Hydrogen-bonded oligo(p-phenylenevinylene) functionalized with perylene bisimide: self-assembly and energy transfer

We describe the synthesis, supramolecular ordering on surfaces and in solution, and photophysical characterization of OPV4UT-PERY, an oligo(p-phenylenevinylene) (OPV) with a covalently attached perylene bisimide moiety. In chloroform, the molecule forms dimers through quadruple hydrogen bonding of the ureido-s-triazine array. This is supported by scanning tunneling microscopy (STM) studies, which reveal dimer formation at the liquid (1,2,4-trichlorobenzene)/solid (graphite) interface. Moreover, contrast reversal in bias-dependent STM imaging provides information on the ordering and different electronic properties of the oligo(p-phenylenevinylene) and perylene bisimide moieties. In dodecane, the molecule self-assembles into H-type aggregates that are still soluble as a result of the hydrophobic shell formed by the dodecyloxy wedges. The donor-acceptor molecule is characterized by efficient energy transfer from the photoexcited OPV to the perylene bisimide. Mixed assemblies with analogous OPVs lacking the perylene bisimide unit have been prepared in dodecane solution and energy transfer to the incorporated perylene bisimides has been studied by fluorescence spectroscopy.     

Hierarchical self-organization of perylene bisimide--melamine assemblies to fluorescent mesoscopic superstructures

A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and the complementary melamine moiety have been determined in several solvents by NMR and UV/Vis titration experiments with monotopic model compounds 5 and 9. The effects of the solvent polarity and specific solvent-solute interactions on the degree of polymerization of (3 x 8)n are discussed, and a general formula to estimate the chain length of [AA-BB]n nylon-type supramolecular polymers is derived. In addition to the formation of a hydrogen-bonded supramolecular chain. pi-pi interactions were observed for perylene bisimide-melamine assemblies 3b x 8b and 3b x 8c in aliphatic solvents. The orthogonal nature of hydrogen bonding and pi-pi interactions leads to three-dimensional growth yielding large-sized aggregates already in dilute solution. On suitable substrates, densely intertwined networks of nano- to mesoscopic strands are formed which have been investigated by electron microscopy, confocal fluorescence microscopy and optical polarization microscopy. The high fluorescence and excellent photostability of these superstructures is promising for future studies on energy migration and artificial light harvesting at the nano- and mesoscopic length scale.     

Self-assembly and characterization of hydrogen-bond-induced nanostructure aggregation.

A supramolecular system of a perylene derivative containing bis(2,6-diacylaminopyridine) units and a perylene bisimide bound through three hydrogen-bonds was synthesized and characterized. 1H NMR spectra confirmed the existence of hydrogen-bonding interactions between the perylene derivative (3) and the perylene bisimide (7). The photocurrent generation of the self-assembled 3.7 film was measured, and a cathodic photocurrent response was obtained. SEM images indicated that well-defined long fibers could be fabricated by self-assembly, by exploiting the hydrogen bonding interactions and pi-pi stacking interactions of perylene rings.     

Formation of supramolecular polymers and discrete dimers of perylene bisimide dyes based on melamine-cyanurates hydrogen-bonding interactions

Melamine-linked perylene bisimide dyes (MPBIs) bearing an ethylene or trimethylene group as linker moieties were synthesized, and their self-aggregation and coaggregation with cyanurates through complementary triple hydrogen bonds have been investigated. UV/vis studies revealed that both the MPBIs self-assemble in nonpolar organic solvent through pi-pi stacking interaction between perylene cores, giving self-aggregates with nearly identical thermal stabilities. Upon addition of 1 equiv of cyanurate components, however, the stabilities of the resulting aggregates were dramatically changed between the two systems, suggesting the formation of different types of hydrogen-bonded supramolecular species. Dynamic light scattering and atomic force microscopic studies revealed that the system featuring ethylene linker moieties generates a discrete dimer of MPBI supported by two cyanurate molecules, whereas the system featuring trimethylene linker moieties affords extended supramolecular polymers hierarchically organizing into nanoscopic fibers. These results demonstrate that it is possible to obtain distinct supramolecular species by just changing the number of carbon atoms at the linker moieties of MPBI components. The present strategy for the fabrication of discrete or polymeric supramolecular assemblies should be applicable to other functional pi-conjugated molecules.     

Self-assembly and characterization of a novel hydrogen-bonded nanostructure

A novel hydrogen-bonded supramolecular system of a [60]fullerene derivative with perylene bisimide was synthesized and characterized. 1H NMR spectra confirmed the existence of strong hydrogen-bonding interaction between compounds 1 and 5. Transmission electron microscopy images of 1.5 aggregates showed spherical particles having a mean diameter of 50 nm. The photocurrent response of the film was measured, and a steady and rapid anodic photocurrent response was obtained.     

