Para-substituted Tetraphenylporphyrin Research Articles

Spectroscopic investigation of the electronic and excited state properties of para-substituted tetraphenyl porphyrins and their electrochemically generated ions

Porphyrins play pivotal roles in many crucial biological processes including photosynthesis. However, there is still a knowledge gap in understanding electronic and excited state implications associated with functionalization of the porphyrin ring system. These effects can have electrochemical and spectroscopic signatures that reveal the complex nature of these somewhat minor substitutions, beyond simple inductive or electronic effect correlations. To obtain a deeper insight into the influences of porphyrin functionalization, four free-base, meso-substituted porphyrins: tetraphenyl porphyrin (TPP), tetra(4-hydroxyphenyl) porphyrin (THPP), tetra(4-carboxyphenyl) porphyrin (TCPP), and tetra(4-nitrophenyl) porphyrin (TNPP), were synthesized, characterized, and investigated. The influence of various substituents, (-hydroxy,-carboxy, and -nitro) in the para position of the meso-substituted phenyl moieties were evaluated by spectroelectrochemical techniques (absorption and fluorescence), femtosecond transient absorption spectroscopy, cyclic and differential pulse voltammetry, ultraviolet photoelectron spectroscopy (UPS), and time-dependent density functional theory (TD-DFT). Spectral features were evaluated for the neutral porphyrins and differences observed among the various porphyrins were further explained using rendered frontier molecular orbitals pertaining to the relevant transitions. Electrochemically generated anionic and cationic porphyrin species indicate similar absorbance spectroscopic signatures attributed to a red-shift in the Soret band. Emissive behavior reveals the emergence of one new fluorescence decay pathway for the ionic porphyrin, distinct from the neutral macrocycle. Femtosecond transient absorption spectroscopy analysis provided further analysis of the implications on the excited-state as a function of the para substituent of the free-base meso-substituted tetraphenyl porphyrins. Herein, we provide an in-depth and comprehensive analysis of the electronic and excited state effects associated with systematically varying the induced dipole at the methine bridge of the free-base porphyrin macrocycle and the spectroscopic signatures related to the neutral, anionic, and cationic species of these porphyrins.

Basicity of para-substituted tetraphenylporphyrins studied by two-phase spectropotentiometric titration

The basicity constants of a series of para-substituted tetraphenylporphyrins have been determined by two-phase spectrophotometric titration with pH monitoring in the chloroform-aqueous electrolyte solution system; the pH ranges of prevailing of the dication and the neutral forms of the porphyrins have been estimated. With introducing the donor substituents at the para-position of phenyl fragments of porphyrins, the compound basicity increases. Ionization constant of the pyrrole nitrogen atoms depends on the donor-acceptor properties of the substituents according to the Hammett equation. Basing on the derived dependence, theoretical basicity constants of the para-substituted porphyrins bearing strongly donor groups have been predicted.

Synthesis, Spectroscopic, and Biological Studies on New Zirconium(IV) Porphyrins with Axial Ligand

A series of parasubstituted tetraphenylporphyrin zirconium(IV) salicylate complexes (SA/5-SSAZr(IV)RTPP, R = p-H, p-CH3, p-NO2, p-Cl, SA = salicylate, and 5-SSA = 5-sulfosalicylate) have been synthesized, and the spectral properties of free base porphyrins, their corresponding metallated, and axially ligated zirconium(IV) porphyrin compounds were compared with each other. A detailed analysis of ultraviolet-visible (UV-vis), proton nulcear magnetic resonance (1H NMR) spectroscopy, infrared (IR) spectroscopy, and elemental analysis suggested the transformation from free base porphyrins to zirconium(IV) porphyrins. The ability of the metal in this complex for extra coordination of solvent molecules was confirmed by ESI-MS spectra. Besides the fluorescence, cyclic voltammetry, and thermogravimetric studies, the complexes were also screened for antimicrobial and anticancer activities. Among all the complexes, 5-SSAZr(p-NO2TPP) shows high antibacterial activity.

