Perylene Radical Cation Research Articles

Role of Brønsted Surface Acid Sites of B2O3–Al2O3 Catalyst Supports in Perylene Radical Cation Formation Studied by Probe EPR with TEMPO Radicals

Role of Brønsted Surface Acid Sites of B₂O₃–Al₂O₃ Catalyst Supports in Perylene Radical Cation Formation Studied by Probe EPR with TEMPO Radicals

Engineering a high-efficient DNA amplifier for biosensing application based on perylene decorated Ag microflowers as novel electrochemiluminescence indicators

DNA-based amplifiers with high programmability and accurate molecular recognition ability have become a versatile platform for target amplification. However, the random diffusion of capture probes (CPs) in most DNA amplifiers limits the target recognition efficiency, affecting the limit of detection. Herein, a high-efficient DNA amplifier was developed by localizing the CPs consisted of the unique palindromic tails and target recognition sequences on Au nanoparticle modified magnetic beads (Au@MBs). In the presence of target K-ras gene, the CPs with high local concentration and orientation could capture the target efficiently to expose their palindromic tails, which could act as primers to trigger the polymerization for target recycling. More importantly, the polymerization products could involve in the next recycle and produce abundant mimic targets (MTs) continuously, thereby achieving the detection of trace K-ras gene. Meanwhile, a novel electrochemiluminescence (ECL) indicator of a thin-layer of perylene (Pe) molecules decorated Ag microflowers (Pe@Ag MFs) was obtained based on the reaction between the perylene cation radical (Pe•+) and Ag atoms. The obtained Pe@Ag MFs exhibited desirable ECL performance because (i) a thin-layer of Pe molecules could reduce the inner filter effect and inactive emitters, (ii) the Ag MFs as coreaction accelerator could react with S2O82− to produce more SO4•− and shorten the distance between Pe•− and SO4•− to significantly enhance the ECL intensity of Pe with less energy loss. This work paves the way for the development of efficient amplification strategy and offers a paradigm for the preparation of high-efficiency ECL indicators.

Rapid‐Scan Electron Paramagnetic Resonance of Highly Resolved Hyperfine Lines in Organic Radicals.

X-band (ca. 9 GHz) fluid solution rapid-scan electron paramagnetic resonance spectra are reported for radicals with multiline spectra and resolution of hyperfine lines as narrow as 30 mG. Highly-resolved spectra of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy, diphenylnitroxide, galvinoxyl, and perylene cation radical with excellent signal-to-noise are shown, demonstrating the capabilities of the rapid-scan technique to characterize very small, well-resolved hyperfine couplings. To acquire high resolution spectra the signal bandwidth must be less than the resonator bandwidth. Signal bandwidth is inversely proportional to linewidth and proportional to scan rate. Resonator bandwidth is inversely proportional to resonator Q. Proper selection of scan rate and resonator Q is needed to achieve resolution of closely-spaced narrow EPR lines.

Using Density Functional Theory Based Methods to Investigate the Photophysics of Polycyclic Aromatic Hydrocarbon Radical Cations: A Benchmark Study on Naphthalene, Pyrene and Perylene Cations

AbstractUnrestricted DFT (UDFT), time‐dependent DFT (TDDFT) and spin‐flip TDDFT (SF‐TDDFT) were used to investigate the potential energy surfaces of the ground and first two electronic excited states of the naphthalene, pyrene and perylene radical cations. In particular, conical intersections (which play a central role in the photophysics of these cations) were located with these DFT‐based methods. The results are consistent with accurate multiconfigurational wavefunction‐based ab initio methods. These show that naphthalene and pyrene cations can quickly relax nonradiatively from their excited states back down to the original ground state species through easily accessible conical intersections, but the perylene cation cannot do so, due to the absence of any accessible funnels between the lowest excited state and the ground state, leaving radiative decay as the most probable photophysical pathway. This study paves the way for using computationally efficient density functional theory (DFT)‐based methods in future investigations of the photophysics of much larger polycyclic aromatic hydrocarbons, for which multiconfigurational wavefunction‐based methods become prohibitively expensive.

