Density functional theory studies on the Raman and IR spectra of meso-tetraphenylporphyrin diacid

Pulse Electrolysis Turns on CO2 Methanation through N-Confused Cupric Porphyrin

Breaking the D4h symmetry in the square-planar M-N4 configuration of macrocycle molecular catalysts has witnessed enhanced electrocatalytic activity, but at the expense of electrochemical stability. Herein, we hypothesize that the lability of the active Cu-N3 motifs in the N-confused copper (II) tetraphenylporphyrin (CuNCP) could be overcome by applying pulsed potential electrolysis (PPE) during electrocatalytic carbon dioxide reduction. We find that applying PPE can indeed enhance the CH4 selectivity on CuNCP by 3 folds to reach the partial current density of 170 mA cm-2 at >60 % Faradaic efficiency (FE) in flow cell. However, combined ex situ X-ray diffraction (XRD), transmission electron microscope (TEM), and in situ X-ray absorption spectroscopy (XAS), infrared (IR), Raman, scanning electrochemical microscopy (SECM) characterizations reveal that, in a prolonged time scale, the decomplexation of CuNCP is unavoidable, and the promoted water dissociation under high anodic bias with lowered pH and enriched protons facilitates successive hydrogenation of *CO on the irreversibly reduced Cu nanoparticles, leading to the improved CH4 selectivity. As a key note, this study signifies the adaption of electrolytic protocol to the catalyst structure for tailoring local chemical environment towards efficient CO2 reduction.

Phthalocyanines and Porphyrins/Polyaniline Composites (PANI/CuPctBu and PANI/TPPH2) as Sensing Materials for Ammonia Detection

We combined a conducting polymer, polyaniline (PANI), with an organic semiconducting macrocyclic (MCs) material. The macrocycles are the phthalocyanines and porphyrins used to tune the electrical properties of the PANI, which benefits from their ability to enhance sensor response. For this, we proceeded by a simple ultrasonically assisted reaction involving the two components, i.e., the PANI matrix and the MCs, to achieve the synthesis of the composite nanostructure PANI/MCs. The composite nanostructure has been characterized and deposited on interdigitated electrodes (IDEs) to construct resistive sensor devices. The isolated nanostructured composites present good electrical properties dominated by PANI electronic conductivity, and the characterization reveals that both components are present in the nanostructure. The experimental results obtained under gas exposures show that the composite nanostructures can be used as a sensing material with enhanced sensing properties. The sensing performance under different conditions, such as ambient humidity, and the sensor's operating temperature are also investigated. Sensing behavior in deficient humidity levels and their response at different temperatures revealed unusual behaviors that help to understand the sensing mechanism. Gas sensors based on PANI/MCs demonstrate significant stability over time, but this stability is highly reduced after experiments in lower humidity conditions and at high temperatures.

UV, FL and IR spectroscopic analysis of N-confused meso-tetra(methoxyphenyl)porphyrins

UV, FL and IR spectra of isomer A (in DCM) and isomer B (in DMAc) of N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer, 1), N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer, 2) and N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer,3) were investigated. Significant red shifts are observed from [Formula: see text]-isomer (1) to [Formula: see text]-isomer (3) in UV-vis absorption and fluorescence spectra. The fluorescence lifetime ([Formula: see text] of isomer A and isomer B of the samples (1, 2 and 3) are ca. 1.39[Formula: see text]1.79 ns and 1.68[Formula: see text]2.09 ns, respectively. In addition, the order of fluorescence quantum yield for isomer A is 1 > 2 > 3, but for isomer B it is 1 < 3 < 2. The isomer B of 2shows the strongest emission in accord with the strongest absorption. The isomer A of 1shows the strongest emission with the fluorescence quantum yield of 0.045, which is nearly double that of 3. The introduction of the methoxy group at the orthoposition increases steric hindrance, the molecular rigidity and the flow of [Formula: see text]-electron, thereby favourable to the fluorescence enhancement. The IR absorption peaks of 1, 2 and 3 were investigated and empirically assigned. The effects of the position of the substituents on the absorption frequency were also discussed. The absorption frequency of the C=C phenyl stretching in plane changed obviously by conjugative effect and steric effect when the methoxy group was at the orthoormetaposition in comparison with paraposition.

