Perylene Molecules Research Articles

Bright Fluorescence and Host–Guest Sensing with a Nanoscale M4L6 Tetrahedron Accessed by Self‐Assembly of Zinc–Imine Chelate Vertices and Perylene Bisimide Edges

AbstractA highly luminescent Zn4L6 tetrahedron is reported with 3.8 nm perylene bisimide edges and hexadentate ZnII–imine chelate vertices. Replacing FeII and monoamines commonly utilized in subcomponent self‐assembly with ZnII and tris(2‐aminoethyl)amine provides access to a metallosupramolecular host with the rare combination of structural integrity at concentrations <10−7 mol L−1 and an exceptionally high fluorescence quantum yield of Φem=0.67. Encapsulation of multiple perylene or coronene guest molecules is accompanied by strong luminescence quenching. We anticipate this self‐assembly strategy may be generalized to improve access to brightly fluorescent coordination cages tailored for host–guest light‐harvesting, photocatalysis, and sensing.

Understanding the modulation mechanism in resonance-enhanced multiphoton probing of molecular dynamics

Time-resolved spectroscopy on isolated molecules gives fundamental insight into the conversion of light energy to other degrees of freedom. Probing of the photoinduced dynamics can be accomplished by ionization, via a single-photon or multiphoton transition. In this Rapid Communication we directly contrast transient spectra on the molecule perylene obtained with multiphoton ionization (MPI) to single-photon ionization (SPI). The photoinduced nuclear geometry relaxation modulates the MPI transient with a decay time constant of $0.9\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.28em}{0ex}}\mathrm{ps}$. In contrast, the SPI transient completely lacks any indication for relaxation. We attribute this difference to a change in resonance enhancement of the MPI probe as the molecular geometry changes. Our results underline the importance of a detailed knowledge about these resonances for a proper interpretation of transient signals of molecular dynamics subject to nuclear and electronic relaxation effects. At the same time, the direct comparison to SPI directly demonstrates the higher sensitivity of resonance-enhanced MPI as a probe in time-resolved dynamical studies.

True perylene epitaxy on Ag(110) driven by site recognition effect.

We present a STM study of room temperature perylene adsorption on the Ag(110) surface. We have found a 2D perylene crystalline phase coexisting with the perylene liquid phase under thermal equilibrium. The reversible precipitation of the liquid phase at sub-monolayer coverage reveals the well ordered chiral crystalline phase existing in two enantiomorphic configurations of the ((-2)(3) (5)(2)) and ((2)(3) (5)(-2)) symmetry. This chiral phase is spatially separated into the 2D enantiopure islands of tens of nanometers size randomly distributed on the substrate and surrounded by the liquid medium. Analysis of surface registry of the crystalline phase combined with modeling of the intermolecular interactions indicates that its structure and symmetry is determined by a specific balance between the intermolecular attraction and intrinsic ability of the perylene aromatic board to recognize adsorption sites. The recognition effect was found to be strong enough to pin half of the perylene molecules into defined adsorption sites providing the structure skeleton. The attractive intermolecular interaction was found to be strong enough to bind another half of the molecules to the perylene skeleton shaping the true epitaxial structure.

Theoretical investigations of the perylene electronic structure: Monomer, dimers, and excimers

The structural and electronic properties of perylene molecule, dimers, and excimers have been computationally studied. The present work represents the first systematic study of perylene molecule and dimer forms by means of long-range corrected time-dependent density functional theory (TDDFT) approaches. Initially, the study explores the photophysical properties of the molecular species. Vertical transitions to many excited singlet states have been computed and rationalized with different exchange-correlation functionals. Differences between excitation energies are discussed and compared to the absorption spectrum of perylene in gas phase and diluted solution. De-excitation energy from the relaxed geometry of the lowest excited singlet is in good agreement with the experimental fluorescence emission. Optimization of several coplanar forms of the perylene pair prove that, contrary to generalized gradient approximation (GGA) and hybrid exchange-correlation functionals, corrected TDDFT is able to bind the perylene dimer in the ground state. Excitation energies from different dimer conformers point to dimer formation prior to photoexcitation. The fully relaxed excimer geometry belongs to the perfectly eclipsed conformation with D2h symmetry. The excimer equilibrium intermolecular distance is shorter than the separation found for the ground state, which is an indication of stronger interchromophore interaction in the excimer state. Excimer de-excitation energy is in rather good agreement with the excimer band of perylene in concentrated solution. The study also scans the energy profiles of the ground and lowest excited states along several geometrical distortions. The nature of the interactions responsible for the excimer stabilization is explored in terms of excitonic and charge resonance contributions. © 2015 Wiley Periodicals, Inc.

