. It is also found that the work function tuning effect of the two PDI-based interlayers allows high work function metals (such as Au and Ag) to act as the cathode. With the conventional device structure with PTB7 as a donor and PC70BM as an acceptor, the PDINO-based devices exhibit an efficiency of 8.24% with Al as the top electrode and 8.16% with Ag as the top electrode, much higher than that of the corresponding Ca/Al-based device (6.98%). The high efficiency of 8.35% is also achieved in the device with PTB7-Th as the donor. The success of the two PDI-interlayers indicates that π-delocalized planar structures with high electron affinities could be particularly useful in developing high-performance organic interlayer materials.

Tuning of the color of the emitted light from new polyperyleneimides containing oxadiazole and siloxane moieties

Four new aromatic poly(peryleneimides) containing electron-withdrawing oxadiazole rings and flexible tetramethyldisiloxane units in the backbone were prepared by a one step polycondensation reaction at high temperature of four aromatic diamines containing preformed oxadiazole units with a mixture, in different ratios, of perylenetetracarboxylic dianhydride and tetramethyldisiloxane-1,3-bis(4-phthalic anhydride). The structure of these polymers was confirmed by FT-IR and 1H NMR spectroscopy. The solubility, thermal stability and glass transition temperature of the poly(peryleneimides) were measured and discussed in correlation with their chemical structure. The solid polymers were studied by X-ray diffraction which revealed a semicrystalline state consisting in face-to-face arranged columns of perylenediimide units for two of the polymers. The film-forming ability and the morphology of the resulting thin films were investigated using scanning electron microscopy which showed that two of the polymer films were organized into self-assembled rod-like structures. An extensive study of the photo-optical properties of these polymers highlighted the ability of the color of the emitted light to be modulated as a function of the excitation wavelengths, as was surveyed in the chromaticity diagrams. The Förster excitation energy transfer phenomenon from oxadiazole to perylenediimide chromophores was observed to occur for some of the polymers, for which the oxygen bridge appears to be responsible. In solution, high fluorescence quantum yields were obtained, up to 24%, while, in the solid state, low fluorescence emission was attained due to aggregation. These poly(peryleneimides) could be considered as promising candidates for high-performance materials to be used in novel optoelectronic applications, e.g. chemiluminescent sensors.

New polymer acceptors for organic solar cells: the effect of regio-regularity and device configuration

Two polymers, r-PDI-diTh and i-PDI-diTh, were synthesized as acceptors applicable for solution-processed BHJ OSCs. By introducing a bulky, dove tailed side chain and thereby suppressing the π–π interactions between perylenediimide units in the backbones of acceptor polymers, more effective phase segregation of these acceptors with a donor polymer (P3HT) was realized. By employing the inverted device configuration to better match the vertical phase separation of donor–acceptor polymers produced by solution processing, undesirable polaron pair recombination was suppressed, and PCE up to 2.17% was achieved from the regio-regular acceptor r-PDI-diTh.

The leverage effect of the relative strength of molecular solvophobicity vs. solvophilicity on fine-tuning nanomorphologies of perylene diimide bolaamphiphiles

Previously, we have found that full protonation of the two pyridyloxyl groups of 1,7-bispyridyloxyl-N,N′-bis(2-ethylhexyl)perylene diimide (PDI) (molecule 1) leads to formation of highly fluorescent nanospheres, due to formation of 1,7-bis(4-oxylpyridinium chloride) dramatically enhancing the inter-chromophore interactions in the bay-region (J. Am. Chem. Soc., 2011, 133, 11022–11025; Chem.–Eur. J., 2012, 18, 12305–12313). Molecular modeling revealed that the two pyridyloxyl groups in molecule 1 pointed outside the same facet of the PDI plane, forming a rigid PDI-based bolaamphiphile. In order to more fully investigate the effects of the molecular solvophobicity on the bay-region vs. the molecular solvophilicity including that from the imide-direction and from the solvophilic PDI unit, Fsolvophob/solvophil, on fine-tuning nanomorphologies and properties, we reduced the molecular solvophilicity by replacing the two 2-ethylhexyl (EH) tails in molecule 1 with two shorter cyclohexyl (CH) tails, while maintaining the two 1,7-bispyridyloxyl units, forming molecule 2. Furthermore, we replaced one pyridyloxyl group in molecule 2 with another weaker solvophobic 2-methoxyethoxyl unit, forming molecule 3 to tune the molecular solvophobicity in the bay-region. Morphological studies demonstrated that molecule 2 formed 70–400 nm sized hollow nanospheres in a polar solvent mixture of dichloromethane (DCM)–ethanol (EtOH) and ∼100 nm sized hollow nanoparticles in a weak apolar environment of DCM–methylcyclohexane (MCH) mixture with RMCH = 10–40% (v/v). Upon a further increase of the surrounding apolarity by increasing the RMCH, plate morphologies of nanorods and microplates formed, accompanying with the π–π-stacking changing from the co-facial mode to slippage mode. Differently, molecule 3 always formed platelike nanostructures such as nanotapes in DCM–EtOH mixtures and nano-rhombuses in DCM–MCH mixtures with the molecules adopting co-facial π–π-stacking in both nanostructures. Taken together, the self-assembly and the final nanomorphologies of the PDI-based bolaamphiphiles are both significantly controlled by a small change of Fsolvophob/solvophil and such a leverage effect of the control from Fsolvophob/solvophil is amplified by changing the solvent polarity, for example, fine-tuning REtOH and RMCH.