Photocontrol Over Self‐Assembled Nanostructures of π–π Stacked Dyes Supported by the Parallel Conformer of Diarylethene

Diarylethenes (DAEs) have rarely been used in the design of photoresponsive supramolecular assemblies with a well‐defined morphology transition owing to rather small structural changes upon photoisomerization. A supramolecular design based on the parallel conformation of DAEs enables the construction of photoresponsive dye assemblies that undergo remarkable nanomorphology transitions. The cooperative stacking of perylene bisimide (PBI) dyes was used to stabilize the parallel conformer of DAE through complementary hydrogen bonds. Atomic force microscopy, UV/Vis spectroscopy, and molecular modeling revealed that our DAE and PBI building blocks coassembled in nonpolar solvent to form well‐defined helical nanofibers featuring J‐type dimers of PBI dyes. Upon irradiating the coassembly solution with UV and visible light in turn, a reversible morphology change between nanofibers and nanoparticles was observed. This system involves the generation of a new self‐assembly pathway by means of photocontrol.     

Synthesis and energy-transfer properties of hydrogen-bonded oligofluorenes

A set of fluorene oligomers has been synthesized by stepwise palladium-catalyzed (Suzuki) couplings of fluorene monomers. Ureidopyrimidinones (UPy), functional groups that can dimerize via quadruple hydrogen bonds, were attached to both ends of the oligofluorenes. The resulting bis-UPy-terminated oligomers self-assemble into supramolecular chain polymers. For comparison, oligofluorenes of the same oligomer lengths but without terminal hydrogen-bonding groups were synthesized. Chains of hydrogen-bonded fluorenes can be simply endcapped by a variety of chain stoppers, molecules that have one UPy group. In this manner, we have endcapped the hydrogen-bonded fluorene chains with either oligo(p-phenylenevinylene) or perylene bisimide. Energy-transfer experiments in solution and the solid state demonstrate that oligofluorenes can donate energy to a variety of energy acceptors, but that this energy transfer occurs most effectively when the donor fluorene is hydrogen-bonded to the acceptor.     

Supramolecular nanoribbons and nanoropes generated from hydrogen-bonded supramolecular polymers containing perylene bisimide chromophores

A perylene bisimide anchored with melamine hydrogen-bonding units has been prepared, and its supramolecular polymerization upon binding with N-dodecylcyanurate (CA) was examined. The resulting flexible supramolecular polymers self-organized via a pi-pi stacking interaction between perylene chromophores, affording ribbonlike aggregates in cyclic alkanes and ropelike aggregates in acyclic alkanes to form gels. [structure: see text]     

Synthesis of n-type perylene bisimide derivatives and their orthogonal self-assembly with p-type oligo(p-phenylene vinylene)s

Four different (chiral) electron-deficient (n-type) perylene bisimides containing aliphatic, aromatic, or ethyleneoxide side chaines have been synthesized and fully characterized. All of them form supramolecular stacks in apolar methylcyclohexane (MCH) solution as demonstrated by concentration- and temperature-dependent absorption, circular dichroism, and fluorescence studies. One derivative was investigated in more detail in the solid state and proven to be liquid crystalline and capable of forming nanometer-sized fiberlike networks when drop-cast from MCH. Optical spectroscopy techniques show that perylene bisimide and an oligo(p-phenylene vinylene) (p-type) derivative orthogonally self-assemble into separate nanosized p-and n-type stacks in MCH. In contrast in toluene only molecularly dissolved species are present. In films deposited from MCH as well as from toluene photoinduced electron transfer takes place from the p-type material to the n-type material. As a result of the orthogonal self-assembly process, in films from MCH an ordered network of fibers was formed, whereas in films from toluene no ordering was observed. However, probably due to the lateral orientation on the surface and the presence of long aliphatic chains pointing toward the electrodes, efficient bulk heterojunction solar cells could not be constructed.     

Oligo(p-phenyleneethynylene)-functionalized Perylenebisimidetriad: Synthesis, Photophysical Properties, and Self-assembly

The rod‐like oligo(p‐phenylene ethynylene)‐functionalized perylene bisimide triad was synthesized and characterized. Aggregation behavior in solvents of different polarity was investigated by absorption and fluorescent spectroscopy. The results showed that stronger aggregations took place in low‐polarity slovent. The experiments also indicated that the energy and electron transfer might takeplace between the two chromophores during the photoinduced excitation. Highly ordered two‐dimensional assemblies could be observed at solid/liquid interfaces.     

