Metal assembly in novel dendrimers with porphyrin cores

A series of phenylazozmethine (DPA) dendrimers with a porphyrin core (PnH2) were synthesized by dehydration using TiCl4 from meso-tetrakis(4-aminophenyl)porphyrin and the DPA dendrons. The addition of SnCl2 to a dichloromethane/acetonitrile solution of dendritic cobalt porphyrin resulted in a stepwise spectral change. By using UV-vis spectroscopy to monitor the complexation of the P4CoIIICl until an equimolar amount of SnCl2 has been added, four changes in the position of the isosbestic point were observed during the addition of SnCl2. Titration results suggest that four different complexes are successively formed upon the SnCl2 addition and that the complexation proceeds in, not a random, but a stepwise fashion from the core imines to the terminal imines of P4CoIIICl. The electrochemical study reveals that their dendrimers with Tb ion act as a multielectron mediator in CO2 reduction at high applied potential on the electrode.     

Spectroscopic detection of excited-state electron transfer in porphyrin viologen systems

Pulsed laser excitation (354.7 nm, 10 ns pulse) of a pyridyltritolylporphyrin chromophore covalently linked to a dibenzylviologen, Bz₂V²⁺, electron acceptor (porphyrin—viologen, PV²⁺) in CH₃CN leads to intramolecular electron transfer quenching of the porphyrin singlet excited state within the laser pulsewidth to reduce the linked Bz₂V²⁺ to Bz₂V^+·. Transient Bz₂V^+· can be detected directly by resonance Raman spectroscopy. The same transient features are obtained from pulsed laser excitation of a mixture of porphyrin (P) and dibenzylviologen in CH₃CN where Bz₂V²⁺ quenches the porphyrin fluorescence, establishing bimolecular excited state electron transfer quenching to yield Bz₂V^+·. Confirmation of our assignment of the transient Bz₂V^+· comes from comparison of the spectra with the resonance Raman spectrum of an authentic sample of Bz₂V^+·, and of electrochemically reduced PV²⁺ which has been spectroscopically confirmed to form PV^+·. Fluorescence lifetime determinations for PV²⁺ and P yield a rate constant for intramolecular electron transfer, k_et = 8 × 10⁷ s⁻¹, consistent with the ability to observe electron transfer within the laser pulsewidth     

Spectroscopic properties and photodynamic effects of new lipophilic porphyrin derivatives: efficacy, localisation and cell death pathways

Photodynamic therapy (PDT) and photodynamic diagnostics (PDD) of cancer are based on the use of non-toxic dyes (photosensitisers) in combination with harmless visible light. This paper reports physicochemical properties, cell uptake, localisation as well as photodynamic efficiency of two novel lipophilic porphyrin derivatives, suitable for use as PDT sensitisers. Both compounds are characterised by high quantum yield of singlet oxygen generation which was measured by time-resolved phosphorescence. Photodynamic in vitro studies were conducted on three cancer cell lines. Results of cell survival tests showed negligible dark cytotoxicity but high phototoxicity. The results also indicate that cell death is dependent on energy dose and time following light exposure. Using confocal laser scanning microscopy both compounds were found to localise in the cytoplasm around the nucleus of the tumour cells. The mode of cell death was evaluated based on the morphological changes after differential staining. In summary, good photostability, high quantum yield of singlet oxygen and biological effectiveness indicate that the examined lipophilic porphyrin derivatives offer quite interesting prospects of photodynamic therapy application.     

Photophysical properties of porphyrin tapes

The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials.     

