H2T PP Research Articles

Thermodynamic studies of sitting-atop complexation between free base meso-tetraarylporphyrins and antimony(III) chloride in chloroform

Interaction of para, meta and ortho-substituted meso-tetraarylporphyrins, (H2t(X)pp, X: OMe, Me, H and Cl) with SbCl3 in chloroform solution afforded 1 : 1 sitting-atop (SAT) complexes ([(SbCl3)(H2t(X)pp)]). The formation constants were calculated by KINFIT and found to decrease with increasing temperature. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained. Formation constants of these complexes change with changing substituent (X) on the aryl rings of H2t(X)pp in the following order: (SbCl3)H2t(4-OMe)pp > (SbCl3)H2t(4-Me)pp > (SbCl3)H2tpp > (SbCl3)H2t(4-Cl)pp > (SbCl3)H2t(3-OMe)pp > (SbCl3)H2t(3-Me)pp> (SbCl3)H2t(2-OMe)pp > (SbCl3)H2t(2-Me)pp.

Thermodynamic investigation of the molecular interactions of 4-nitrophenol with free-bases meso-tetraarylporphyrins

The molecular interactions of 4-Nitrophenol (4NP) with free-base meso-tetraarylporphyrins (H2T(4-X)PP; X = OCH3, CH3, H, Cl) have been studied. The formation constants and other thermodynamic parameters were calculated by using UV-Vis spectrophotometry titration results. The formation constants show the following trend relative to X substituent of porphyrins: H2T(4-CH3O)PP > H2T(4-CH3)PP > H2TPP > H2T(4-Cl)PP.

Nanoassembly of meso-Tetraphenylporphines on Surfaces of Carbon Materials: Initial Steps as Studied by Molecular Mechanics and Scanning Tunneling Microscopy

We employed MM+ molecular mechanical modeling and scanning tunneling microscopy (STM) in order to analyze the initial steps of nanoassembly of meso-tetraphenylporphine H2TPP and its cobalt(II) complex CoTPP on the surface of highly-oriented pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). According to the MM+ results, monolayer H2TPP adsorption is more favorable energetically than the formation of porphyrin stacks on both graphite and nanotube sidewall; the formation of parallel interacting chains of H2TPP on graphite is more preferable than the growth of long single chains; and the assembly into a long-period helix is favored versus the formation of a short-period helix on SWNT sidewall. STM observations of CoTPP complex deposited onto bare HOPG and onto the graphite with deposited SWNTs are consistent with theoretical results. At the same time, both CoTPP single chains and ribbons were observed on HOPG. The formation of short-period helices on the nanotube sidewalls was concluded to be more likely than the long-period helical nanoassembly.

Surface Photovoltage and Electric Field‐Induced Surface Photovoltage Study on a Series of Lanthanide (III) Monoporphyrin Compounds

The photoelectric properties of Meso‐tetra‐(p‐chlorophenyl)porphyrin‐hydroxy‐rare earth complexes Ln (P‐Cl) TPP (OH)·Im[H2(P‐Cl)TPP: (p‐chlorophenyl) porphyrin; Ln: Gd, Tb, Dy, Er, Yb, Lu; Im: imidazole] were studied with surface photovoltaic spectroscopy (SPS) and electric field induced surface photovoltaic spectroscopy (FISPS). The photovoltaic responses are analogous to the corresponding UV‐Visible absorption spectrum, thus proving that the two spectra originate from the same electron transition process.

Synthesis and Spectroscopic Characterization of New Molecular Complexes of Bismuth(III) Chloride with Free Base meso-Tetraarylporphyrins

Abstract Reaction of bismuth(III) chloride (BiCl3) with free base meso-tetraarylporphyrins (H2t(X)pp, X = 4-Me, 4-OMe, 3-Me, 3-OMe, and H) in CHCl3 under mild conditions gives exclusively 1:1 molecular complexes with the general formula [(BiCl3{H2t(X)pp})2]. The remarkable agreement between 1H and 13C NMR and UV–vis spectra of the porphyrin macrocycle in these complexes and those of meso-tetraarylporphyrin molecular complexes with DDQ, TCNE, SiR3Cl, and BF3 indicates that they all have a similar porphyrin core. The molecular complexes have a dimer structure containing a Bi2Cl6 moiety. In the proposed structures for the complexes, four pyrroles are tilted alternatively up and down with respect the porphyrin mean plane, which leads to the appropriate orientation of the nitrogen lone pairs towards the central bismuth atoms. Therefore, octahedral geometry for the bismuth center is proposed.