Benzodithiophene bridged dimeric perylene diimide amphiphiles as efficient solution-processed non-fullerene small molecules

Two amphiphilic and highly twisting perylene diimide (PDI) dimers, Bis-PDI-BDT-EG, were synthesized by using 4,8-bis(2-(2-ethylhexylthienyl) benzo[1,2-b:4,5-b′]dithiophene (BDT-T) and 4,8-bis(2-ethylhexyloxy) BDT (BDT-O) as covalent bridges at the 7,7′-positions, while at the 1,1′-positions, they were functionalized with weakly solvophobic 2-methoxylethoxyl (EG) units. The subtle structural differences between BDT-O and BDT-T lead to distinct aggregation abilities: with respect to the over-strong aggregation ability of the BDT-O bridged dimer 2, the BDT-T bridged dimer 1 shows largely reduced aggregation ability and is solution-processable in the commonly used organic solvent. The highly twisted conformation between the PDI–BDT–PDI planes produced steric-pairing effects, which directed ordered packing of dimer 1. When dimer 1 was blended with P3HT in a weight D/A ratio of 1 : 2.5, the electron mobility (μe) was 3.4 × 10−5 cm2 V−1 s−1 and the best PCE was 1.72%. Slowing the solvent evaporation speed benefited the packing order of the PDI dimer, and the μe value was slightly increased to 6.0 × 10−5 cm2 V−1 s−1. The best PCE was improved up to 1.87%. The μe was further increased up to 3.4 × 10−4 cm2 V−1 s−1 when the D/A ratio was decreased down to 1 : 2.2 and the best PCE of 1.95% was achieved. Solid absorption spectra and XRD data of the blended films supported the improvement of the packing order of the PDI dimer by slowing the solvent annealing speed. AFM images supported the largely reduced aggregation ability of dimer 1 when blended with P3HT. The observed phase size of 35 nm is formed under the slow solvent annealing speed and a D/A ratio of 1 : 2.2. Our results revealed that the amphiphilic nature of the bridged aromatic unit reduces the aggregation ability and facilitates the ordered packing of the PDI units, contributing to the improvement of efficiency.

Excitonic Coupling in Linear and Trefoil Trimer Perylenediimide Molecules Probed by Single-Molecule Spectroscopy

Perylenediimide (PDI) molecules are promising building blocks for photophysical studies of electronic interactions within multichromophore arrays. Such PDI arrays are important materials for fabrication of molecular nanodevices such as organic light-emitting diodes, organic semiconductors, and biosensors because of their high photostability, chemical and physical inertness, electron affinity, and high tinctorial strength over the entire visible spectrum. In this work, PDIs have been organized into linear (L3) and trefoil (T3) trimer molecules and investigated by single-molecule fluorescence microscopy to probe the relationship between molecular structures and interchromophoric electronic interactions. We found a broad distribution of coupling strengths in both L3 and T3 and hence strong/weak coupling between PDI units by monitoring spectral peak shifts in single-molecule fluorescence spectra upon sequential photobleaching of each constituent chromophore. In addition, we used a wide-field defocused imaging technique to resolve heterogeneities in molecular structures of L3 and T3 embedded in a PMMA polymer matrix. A systematic comparison between the two sets of experimental results allowed us to infer the correlation between intermolecular interactions and molecular structures. Our results show control of the PDI intermolecular interactions using suitable multichromophoric structures.