Effect of Perylene Photosensitizer Attachment to [Pd(triphosphine)L]2+ on CO2 Electrocatalysis.

Two new covalently linked chromophore-CO2 reduction catalyst systems were prepared using a perylene chromophore and a bis[(dicyclohexylphosphino)ethyl]phenylphosphinopalladium(II) catalyst. The primary goal of this study is to probe the influence of photosensitizer attachment on the electrocatalytic performance. The position either para or meta to the phosphorus on the phenyl group of the palladium complex was linked via a 2,5-xylyl group to the 3 position of perylene. The electrocatalytic CO2 reduction activity of the palladium complex is maintained in the meta-linked system, but is lost in the para-linked system, possibly because of unfavorable interactions of the perylene chromophore with the glassy carbon electrode used. Following selective photoexcitation of the perylene, an enhanced perylene excited-state decay rate was observed in the palladium complexes compared to perylene attached to the free ligands. This decrease is accompanied by formation of the perylene cation radical, showing that electron transfer from perylene to the palladium catalyst occurs. Electron transfer and charge recombination were both found to be faster in the para-linked system than in the meta-linked one, which is attributed to stronger electronic coupling in the former. These results illustrate the need to carefully tune the electronic coupling between a photosensitizer chromophore and the catalyst to promote photodriven electron transfer yet inhibit adverse electronic effects of the chromophore on electrocatalysis.

Modeling of the mechanism of one-electron transfer from the perylene molecule to the oxygen molecule 3O2 in the HF medium

The thermodynamic parameters of the formation of the perylene radical cation in anhydrous hydrogen fluoride containing dissolved dioxygen were calculated by the ab initio method MP2. The protonated product of HF autoprotolysis was modeled as the H(FH) 3 + cluster. The 3O2 molecule was found to bind to the linear H(FH) 3 + cluster via a hydrogen bond. As the charge and multiplicity of the system change upon the capture of an electron, the oxygen-hydrogen fluoride cluster complex undergoes rearrangement to yield the hydroperoxyl radical OOH incorporated in a cycle formed by HF molecules. The free energy of electron transfer from the perylene molecule to the 3O2 molecule in the HF medium is about −38 kcal/mol.

Ultrafast Intramolecular Charge Transfer of Formyl Perylene Observed Using Femtosecond Transient Absorption Spectroscopy

The excited-state photophysics of formylperylene (FPe) have been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of experimental and theoretical methods were employed including femtosecond transient absorption (fs-TA) spectroscopy with 130 fs temporal resolution. We report that the ultrafast intramolecular charge transfer from the perylene unit to the formyl (CHO) group can be facilitated drastically by hydrogen-bonding interactions between the carbonyl group oxygen of FPe and hydrogen-donating solvents in the electronically excited state. The excited-state absorption of FPe in methanol (MeOH) is close to the reported perylene radical cation produced by bimolecular quenching by an electron acceptor. This is a strong indication for a substantial charge transfer in the S(1) state in protic solvents. The larger increase of the dipole moment change in the protic solvents than that in aprotic ones strongly supports this observation. Relaxation mechanisms including vibrational cooling and solvation coupled to the charge-transfer state are also discussed.

Fluorescence of the perylene radical cation and an inaccessible D/D1 conical intersection: An MMVB, RASSCF, and TD-DFT computational study

The photophysics of the perylene radical cation (Pe(+)) was studied using the molecular mechanics-valence bond (MMVB) hybrid force field. Potential energy surfaces of the first three electronic states were investigated. Geometry optimizations of critical points-including conical intersections between the relevant electronic states-were performed using the MMVB analytical energy gradient for cations. No accessible planar conical intersection between the D(0) and D(1) states of Pe(+) was found; this is consistent with the experimentally observed D(1) lifetimes and the observation of D(1) emission from this cation in the condensed phase. Benchmark RASSCF and TD-DFT calculations support the reliability of the MMVB results.

