Parent Porphyrin Research Articles

Synthesis and in vitro photobiological studies of porphyrin capped gold nanoparticles $$^{\S }$$ §

We describe the synthesis and characterization of a thiol-functionalized porphyrin derivative 2 and its gold nanoparticle conjugates. The porphyrin 2 exhibited its characteristic intense Soret absorption at 420 nm with a molar extinction coefficient value of $$3.6\times 10^{5}\, \hbox {M}^{-1}\, \hbox {cm}^{-1}$$ and good fluorescence in the region of 650–660 nm. The porphyrin-capped gold nanoparticles (POPNPs) were synthesized from the citrate-capped gold nanoparticles by the ligand exchange method and characterized by spectroscopic and morphological analyses (UV–Vis, DLS and TEM). The broadening of the absorption spectrum and quenching of the fluorescence intensity for the porphyrin gold nanoconjugates suggest efficient incorporation of the porphyrin moiety onto the gold surface. The results of DLS and TEM analyses indicate that the nanoconjugate POPNPs are uniformly spherical in shape with a size of ca. $$25 \pm 5\, \hbox {nm}$$ and exhibits a negative zeta potential value of $$-\,16.0 \pm 2\, \hbox {mV}$$ . The singlet oxygen generation efficiency of the porphyrin 2 and POPNPs was calculated and are found to be ca. $$0.53 \pm 0.02$$ and $$0.43 \pm 0.03$$ , respectively. The in vitro photobiological studies revealed that POPNPs exhibited enhanced photodynamic activity compared to their parent porphyrin derivative 2 with an $$\hbox {IC}_{50}$$ value of $$5\, \upmu \hbox {M}$$ in MDA MB 231 cell lines. The mechanism of the cell destruction was studied by Annexin-FITC and confirmed through TMRM assay. We observed the increase in the percentage of cell population corresponding to the late apoptotic stage ca. 37.7% and 51.2% for 5 and $$10\, \upmu \hbox {M}$$ of POPNPs, respectively, thereby demonstrating their apoptotic-mediated cell destruction and use in PDT applications. Synopsis We synthesized a thiol-functionalized porphyrin-based sensitizer 2 and its gold nanoparticles (POPNPs) and have investigated their photophysical properties, singlet oxygen generation and in vitro photobiological efficacy. Our results demonstrate that the incorporation of the sensitizer onto the surface of nanoparticles not only improved its solubility in the aqueous medium, photophysical and photobiological properties but also its potential as a novel sensitizer for photodynamic therapeutical applications.

Anionic Effect of δ and χ Forms of Tris(alkoxo) Ligand Functionalized Anderson-Type Polyoxometalates on Nonlinear Optical Response of Porphyrin–POM Based Supramolecular Compounds

The electrostatic interaction of tris(alkoxo) ligand functionalized Anderson-type polyoxometalate (POM for short) anions [XMo6O18{(OCH2)3CNH2}2]3– (where X = Mn or Fe) having δ-type structures and [H2ZnMo6O18{(OCH2)3CNH2}2]2– having χ-type structure with porphyrin-based cation [H2TPP]2+ results in formation of three supramolecular compounds [H2TPP]1.5[MnMo6O18{(OCH2)3CNH2}2] (1), [H2TPP]1.5[FeMo6O18{(OCH2)3CNH2}2]·2C3H7NO (2), and [H2TPP][H2ZnMo6O18{(OCH2)3CNH2}2]·2(C2H5)2O (3). All the supramolecular compounds have significant nonlinear reverse saturated absorption (RSA) and self-defocusing behavior especially the compound 3 has noteworthy improvement of second hyperpolarizability γ value (1.35 × 10–27 esu) compared to parent porphyrin (7.7 × 10–28 esu). Fluorescence is quenched by ca. 74% in compound 3, 37% in compound 1 and 30% in compound 2 compared to that of parent porphyrin, respectively, indicating different quenching effect of the different POM anions. Parallelly, it was found that the three POM anions have different onset reduction potentials due to different central metal atom and overall cluster structure, corresponding to different HOMO–LUMO gaps (Eg) of the resulting supramolecular compounds with Eg (3) <Eg (1) <Eg (2) <Eg (parent porphyrin). Thus, we thought that the easier electronic charge transfer from porphyrin to POM anions by irradiation with laser light plays a key role in the enhancement of nonlinear optical response in supramolecular compounds.

