Synthesis of meso-furyl porphyrins with N4, N3S, N2S2 and N3O porphyrin cores

A series of meso-furyl porphyrins with four different porphyrin cores (N₄, N₃S, N₂S₂ and N₃O) were synthesized and characterized. The comparison of NMR, optical and fluorescence properties of meso-furyl porphyrins with porphyrins with six-membered aryl groups indicates that electronic properties of porphyrins were changed drastically on the introduction of furyl groups at meso positions. The maximum shifts in spectral bands were observed for meso-furyl porphyrins with N₂S₂ core. On protonation, the absorption bands of meso-furyl porphyrins were further red shifted. All these changes were ascribed to the possibility of more planarity of the meso-furyl porphyrins due to the small size of the furyl groups which results in extending the π-delocalisation of the porphyrin ring in to the furyl groups.     

Synthesis and fluorescence properties of covalently linked homo- and hetero-porphyrin dyads containing meso-tolyl porphyrin and meso-furyl porphyrin sub-units

Three porphyrin building blocks with N₄, N₃S and N₂S₂ cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N₄-N₄, N₃S-N₃S, N₂S₂-N₂S₂, N₄-N₃S, N₄-N₂S₂ and N₃S-N₂S₂ containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form.     

Synthesis of β-pyrrole and β-thiophene substituted 21,23-dithia and 21-monothiaporphyrins

A series of β-pyrrole and β-thiophene substituted porphyrins with N₂S₂ and N₃S porphyrin cores were synthesized and characterized. The introduction of substituents at β-pyrrole and β-thiophene carbons resulted in significant shifts in ¹H NMR, absorption and fluorescence maxima. These effects were attributed to alteration of the porphyrin ring current caused by substituents at β-positions.     

Solvent effects on some new meso -aryl substituted octabromoporphyrins

A series of porphyrins with tolyl and naphthyl substituents at themeso positions, their octabromoderivatives (OBP) with Br substituents at β-pyrrole positions are synthesised and characterised by chemical analysis,¹H NMR and electronic spectral studies. It is seen that all the OBPs exhibit pronounced red shifts in both the Soret andQ bands of their electronic spectra compared to their non-brominated form in various polar and nonpolar solvents, the energy difference Δv being in the range 2300–2700 cm₋₁. The high energyB band of naphthyl porphyrins (both brominated and nonbrominated) are found to be more red-shifted than that of tolyl porphyrins, owing to the noticeable mesomeric effect of the naphthyl groups. Detailed spectral studies reveal that while none of the nonbrominated porphyrin show solvent-dependent change in theirB andQ bands, all the OBPs manifest significant shifts depending on the nature of solvents. Solvent-solute interaction can be considered to be of strong dipole-dipole nature for OBPs with polar solvents and of π-π type with aromatic non-polar solvents. In the brominated form we find two categories of porphyrins exhibiting distinctly different absorption phenomena in aromatic solvents. The OBPs havingmeso-groups not shielding the porphyrin π-framework exhibit additional absorption peaks (split Soret peaks and broadened Q bands) in some aromatic solvents. This could be explained in terms of π-π type donor-acceptor (DA) complex formation between such bromoporphyrins (acceptor) and the aromatic solvent molecules (donor) that is not possible for OBPs that have bulkymeso groups that block the approach of aromatic solvent molecules close to the porphyrin framework     

Mononuclear hydridocarbonyl ruthenium complexes incorporating N2O2 bis-chelating ligands

The reactions of [RuH(CO)Cl(PPh₃)₃] with N,N^′-bis(salicylidine)-hydrazine (H₂bsh) and N,N^′-bis(salicylidine)-p-phenylene diammine (H₂bsp) in presence of KOH in methanol led in the formation of neutral mononuclear complexes with the formulations [RuH(CO)(PPh₃)₂(L)] (LHbsh or Hbsp). These present the first examples where the ligands H₂bsh or H₂bsp provide only two of its available donor sites for interaction with the metal centre. The complexes have been characterized by elemental analyses, FAB-MS, IR, ¹H, ¹³C, ³¹P NMR and electronic spectral studies. Molecular structure of the representative complex [RuH(CO)(PPh₃)₂(Hbsh)] have been determined by single crystal X-ray analysis.     