Dioxygen reduction catalyzed by substituted iron tetraphenylporphyrins in acidic media

Five iron tetraphenylporphyrins including the (TPP)FeCl and its derivatives which contain electron-withdrawing or electron-donating substituents on the meso-phenyl rings of the porphyrin macrocycle were examined as catalysts for the electoreduction of dioxygen in 1.0 M HClO4. The investigated compounds are represented as ( T p RPP ) FeCl , where T p RPP is the dianion of the para-substituted tetraphenylporphyrin and R = NEt2, OMe , H , Br or CF3. Cyclic voltammetry and linear sweep voltammetry at a rotating disk electrode (RDE) or a rotating ring disk electrode (RRDE) were utilized to examine the catalytic activity of the compounds. The number of electrons transferred and the percentage of H2O2produced as the product of O2electroreduction were calculated. The investigated iron porphyrins containing electron-withdrawing substituents ( R = Br and CF3) were shown to be more efficient catalysts for O2reduction than the compounds having electron-donating groups ( R = NEt2and OMe ) on the four phenyl rings of the porphyrin macrocycle.

NMR Studies into the Potential Interactions of Fullerene C60 with Tetraphenylporphyrin and Some of Its Derivatives

1H NMR relaxation studies were employed to investigate potential interactions between C60 and tetraphenylporphyrin, H2[TPP], and parasubstituted tetraphenylporphyrins, H2[(p-X)4TPP], where X = CN and OCH3 in solution. The substituted porphyrins provided a means by which to investigate the role that electronic effects play in the interaction process. A comparison of the relaxation rates, R1, and correlation times, τC, of the pyrrole and phenyl hydrogens in these complexes, without and with the presence of C60, revealed that the introduction of C60 into solution did not have a noticeable effect on R1 and τC of these protons in H2[TPP], indicating the absence of long-term intermolecular interaction at either of these two sites. A similar analysis of the two protons in the other two substituted tetraphenylporphyrin analogs revealed slower molecular dynamics indicating the presence of intermolecular interactions. Stronger interactions were observed in H2[(p-OCH3)4TPP] indicating that the electron-donating abilities of the -OCH3 group promote the interaction process. Our results indicate that it is very likely that enhanced selectivity in the chemical purifications of fullerenes and metallofullerenes can be achieved by employing tetraphenylporphyrin-silica stationary phases which have been modified with electron-donating groups.

Supramolecular selectivity of [60]-fullerene among equivalently photoactive porphyrins

The photophysical investigation of different para-substituted tetraphenylporphyrins (TP), viz., meso-tetra(4′-hydroxyphenyl)-21H-23H-porphyrin( 1), meso-tetrakis(4′-hex-5-enyloxyphenyl)-21H-23H-porphyrin( 2), m eso-tetrakis(4′-oct-7-enyloxyphenyl)-21H-23H-porphyrin( 3) and meso-tetrakis(4′-undecyloxyphenyl)-21H-23H-porphyrin ( 4) revealed that except for quantum yield (φ) the para-substitution has little effect on any other photophysical properties like lifetime, excitation, emission wavelength, etc. The host–guest type interactions of these tetraarylporphyrins (TP 1– 4), with [60]-fullerene ( F) have been studied with 1H NMR and fluorescence spectrometric techniques in carbon tetrachloride medium. Fluorescence studies revealed that the Q band of the TPs was sufficiently quenched upon addition of F. All the fullerene/porphyrin systems were found to produce stable complexes with 1:1 stoichiometry. Binding constants ( K) of all the fullerene/porphyrin complexes have been determined by fluorescence quenching method. The association constant values for 1/ F have been determined from plots of the Stern–Volmer equation (103.713×10 4) and the Benesi–Hildebrand equation (110.440×10 4). It has been observed that the insertion of long chain oxo-alkenyl/alkyl group in the para position of TPs in 2, 3 and 4 diminished the K values for F by two, four and even ten times with respect to that of 1. The observed trend in variation of the binding constants was supported by a gradual variation in the shift of 1H NMR signal when measurements were carried out in CDCl 3.