Diboron Porphyrins: The Raman Signature of the In-Plane Tetragonal Elongation of the Macrocycle

We describe an unusual in-plane type of porphyrin core distortion, tetragonal elongation (TE), observed experimentally in diboron porphyrins. The vibrational spectra of several of these complexes exhibit shifts that we have assigned to this TE distortion by comparing experimental spectra with DFT computational findings. The influence of TE in porphyrin systems was isolated using DFT analysis of the well-known model compounds Ni(II)porphine and Zn(II)porphine, with the macrocycle ring constrained to eliminate the influence of out-of-plane (OOP) distortions. A significant down-shift in frequencies was observed for porphyrin normal vibrational modes, particularly the in-plane A_1g/B_1g modes that are dominated by contributions from stretching and bending of C_α-C_m coordinates. In contrast, TE had little effect on the v(Pyr_halfring) and δ(Pyr_def) modes, though the lowered symmetry of the system resulted in significant splitting of the B_2u and B_3u modes. The impact of the TE distortion upon the diboron porphyrin vibrational spectrum was probed experimentally using Raman spectroscopy of B₂O₂(BCl₃)₂(TTP), B₂OF₂(TTP), and B₂OPhOH₂(TTP) (TTP = 5,10,15,20-(tetra- p-tolyl)porphyrin). Comparing the experimentally obtained spectral signatures to the computational findings allowed us to assign the large shifts observed for the v₂ and v₃ modes to the TE distortion in diboron porphyrins.

Resonance Raman spectroscopy study of protonated porphyrin

Resonance Raman microscopy was used to study the resonance Raman scattering of the diacid (diprotonated form) of free-base porphyrin (21H,23H-porphine) in a crystal powder and KBr pellets. Intensive lines in the spectral range between 100÷1000cm^-1 have been detected and assigned as spectral manifestation of out-of-plane modes. The Raman spectra were simulated by means of DFT methods and compared with the experimental data. It is evident from experimental and theoretical results that the activation of out-of-plane modes arises from saddle distortion of the porphyrin macrocycle upon formation of its diprotonated form.

Vibrational analysis and valence force field for nitrotoluenes, dimethylanilines and some substituted methylbenzenes

The Fourier transform infrared (FTIR) and Raman spectra of 2-amino-4-nitrotoluene; 2-amino-5-nitrotoluene; 2,4-dimethylaniline; 2,5-dimethylaniline; 2,6-dimethylaniline; 1,2,4-trimethylbenzene; 1,3,5-trimethylbenzene and pentamethylbenzene have been recorded in the range 4000-400 cm(-1) and 4000-30 cm(-1), respectively. A normal coordinate analysis was carried out for both in-plane and out-of-plane vibrations of these molecules using an 81-parameter modified valence force field. The force constants were refined using 369 frequencies of eight molecules in the overlay least-squares technique. The reliability of the force constants was tested by making a zero-order calculation for both in-plane and out-of-plane vibrations for five related molecules. The potential energy distributions and eigen vectors calculated in the process were used to make unambiguous vibrational assignments of all the fundamentals.

Structural parameters and vibrational spectra of a series of zinc meso-phenylporphyrins: a DFT and experimental study