Kinetic study and UV–Vis spectra of 1:2 complexation of free base para‐substituted meso‐tetraphenylporphyrins with trimethylsilyl chloride

AbstractThe UV–Vis spectra for 1:2 complexation of four different para‐substituted meso‐tetraphenylporphyrin (H2t(4‐X)pp) and meso‐tetraphenylporphyrins (H2tpp) with trimethylsilyl chloride (TMSC) displayed large and different redshifts (28–32.4 nm) of Soret and (15–41.7 nm) Q(0‐0) bands, whereas 1:2 complexation of the less flexible tetramesitylporphyrin (H2tmp) with TMSC led to rather small redshift (24.8 nm) of the Soret band and blueshift (−7.4 nm) of the Q(0‐0) band. The varying spectral behavior for the porphyrins complexation seems to essentially reflect the different extent of π‐interactions between the meso‐aryl groups and the presumably saddled porphyrin macrocycle, through their relative coplanarity. The observed order of the rate constants for the complexation of various para‐substituted porphyrins, H2t(4‐OCH3)pp (9.27 ± 0.03) × 10−3 > H2t(4‐CH3)pp (6.68 ± 0.05) × 10−3 > H2tpp (3.2 ± 0.05) × 10−3 > H2t(4‐Cl)pp (8.36 ± 0.06) × 10−4, clearly demonstrated a higher reaction rate for the porphyrins containing para‐substituents with stronger electron donor ability. The calculated order for porphyrins (0.9 ± 0.1) and for TMSC (1.0 ± 0.1) suggests rate = K[Por][TMSC] for the complexation. Attempts were made to explain the absence of spectral evidence for the presence of an intermediate 1:1 (TMSC) Por adduct in terms of its high reactivity and/or relative instability. © 2007 Wiley Periodicals, Inc. 39: 231–235, 2007

Interaction of para-substituted meso-tetraphenylporphyrins and meso-tetra(n-propyl)porphyrin with weak and strong carboxylic acids: A UV–Vis spectroscopic study

N-protonation of H2t(n-Pr)p and a series of para-substituted meso-tetraphenylporphyrins (arylpor), using carboxylic acids of different strength and size, CF3COOH, HCOOH, H2C2O4, CH2ClCOOH, CH3COOH and CH3CH2COOH, has led to a shift of the Soret and Q(0,0) bands with respect to those of the corresponding free base porphyrins. The size of central acceptor as well as the strength of N–H⋯carboxylate hydrogen bonding are the main factors influencing the red shift of the Soret band; the Soret band of H2t(n-Pr)p(CH3CH2COOH)2 is red shifted in comparison to those of the other dications of H2t(n-Pr)p. It may be shown that the out-of-plane deformation of the porphyrin core, which decreases the antibonding interactions in the frontier orbitals of the porphyrin core, leads to greater stabilization of the eg orbitals relative to the a1u one and consequently causes the red shift of the Soret band. Although the Q(0,0) band is blue shifted with respect to the free base porphyrin, the blue shift may be shown to be due to the protonation of the pyrrolenine nitrogen atoms rather than the saddling of the macrocycle. A comparison of the spectral data of the dications of arylpor, bearing strong electron donating para-substituents, with those of the related H2t(n-Pr)p adducts clearly indicates the importance of the π-resonance interactions in the observed spectral shifts of the Q(0,0) bands and, to less an extent, the Soret bands. The unusually large red shift observed for the Soret band of the H2t(4-NO2)pp dications seems to be due to the stabilization of eg orbitals through overlap with the proper unoccupied π∗ orbital of the electron withdrawing (4-NO2)phenyl in the excited state, a1u1eg1.

The Thermodynamic Studies of the Molecular Interactions of Tetracyanoethylene with Free Base meso-Tetraarylporphyrins

Abstract The interactions of tetracyanoethylene (TCNE) with 4-substituted meso-tetraphenylporphyrins (H2T(4-X)PP) results adducts of composition 2:1 of TCNE to H2T(4-X)PP, [(TCNE)2H2T(4-X)PP)]. Formation constants, K, as well as other thermodynamic parameters, ΔH°, ΔS°, and ΔG° of adducts were determined by UV–vis titration method. Adducts have positive values of ΔS° and ΔH°. These interactions are favorable with considerable negative values of ΔG°. Adducts stabilities are in the order: H2T(4-OCH3)PP > H2T(4-CH3)PP > H2TPP > H2T(4-Cl)PP.