The electronic effect in supramolecular self-assembly of para-substituted tetraphenylporphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) by coordinative bonding

The supramolecular self-assembly of para-substituted tetraphenylporphyrin complexes of zinc(II), Zn(p-X)TPP, with imidazolyl-linked porphyrinatomanganese(III), Mn(p-lmBPTPP)Cl, driven by coordinative bonding has been investigated by fluorescence spectra, electrospray mass spectrometry, 1H-n.m.r. and u.v.–vis. spectra. The association constants of the supramolecular complexes, Kc, were calculated using fluorescence spectroscopic titration data at suitable dilute concentration ranges in which the fluorescent quenching of Zn(p-X)TPP by Mn(p-ImBPTPP)Cl is a static process. The electronic effect in the supramolecular self-assembly of para-substituted . porphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) is discussed. The non-linear dependence of log Kc on the Hammett constants was found, which suggested that the electronic effect in para-substituents of tetraphenylporphyrin complexes of zinc(II) is an important, but not a sole factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes. The results indicate that the closed conformation of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complex is another important factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes.

Platinum(IV) tetraphenylporphyrin dibromide complexes: synthesis, characterization, and electrochemistry

Platinum(IV) porphyrins of the type [Pt IV( p-X) 4TPP]Br 2 where ( p-X) 4TPP is a para-substituted tetraphenylporphyrin have been synthesized by direct oxidation of their Pt(II) precursors with Br 2. Both the Pt(II) and Pt(IV) complexes have been characterized by visible and 1H NMR spectroscopy and their electrochemical properties. In both the oxidation and reduction processes, a substituent effect is evident, and the reduction of Pt IV→Pt II is identified. The oxidation and reduction potentials of the [Pt IV( p-X) 4TPP]Br 2 complexes are compared to those of the [Pt II( p-X) 4TPP] precursors and [Pt IV( p-X) 4TPP]Cl 2 analogs. Addition of I 2 or I − to Pt(II) porphyrins does not result in oxidative-addition to form Pt(IV) porphyrins. Instead, the addition of I − to [Pt IV( p-X) 4TPP]Br 2 results in the reduction of the platinum to form the corresponding [Pt II( p-X) 4TPP)].

Microscale Synthesis and 1H NMR Analysis of Tetraphenylporphyrins

The synthesis of tetraphenylporphyrin, H2[TPP], and para-substituted tetraphenylporphyrins, H2[(p-X)4TPP], where X = CN, CH3, and OCH3, is easily accomplished using microscale glassware. The compou...

Mössbauer and visible spectra of iron(III) complexes of para-substituted tetraphenylporphyrins—electronic effects of substituents and axial ligands—

Mössbauer and visible spectra of iron(III) complexes of para-substituted tetraphenylporphyrins—electronic effects of substituents and axial ligands—

Platinum(II) and platinum(IV) porphyrin complexes: synthesis, characterization, and electrochemistry

Platinum(IV) porphyrins of the type [ Pt IV ( p- X) 4 TPP] Cl 2 is a para-substituted tetraphenylporphyrin have been synthesized by the direct oxidation of their Pt II precursors with Cl 2. Both the Pt II and Pt IV complexes have been characterized by visible and 1H NMR spectroscopy and their electrochemical properties. The Soret, α and β bands of the visible spectra are shifted to longer wavelengths upon oxidation of the Pt II. All 1H resonances experience a downfield shift upon oxidation of the Pt II to Pt IV. Each [ Pt II ( p- X) 4 TPP] complex shows two oxidations and two reductions and their potentials are dependent upon the X substituent on the porphyrin ring. In general, the [ Pt IV ( p- X) 4 TPP] Cl 2 complexes show a similar oxidation and reduction pattern and a substituent effect is evident. There is an additional reduction that can be attributed to Pt IV → Pt II.