Neocuproine-extended porphyrin coordination complexes. 2. Spectroscopic properties of the metalloporphyrin derivatives and investigations into the HOMO ordering

The synthesis of a porphyrin compound, 1, containing a 2,9-dimethyl-1,10-phenanthroline moiety that is fused at the beta-pyrrole positions is reported. The absorption spectra of the free-base, copper(II), and zinc(II) derivatives have been studied. On the basis of absorption band intensities, the HOMO of the free base (H21) and its copper and zinc complexes (Cu1 and Zn1) was determined to be of a1u symmetry. Relative to H21, compounds Cul and Znl show enhanced spectral changes upon external metal ion binding. Although the HOMO is the same in all three compounds, the energy gap between the two highest occupied orbitals is greater for Cu1 and Zn1 than it is for the free-base compound. Several metal ions (Ni2+, Cu+, Cu2+, Zn2+, Li+) were examined in their binding to the phenanthrolinic group by measuring the resulting changes in the absorption spectra. It is shown that the observed changes in the absorption spectra are insensitive to the nature of the metal ion coordinated by the phenanthroline moiety. Significant differences in the absorption and emission spectra between Zn1 and [Zn(Zn1)2]2+ clearly demonstrate that the porphyrin pi-system is strongly affected by the binding of metal ions at the fused phenanthrolinic moiety.     

Dendrimers made of porphyrin cores and carbazole chromophores as peripheral units. Absorption spectra, luminescence properties, and oxidation behavior

Luminescent and redox-active porphyrin-based dendrimers of first and second generation have been synthesized, and their absorption spectra, photophysical properties, and oxidation behavior have been investigated, together with those of the corresponding aldehyde carbazole precursors. All the dendrimers contain a porphyrin core and carbazole-based chromophores as branches. The structural formulas of the new species are represented in Figures 1 and 2, with the corresponding schematizations. The absorption spectra of the aldehyde carbazole precursors A1-A6 in dichloromethane exhibit intense transitions in the UV region, centered on the carbazole and benzaldehyde subunits. The lowest-energy absorption bands receive contribution from charge-transfer transitions. Compounds A1-A6 are luminescent at room temperature in fluid solution; such a luminescence is attributed to twisted intramolecular charge-transfer excited states. The luminescence at 77 K in a rigid matrix is blue-shifted with respect to room-temperature emission and is assigned to locally excited states. Absorption spectra of the porphyrin-cored dendrimers P1-P6 appear additive as they are constituted by visible bands due to porphyrin absorption and bands in the UV region due to transitions centered on the carbazole-based branches. Emission spectra of P1-P6 both at 77 K and at room temperature are typical of porphyrin species and independent of excitation wavelength, indicating that the light collected by the peripheral chromophores is quantitatively transferred to the core. All the compounds exhibit a rich oxidation behavior in 1,2-dichloroethane solution, with reversible processes centered on the different carbazole subunits. Interaction between the different carbazole centers depends on the size of the spacer interposed.     

Metal complexes of a phenol-tailed porphyrin with different hydrogen bonds

Hydrogen bonds are very common and important interactions in biological systems, they are used to control the microenvironment around metal centers. It is a challenge to develop appropriate models for studying hydrogen bonds. We have synthesized two metal complexes of the phenol-tailed porphyrin, [Zn(HL)] and [Fe(HL)(C₆H₄(OH)(O))]. X-ray crystallography reveals that the porphyrin functions as a dianion HL^2? and the phenol OH is involved in hydrogen bonds in both structures. In [Zn(HL)], an intramolecular hydrogen bond is formed between the carbonyl oxygen and OH. In [Fe(HL)(C₆H₄(OH)(O))], the unligated O(5) of the ligand is involved in two hydrogen bonds, as a hydrogen bond donor and a hydrogen bond acceptor. The overall electronic effect on the ligand could be very small, with negligible impact on the structure and the spin state of iron(III). The structural differences caused by the hydrogen bonds are also discussed.     

Excited-state properties of water-soluble porphyrin dimers

The excited-state properties of heterodimers oftetra(4-carboxyphenyl)porphyrin (TPPC) and tetra(N-methylpyridyl) porphyrin (TMPyP) are studied by absorption and emission spectroscopy, EPR and zero-field ODMR. The excited singlet and triplet states of dimers formed by pairing H₂TPPC with H₂TMPyP or ZnTMPyP are localized on H₂TPPC. The dimers formed by pairing H₂TPPC with CuTMPyP and H₂TMPyP with ZnTPPC or CuTPPC are non-fluorescent due to intramolecular electron transfer.     