Simultaneous multi-photon ionization of aromatic molecules in polymer solids with ultrashort pulsed lasers

Radical cations of perylene, terthiophene, N, N, N′, N′-tetramethylbenzidine, N, N, N′, N′-tetramethyl- p-phenylenediamine, and N-ethylcarbazole were formed in poly(methyl methacrylate) solids by the direct excitation of each absorption band with a 355-nm picosecond (ps) laser and a 400-nm femtosecond (fs) laser and also by the indirect excitation with a 800-nm fs laser. The photoionization yields of perylene with ps and fs lasers were independent of the concentration of tetracyanobenzene, indicating that the relaxed singlet excited state of perylene is not involved in the photoionization. These results show that radical cations are formed through simultaneous multi-photon ionization enhanced by resonance with the lowest singlet excited state.

Direct Analysis of Liquid Samples by Desorption Electrospray Ionization-Mass Spectrometry (DESI-MS)

Desorption electrospray ionization-mass spectrometry (DESI-MS) was evaluated for the direct analysis of liquid samples. Several interesting results were found. First, in contrast to the previous DESI analysis of dried solid samples that was limited to proteins with MW < or = 25 kDa (Anal. Chem. 2007, 79, 3514), bovine serum albumin (BSA, 66 kDa) was successfully ionized from solutions by DESI with observation of corresponding multiply charged ions. Second, direct DESI analysis of protein tryptic digest solutions without chromatographic separation, sample clean-up, and the sample drying step was demonstrated, providing reasonably good sequence coverage of 52% to 97%. Third, direct analysis of biofluids such as an undiluted urine sample without sample pretreatment is possible, emphasizing the high tolerance of DESI with salt. These results suggest that a charged droplet pick-up mechanism is responsible for desorption and ionization of liquid samples by DESI. Also, unlike in electrospray ionization (ESI), inhibition of electrochemical reduction in the negative ion mode was observed for liquid sample DESI. In addition, reactive DESI can be performed with ion/ion reactions of Zn(II) complexes for the selective binding of phosphoserine in the presence of serine. DESI experiment can also be carried out directly to liquid samples flowing out of a pumped syringe needle tip, allowing rapid analysis. Furthermore, on-line coupling of electrochemical cell with DESI-MS was demonstrated, in which perylene radical cations generated in the cell were successfully transferred to the gas-phase for MS detection by DESI. This study extended the scope of DESI-MS applications, which could have potentials in bioanalytical and forensic analysis.

Ultrafast Excited State Dynamics of the Perylene Radical Cation Generated upon Bimolecular Photoinduced Electron Transfer Reaction

The ultrafast ground state recovery (GSR) dynamics of the radical cation of perylene, Pe(*+), generated upon bimolecular photoinduced electron transfer in acetonitrile, has been investigated using pump-pump-probe spectroscopy. With 1,4-dicyanobenzene as electron acceptor, the free ion yield is substantial and the GSR dynamics of Pe(*+) was found to depend on the time delay between the first and second pump pulses, Deltat(12), i.e., on the "age" of the ion. At short Deltat(12), the GSR dynamics is biphasic, and at Deltat(12) larger than about 500 ps, it becomes exponential with a time constant around 3 ps. With trans-1,2-dicyanoethylene as acceptor, the free ion yield is essentially zero and the GSR dynamics of Pe(*+) remains biphasic independently of Deltat(12). The change of dynamics observed with 1,4-dicyanobenzene is ascribed to the transition from paired to free solvated ion, because in the pair, the excited ion has an additional decay channel to the ground state, i.e., charge recombination followed by charge separation. The rate constants deduced from the analysis of these GSR dynamics are all fully consistent with this hypothesis.