Comparative study of Mössbauer spectra of iron(III) complexes of para-substituted tetraphenylporphyrins. Electronic effects of substituents and axial ligands

The Mossbauer spectra of high-spin iron(III) complexes of tetra-para-substituted derivatives of 5,10,15,20-tetraphenylporphyrin [FeL(X)](R = OMe, H, F or Cl; X = Cl, Br or I), have been compared with each other to clarify the electronic effects of the phenyl substituents and the axial ligands. They show a variety of patterns depending on the temperature: asymmetric broadening of the high-velocity line at higher temperatures, a symmetric doublet at a temperature Tr, and reversal in asymmetry below Tr. The temperature dependence results from the temperature-dependent spin–spin relaxation of high-spin iron(III) ion and the off-diagonal terms of the hyperfine operator, and reflects the ionic zero-field splitting. The reversal temperature, Tr, and the quadrupole splitting, ΔEQ, show two kinds of dependence on R. This is explained by considering the σ- and π-bonding characteristics of the porphyrins under the influence of the substituents. With a given R, the values of both Tr and ΔEQ increase in the order X = Cl < Br < I. This is interpreted as due to the predominantly ionic character of the bond between the halide and iron ions, except for R = OMe.

Kinetics of C–H bond and alkene oxidation by trans-dioxoruthenium(VI) porphyrins

A. Series of [RuVILO2] complexes (H2L =Para-substituted tetraphenylporphyrins) have been synthesised and characterized, and the kinetics and mechanism of oxidation of the C–H bond and alkenes investigated. The complexes were selective towards tertiary C–H bonds in saturated alkanes but were almost inactive towards secondary C–H bonds. However, they were reactive towards aromatic hydrocarbons and the second-order rate constants (k2) for the oxidation of ethylbenzene and cumene by [Ru(tpp)O2](tpp = 5, 10, 15, 20-tetraphenylporphyrinate) were 2.21 × 10–4 and 3.16 × 10–4dm3 mol–1 s–1 respectively. A kinetic isotope effect (KH/KD) of 11.7 was found for the allylic oxidation of cyclohexene by [Ru(tpp)O2]. The major organic products of the oxidation of alkenes in CH2Cl2–MeOH mixtures were epoxides and [Ru(tpp)O2] gave a monomeric product formulated as [RuIV(tpp)O]·EtOH. or [RuIV(tpp)(OH)2·]EtOH. Similar reactions with [RuVI(oep)O2](oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate) gave [{RuVI(oep)(OH)}2O] in non-co-ordinating solvents. The observed rate law for alkene oxidation was rate =K2[RuVI][alkene]. There exists an almost linerar free-energy relationship between log k2 and E½(one-electron oxidation potentials of alkenes) with slope =–1.1 V–1 for the [Ru(tpp)O2] system. Activation parameters have been determined for the oxidation of styrene, norbornene and cyclooctene by [RuVILO2]. Non-linear and U-shaped Hammett plots were observed for the oxidation of substituted styrenes. The mechanism of alkene oxidation is proposed to involve a continum of transition states, the structures of which may change and be stabilized by defferent substituents.

Infrared studies of symmetrically and asymmetrically substituted tetrapyrrolic macrocycles: Free bases and indium derivatives

The infrared spectra of symmetrically and asymmetrically para-substituted tetraphenylporphyrins as well as their indium complexes and their aminoacid ethyl ester derivatives have been investigated and the assignment of absorption bands to characteristic vibrational modes has been proposed.