Electron-Deficient Near-Infrared Pt(II) and Pd(II) Benzoporphyrins with Dual Phosphorescence and Unusually Efficient Thermally Activated Delayed Fluorescence: First Demonstration of Simultaneous Oxygen and Temperature Sensing with a Single Emitter.

We report a family of Pt and Pd benzoporphyrin dyes with versatile photophysical properties and easy access from cheap and abundant chemicals. Attaching 4 or 8 alkylsulfone groups onto a meso-tetraphenyltetrabenzoporphyrin (TPTBP) macrocylcle renders the dyes highly soluble in organic solvents, photostable, and electron-deficient with the redox potential raised up to 0.65 V versus the parent porphyrin. The new dyes intensively absorb in the blue (Soret band, 440-480 nm) and in the red (Q-band, 620-650 nm) parts of the electromagnetic spectrum and show bright phosphorescence at room-temperature in the NIR with quantum yields up to 30% in solution. The small singlet-triplet energy gap yields unusually efficient thermally activated delayed fluorescence (TADF) at elevated temperatures in solution and in polymeric matrices with quantum yields as high as 27% at 120 °C, which is remarkable for benzoporphyrins. Apart from oxygen sensing, these properties enable unprecedented simultaneous, self-referenced oxygen and temperature sensing with a single indicator dye: whereas oxygen can be determined either via the decay time of phosphorescence or TADF, the temperature is accessed via the ratio of the two emissions. Moreover, the dyes are efficient sensitizers for triplet-triplet annihilation (TTA)-based upconversion making possible longer sensitization wavelength than the conventional benzoporphyrin complexes. The Pt-octa-sulfone dye also features interesting semireversible transformation in basic media, which generates new NIR absorbing species.

Conformational Landscapes of Metal(II) Porphyrinato, Chlorinato, and Morpholinochlorinato Complexes.

The macrocycle conformation of [meso-tetraarylporphyrinato]metal complexes is metal-dependent. Furthermore, hydroporphyrins and some of their analogues are known to be more conformationally flexible than the parent porphyrins, but the extent to which this is reflected in their metal-dependent conformations was much less studied. meso-Tetraarylmorpholinochlorins are intrinsically nonplanar chlorin analogues in which the five-membered pyrroline moiety was replaced by a six-membered morpholine moiety. The metal complexes (M = Ni2+, Cu2+, Zn2+, Pd2+, Ag2+) of meso-aryl-2,3-dimethoxychlorins and meso-arylmorpholinochlorins were prepared. Their conformations were determined using X-ray crystal structure diffractometry and compared against those of their free bases, as well as against the conformations of the corresponding metalloporphyrins. Out-of-plane displacement plots visualized and quantified the conformational changes upon stepwise conversion of a pyrrole moiety to a dimethoxypyrroline moiety and to a dialkoxymorpholine moiety, respectively. The generally nonplanar macrocycle conformations were found to be central-metal-dependent, with the smaller ions showing more nonplanar conformations and with the metallomorpholinochlorins generally showing a much larger conformational range than the corresponding metallochlorins, which, in turn, were more nonplanar than the corresponding porphyrins. This attests to the larger conformational flexibility of the morpholinochlorin macrocycle compared to that of a chlorin or even a porphyrin macrocycle. The degree of nonplanarity affects the electronic structure of the metal complexes, as can also be seen in a comparison of their UV-vis spectra. We thus further define the conformational and electronic effects governing pyrrole-modified porphyrins.

A synchrotron study of [5,10,15,20-tetrakis(3-cyanophenyl)porphyrinato-κ4N5,N10,N15,N20]copper(II) nitrobenzene trisolvate at 80 K.