Synthesis and Photovoltaic Performances of a Novel Phthalocyanine- perylene Molecular Heterojunction

A novel phthalocyanine (Pc)-perylene diimide (PDI)-Pc donor-acceptor molecular heterojunction was synthesized through amidation of an asymemetric Pc-carboxylic acid and PDI-diamines, and it is well soluble in common solvent such as dichloromethane, chloroform, and tetrahydrofuran. It shows an broad absorption band covering the whole visible region from 300 to 780 nm, and its molar extinction coefficient reaches as high as 10 L•mol•cm. Such an adsorption band originates from both the PDI and PC units. Considering the excellent light-harvesting ability, organic solar cells (OSCs) based on the synthetic compound and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) were fabricated with the configurations of ITO/poly(3,4-ethylenedioxythiophene):poly-styrenesulfonate (PEDOT:PSS)/phthalocyanine-perylene:PC61BM/Ca/Al. One of the OSC devices showed a power conversion efficiency (PCE) of 0.009% with an open-circuit voltage (Voc) of 0.472 V, a short circuit current (Jsc) of 0.104 mA/cm and a fill factor (FF) of 18.2%.

Supramolecular Zinc Phthalocyanine–Imidazolyl Perylenediimide Dyad and Triad: Synthesis, Complexation, and Photophysical Studies

Two new supramolecular architectures based on zinc phthalocyanine (Pc) and imidazolyl-substituted perylenediimide (PDI), ZnPc/DImPDI/ZnPc 1 and ZnPc/ImPDI 2, have been prepared. A strong electron-donor, ZnPc-8, which contained eight tert-octylphenoxy groups was synthesized to ensure high solubility, thereby reducing aggregation in solution and providing σ-donor features while avoiding regioisomeric mixtures. Also, PDI units were functionalized with tert-octylphenoxy groups at the bay positions, which provide solubility to avoid aggregation in solution, together with one and two imidazole moieties in the amide position, PDI-6 and PDI-4, respectively, to be able to strongly coordinate with the ZnPc complex. Supramolecular complexation studies by (1)H NMR spectroscopy and ESI-MS demonstrate a high coordinative binding constant between imidazole-substituted PDI-4 or PDI-6 and ZnPc-8. The same results were confirmed by UV/Vis and fluorescence titration studies. UV/Vis titration studies revealed the formation of a 1:1 complex ZnPc/ImPDI 2 for the systems ZnPc-8 and PDI-6 and a 2:1 complex ZnPc/DImPDI/ZnPc 1 for the interaction of ZnPc-8 and PDI-4. The binding constant in both cases was determined to be on the order of 10(5) M(-1). Femtosecond laser flash photolysis measurements provided a direct proof of the charge-separated state within both supramolecular assemblies by observing the transient absorption band at 820 nm due to the zinc phthalocyanine radical cation. The lifetimes of charge-separated states are (9.8±3) ns for triad 1 and (3±1) ns for dyad 2. As far as we know, this is the first time that a radical ion pair has been detected in a supramolecular assembled ZnPc-PDI system and has obtained the longest lifetime of a charge-separated state published for ZnPc-PDI assemblies.

Preparation of multifunctional mesoporous silica particles: the use of an amphiphilic silica precursor with latent amine functionality in selective functionalization of the inner surface

The mesoporous silica particle has three different areas as a functionalization site, including an outer surface, a silica framework and an inner surface. We functionalized the inner surface selectively using an amphiphilic silica precursor with latent amine functionality and prepared a multifunctional mesoporous silica particle showing fluorescence resonance energy transfer (FRET). An organotriethoxysilane consisting of a perylene diimide unit and two triethoxysilyl groups was co-condensed with tetraethoxysilane and the amphiphilic organotriethoxysilane [(4-octylphenyl-3-(triethoxysilyl)propylcarbamate)] in the presence of cetyltrimethylammonium bromide under basic conditions. The resulting periodic mesoporous silica particle contained perylene diimide units in a silica framework as a FRET donor. The hydrophobic part of the amphiphile was tethered to the pore wall through a thermally reversible urethane bond. The surfactant molecules were extracted by reflux in a mixture of 1,4-dioxane, HCl and water. In this process, hydrophobic groups in the pore were also removed to produce amino groups on the inner surface. The rhodamine units were introduced into the pore as a FRET acceptor by the reaction of the isothiocyanate group of Rhodamine B isothiocyanate with the amino group on the inner surface, forming a thiourea linkage. The outer surface of the silica particle could be also functionalized by grafting with 3-(trimethoxysilyl)propyl acrylate before extraction of the surfactant molecules. A silica–polymer thin film was prepared where the silica particles were embedded in a poly(2-hydroxyethyl methacrylate) matrix. Both the suspension of the silica particles in ethanol and their polymer composite film showed the efficient FRET effect.