Synthesis,electrochemical and in situ spectroelectrochemical studies of new transition metal complexes with two new Schiff-bases containing N2O2/N2O4 donor groups

New Schiff-base copper and cobalt complexes, [Cu(L¹)], [Cu(L²)] and [Co(L¹)], [Co(L²)] (where L¹ = N-N′-bis(3,5-di-tert-butylsalicylaldimine)-1,4-cyclohexane bis(methylamine) and L² = N-N′-bis(3,5-di-tert-butylsalicylaldimine)-1,8-diamino-3,6-dioxaoctane), were synthesized and characterized using elemental analysis, IR spectra, UV–Vis spectra, magnetic susceptibility measurements, ¹H and ¹³C NMR spectroscopy, thermal analysis and molar conductance (Λ_M). Their electro-spectrochemical properties were investigated using cyclic voltammetric (CV) and thin-layer spectroelectrochemical techniques in a dichloromethane solution (CH₂Cl₂). The CV of [Cu(L²)] showed a lower oxidation potential than that of [Cu(L¹)] under the same experimental conditions. The oxidation wave (II) of [Cu(L²)] was accompanied by an EC process (II′), which was not observed for [Cu(L¹)]. Also, [Cu(L²)] exhibited a reduction process, but [Cu(L¹)] did not. These results indicate that the Cu(II) ion in [Cu(L²)] is coordinated by N₂O₄ donor sites while [Cu(L¹)] presents a square-planar structure with N₂O₂ donor sites. Both oxidation processes for [Co(L¹)] and [Co(L²)] are based on the cobalt center, and they are assigned to Co(II)/Co(III) couples. The spectroelectrochemical results indicate that the oxidized species of [Cu(L²)] is similar to that of [Cu(L¹)], the only difference being that the absorption bands of the oxidized species for [Cu(L²)] shift to lower energy compared with those of [Cu(L¹)] because of their different coordination environment. The geometry of [Cu(L²)] changed into square-planar after the complex was totally oxidized and the neutral complex was only recovered following the EC process, as observed from the CV of [Cu(L²)]. For the two cobalt complexes, the bands corresponding to the π → π^∗transitions disappeared and new bands with small red shifts and of lower intensity were observed during the oxidation process. These new bands are attributed to the LMCT transition as observed in the case of the oxidation processes of the cobalt complexes.     

Spectroscopic properties of meso-thienylporphyrins with different porphyrin cores

The absorption and fluorescence properties of a series of meso-thienylporphyrins with different porphyrin cores (N₄, N₃O, N₃S and N₂S₂ cores) were studied and compared with the corresponding meso-tetraarylporphyrins. The replacement of six-membered phenyl groups with five-membered thienyl groups at meso-positions resulted in red shifts and broadening of absorption and emission bands, low quantum yields and decreased S₁ state lifetimes and the maximum effects were observed for meso-tetrathienylporphyrin with N₂S₂ porphyrin core. Similar observations were noted for the dications of meso-thienylporphyrins compared to the dications of the corresponding meso-tetraarylporphyrins. These results suggest that the replacement of six-membered aryl group with five-membered thienyl groups at meso-positions, the electronic properties of the porphyrin were altered significantly.     

Collision-induced absorption of infrared radiation by N2, O2 and CO2

The collision-induced absorption of the symmetric vibration of CO₂ has been observed in the pure gas at densities from 20.0 to 40.0 amagat and at temperatures of 273, 298, and 323 K using infrared techniques. From the integrated intensities of the bands and using the (exp ?4) model of van Kranendonk, it is possible to deduce a value for the first derivative of the quadrupole moment with respect to the vibrational coordinate. For CO₂ the contribution from quadrupole distortion to the binary absorption coefficient is reported for several temperatures. The (exp ?4) model of van Kranendonk is used to calculate the binary absorption coefficients for the fundamental vibrational bands of N₂ and O₂ at temperatures from 70 to 340 K. The parameters λ and p/σ describing the magnitude and range of the short-range collision-induced dipole moments were determined using the known experimental absorption coefficients. The contributions from atomic distortion and quadrupole distortion to the binary absorption coefficient are calculated for N₂ and O₂.     

Synthesis of A2B2 type cis-doubly N-confused porphyrins from N-confused dipyrromethanes

A₂B₂ type of cis-doubly N-confused porphyrins (cis-N₂CP) bearing 2,6-dichloro-, 2-nitro-, 3-nitro-, and 4-nitro-phenyl groups and pentafluorophenyl groups at meso-positions were synthesized by the condensation of aryl-substituted N-confused dipyrromethanes and pentafluorobenzaldehyde. The complexation of rare high oxidation states of metals, Cu(III) and Ag(III), was demonstrated.     