Fluorescent porphyrins trapped in monolithic SiO2 gels

Macrocyclic molecules play key roles in basic processes in living organisms. Free bases and the metal complexes of porphyrins exhibit a wide range of important optical properties. In these systems the position of the most intense absorption band depends on the peripheral substituents of the macrocycle. Sol-gel methods have generally allowed the successful trapping of porphyrins into inorganic networks. The materials obtained are strong and transparent monolithic gels, but in the majority of cases the red fluorescence of the porphyrins disappears with ageing. We have evaluated the effect of the type and spatial disposition of the substituents in the porphyrin macrocycle periphery on key optical properties, with particular emphasis on the conservation of red fluorescence when porphyrins are simply trapped or covalently bonded to the inorganic matrix. Here, we report the use of the sol-gel procedures to obtain monolithic gels with the hydroxyl- or amino-substituted α, β, γ, δ-tetraphenylporphyrins, (H2T(S)PP), simply trapped or covalently bonded to the SiO2 matrix.

The Thermodynamic Studies of the Molecular Interactions of Diethyl- and Dibutyltin(IV) Dichloride with Free Base meso-Tetraarylporphyrins

Abstract The thermodynamic parameters for the interactions of Et2SnCl2 and Bu2SnCl2 with para-substituted meso-tetraphenylporphyrins (H2T(4-X)PP; X = OCH3, CH3, H, Cl) were determined. The overall formation constants K (mol-2 dm6), where (K = K1×K2), were calculated by using UV–vis spectrophotometry titration, and a data refinement was carried out with a computer program, SQUAD. The adducts had a 2 : 1 composition of R2SnCl2 to porphyrin. The overall formation constants decreased with decreasing electron releasing of porphyrins and increasing steric hindrance on an organotin compound, as follow: H2T(4-CH3O)PP > H2T(4-CH3)PP > H2TPP > H2T(4-Cl)PP and Et2SnCl2 > Bu2SnCl2.

Preparation and Spectroscopic Characterization of 2 : 1 Molecular Complexes of Tetracyanoethylene andmeso-Tetraphenylporphyrins

Different para-substituted meso-tetraphenylporphyrins (H2T(4-X)PP, X = H, Cl, CH3, CH(CH3)2, OCH3) react with various molar ratios of tetracyanoethylene (TCNE) in dichloromethane or benzene and produce only the 1 : 2 molecular complex, (TCNE)2H2T(4-X)PP. The remarkable agreement between the corresponding 1H, 13C solution (CDCl3) NMR resonances of the porphyrin moiety in these complexes with those of tetraphenylporphyrin dication, H4TPP2+, and also the strong resemblance between their UV-vis spectra and the spectra of the related diprotonated porphyrins indicates similar out-of-plane distorted porphyrin core structure in all of them. Based on these close spectral correspondences among the various molecular complexes and the related diprotonated porphyrins, and also consideration of the known structure of H4TPP2+Cl2- species, it is proposed that the two TCNEs in (TCNE)2H2T(4-X)PP complexes are bonded from above and below the mean porphyrin plane to the lone electron pairs of the pyrrolenine nitrogens of the...

Exclusive 2∶1 molecular complexation of 2,3-dichloro-5,6-dicyanobenzoquinone and para-substituted meso-tetraphenylporphyrins: spectral analogues for diprotonated meso-tetraphenylporphyrin

Various molar ratios of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and para-substituted meso-tetraphenylporphyrins (H2T(4-X)PP, X = H, Cl, CH3, CH(CH3)2, OCH3) in dichloromethane at room temperature in several days always afforded (DDQ)2H2T(4-X)PP molecular complexes as the sole products. The very close correspondence between the optical spectra of these 2∶1 molecular complexes and their related diprotonated porphyrins, and particularly the remarkable agreement of their corresponding 1H, 13C NMR resonances with those of tetraphenylporphyrin dication, H4TPP2+, strongly suggest similar distorted porphyrin core structures in all these compounds. 13C NMR and IR spectra of the complexed DDQs appear to be consistent with the interaction of one of their empty CN π* orbitals with a lone pair of a pyrrolenine nitrogen of the porphyrin. Also the loss of pyrrolic NH stretchings of the porphyrins in the IR spectrum of the molecular complexes indicates the occurrence of intramolecular H-bondings. It is proposed that coordination of DDQs in (DDQ)2H2T(4-X)PP complexes occurs from above and below the “plane” of the porphyrins, and they occupy the same positions as HCls in the structure of [H4TPP]2+, 2Cl− species.