Time-Resolved EPR Study of the Photophysics and Photochemistry of 1-(3-(Methoxycarbonyl)propyl)-1-phenyl[6.6]C61

Time-resolved (TR) EPR was used to study the photophysics and photochemistry of 1-(3-(methoxycarbonyl)propyl)-1-phenyl[6.6]C61 (M1). The CW TREPR spectra of M1 in the photoexcited triplet state, frozen in a rigid matrix and in liquid solution at room temperature, were compared with those of 3C60. The introduction of the substituent on C60 has a striking effect on the spectra of the triplets, which is attributed to the lifting of the orbital degeneracy by the reduction in symmetry. Fourier transform (FT) EPR was used in an investigation of electron-transfer reactions in liquid solutions mediated by 3M1. Of particular interest was the system of M1/chloranil (CA)/perylene (Pe). Photoexcitation of M1 is found to lead to the formation of the chloranil anion radical and the perylene cation radical. From the chemically induced dynamic electron polarization (CIDEP) patterns in the FTEPR spectra and the dependence of the reaction kinetics on reactant concentrations, it was deduced that CA- is formed by two competing pathways following photoexcitation of M1: (1) direct electron transfer from 3M1 to CA followed by electron transfer from Pe to M1+ and (2) energy transfer from 3M1 to Pe followed by oxidative quenching of 3Pe by CA. In both pathways, M1 acts as a light-energy harvester and mediator of electron-transfer reactions from Pe to CA without itself being consumed in the process, that is, as a photocatalyst. It is found that the functionalization of C60 makes its triplet state a worse electron donor and acceptor, but it has no significant effect on the triplet energy transfer reaction.

Anisotropy of charge and spin motion in perylene hexafluoroarsenate salts

Conduction electron spin echo attenuation in well defined magnetic field gradients providesmore accurate values of the anisotropy of electron spin motion than microwave conductivitymeasurements. The electron spin diffusion coefficient for motion along the perylene (PE)radical cation stack, , in the PE hexafluoroarsenate salt is influenced temperature dependently byperpendicular-to-stack motion and reflects the varying average unrestricted chain length,. The anisotropy of is larger than 7300:1 at 250 K.

Magnetic induced vertical crystal growth of perylene cation radicals on ITO glass surface

Perylene–acetonitrile solution with tetra- n-butyl-ammonium perchlorate (TBAP) is a substance that tends to electro-crystallize and form particular needle-like structures. These perylene materials are studied extensively for their peculiar electrical and optical properties and for the interest in the fundamental phenomena occurring in the electro crystallization process. We introduce here a novel methodology to orient the needle-like crystals by means of electro crystallization in presence of a weak magnetic field. We report details on the technique we used and we present several exceptional SEM pictures of the aggregates growing vertically from the substrate by the effect of the magnetic field. The method introduce a new simple way to control the growth of these intriguing materials and the approach is potentially the basis for the fabrication of new miniaturized devices.

Surface and adsorbates effects on the photochemistry and photophysics of adsorbed perylene on unactivated silica gel and alumina

The effect of the nature of the surface and solvent, the presence of coadsorbed species (O 2, Ar and H 2O) and the surface loading on some photophysical and photochemical properties of perylene (Per) are reported. Although the absorption and emission spectra of perylene adsorbed on alumina and silica gel of different average pore diameters are very similar to those observed in solution, adsorbed perylene presented spectra with broader bands, loss of vibrational structure, and a small red shift and extension to longer wavelengths. These are consequence of aggregate formation, π-stacking, and surface interactions. The nature of the environment affects also the lifetime of the first excited state, presenting a single-exponential decay when in solution and, at least, a double-exponential decay when adsorbed suggesting the adsorption on at least two major surface regions. As the average pore size increases, the emission spectra resembled more to that in solution and the photodegradation rate also increased. Sample loading causes a red shift of the bands on the emission spectrum and a change in the relative intensities of the first and second bands. Oxygen quenched significantly the fluorescence and accelerated the photodegradation. The participation of 1 O 2 in the photodegradation process was confirmed as well as the participation of a perylene radical cation, identified by laser diffuse reflectance transient and EPR spectroscopy. Coadsorbed water induced the formation of a new species, probably a perylene–H 2O complex on the surface.