Synthesis of covalently linked unsymmetrical porphyrin pentads containing three different porphyrin subunits

The tetrafunctionalized AB3-type porphyrin building blocks containing two different types of functional groups with N4, N3O, N3S, and N2S2 porphyrin cores were synthesized by following various synthetic routes. The AB3-type tetrafunctionalized N4 porphyrin building block was synthesized by a mixed condensation approach, the N3S and N3O porphyrin building blocks by a mono-ol method, and N2S2 porphyrin building block by an unsymmetrical diol method. The tetrafunctionalized porphyrin building blocks were used to synthesize monofunctionalized porphyrin tetrads containing two different types of porphyrin subunits by coupling of 1 equiv of tetrafunctionalized N4, N3O, N3S, and N2S2 porphyrin building block with 3 equiv of monofunctionalized ZnN4 porphyrin building block under mild copper-free Pd(0) coupling conditions. The monofunctionalized porphyrin tetrads were used further to synthesize unsymmetrical porphyrin pentads containing three different types of porphyrin subunits by coupling 1 equiv of monofunctionalized porphyrin tetrad with 1 equiv of monofunctionalized N2S2 porphyrin building blocks under the same mild Pd(0) coupling conditions. The NMR, absorption, and electrochemical studies on porphyrin tetrads and porphyrin pentads indicated that the monomeric porphyrin subunits in tetrads and pentads retain their individual characteristic features and exhibit weak interaction among the porphyrin subunits. The steady state and time-resolved fluorescence studies support an efficient energy transfer from donor porphyrin subunit to acceptor porphyrin subunit in unsymmetrical porphyrin tetrads and porphyrin pentads.     

The tumour-localizing properties of porphyrin derivatives

The tumour-localizing abilities of various kinds of porphyrin derivatives in tumour-bearing hamsters were assessed by nitrogen-pulsed laser spectrofluorometry (N2-PLS). On examination of porphine derivatives (from haemoglobin), it was found that the dimer and acetylated and amidated compounds had a high affinity for tumour tissue; the dimer and hydroxylated compound of phorbine derivatives (from chlorophyll) also showed a high affinity. Furthermore, of the metalloporphines (gallium, zinc and indium complexes), those which contained hydrophilic groups showed a high affinity for tumour tissue; of the metallophorbines (gallium, zinc and indium complexes), those which contained hydrophobic groups showed a high affinity. A correlation was found between the side-chain structure of the porphyrins and metalloporphyrins and their affinity for tumour tissue.     

Spectroscopic and optical characterization of porphyrin chromophores incorporated into ultrathin polyimide films

Polyamic acid (PAA) containing free-base porphyrin and zinc(II) porphyrin chromophores was synthesized by copolymerization of diphenylether-type tetracarboxylic dianhydride and diamines. The monolayer of the alkylamine salts of PAA (PAASs) at the air/water interface was deposited on solid substrates by the Langmuir-Blodgett (LB) technique. The PAAS LB films thus obtained were converted to polyimide (PI) LB films by chemical treatment. The fluorescence of porphyrin moieties in the PI LB film was observed, because of the weak electron-accepting properties of the diphenylether unit. Therefore, the photophysically important processes, such as photoinduced electron transfer, excitation energy transfer, and excitation energy migration could be investigated in relation to the layered nanostructures of the ultrathin PI films. The fluorescence spectrum suggested that the aggregation of porphyrin moieties in the PI LB films was effectively prevented by the use of polymeric films. The surface plasmon (SP) measurement showed that the thickness of the monolayers was 0.9-1.0 nm for PAAS films and 0.32-0.40 nm on average for PI LB films. The absorption dichroism of the Soret band of porphyrin indicated that porphyrin moieties in the PAAS and PI LB films are oriented in parallel with the substrate. These results showed that the orientation and the spatial distribution of porphyrin units can be efficiently regulated in the PI LB films in a nanometer dimension.     