Kinetics and mechanism of zinc(II), cadmium(II), and mercury(II) incorporation into meso tetrameta‐tolueneporphyrin

The kinetics of Zn(II), Cd(II), and Hg(II) incorporation into meso tetrameta-tolueneporphyri n (H2T(m-CH3)PP) in acetone have been studied by means of stopped-flow method. A unified reaction mechanism was proposed and the kinetic parameters were obtained by nonlinear least-square methods. The effect of ionic strength (I) on Cd(II)/H2T(m-CH3)PP was investigated. It has been found that there is a negative kinetic salt effect and the relationship of rate constants with ionic strength was obtained. Some solvent effects have also been investigated in this article. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 277–283, 1998.

Volumetric properties of methyl,tert-butyl, and alkoxy derivatives of tetraphenylporphyrin in benzene solution

Densities, apparent molar volumes, and partial molar volumes of benzene solutions ofmeso-tetradimethylphenyl porphyrin derivatives H2T(i,j-CH3)PP (where i,j = 2,3-; 2,4-; 3,4-; 2,5-; 3,5-);meso-tetra-4-alkoxyphenyl porphyrin derivatives H2T(4-OCnH2n+1)PP (wheren = 2–4,6–8,10,12,16);meso-tetra-3-butoxyphenyl porphyrin H2T(3-OC4H9)PP;meso-tetra-4-tert-butylphenyl porphyrin H2T(4tBu)PP;meso-tetra-3,5-ditert-butylphenyl porphyrin H2T(3,5-tBu)PP at 25°C and tetraphenylporphyrin, H2TPP,H2T(4-OC10H21)PP;H2T(4-OC12H25)PP and H2T(4tBu)PP at 20°C; 30°C; 40°C; 50°C were determined. The solubilities of the compounds in benzene at 25°C were measured. The solvent excluded volumes for different conformational states and the topology of dimethyl derivatives of tetraphenylporphyrin were calculated and compared with partial molar volume data. The correlation between the partial molar volumes and van der Waals volumes for the derivatives H2TPP,n-alkanes,n-alkanols, fatty acids, cyclic compounds, and crown ethers using the equation of Terasawa was elaborated. The average increment of the methylene group for alkoxy-substituted H2TPP was calculated as δV 2 o (CH2) = 16.6±0.4cm3-mol-1. The volumetric expansion coefficients of benzene solutions of H2TPP; H2T(4-OC10,H21)PP; H2T(4-OC12H25)PP and H2T(4-tBu)PP were determined and discussed. The importance of packing efficiencies around the solute molecules were examined.

Volumetric properties of tetraphenylporphine, their metallo-complexes and some substituted tetraphenylporphines in benzene solution

Densities, apparent molar volumes and partial molar volumes of benzene solutions of tetraphenylporphine, H2TPP, tetraphenylporphine metallo-complexes, MTPP (where M=Ni,Cu,Zn,Pd,Ag, and Cd), and some substituted tetraphenylporphines H2T(i-R)PP (where i=2–4 and R=−Cl,−CH3,−OCH3) H2T(i-F)PP (where i-2,3), H2T(3-Br)PP, and H2T(3-I)PP were determined at 25°C. It was found that the partial molar volumes of the studied compounds correlate linearly with the first ionization potential of the corresponding metal atom. The calculated values of the surface and volume accessible to the solvent, and the solvent-excluded volume for different conformations of H2TPP, were compared with experimental data. The volume per molecule for different crystalline forms of H2TPP and MTPP were compared with the partial molar volumes of the corresponding compounds in benzene solutions. The correlation between the partial molar volumes of H2T(3-R)PP and their Van der Waals volumes are presented for R=−H, −F,−CH3,−Cl,−Br,−OCH3, and −I. The experimental data are rationalized in terms of differences in the conformational states of the molecules.