Shift of absorption energy during thin dye film growth: interpretation by geometric models of the growth morphology

We measure absorption spectra of two different perylene molecules in thin films with thicknesses varied between 1 and 30nm physical vapor deposited on glass substrates. Atomic force microscopy (reveals the formation of crystallized needles for N, N`-dimethyl perylene tetracarboxylic acid diimide and amorphous round-shaped islands for 1,6,7,12-tetrachloro-N,N`-dimethyl perylene tetracarboxylic. For both molecules, a spectral shift of the lowest energy transition to lower energies was observed with increasing film thickness. Common models taking electric fields, electronic coupling or exciton confinement into account cannot completely describe the observed spectral shift. Here we show that the experimental values can be fitted with an advanced layering model based on the energetic difference between bulk and interface/surface materials. In contrast to the known simple d−1 model, which describes the energetic shift for the special case of a layer-by-layer growth, we extend this idea to other film morphologies.

Physical Factors Affecting Charge Transfer at the Pe-COOH–TiO2 Anatase Interface

In this work we address the factors affecting the rate and the completeness of the excited state electron transfer from a COOH-anchored perylene molecule to the (101) anatase surface. To investigate the electron injection at the Pe-COOH–TiO2 interface, a pure electron dynamics and a coupled electron–ion dynamics simulations are conducted within the real-time time-dependent density functional theory (RT-TDDFT) and RT-TDDFT-based Ehrenfest dynamics formalisms, respectively. The role of ionic dynamics, the influence of the adsorption mode, the surface coverage by the adsorbate, as well as the impact of the initial excitation energy on the charge transfer process are analyzed. The dissociative adsorption is shown to be less favorable for the charge transfer than the nondissociative one. The ionic dynamics turns out to have a limited effect on the total amount of the transferred charge, but it is responsible for the retardation of the electron transfer. The energy of initial excitation is revealed to be a determinant factor of the electron injection efficiency in the Pe-COOH–TiO2 system: the excitation of an electron to the LUMO+1 molecular orbital, instead of the LUMO one, doubles the total amount of the transferred charge. Meanwhile, a complete CT can only be achieved in conjunction with specific coverage and slab thickness characteristics, with all other factors being fixed. A surface coverage ratio equal to or less than 0.25 molecule/nm2 and a slab thickness of at least 4 TiO2 layers, corresponding to 192 Ti sites per 1 molecule of chromophore, are required.

Orientational and vibrational relaxation dynamics of perylene in the cyclohexane-ethanol binary solvent system.

The rotational dynamics and vibrational population relaxation of the nonpolar probe molecule perylene have been studied in a series of ethanol-cyclohexane binary solvent mixtures, with the goal of relating solvent system composition to local organization. Steady-state spectroscopic data show that there is a discontinuous dependence of the spectroscopic origin on binary solvent system composition for perylene. Both rotational diffusion and vibrational population relaxation time constants show a clear discontinuity between 5% and 7.5% (v/v) ethanol in cyclohexane, suggesting a discontinuous change on molecular scale rearrangement in the chromophore local environment. We interpret these results in the context of the chromophore residing in an environment that is not homogeneous on the molecular scale and changes in its average conformation with binary solvent system composition.

Förster-Induced Energy Transfer in Functionalized Graphene.

Carbon nanostructures are ideal substrates for functionalization with molecules since they consist of a single atomic layer giving rise to an extraordinary sensitivity to changes in their surrounding. The functionalization opens a new research field of hybrid nanostructures with tailored properties. Here, we present a microscopic view on the substrate–molecule interaction in the exemplary hybrid material consisting of graphene functionalized with perylene molecules. First experiments on similar systems have been recently realized illustrating an extremely efficient transfer of excitation energy from adsorbed molecules to the carbon substrate, a process with a large application potential for high-efficiency photovoltaic devices and biomedical imaging and sensing. So far, there has been no microscopically founded explanation for the observed energy transfer. Based on first-principle calculations, we have explicitly investigated the different transfer mechanisms revealing the crucial importance of Förster coupling. Due to the efficient Coulomb interaction in graphene, we obtain strong Förster rates in the range of 1/fs. We investigate its dependence on the substrate–molecule distance R and describe the impact of the momentum transfer q for an efficient energy transfer. Furthermore, we find that the Dexter transfer mechanism is negligibly small due to the vanishing overlap between the involved strongly localized orbital functions. The gained insights are applicable to a variety of carbon-based hybrid nanostructures.

