Revised vibrational band assignments for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile based on ab initio, DFT and normal coordinate calculations

In the present study, a systematic vibrational spectroscopic investigation for the experimental IR and Raman spectra of 2,3,4-trifluorobenzonitrile (TFB), aided by electronic structure calculations has been carried out. The electronic structure calculations – ab initio (RHF) and hybrid density functional methods (B3LYP) – have been performed with 6-31G* basis set. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. The results of the calculations have been used to simulate IR and Raman spectra for TFB that showed excellent agreement with the observed spectra. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed. A complete assignment of the observed spectra has been proposed.     

A Charge‐Stabilizing,Multimodular, Ferrocene–Bis(triphenylamine)–Zinc‐porphyrin–Fullerene Polyad

A novel multimodular donor–acceptor polyad featuring zinc porphyrin, fullerene, ferrocene, and triphenylamine entities was designed, synthesized, and studied as a charge‐stabilizing, photosynthetic‐antenna/reaction‐center mimic. The ferrocene and fullerene entities, covalently linked to the porphyrin ring, were distantly separated to accomplish the charge‐separation/hole‐migration events leading to the creation of a long‐lived charge‐separated state. The geometry and electronic structures of the newly synthesized compound was deduced by B3LYP/3‐21G(*) optimization, while the energy levels for different photochemical events was established using data from the optical absorption and emission, and electrochemical studies. Excitation of the triphenylamine entities revealed singlet‐singlet energy transfer to the appended zinc porphyrin. As predicted from the energy levels, photoinduced electron transfer from both the singlet and triplet excited states of the zinc porphyrin to fullerene followed by subsequent hole migration involving ferrocene was witnessed from the transient absorption studies. The charge‐separated state persisted for about 8.5 μs and was governed by the distance between the final charge‐transfer product, that is, a species involving a ferrocenium cation and a fullerene radical anion, with additional influence from the charge‐stabilizing triphenylamine entities located on the zinc‐porphyrin macrocycle.     

An ab initio study on the vibrational and electronic spectra of the molybdenum–sulfur clusters with Mo2OnS4−n(n=0–4) core

Using the ab initio method, the vibrational and electronic spectra of binuclear molybdenum clusters which contain Mo₂O_nS_4−n(n=0–4) core were investigated. The main absorption bands in the IR spectra of these clusters are assigned and compared with each other, especially for the case of the trans isomers. The electronic spectra were studied by performing the CIS calculations. The ground state and the first excited state of the clusters were discussed by using the natural bond orbital method. It is shown that the band corresponding to the longest wavelength can be assigned to three kinds of transition types. Two transitions, σ(Mo–Mo)→π*(Mo–X_t)(X=S,O) and σ(Mo–Mo)→σ*(Mo–Mo), can be seen in most cases.     

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the Förster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot–porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism.     

Synthesis of New Porphyrin–Fullerene Dyads Capable of Forming Charge‐Separated States on a Microsecond Lifetime Scale

A series of covalently linked axially symmetric porphyrin–fullerene dyads with a rigid pyrrolo[3,4‐c]pyrrolic linker enabling a fixed and orthogonal arrangement of the chromophores has been synthesized and studied by means of transient absorption spectroscopy and cyclic voltammetry. The lifetime of the charge‐separated state has been found to depend on the substituents on the porphyrin core, reaching up to 4 μs for a species with meso‐(p‐MeOC₆H₄) substituents. The ground and excited electronic states of model compounds have been calculated at the DFT and TD‐DFT B3LYP(6‐31G(d)) levels of theory and analyzed with regard to the effect of the substituent on the stabilization of the charge‐separated state in the porphyrin–fullerene ensemble with a view to explaining the observed dependence.     