Synthesis and studies of covalently linked meso-furyl boron-dipyrromethene-ferrocene conjugates

Four meso-furyl BODIPY-ferrocene conjugates 1–4 in which one or more ferrocene groups were connected directly to BODIPY core or meso-furyl group were synthesized by coupling of appropriate bromo meso-furyl BODIPYs with α-ethynylferrocene under mild Pd(0) coupling conditions. The compounds were characterized by HR-MS mass, NMR, absorption, electrochemistry and fluorescence techniques. The absorption studies of compounds 1–4 showed charge transfer band in addition to BODIPY absorption bands indicating that the BODIPY and ferrocene moieties interact within the conjugates. On the other hand, the charge transfer band is absent in meso-phenyl BODIPY-ferrocene conjugate due to the orthogonal arrangement of ferrocene appended meso-phenyl group with BODIPY core which prevents the interaction between the two moieties. The electrochemical studies showed strong oxidation due to ferrocene moiety and reduction due to meso-furyl BODIPY unit. The compounds 3 and 4 which contain two and three ferrocenyl groups respectively were oxidized at the same potential with two and three electrons involved in the redox process. The compounds 1–4 are weakly fluorescent due to electron transfer from ferrocene unit to BODIPY unit. However, the fluorescence can be restored by oxidizing the ferrocene to ferrocenium ion which prevents the electron transfer between the two moieties. The computational studies support the experimental results.     

Rate constants for: OH + NO2 (+ N2) → HNO3 (+ N2) between 220 and 358 K

Rate constants have been determined for the reaction OH + NO₂ (+ N₂) → HNO₃ (+ N₂), using time-resolved resonance absorption to follow the removal of OH radicals produced by flash photolysis of HNO₃. The measurements cover the ranges: 220 ? T ? 358 K and 3.2 × 10¹⁷ ? [N₂] ? 4.0 × 10¹⁸ molecule cm^?3.     

Microscopic structures of adsorbed cationic porphyrins on clay surfaces: molecular alignment in artificial light-harvesting systems

The intercalation behavior of cationic porphyrin derivatives within the interlayer spaces of nano-layered clay minerals has been investigated. The porphyrins were successfully intercalated by the newly adopted method of repeated freeze-thaw cycles. The absorption spectra of the porphyrins were compared in the solution phase, adsorbed onto the exfoliated clay nano-sheets, intercalated within the interlayer spaces of clay sheets dispersed in water and intercalated in dry films. Substantial red shifts of the λ_max values in the absorption spectra of the porphyrins were observed on the exfoliated clay sheets, and further red shifts were induced within the interlayer space. The dry films of the intercalated samples exhibited the largest red shifts. X-ray diffraction studies revealed that the clearance space between the layers in these intercalated hybrid compounds is only large enough for the porphyrins to be rigidly packed parallel to the clay layer. For the exfoliated clay nano-sheets, theoretical calculations were carried out on the correlation between the dihedral angle of the meso-substituted pyridiniumyl plane vs. the porphyrin ring and the λ_max of the porphyrin Soret band. An extrapolation of the experimental λ_max value to the correlation curve, afforded the dihedral angle to be 61.6°. The microscopic structure of the adsorbed state of the cationic porphyrins on the exfoliated clay nano-sheets was, thus, proposed to involve an orientation parallel to the clay surface, with a distance of 0.15 nm from the surface, which implies the expulsion of the solvent water molecules.     

Self-assembly via intermolecular hydrogen-bonding between o-/m-/p-NH2 and BF2 groups on dipyrromethenes

Boron difluoride dipyrromethenes bearing configurationally different amine groups on a meso-phenyl ring were prepared and crystallized. The ortho- and para-amino groups allow the phenyl group to inductively release greater electron density into the dipyrromethenes resulting in relatively strong intermolecular hydrogen-bonding with the terminal BF₂ groups, whereas the meta-analog formed weaker hydrogen-bonds. The intensities of the ¹H NMR peaks in concentrated solutions all increased with F-decoupling.     

meso-Multi(iodophenyl) porphyrins: synthesis, isolation, and identification

We report on a simple method for identification of a series of six meso-substituted porphyrins by ¹H NMR spectroscopy. The meso-substituted porphyrins are synthesized by a simple mixed-aldehyde condensation approach [3,5-di-tert-butylstyrylbenzaldehyde (A) and 4-iodobenzaldehyde (B)] to give the two parent porphyrins (A₄, B₄) and four hybrid porphyrins (A₃B, cis-A₂B₂, trans-A₂B₂, AB₃) which are isolated and characterized.     