Ab initio calculations of polycyclic aromatic hydrocarbons adsorbed on graphite edge for molecular-scale surface coatings of lithium-ion battery anodes

We have investigated the atomic configurations and electronic structures of graphite edges adsorbed by polycyclic aromatic hydrocarbons, aiming for application to lithium-ion-battery anodes, where thin and robust coating layers are required for fast charge/discharge processes and long lifetime. In particular, we examined the adsorption of a perylene molecule on an edge of graphite. We considered that the edge of perylene connects two layers of graphite with σ-bonds. We found that the optimized atomic structures are stable and the planar surface of perylene is parallel to the insertion direction of lithium ions similar to the original graphite edges. Therefore, the coating does not disturb the diffusion of lithium ions during charge/discharge processes. Furthermore, there is no hybridization between the graphite edge and the perylene molecule near the Fermi level, even though they have chemical bonds between them. Thus, the electronic states of the chemisorbed perylene molecule are insensitive to the change in the electric potential of the graphite. Consequently, we expect them to suppress the electrochemical decomposition of electrolytes and solvents on the anode surface. Hence, polycyclic aromatic hydrocarbons are one of the best candidates for the coating materials of graphite anodes for realizing a higher charge/discharge rate and longer lifetime.

Photoinduced Energy and Electron Transfer in Micellar Multilayer Films

Micellar multilayer films were prepared from an amphiphilic comb-like polycation (“polysoap”) and the polyanion poly(styrene sulfonate) (PSS) using alternate polyelectrolyte layer-by-layer (LbL) self-assembly. Linear growth of the film thickness was evidenced by UV–vis spectroscopy and spectroscopic ellipsometry. Imaging by atomic force microscopy (AFM) indicated that the micellar conformation adopted by the polycation in solutions was preserved in the films. Thus, hydrophobic photoactive molecules, which were solubilized by the hydrophobic nanodomains of the micellar polymer prior to deposition, could be transferred into the films. Photoinduced energy transfer was observed in the nanostructured multilayers between naphthalene (donor) and perylene (acceptor) molecules embedded inside the polymer micelles. The efficiency of the energy transfer process can be controlled to some extent by introducing spacer layers between the layers containing the donor or acceptor, revealing partial stratification of the mi...

Structural diversities of charge transfer organic complexes. Focus on benzenoid hydrocarbons and 7,7,8,8-tetracyanoquinodimethane

We have obtained three-component systems: the complexes comprising of two different benzenoid hydrocarbons together with one molecule of 7,7,8,8-tetracyanoquinodimethane (TCNQ). The X-ray single-crystal structures of naphthalene–perylene–TCNQ and pyrene–perylene–TCNQ revealed that they form face-to-face stacking between perylene and TCNQ molecules containing another hydrocarbon as a guest in the structure. We also present a pyrene–TCNQ complex with two pyrene moieties acting in similar way. In this system, charge transfer is far more efficient than in any other complexes of TCNQ with benzenoid hydrocarbons. Additionally, we have also obtained as references pyrene–TCNQ, chrysene–TCNQ, phenanthrene–TCNQ and naphthalene–TCNQ with 1 : 1 molecular ratios. These systems were also used to estimate the degrees of charge transfer.

A fluorescent perylene-assembled polyvinylpyrrolidone film: synthesis, morphology and nanostructure

A fluorescent polyvinylpyrrolidone (PVP) film with assembled nanostructures is successfully prepared in one pot by using perylene-3,4,9,10-tetracarboxylic acid dianhydride (PDA) as the fluorophore. The reactive anhydride groups in PDA play an important role in the covalent bonding of fluorescent molecules in the fluorescent PVP film, which has been demonstrated by a small-molecule model reaction. Interestingly, rod-like structures are found on the surface of the fluorescent film, which is attributed to the π-π interaction of PDA that occurred in the crosslinked PVP film. Further polarized optical microscopy (POM), X-ray diffraction (XRD) and optical analyses demonstrate the stable existence of π-conjugated nanostructures in the fluorescent PDA-based PVP film. The reactive anhydrides and the π-π interaction of perylene molecules are essential for the fabrication of the fluorescent perylene-assembled PVP film. This method could be extended to the preparation of the fluorescent PVP film with self-assembled nanostructures.