Substituent effects in porphyrin dimer complexes studied by IR spectroscopy

A series of lanthanide porphyrin dimers have been synthesized and investigated with IR spectroscopic techniques. The spectra of the porphyrin dimers are compared not only with each other but also with those of their component monomer units. The experimental results exhibit that the IR spectra of the porphyrin dimers are closely related to those of their corresponding monomers. A detailed analysis of the IR spectra between the porphyrin dimers and monomers suggest that the dimer molecules can be treated as regular derivatives of metalloporphyrin monomers despite the symmetries of these two systems being different. The dimerization of the porphyrin rings only result in frequency shifts and intensity changes of the IR spectra. These shifts are attributed to the induced π–π interactions between these two macrocycles. The downshifts of the frequencies observed in Ce(OEP)₂ further indicate that the π–π interactions intrinsically decrease the bond strength of the entire molecule. Additionally, only the relative intensities instead of the frequencies of the ethyl vibrations in the region 2800–3000 cm⁻¹ are observed to be sensitive to the types and the positions of the substituent groups. These observations suggest that these ethyl vibrational modes of the OEP moiety can be used as characteristic bands to monitor subtle deformations of the porphyrin rings caused by the substituent groups in the dimer complexes.     

Redox Active Two‐Component Films of Palladium and Covalently Linked Zinc Porphyrin–Fullerene Dyad

Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C₆₀ covalently linked to zinc meso‐tetraphenyloporphyrin, ZnP? C₆₀, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnP? C₆₀/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties.     

新颖的5,15-二(4-(5-乙酰基硫戊氧基)苯基)卟啉化合物的结构和性质的密度泛函理论计算

通过密度泛函理论计算比较性地研究了5,15-二(4-(5-乙酰基硫戊氧基)苯基)自由卟啉及其锌配合物的分子结构、电荷性质、分子轨道、电子吸收光谱和红外光谱.这类化合物具有在卟啉相对的两个中位的苯环上连有5-乙酰基硫戊氧基的新颖结构.模拟得到的这两个化合物的分子结构和电子吸收光谱以及红外光谱都与实验测得的符合得很好.通过与未取代的自由卟啉和卟啉锌的结构和性质进行比较,研究了中位取代基、极性溶剂和中心金属取代对此类卟啉化合物结构和性质的影响规律.对化合物的电子吸收光谱中的电子跃迁本质进行了归属,并通过基于正则坐标分析产生的动画对红外光谱的振动模式进行了指认.目前的工作将对理解此类新颖卟啉化合物的结构和性质以及取代基和溶剂效应提供很大的帮助.     

Microscopy of large-scale porphyrin aggregates formed from protonated TPP dimers in water–organic solutions

Properties of porphyrin aggregates were investigated by absorption spectroscopy (UV–Vis and IR) in water–tetrahydrofuran (THF) solutions in the presence of different concentrations of HCl. The morphology of the aggregates was observed by scanning electron microscopy (SEM) and atomic force microscopy in thin films. A new protonated meso-tetraphenylporphine (TPP) form that shows characteristic absorptions in the UV–Vis spectra was found in the aggregated porphyrin in the presence of 2N HCl. Two types of changes with time were observed in these spectra, one of which is due to sticking together of the porphyrin aggregates. The second is associated with the formation of complexes between the protonated TPP dimer with λ_max=465 nm and metal ions that are probably leached out from the support by the acid. IR spectra of porphyrin aggregates prepared in the presence of different concentrations of HCl show huge water contents in the thin films and different characteristics of the water bound in the aggregates. Porphyrin aggregates prepared at different concentrations of HCl exhibited different surface properties. TPP aggregates prepared in the presence of 0.4N HCl and observed by SEM exhibit smooth surfaces over ranges of several micrometers. TPP aggregates prepared in the presence of 2N HCl form a continuous thin layer with 3–5 μm wide domains that consist of submicroscopic grains. These appear to be the result of 200–400 nm wide spherical particles that stick together.     

Nanolayers of selected porphyrin and phthalocyanine dyes on solid substrates studied by electronic absorption and IR reflection–absorption spectroscopy