The influences of meso-phenyl substitution on the geometric structure and vibrational spectra have been studied by DFT calculation (B3LYP/6-31G(d)) and experiment on a series of zinc porphyrins (ZnTPP: zinc 5,10,15,20-tetraphenylporphyrin; ZnTrPP: zinc 5,10,15-triphenylporphryin; ZnDPP: zinc 5,15-dipenylporphyirn; ZnMPP: zinc 5-monophenylporphyrin; ZnP: zinc porphine). Calculation indicates that meso-phenyl substitution gives rise to slight out-of-plane distortion but significant in-plane distortion, especially for the configuration around C(m) atom, to zinc porphyrin. The assignment of experimental vibrational spectra was proposed mainly on the basis of calculation. Different shifting tendency upon meso-phenyl substitution is observed for different structure-sensitive bands, such as the shifting of nu(2), nu(3), nu(6), and nu(8) modes toward higher frequencies and nu(4) and nu(28) modes toward lower frequencies, upon meso-phenyl substitution. This is attributed primarily to in-plane nuclear reorganization effect (IPNR), though the contribution from out-of-plane distortion cannot be excluded completely. Analysis on vibrational structure reveals that asymmetric meso-phenyl substitution, especially the 5,15-diphenyl substitution of ZnDPP, brings about asymmetric vibrational displacement, or even splitting of vibrational structure to normal modes involving mainly the motion of meso-C(m). This is ascribed to the reduction of symmetry of porphyrin skeleton caused by asymmetric meso-phenyl substitution.

Experimental and theoretical study on vibrational spectra of nickel and zinc complexes of 5,10-diphenylporphyrin

The vibrational spectra of nickel and zinc 5,10-diphenylporphyrin (NiDaPP and ZnDaPP) have been studied by density functional theory (B3LYP/6-31G(d)) and experimental measurement. The assignment of observed Raman and IR bands are proposed based on theoretical calculation. Theoretical study indicates that 5,10-diphenyl substitution together with out-of-plane distortion diversify the structure of four pyrrole rings and the environment around C(m) atoms, which lowers the symmetry of porphyrin skeleton and brings about some variation to vibrational spectra. The first is the activation of all normal modes both in Raman and IR spectra. The second is the lifting of original degenerate E(u) representation and its splitting into two A modes in NiDaPP (C(1) group point) and A'/A'' presentation in ZnDaPP (C(s) group point), respectively. Furthermore, one or both of the two split components, especially for some vibration involving the motion of C(m) atom, undergoes further mixing with original non-degenerate mode (A(1g), A(2g), B(1g), or B(2g)) of same vibration. This produces new modes involving only partial motion of original mode. Besides general increasing frequency of NiDaPP with respect to ZnDaPP, different vibrational structure is also indicated by calculation for some structure-sensitive bands, especially nu(8) mode that couples with gamma(6) mode and split into two modes for NiDaPP but not for ZnDaPP.

Density functional theory studies on the electronic and vibrational spectra of octaethylporphyrin diacid

The ground-state structure and electronic and vibrational spectra of octaethylporphyrin diacid (H4OEP2+) have been studied with the density functional theory. The geometrical parameters computed with B3LYP, PBE1PBE and mPW1PW91 functionals and 6-31G* basis sets are well consistent with the experimental values. Electronic absorption spectrum of H4OEP2+ has been studied with the time-dependent DFT method, and the calculated excitation energies and oscillator strengths are compared with the experimental results. The Raman and IR spectra of H4OEP2+ and the Raman spectrum of its N-deuterated analogue (D4OEP2+) were measured. The observed Raman and IR bands have been assigned based on the frequency calculations at the B3LYP/6-31G* level of theory.

UV Near-Resonance Raman Spectroscopic Study of 1,1‘-Bi-2-naphthol Solutions

The normal and UV near-resonance Raman (UVRR) spectra of 1,1'-bi-2-naphthol (BN) in basic solution were measured and analyzed. Density functional theory (DFT) calculations were carried out to study the ground state geometry structure, vibrational frequencies nu, off-resonance Raman intensities I, and depolarization ratios rho of 1,1'-bi-2-naphtholate dianion (BN(2-)). On the basis of the calculated and experimental results of nu, I, and rho, the observed Raman bands were assigned in detail. The 1612 cm(-1) Raman band of BN in basic solution was found dramatically enhanced in the UV resonance Raman spectrum in comparison with the normal Raman spectrum. Analyzing the depolarization ratios of the 1366 and 1612 cm(-1) bands in the RR spectra manifests that both the symmetric and antisymmetric parts of transition polarizabilities contribute to the 1366 cm(-1) band, but that only the symmetric part contributes to the 1612 cm(-1) band.