Spectroscopic investigation and molecular modeling on porphyrin/PAMAM supramolecular adduct

Noncovalent adducts (TPPC@PAMAM) between meso-tetrakis(4-carboxyphenyl)porphyrin (TPPC) and polyamidoamine PAMAM dendrimer (generation 2.0) have been obtained by simply mixing the two components at different stoichiometric amount. The resulting species are readily soluble and stable in aqueous solution up to millimolar concentration. Electrostatic interactions between the anionic carboxylate groups of TPPC and the protonated amino groups of the PAMAM dendrimer play an important role in the stabilization of these adducts. UV/Vis absorption, steady state and time-resolved fluorescence emission and anisotropy measurements suggest the presence of equilibria involving different species as function of the [PAMAM]/[TPPC] ratio. At low ratios the observed spectroscopic behavior evidence the presence of H-aggregates, while at higher ratios well-defined species containing monomeric TPPC strongly interacting with the charged dendrimer are formed. Docking of the binary supramolecular adduct further supports the experimental results showing a favorable interaction with the porphyrin being completely included in the dendrimer. The interaction of the binary TPPC@PAMAM adduct (1/1 ratio) with calf-thymus DNA has been investigated through spectroscopic and photophysical techniques. All the experimental results point to the formation of a ternary complex between the binary adduct and the DNA backbone.     

Synthesis of covalently linked linear porphyrin triad and tetrad containing different porphyrin sub-units

Covalently linked diarylethyne bridged unsymmetrical porphyrin triad containing ZnN₄, N₄, and N₂S₂ porphyrin sub-units and porphyrin tetrad containing ZnN₄, N₄, N₃S, and N₂S₂ porphyrin sub-units were synthesized over sequence of Pd(0) mediated coupling reactions. The triad and tetrad are freely soluble in all common organic solvents and characterized by ES-MS, NMR, absorption, fluorescence, and electrochemical techniques. The ¹H NMR, absorption, and electrochemical studies indicated a weak interaction between the porphyrin sub-units of porphyrin triad and porphyrin tetrad. The steady state and time-resolved fluorescence studies supported an energy transfer from one end of porphyrin array to the other end. This kind of porphyrin arrays containing different porphyrin sub-units will be useful for molecular electronics applications.     

Synthesis and photophysical properties of triphenylamine-based dendrimers with 1,3,5-triphenylbenzene cores

Two new conjugated dendrimers bearing a triphenylamine moiety as dendrons and 1,3,5-triphenylbenzene as a core have been synthesized through a convergent synthetic strategy. These conjugated dendrimers have high fluorescence quantum yields and exhibit similar absorption and emission behaviors in solutions and in solid films, which demonstrate that these dendrimers form good amorphous states.     

Unusual optical properties of porphyrin fractal J-aggregates

A simple mix and shake procedure in aqueous solution from water-soluble tetrakis(4-sulfonatophenyl)porphyrin and spermine leads to fractal non-covalent supramolecular systems which exhibit unusual large enhancement of resonant light scattering, behaving as metal particles.     