Electronic absorption and IR reflection–absorption spectra in non-polarized and in polarized light for lead porphyrin as well as magnesium and lead phthalocyanine dyes when deposited in the form of Langmuir–Blodgett (LB) nanolayers on solid inorganic surfaces (quartz, semiconductor and metal) were measured. Some IR bands of the Langmuir–Blodgett dye layers’ spectra show frequency shifts and changes in the relative intensities as well as in half widths when compared with the vibrational features of powdered dyes dispersed in KBr pellets, which were used as references. The FT-IR spectroscopic examination of the Langmuir–Blodgett layers allowed to estimate electron redistribution at the interface between dye layer and solid substrates. The Langmuir–Blodgett films of different thicknesses (3, 5, 10 layers) were studied at various angles of IR beam incidence and different light polarizations. The most spectacular results were obtained for the grazing incidence (80°) and films of 5 layers for dyes on the Au substrate. The IR spectroscopy was supported with electronic absorption studies (UV–vis) to follow interaction at interface between the dye layers and the substrates as well as to evaluate linear dichroism and to determine arrangement of molecules in the Langmuir–Blodgett films. Molecular arrangement in the Langmuir–Blodgett layers was discussed. It was shown that the dye molecular planes are rather randomly oriented in the Langmuir–Blodgett films with a tendency that the Q_y and Q_x transition moments in the phthalocyanine macroring are slightly directed along the y-axis (Langmuir–Blodgett dipping direction) and the x-axis direction, respectively.     

A π‐Stacked Porphyrin–Fullerene Electron Donor–Acceptor Conjugate That Features a Surprising Frozen Geometry

A “frozen” electron donor–acceptor array that bears porphyrin and fullerene units covalently linked through the ortho position of a phenyl ring and the nitrogen of a pyrrolidine ring, respectively, is reported. Electrochemical and photophysical features suggest that the chosen linkage supports both through‐space and through‐bond interactions. In particular, it has been found that the porphyrin singlet excited state decays within a few picoseconds by means of a photoinduced electron transfer to give the rapid formation of a long‐lived charge‐separated state. Density functional theory (DFT) calculations show HOMO and LUMO to be localized on the electron‐donating porphyrin and the electron‐accepting fullerene moiety, respectively, at this level of theory. More specifically, semiempirical molecular orbital (MO) configuration interaction (CI) and unrestricted natural orbital (UNO)‐CI methods shed light on the nature of the charge‐transfer states and emphasize the importance of the close proximity of donor and acceptor for effective electron transfer.     

Molecular structure and vibrational spectra of lepidine and 2-chlorolepidine by density functional theory and ab initio Hartree–Fock Calculations

The molecular geometry and vibrational frequencies of lepidine and 2-chlorolepidine in the ground state have been calculated by using the Hartree–Fock and density functional methods (B3LYP) with 6-31G (d) as the basis set. The optimized geometric bond lengths obtained by using B3LYP and bond angles obtained by HF that correspond to the experimental values of 2-cl-lepidine molecule were given. Comparison of the observed fundamental vibrational frequencies of lepidine and 2-chlorolepidine, and calculated results by density functional B3LYP and Hartree–Fock methods indicates that B3LYP is superior to the scaled Hartree–Fock approach for molecular vibrational problems.     

Synthesis and Photophysical Properties of Porphyrin–Arylimidazole Heterodyads

A series of directly linked metalloporphyrin–arylimidazole heterodyads ( 3 , 4 , and 6 ) with an arylimidazole unit at the meso‐ or β‐pyrrolic position of the porphyrin were synthesized via Debus–Radziszewsk reaction. Introduction of a copper ion into the porphyrin contributed significantly to the overall stability of the heterodyads. The absorption spectra indicated that the basic electronic characteristics of both individual units (i.e., metalloporphyrin and arylimidazole) were retained in the heterodyads. In addition, strong fluorescence quenching was observed in the case of the heterodyads containing copper(II) porphyrin. Cyclic voltammetric studies revealed that the heterodyads were more difficult to oxidize compared with the pristine metalloporphyrins.     

Metal‐Atom Impact on the Self‐Assembly of Cup‐and‐Ball Metalloporphyrin–Fullerene Conjugates

A fullerene ammonium derivative has been combined with different metalloporphyrin–crown ether receptors to generate very stable supramolecules. The combination of fullerene–porphyrin and ammonium–crown ether interactions leads to a strong chelate effect as evidenced by a high effective molarity (3.16 M ). The different parameters influencing the stability of the supramolecular ensembles, in particular the nature of the metal in the porphyrin moiety, have been rationalized with the help of theoretical calculations thus providing new insights into fullerene–porphyrin interactions.     