Excimer Luminescence From Nonresonantly Excited Pyrene and Perylene Molecules in Solution

By nonresonant excitation below the absorption edge of pyrene and perylene molecules in solution, efficient excimer luminescence is observed. For perylene in solution, there are two kinds of nonresonant excimer emission that closely resemble Y- and E-emissions in perylene crystal and perylene in polymer. The concentration dependence of the photon flux density of monomer and excimer emission is reasonably explained by a simple model with a few fitting parameters based on the ordinary excimer formation process, in which the excited-state monomer interacts with a ground-state monomer. Observed quantum efficiency of excimer formation is by orders of magnitude higher than that expected if a monomer is excited from thermally populated vibrational levels. The experimental evidence for direct resonant excitation of excimers in perylene nanocrystals is obtained from the absence of anti-Stokes emission. This is due to a symmetry-breaking effect close to crystal surface, suggesting that excimers are formed through a more efficient process in solution, such as resonant excitation of weakly interacting molecules with a symmetry-broken intermolecular configuration.

Morphology of a graphene nanoribbon encapsulated in a carbon nanotube

The morphologies of graphene nanoribbons (GNRs) encapsulated in single-walled carbon nanotubes (SWNTs) are investigated using molecular-dynamics (MD) simulation. The GNRs are assumed to be hydrogen-terminated and formed by connecting polycyclic aromatic hydrocarbons, perylene or coronene molecules. The combined structures consisting of a GNR and an encapsulating SWNT are equilibrated at room temperature. It is shown that if the diameter of a SWNT is larger than the sum of the width of the GNR and twice the length of a C-H bond, a twisted GNR is obtained, whereas if the diameter of a SWNT is smaller than the sum of the two, the cross section of the SWNT cannot maintain its original circular shape and elliptically distorts, and a non-twisted GNR or a twisted GNR of long pitch is obtained. The estimated pitch of a regularly-twisted GNR agrees with the experimentally observed one in order of magnitude.

Femtosecond time-resolved laser desorption/ionization mass spectrometry of perylene crystals using Raman-induced vibrational excitation

Femtosecond pump–probe mass spectrometry was carried out for perylene crystals. Perylene crystals were vibrationally excited by a Raman-induced process using two near-infrared pulses, and then the perylene molecules were ionized by time-delayed probe pulses. The number of perylene ions was markedly enhanced by excitation of intramolecular vibrations in perylene, but it was enhanced very slightly by excitation of intermolecular vibrations. It was also found that dimer cations were desorbed earlier than monomer cations, reflecting the crystal structure of perylene.

Self-Assembled Containers Based on Extended Tetrathiafulvalene

Two original self-assembled containers constituted each by six electroactive subunits are described. They are synthesized from a concave tetratopic π-extended tetrathiafulvalene ligand bearing four pyridyl units and cis-M(dppf)(OTf)2 (M = Pd or Pt; dppf = 1,1'-bis(diphenylphosphino)ferrocene; OTf = trifluoromethane-sulfonate) complexes. Both fully characterized assemblies present an oblate spheroidal cavity that can incorporate one perylene molecule.

Fluorescence enhancement effect in pyrene and perylene doped nanoporous polystyrene films: Mechanistic and morphology