Synthesis and properties of hybrid porphyrin tapes

Hybrid porphyrin tapes 3 and 4 , consisting of a mixture of 3,5‐di‐tert‐butylphenyl‐substituted donor‐type Zn^II–porphyrins and pentafluorophenyl‐substituted acceptor‐type Zn^II–porphyrins, were prepared by a synthetic route involving cross‐condensation reaction of a Ni^II–porphyrinyldipyrromethane and pentafluorophenyldipyrromethane with pentafluorobenzaldehyde followed by appropriate demetalation, remetalation, and oxidative ring‐closure reaction. The Ni^II‐substituted porphyrin tapes 5 (Ni‐Zn‐Ni) and 6 (Ni‐H₂‐Ni) were also prepared through similar routes. The hybrid porphyrin tapes 3 and 4 are more soluble and more stable than normal porphyrin tapes 1 and 2 consisting of only donor‐type Zn^II–porphyrins. The solid‐state and crystal packing structures of 3 , 4 , and 5 were elucidated by single‐crystal X‐ray diffraction analysis. Singly meso–meso‐linked hybrid porphyrin arrays 12 and 14 exhibit redox potentials that roughly correspond to each constituent porphyrin segments, while the redox potentials of the hybrid porphyrin tapes 3 and 4 are positively shifted as a whole. The two‐photon absorption (TPA) values of 1–6 were measured by using a wavelength‐scanning open aperture Z‐scan method and found to be 1900, 21 000, 2200, 27 000, 24 000, and 26 000 GM, respectively. These results illustrate an important effect of elongation of π‐electron conjugation for the enhancement of TPA values. The hybrid porphyrin tapes show slightly larger TPA values than the parent ones.     

Synthesis and different substituent effects on spectral and electrochemical properties of porphyrin nicotinic acid binary compounds

The porphyrin nicotinic acid binary compounds with different substituents in porphine rings (5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-triphenylporhyrin 2a, 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-chlorophenyl)porphyrin 2b and 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-methoxyphenyl)porphyrin 2c) were synthesized. All of them have been characterized, assigned and analyzed by UV–vis, IR, MS and ¹H NMR spectra. Their electrochemical and spectroscopic properties were studied by using cyclic voltammetry, fluorescence spectra and Resonance Raman spectra. Different substituents have a little influence on electrochemical behavior and fluorescence spectra. In the Resonance Raman spectra, the substituent has little influence on the skeleton vibration of porphyrin and has much influence on the vibration of phenyl.     

Electronic,optical, and charge transfer properties of porphyrin and metallated porphyrins in different media

Porphyrin and M-Porphyrin (M = Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) complexes were designed to examine their organic light-emitting diode (OLED) properties. All calculations were performed in different media, which are gas, benzene, DMSO, and water phases. The calculations of both porphyrin and its metal complexes as a monomer form were performed at B3LYP/6-31G(d) level by using the Gaussian 16 and GaussView 6 package programs. On the other hand, emission calculations for the monomer form and dimer form computations of the studied compounds were carried out at PBE0/TZP and B3LYP/TZP levels, respectively, by using Amsterdam density functional (ADF) 2019 package program. The OLED tensors of the mentioned molecules, which are emission energies, reorganization energies (λ_e and λ_h), the ionization potentials and the electron affinities (adiabatic and vertical), the effective transfer integrals (V_e and V_h), and the charge transfer rates (W_e and W_h), were calculated to evaluate the OLED behaviors and determine the best OLED structure.     

Spectroscopic studies of water-soluble superstructured iron(III) porphyrin. Interaction with the bovine serum albumin protein

Abstract

Acid-base equilibrium of the “one-face”-hindered sulfonated porphyrin, α5,15-[2,2′(dodecamethyleneoxy),(5-sulfonato)diphenyl]-10,20-bis(2-hydroxy,5-sulfonatophenyl)porphyrinato iron(III), has been studied by paramagnetic ¹H NMR. The isotropically shifted signals change in a fast exchange regime on the NMR time-scale. ¹H longitudinal relaxation times and temperature dependence of the chemical shifts were measured and analyzed. The electronic structure of hydroxo specie is characteristic of a six- or five-coordinate high-spin iron(III) porphyrin with an S = 5/2 ground state. The ¹H NMR titration allowed determination of the acidity constant, pK_a 6.2 (0.1 M KNO₃, 25 °C). In addition, we also report the interaction between the monohydroxo iron(III) porphyrin and the bovine serum albumin protein. From a ¹H NMR titration, we have determined the affinity apparent constant, log K_ap 3.2 (pH 7, KNO₃ 0.1 M, 25 °C). The formation of superstructured iron porphyrin-albumin protein adduct was confirmed by electronic absorption spectroscopy and electron paramagnetic resonance.