Temperature dependence of intra-stack defect spin–conduction-electron spininteraction in fluoranthene and perylene radical cation salts

The electron spin resonance line-width anisotropy and intensity areanalysed for the quasi-one-dimensional organic conductors (fluoranthene)2PF6and (perylene)2PF6·2/3tetrahydrofurane in the metallic phase above the Peierls transition temperature.Based on the bottleneck model of relaxation, the temperature dependence of theintra-stack exchange constant between conduction-electron spins and localizeddefect spins is derived and discussed.

Femtosecond Resonance-Enhanced Multiphoton Ionization of Perylene in Hexane. Electronic Excitation of the Radical Cation and Evidence of Hydrogen Abstraction from the Solvent

We demonstrate that perylene in solution can be highly excited with relatively weak femtosecond radiation via two-photon resonance-enhanced multiphoton ionization and excitation. The femtosecond multiphoton excitation spectra of two different observables are presented for perylene dissolved in hexane. The first of these is the normal S 1 → S 0 fluorescence that arises from relaxation of perylene through the singlet manifold after multiphoton excitation. The second observable is the ion yield that results from multiphoton ionization. A comparison of these two excitation spectra is presented, and their striking similarity indicates that both processes occur via the same initial two-photon resonance in the 500-550 nm region. A mechanism is presented illustrating the predicted excitation and relaxation pathways. The multiphoton-excited emission spectrum of the sample exhibits anomalous emission in the 550-620 nm range. Comparison of this emission with the one-photon-excited emission spectrum of perylene in concentrated sulfuric acid shows that the anomalous emission originates from electronic excitation of cationic species present in sulfuric acid. Previous assignment of emission from perylene dissolved in sulfuric acid to the protonated cation implies that the perylene radical cation in hexane abstracts a hydrogen atom from the solvent on an ultrafast time scale.

A study of the elemental reactions involved in the initiation of the polymerization of tetrahydrofuran induced by the photosensitization of a triphenylsulphonium salt by perylene

The photopolymerization of THF was studied in the presence of a triphenylsulphonium salt and perylene. The mechanism involves an electron transfer from the excited singlet state of perylene to triphenylsulphonium ions, resulting in perylene cation radicals that react with tetrahydrofuran. The calculated apparent yield of cation radicals follows the same general trend than the measured polymerization rates.

Study of the fluorescence of perylene cation radical salts with a near field optical setup

A perylene-acetonitrile solution with TBAP (tetra-n-butylammonium perchlorate) electrocrystallizes on the electrode surface, under opportune conditions. It forms particular needle-like micro-crystals that have been studied recently for their peculiar electrical and optical properties and for the fundamental processes involved in the electron transfer responsible for the electrocrystallization. These intriguing structures present various fractal-like morphological organizations and diverse crystal shapes on the same deposition process. Up to now these formations have been studied optically by conventional standard microscopy. We introduce here a novel methodology to collect information on the actual orientation and crystal structure by a near field optical setup with originally fabricated probes. We performed, for the first time on these samples, near field fluorescence imaging showing evidence that the perylene aggregations actually have a distinct optical orientation.

Anion-controlled electrocrystallization of perylene cation radical salts

Formation of perylene cation radical salts initiated by the electrochemical oxidation was observed directly on a Pt electrode surface using a microscopic CCD detection system. Depending on the sort of the coexisting anions (X −) as supporting electrolytes, considerable changes were observed in the deposition processes in acetonitrile. That is, while no deposition was observed with PF 6 −, the formation of bold needle-like black crystals were observed to grow sparsely on the electrode surface in the case with BF 4 −. In the latter, the following reduction and re-oxidation experiments revealed that golden crystals were formed in diverse shapes as a result of the redox reactions. On the other hand, in the oxidation of perylene with ClO 4 −, very thin golden whisker crystals were found to grow proportionally on the whole electrode surface, and then they became dense in course of time. However, after 1 min, black thin needle-like crystals were initiated to form over the golden micro whisker crystals that grew densely on the electrode. The difference in color is expected to be in relation to the redox states of perylene cation radical salts.