以苝酰亚胺为构筑单元的氢键型超分子聚合物的组装与应用

以苝酰亚胺为构筑单元的氢键型超分子聚合物具有动态可逆的特征和独特的聚集体结构,呈现出许多新颖的光电功能特性,在有机太阳能电池,场效应晶体管和光收集材料等高新技术领域有着广阔的应用前景。本文在介绍苝酰亚胺衍生物的化学结构及其氢键组装特点的基础上,主要综述了近年来以苝酰亚胺为构筑单元,采用三重氢键,多重氢键以及其他形式氢键引导构筑的超分子聚合物的研究动态,这类超分子聚合物展示了丰富的组装体形貌结构,独特的性质功能以及在光电功能器件上的广阔的应用前景。最后,对其发展前景作了展望。     

Photoinduced electron transfer in hydrogen-bonded oligo(p-phenylene vinylene)-perylene bisimide chiral assemblies

Well-defined chiral fibers incorporating hydrogen-bonded oligo(p-phenylene vinylene) donor and perylene bisimide acceptor chromophores have been realized by self-assembly. Upon photoillumination of these fibers electron-transfer takes place, leading to charge separation within the aggregated dyes.     

Fluorescent and electroactive cyclic assemblies from perylene tetracarboxylic acid bisimide ligands and metal phosphane triflates

Tetraaryloxy-substituted perylene tetracarboxylic acid bisimides with one or two 4-pyridyl receptor substituents at the imide functionality were synthesized and employed in transition metal directed self-assembly with Pd(II) and Pt(II) phosphane triflates. Upon mixing of the components, quantitative formation of functional molecular square-type complexes containing four dye molecules and model complexes of a 2:1 (perylene bisimide ligand:transition metal ion) stoichiometry was observed. The isolated metallosupramolecular squares were characterized by 1H and 31P [1H] NMR spectroscopy as well as conventional electrospray ionization (ESI) and ESI-FTICR mass spectrometry, which gave evidence for the structure and the high stability of these giant cyclic dye assemblies (molecular weight (3a) 8172, Pt-Pt corner diagonal ca. 3.4 nm). Studies of the optical absorption and fluorescence properties and the electrochemistry and spectroelectrochemistry of both the perylene bisimide ligands and the perylene bisimide metal complexes show that Pt(II) coordination does not interfere with the optical and electrochemical properties of the perylene bisimide ligands; this gives squares with high fluorescence quantum yields (phiF (3a)=0.88) and three fully reversible redox couples. The latter could be unambiguously related to quantitative formation of perylene bisimide radical cations (E1/2 = +0.93 V vs. Fc/Fc+), radical anions (E1/2= - 1.01 V vs. Fc/Fc+), and dianions (E1/2 = -1.14 V vs. Fc/Fc+); these redox reactions change the charge state of the cyclic assembly from +12 to zero. In contrast, Pd(II) coordination influenced the electrochemical properties of the assembly because of an irreversible palladium reduction at E1/2= -1.15 V versus Fc/Fc+. Finally, dynamic ligand exchange processes between different metallosupramolecular assemblies were investigated by multinuclear NMR and electrospray mass spectrometry. These studies confirmed the reversible nature of the pyridine-Pt(II)/Pd(II) coordination process.     

Hydrogen bond directed self-assembly of core-substituted naphthalene bisimides with melamines in solution and at the graphite interface

A series of red and blue highly fluorescent core-substituted naphthalene bisimide dyes has been synthesized and they have been investigated as supramolecular building blocks. NMR and UV-Vis titration experiments of these dyes with complementary melamines revealed the formation of triple hydrogen bonds (DAD-ADA arrays) in solution. At stoichiometric ratios, ditopic melamine receptors could dissolve otherwise insoluble bisimides by means of hydrogen bonding, even in aliphatic solvents. At the solution/graphite interface, one-dimensional chains of hydrogen bonded naphthalene bisimides and two-dimensional adlayers of ditopic melamines are formed for the pure compounds but little evidence for heterocomplexes between the two complementary building blocks could be obtained.     

Explosives Sensing by Using Electron‐Rich Supramolecular Polymers: Role of Intermolecular Hydrogen Bonding in Significant Enhancement of Sensitivity

We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron‐deficient nitro‐aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War II. In this study, we have synthesised a series of pyrene‐based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron‐deficient NACs through a fluorescence quenching mechanism. A Stern–Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen‐bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent‐dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid‐state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid–solid interface, in which structures of self‐assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water.     

Controllable Self‐Assembly of Amphiphilic Zwitterionic PBI Towards Tunable Surface Wettability of the Nanostructures

Amphiphilic molecules have received wide attention as they possess both hydrophobic and hydrophilic properties, and can form diverse nanostructures in selective solvents. Herein, we report an asymmetric amphiphilic zwitterionic perylene bisimide ( AZP ) with an octyl chain and a zwitterionic group on the opposite imide positions of perylene tetracarboxylic dianhydride. The controllable nanostructures of AZP with tunable hydrophilic/hydrophobic surface have been investigated through solvent‐dependent amphiphilic self‐assembly as confirmed by SEM, TEM, and contact angle measurements. The planar perylene core of AZP contributes to strong π–π stacking, while the amphiphilic balance of asymmetric AZP adjusts the self‐assembly property. Additionally, due to intermolecular π–π stacking and solvent–solute interactions, AZP could self‐assemble into hydrophilic microtubes in a polar solvent (acetone) and hydrophobic nanofibers in an apolar solvent (hexane). This facile method provides a new pathway for controlling the surface properties based on an asymmetric amphiphilic zwitterionic perylene bisimide.     