Molecular structure and vibrational spectra of N-mesylhydroxylamin and N-mesyl-O-methylhydroxylamin by density functional theory and ab initio Hartree–Fock calculations

The molecular geometry and vibrational frequencies of N-mesylhydroxylamin (N-MHN) and N-mesyl-O-methylhydroxylamin (N-MMHN) in the ground state have been calculated using the Hartree–Fock and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric band lengths and bond angles obtained by using HF and DFT (B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of N-MHN and N-MMHN and calculated results by density functional B3LYP and Hartree–Fock methods indicate that B3LYP is superior to the scaled Hartree–Fock approach for molecular vibrational problems.     

Molecular structure and vibrational spectra of indole and 5-aminoindole by density functional theory and ab initio Hartree–Fock calculations

The molecular geometry and vibrational frequencies of indole and 5-aminoindole in the ground state have been calculated by using the Hartree–Fock and density functional method with 6-311++G(d,p) basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of indole and 5-aminoindole with the calculated results by density functional and Hartree–Fock methods indicates that B3LYP is superior to the scaled Hartree–Fock approach for molecular vibrational problems. The theoretical spectrograms for FT-IR spectrum of 5-aminoindole have been constructed.     

Role of the Bridge in Photoinduced Electron Transfer in Porphyrin–Fullerene Dyads

The role of π‐conjugated molecular bridges in through‐space and through‐bond electron transfer is studied by comparing two porphyrin–fullerene donor–acceptor (D–A) dyads. One dyad, ZnP–Ph–C₆₀ (ZnP=zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP–EDOTV–C₆₀, introduces an additional 3,4‐ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge‐separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP–Ph–C₆₀ dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D–A bridge.     

Ultrafast Photoinduced Energy and Electron Transfer in Multi‐Modular Donor–Acceptor Conjugates

New multi‐modular donor–acceptor conjugates featuring zinc porphyrin (ZnP), catechol‐chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C₆₀), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction‐center mimics. The X‐ray structure of triphenylamine‐BDP is also reported. The wide‐band capturing polyad revealed ultrafast energy‐transfer (k_ENT=1.0×10¹² s^?1) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA‐BDP‐ZnP triad through metal–ligand axial coordination resulted in electron donor–acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron‐transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion‐pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non‐polar toluene were in the range of 5.0×10⁹–3.5×10¹⁰ s^?1. Stabilization of the charge‐separated state in these multi‐modular donor–acceptor polyads is also observed to certain level.     

碳笼氧化物的结构和谱学性质

碳笼氧化物对碳笼的官能团化研究具有重要意义,因而激起了人们广泛的研究兴趣。本文对碳笼氧化物C₆₀O_n、C₇₀O_n、C₇₆O_n、C₇₈O_n及C₈₀O_n的结构、电子光谱、红外光谱及核磁共振谱的研究进展进行综合评述。介绍了国内外近十几年来众多研究小组的工作,并结合作者本人在此方面的理论研究成果,进一步探索碳笼氧化物的结构特点以及光谱性质的规律性。在对C₆₀及C₇₀氧化物研究结果与实验符合的基础上,预测高碳笼氧化物的结构和光谱。     

Synthesis and evaluation of thermal, photophysical and magnetic properties of novel starlike fullerene–organosilane macromolecules

Thermal, photophysical and magnetic properties of some novel fullerenol–silane adducts are described. Excellent improvement of thermal stability and high char yield due to the presence of silicon is the key feature of these adducts. Highest luminescence quenching due to maximum π–π electronic interactions between phenyl ring and fullerene are observed in the aromatic-silane adducts and the quenching ability of the aromatic ring reduces with further delocalization of the π-electrons as in naphthyl silane. The alkyl vinyl silane, on the other hand, records better fluorescence intensity owing to increase population of the electron density (+I effect) and non-effective charge transfer complex formation between isolated vinylic double bond and fullerene. Emission peak positions of these adducts are comparable to fullerenol because of control derivatization of fullerene ring causing less perturbation of the symmetric π-electronic system. These adducts are paramagnetic in nature with peaks around 3515 G and higher g-values (2.005–2.009) compared to fullerenol (1.985). The fullerenol–silane adducts are synthesized using fullerenol as substrate and different chloro and alkoxy silanes as silylating agents adopting simple nucleophilic displacement and transesterification reactions. All the fullerenol–silane adducts are characterized spectroscopically.