Kinetics and Mechanism of Copper(II), Zinc(II), and Cadmium(II) Incorporation into 5,10,15,20-Tetraphenylporphine and N-Methyl-5,10,15,20-tetraphenylporphine in N,N-Dimethylformamide

Abstract The kinetics of reactions of 5,10,15,20-tetraphenylporphine (H2(tpp)) and N-methyl-5,10,15,20-tetraphenylporphine (H(metpp)) with CuII, ZnII, and CdII ions was studied spectrophotometrically in N,N-dimethylformamide. The rate of incorporation of metal ions (M2+ : Cu2+, Zn2+, Cd2+) into H(metpp) is first order with respect to both H(metpp) and metal ion: d[M(metpp)+]/dt=[k[H(metpp)][M2+] with k(25 °C)=11.5±0.5 mol−1 dm3 s−1 for Zn2+ and (5.8±0.8)×102 mol−1 dm3 s−1 for Cd2+. The rate of incorporation of copper and zinc into H2(tpp) is first order in H2(tpp) and the conditional first-order rate constants are expressed as follows: k0(M)=K[M2+](1+K[M2+])−1(k1+k2[M2+]) where for Cu2+ and Zn2+ K/mol−1 dm3, k1/s−1, and k2/mol−1dm3 s−1 at 25°C are (1.6±0.2)×104 and (7.2±1.5)×102, (1.2±0.1)×10−4 and (3.5±0.7)×10−5, and (5.2±0.2)×10−2 and (8.6±0.2)×10−4, respectively. Metal ion incorporation into H2(tpp) proceeds through the formation of intermediates prior the rate-limiting step. For the H(metpp) system, the methyl group on the pyrrole in H(metpp) prevents the formation of such an intermediate. On the other hand, the rate of cadmium incorporation into H2(tpp) is first order with respect to Cd2+ and H2(tpp) and its second order rate constant k is (6.5±1.0)×10−3 mol−1 dm3 s−1. The large cadmium(II) ion can not fit into the porphyrin nucleus and its reaction proceeds through a pathway involving a mononuclear activated complex.

High pressure luminescence studies of metalloporphyrins in polymeric media

High pressure luminescence measurements have been made on free base tetraphenylporphyrin (H2–TPP), as well as on Zn–TPP, Mg–TPP, Cr–TPP, and Cu–octaethylporphyrin (Cu–OEP), in PMMA and PS. In the case of H2–TPP, Zn–TPP, and Mg–TPP the efficiency of fluorescence and phosphorescence (Zn–TPP) was pressure dependent as was the relative energy of the excited singlet and triplet states. The relative transfer rates have been calculated, and it was shown that the fluorescence efficiency is limited by intersystem crossing while the phosphorescence efficiency is limited by both radiationless rates S1→T1 and T1→S0. The rate S1→T1 scaled very well with the S1–T1 energy difference, and the rate T1→S0 with the T1–S0 energy difference. In the case of Cu–OEP and Cr–TPP only phosphorescence was observed from two states. At low pressure phosphorescence comes mainly from the high energy excited state (2T1), while at high pressures it comes from the low energy excited state (4T1). The excitation maximum was found to be strongly dependent on pressure. The large red shift of the excitation maximum causes changes in the feeding of 2T1 and 4T1 states, which result in an apparent increase of the radiative rates. Some experimental results on three phthalocyanines are also briefly presented and discussed.

Analysis of the transient EPR signals in the photoexcited triplet state. Application to porphyrin molecules

Anomalous EPR line intensities observed in the photoexcited triplet state of porphyrins at 100°K are discussed. A kinetic model consisting of the singlet ground state and the first excited triplet state is developed. The EPR signal intensities are expressed in terms of the kinetic rate constants and are given as linear combinations of two exponents. With these expressions the transient effects on the line intensities can be explained. Experimental results for two porphyrin molecules H2TPP (tetraphenyl porphyrin free base) and H2(PF)TPP (pentafluorotetraphenyl porphyrin free base) are presented and compared with the theory. From the analysis we evaluated the spin lattice relaxation rate W, the depopulation rate constants kp and the ratio between the population rate constants Ap: For H2TPP, kx =(6±2)×102 sec−1, ky =(3±1)×102 sec−1, kz =(1.5±0.5)×102 sec−1, Ax:Ay:Az≃1:0.6:0.2, and W =3.3×103 sec−1. For H2(PF)TPP, kx =(5±2)×102 sec−1, ky =(1.4±0.4)×102 sec−1, kz =(1.0±0.3)×102 sec−1, Ax:Ay:Az≃1:0.2:0.3, and W =1.7×104 sec−1.