Reactions of ruthenium(II) para-substituted tetraphenylporphyrin complexes with carbon monoxide oxygen: A kinetic investigation

The reaction of Ru(XTPP)(DMF) 2, where XTPP is the dianion of para substituted tetraphenylporphyrins and X is MeO, Me, H, Cl, Br, I, F, with O 2 and CO were studied in DMF. The process was found to be first-order in metalloporphyrin, first-order in molecular oxygen and carbon monoxide, and second-order overall. Second-order rate constants for the CO reaction ranged from 0.170 to 0.665 M −1 s −1 at 25°C, those for the O 2 reaction from 0.132 to 0.840 M −1 s −1 at 25°C. Similar activation parameters (ΔH CO ± = 87 ± 1 kJ mol −1, ΔS CO ± = 22 ± 4 JK −1 mol −1; ΔH O 2 ± = 81 ± 1 kJ mol −1, and ΔS O 2 ± = 11 ± 5 JK −1 mol −1) were found within each series. Reactivities of X substituted metalloporphyrins were found to follow different Hammett σ functions. The CO reactions correlated with σ ϱ following normal behavior; the O 2 reactions correlated with σ 8 ° indicating O 2 is π-bonded in the transition states. A dissociative mechanism is postulated for the process.

Substituent effects on the redox reactions of para-substituted tetraphenylporphyrin complexes of ruthenium(II)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSubstituent effects on the redox reactions of para-substituted tetraphenylporphyrin complexes of ruthenium(II)T. Malinski, D. Chang, L. A. Bottomley, and K. M. KadishCite this: Inorg. Chem. 1982, 21, 12, 4248–4253Publication Date (Print):December 1, 1982Publication History Published online1 May 2002Published inissue 1 December 1982https://doi.org/10.1021/ic00142a028RIGHTS & PERMISSIONSArticle Views133Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (751 KB) Get e-Alerts Get e-Alerts

SUBSTITUENT EFFECTS ON THE PHOTOCURRENT QUANTUM YIELDS OF PARA-SUBSTITUTED TETRAPHENYLPORPHYRINS

Abstract The photocurrent quantum yields of para-substituted tetraphenylporphyrins were found to be increased by electron-donating groups. Semi-logarithmic plots of the quantum yields vs. the half-wave potentials for the first ring oxidations of the porphyrins or the Hammett σ of substituents yielded a linear relationship.

Spectrophotometric Study on the Complex Formation of Hydroperoxide with Tetraphenylporphyrin Cobalt(II)

Abstract The rate constants, activation energies, activation entropies and equilibrium constants for the coordination of 1,2,3,4-tetrahydro-1-naphthyl hydroperoxide (THP), 1-methyl-1-phenylethyl hydroperoxide (CHP) and t-butyl hydroperoxide (BHP) to para-substituted tetraphenylporphyrin Co(II), Co(p-X)TPP (X=OCH3, H, Cl) were obtained by the visible spectral method at 235–245 K. The rate constants of coordination were k=0.097–2.03×102 M−1 s−1, the equilibrium constants being K=0.692–2.5×10−6 M−1. As a para-substituent effect on k and K, the constants were found to increase with increase in the electron donating property of the substituent group. They also depend on the kind of hydroperoxide, the rate constants decreasing in the order kTHP&amp;gt;kCHP&amp;gt;kBKP, and the equilibrium constants in the order KCHP&amp;gt;KBHP&amp;gt;KTHP. Activation energies were 7.0—7.8 kcal mol−1 and activation entropies −21–−25 cal K−1. No spectral change by the addition of hydroperoxide to CuTPP and NiTPP was observed.

Effect of para substituent on rates of phenyl ring rotation in gallium complexes of para-substituted tetraphenylporphyrins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of para substituent on rates of phenyl ring rotation in gallium complexes of para-substituted tetraphenylporphyrinsS. S. Eaton, D. M. Fishwild, and G. R. EatonCite this: Inorg. Chem. 1978, 17, 6, 1542–1545Publication Date (Print):June 1, 1978Publication History Published online1 May 2002Published inissue 1 June 1978https://doi.org/10.1021/ic50184a031RIGHTS & PERMISSIONSArticle Views139Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (563 KB) Get e-Alerts Get e-Alerts

Effects of para substituent and metal ion on rates of phenyl ring rotation in ruthenium, indium, and titanium complexes of para-substituted tetraphenylporphyrins.

Effects of para substituent and metal ion on rates of phenyl ring rotation in ruthenium, indium, and titanium complexes of para-substituted tetraphenylporphyrins.