Meso位单取代卟啉及其配合物的合成、表征和光谱性质

设计合成了一系列新型的meso位N,N-二甲氨基苯基或N-苯基咔唑基单取代卟啉（5a~c）及其锌配合物（6a~c）,用高分辨质谱、¹H NMR、紫外-可见光谱及X射线单晶衍射方法等对结构进行了表征;研究了卟啉化合物及其配合物的热稳定性及荧光性质。结果表明,这些卟啉化合物及其锌配合物在400~410 nm之间具有强的吸收且具有很好的热稳定性,荧光量子产率在0.05~0.09;另外还分析了meso位不同取代基对光谱性质的影响。     

Infrared studies of the diatomic molecules O2, N2, NO and H2 adsorbed on Fe2O3

An infrared spectroscopic study of the diatomic molecules O₂, N₂, NO and H₂ adsorbed under different conditions on Fe₂O₃ has been performed.Complex patterns of absorption on both α-Fe₂O₃ and γ-Fe₂O₃ activated in O₂ at high temperature are assigned to vibrations of two different chemisorbed O₂ species.N₂ molecules do not interact with “oxygen rich” α-Fe₂O₃ surfaces, but give N₂O^? and N₂O₂^2? species when chemisorbed on evacuated surfaces.NO molecules give complex patterns of absorption, depending on the gas pressure. Three different types of nitrate structures can be identified, as well as NO, NO^? and cis-N₂O₂ chemisorbed species. Chemisorbed water molecules are formed by contact of H₂ with Fe₂O₃ surfaces even at room temperature.     

Further studies of the N2+ + N2 → N4+ association reaction

Data are presented which strongly suggest that stabilisation of the excited intermediate (N₄⁺)* complex in the reaction (1) N₂⁺ + 2N₂ (rate coefficient k₁) occurs via N₂ switching whereas for (2) N₂⁺ + N₂ + He (rate coefficient k₂) it occurs via superelastic He collisions. This explains the differing temperature variations of k₁ and k₂ previously obtained for these reactions. Drift tube data are also presented which show how k₁ varies with N₂⁺/N₂ centre-of-mass energy as compared with thermal energy.     

Intermolecular forces for D2, N2, O2, F2 and CO2

The intermolecular potentials for D₂, N₂, O₂, F₂ and CO₂ are determined on the basis of the second virial coeffincients, the polarizabilities parallel and perpendicular to the molecular axes, and the electric quadrupole moment. The repulsive parts of the potentials are taken from the corresponding Kihara core-potentials. Effects of the octopolar induction are taken into consideration in a unique way. The potential depends on relative orientations of the two molecules as well as the distance r between the molecular centers. This dependence is shown in graphs. A measure of the anisotropy of the potential depth is 0.72 for CO₂ 0.36 for D₂, and smaller than 0.27 for N₂ O₂ and F₂. The remarkable anisotropy for CO₂ and D₂ is due to strong electrostatic quadrupole interactions.     

Complex Formation and Spectral Properties of meso-Phenyltetrabenzoporphyrins in Pyridine and N,N-Dimethylformamide

Contributions of structural (macroring distortion) and polarization (in asymmetrically substituted derivatives) effects into the reactivity and chromophoric properties of substituted porphyrins were revealed on the basis of the kinetics of complex formation of nona-, deca-, undeca-, and dodecasubstituted porphyrins (meso-phenyltetrabenzoporphyrins) with Zn(OAc)₂ in pyridine and the electronic absorption spectra of the ligands and their complexes with Zn(II) and Cu(II) in pyridine and N,N-dimethylformamide (DMF). Dodecaphenyl substitution produces a weaker ring distortion in the more aromatic tetrabenzoporphyrin compared with porphyrins themselves. Irrespective of the degree of macroring nonplanarity, the Zn (II) and Cu complexes of tetrabenzoporphyrins with increasing degree of meso-phenyl substitution meet a spectral stability criterion.     

Kinetics of O(1D) interactions with the atmospheric gases N2, N2O,H2O,H2, CO2, and O3

Rate coefficients for collisional removal of O(¹D) by six atmospheric gases have been measured by monitoring the appearance of O(³P) following photolytic production of O(¹D). The measured values, k_M±2σ, in units of 10^?11 cm^?3 molecule ^?1 s^?1 are k_O3 = 22.8±2.3, k_N2 = 2.52 ± 0.25, k_CO2 = 10.4 ± 1.0,k_H2O 195± 2.0, k_N2O = 11.7 ± 1.2, and k_H2, = 11.8±1.2.