Enantioselective cyclization of racemic supramolecular polymers

Homochiral hydrogen-bonded cyclic assemblies are formed in dilute solutions of racemic supramolecular polymers based on the quadruple hydrogen bonding 2-ureido-4[1H]-pyrimidinone unit, as observed by 1H NMR and SEC experiments. Preorganization of the monomers and the combined binding strength of the eight hydrogen bonds result in a very high stability of the cyclic aggregates with pronounced selectivity between homochiral and heterochiral cyclic species, usually only observed in crystalline or liquid crystalline phases.     

Synthesis,optical properties,and aggregation behavior of a triad system based on perylene and oligo(p-phenylene vinylene) units

A donor-acceptor-donor triad molecule with a perylene bisimide derivative as electron acceptor, and an oligo(p-phenylene vinylene) (OPV) derivative as electron donor was synthesized (OPV-PERY-OPV). The structure of the triad was characterized by (1)H and (13)C NMR spectroscopy, size-exclusion chromatography (SEC), and MALDI-TOF spectrometry. Absorbance spectra and CD spectroscopic measurements of the triad molecule indicated the formation of aggregates in solvents such as toluene, chloroform, and tetrachloroethane, whereas it was present in the molecularly dissolved state in THF. The (1)H NMR spectra of the molecule in chloroform had, unexpectedly, four doublet peaks for the perylene protons, instead of the two doublets that is generally seen in N,N'-substituted perylene molecules. To understand the aggregation behavior and the splitting of the signals in the (1)H NMR spectra, a simple model compound was synthesized, in which the OPV units were replaced by phenyl groups (Ph-PERY-Ph). (1)H NMR spectra in CDCl(3) and tetrachloroethane again had four doublet peaks for the perylene protons, whereas in THF the perylene protons gave only a single peak. NOE and COSY spectroscopy were used to assign the peaks to their corresponding perylene protons. UV/Vis and CD spectroscopic measurements indicated that, similar to the OPV-PERY-OPV triad molecule, the model compound Ph-PERY-Ph was also present in the aggregated form in solvents such as toluene, chloroform, and tetrachloroethane, and in the molecularly dissolved state in THF. IR measurements of the model molecule in the first set of solvents indicated carbamate bond (bond;OCObond;NHbond;)-induced intermolecular hydrogen bonding, whereas in THF, the molecule was mostly present in the free form. CPK models with a dimeric structure, in which two perylene molecules are held together by intermolecular hydrogen bonding with the perylene core shifted slightly with respect to one another, could account for the optical properties and the observation of the four different peaks in the (1)H NMR spectra in polar solvent. Temperature-dependent (1)H NMR spectroscopic, UV/Vis, and CD measurements indicated that the transition from the aggregated to the molecularly dissolved state took place at higher temperatures. The electrochemical studies indicated that OPV-PERY-OPV was both p- and n-dopable, whereas Ph-PERY-Ph was only n-dopable. Cyclic voltammetry measurements of Ph-PERY-Ph in THF had two reduction peaks corresponding to the reduction of the perylene core to the monoanion and dianion, respectively. In dichloromethane, however, an additional reduction peak at lower potential was observed. This new reduction peak might arise from the hydrogen-bonded species.     

Self-assembly of diorganotin(IV) oxides (R = Me, nBu, Ph) and 2,5-pyridinedicarboxylic acid to polymeric and trinuclear macrocyclic hybrids with porous solid-state structures: influence of substituents and solvent on the supramolecular structure

2,5-Pyridinedicarboxylic acid has been reacted with three different diorganotin(IV) oxides (R = Me, nBu, Ph) to study the molecular and supramolecular structures of the resulting diorganotin(IV) 2,5-pyridinedicarboxylates. It has been found that coordinating solvent molecules can change the supramolecular structure completely. The molecular structures found are either polymeric (zigzag) or cyclotrimeric; the supramolecular arrangements include (i) systems having only loosely bound discrete molecules (van der Waals contacts), (ii) systems having a 2D or 3D hydrogen-bonded structure, and (iii) systems having a 3D polymeric coordination structure. Channels or cavities are formed in several cases. For a particular case, evidence has been provided that molecular aggregation to capsules through hydrogen bonding interactions is possible in solution.