AbstractLuminescent porous polystyrene (PS) films containing pyrene and various amounts of perylene were prepared in humid atmosphere by solution casting technique for use as a plastic scintillator. The fluorescence spectra of doped PS films monitored at pyrene excitation show quenching of monomer fluorescence of pyrene with simultaneous sensitization of perylene monomer fluorescence appearing towards red. The observed enhancement in fluorescence of perylene was explained by considering excitation energy transfer (EET) from pyrene to perylene molecules accommodated in the pores generated during film formation. The fluorescence quenching data do not fit into the Stern–Volmer relation, but the sensitized fluorescence is fitted by an exponential growth equation, y = 201 860 433.29 ex/0.64366 + 0.49262, with correlation coefficient R2 = 0.997. The results on absorption and excitation spectroscopy indicated that the pyrene and perylene filled in pores of the PS films exist as isolated molecules. The porosity of the films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), showing randomly oriented holes, and their mean size and size distribution were found to be depending upon the dopant concentration.Pyrene and perylene doped porous PS films prepared by solution casting method in humid atmosphere showed highly intense blue perylene fluorescence by fluorescence resonance energy transfer (FRET) at pyrene excitation. The SEM and AFM images revealed that nanosized pores are perylene concentration dependent, both pyrene and perylene held in the cavity of the pores in close proximal distance less than 10 nm is required to cause efficient energy transfer between them.

Perylene Monolayer Protected Gold Nanorods: Unique Optical, Electronic Properties and Self-Assemblies

Here we report the synthesis and characterization of organosoluble perylene monolayer protected gold nanorods. From 1H NMR, FT-IR, and differential scanning calorimetry experiments, the successful thiol exchange and stacking of perylene molecules on gold nanorods were confirmed. The resulting gold nanorods encapsulated with perylene thiol molecules via strong covalent Au–S linkages showed unique optical and electronic properties compared to the initial free perylene molecules and gold nanorods, indicating there were strong interactions between perylene chromophores and gold nanorods. When attached on gold nanorods, the perylene chromophores did not exhibit any typical UV–vis absorption or fluorescence emission signal, originating from the charge transfer from gold nanorods to perylene chromophores. However, the missing signals reappeared upon the addition of iodine, which detached the perylene molecules from gold nanorods. For the hybrid gold nanorods, particular electronic properties were also investigated by cyclic voltammetry and electron diffraction. Furthermore, with strong π–π intermolecular interactions, the perylene thiol monolayer protected gold nanorods were able to aggregate. When drying from highly diluted solution, gold nanorods formed well-organized side-by-side self-assembly arrays.

Plasma Deposition of Perylene–Adamantane Nanocomposite Thin Films for NO2 Room-Temperature Optical Sensing

This work reports the preparation, by a new remote assisted plasma deposition process, of luminescent nanocomposite thin films consisting of an insoluble organic matrix where photonically active perylene molecules are embedded. The films are obtained by the remote plasma deposition of adamantane and perylene precursor molecules. The results show that the adamantane precursor is very effective to improve the perylene–adamantane nanocomposite transparency in comparison with plasma deposited perylene films. The plasma deposited adamantane films have been characterized by secondary-ion mass spectrometry and FT-IR spectroscopy. These techniques and atomic force microscopy (AFM) have been also used for the characterization of the nanocomposite films. Their optical properties (UV–vis absorption, fluorescence, and refractive index) have been also determined and their sensing properties toward NO2 studied. It is found that samples with the perylene molecules embedded within the transparent plasma deposited matrix are highly sensitive toward this gas and that the sensitivity of the films can be adjusted by modifying the aggregation state of the perylene molecules, as determined by the analysis of their fluorescence spectra. By monitoring the fluorescence emission of these films, it has been possible to detect a NO2 concentration as low as 0.5 ppm in air at room temperature. Because of their chemical stability and transparency in the UV region, the remote plasma deposited adamantane thin films have revealed as an optimum host matrix for the development of photonically active composites for sensing applications.

Modifying the STM Tip for the ' Ultimate ' Imaging of the Si(111)-7×7 Surface and Metal-supported Molecules

We report on high-resolution STM measurements with modified probe tips. First, both the rest atoms and adatoms of a Si(111)-7×7 surface are observed simultaneously. The visibility of rest atoms is dependent upon the sample bias voltage (less than -0.7 V) and is enhanced by sharpening the tip, which is rationalized by first-principles calculations. Second, a tip with a perylene molecule adsorbed at its apex is used to discriminate the molecular states and the metal states of the underlying Ag(110) surface, which is attributable to a mismatch between the energy levels of the functionalized tip and the adsorbates on silver. Lastly, high-resolution images of iron phthalocyanine (FePc) and zinc phthalocyanine (ZnPc) molecules on Au(111) are obtained by using an O(2)-terminated tip, and the images reveal rich intramolecular features arising from molecular orbitals that are not observed when using clean metallic tips.