Porphyrin assemblies display interesting photophysical properties and a relatively high thermal stability. Moreover, meso-functionalized porphyrins with virtually fourfold symmetry can be relatively readily synthesized from pyrrole and the appropriate aldehyde. A number of metallo derivatives of 5,10,15,20-tetrakis(4-cyanophenyl)porphyrin, where the N atom of the linear cyano group can act both as a donor for coordination bonds or as an acceptor for hydrogen bonds, have been structurally characterized by single-crystal X-ray analysis. The supramolecular and structural chemistry of the corresponding 2- and 3-cyanophenyl isomers of the parent porphyrin, however, has remained largely unexplored. The crystal structure of [5,10,15,20-tetrakis(3-cyanophenyl)porphyrinato]copper(II) (CuTCNPP) nitrobenzene trisolvate, [Cu(C48H24N8)]·3C6H5NO2, has been determined at 80 K by synchrotron single-crystal X-ray diffraction. CuTCNPP exhibits a C2h-symmetric ααββ conformation, despite an unsymmetrical crystal environment, and is situated on a crystallographic centre of symmetry. The CuII ion adopts a genuine square-planar coordination by the four pyrrole N atoms. The 24-membered porphyrin ring system shows no marked deviation from planarity. In the crystal, the CuTCNPP molecules and two nitrobenzene molecules are face-to-face stacked in an alternating fashion, resulting in corrugated layers. The remaining nitrobenzene guest molecule per CuTCNPP resides in the region between four neighbouring columnar stacks of CuTCNPP and sandwiched nitrobenzene molecules, and is disordered over four positions about a centre of symmetry.

Synthesis and characterization of a hydrophilic conjugated 4+4 Re(I)-porphyrin metallacycle

The preparation and the full characterization, including the X-ray structure determination, of a polar trans-dipyridylporphyrin functionalized with two short polyoxyethylene chains is reported. Reaction of the porphyrin with a Re(I) complex yielded a 4+4 metallacycle showing an improved solubility and a lower tendency to aggregate with respect to analogous porphyrin cyclic derivatives. These properties allowed a full NMR characterization of the metallacycle including VT 1H DOSY-NMR experiments and, for the first time, the recording of a 13C-NMR spectrum giving further insight into the structural definition of these type of metallacycles. Spray deposition of the metallacycle on a heated mica substrate shows the formation of regular ring-like nano-structures which are not formed by the parent porphyrin.

Flexible Tuning of Unsaturated β-Substituents on Zn Porphyrins: A Synthetic, Spectroscopic and Computational Study.

A series of zinc porphyrins substituted at adjacent β-positions with a CN group and para-substituted ethenyl/ethynyl-phenyl group have been studied using electronic absorption spectroscopy, resonance Raman spectroscopy and DFT calculations. The oxidative nucleophilic substitution of hydrogen was utilized for the introduction of a cyano substituent on the porphyrin ring. This modification has a remarkable electronic effect on the ring. The resulting porphyrin cyanoaldehyde was further modified in Wittig condensations to give series of arylalkene- and arylalkyne-substituted derivatives. This substitution pattern caused significant redshifting and broadening of the B band, tuning from 433-446 nm. Additionally the Q/B band intensity ratios show much higher values than observed for the parent porphyrin ZnTPP (0.20 vs. 0.03). Careful analysis of the electronic transitions using DFT and resonance Raman spectroscopy reveal that the substituent does not significantly perturb the electronic structure of the porphyrin core, which is still well described by Gouterman's four-orbital model. However, the substituents do play a role in elongating the conjugation length and this results in the observed spectral changes.

Corroles-porphyrins: a teamwork for gas sensor arrays.

Porphyrins provide an excellent material for chemical sensors, and they have been used for sensing species both in air and solution. In the gas phase, the broad selectivity of porphyrins is largely dependant on molecular features, such as the metal ion complexed at the core of the aromatic ring and the peripheral substituents. Although these features have been largely exploited to design gas sensor arrays, so far, little attention has been devoted to modify the sensing properties of these macrocycles by variation of the molecular aromatic ring. In this paper, the gas sensing properties of a porphyrin analog, the corrole, are studied in comparison with those of the parent porphyrin. Results show that changes in the aromatic ring have important consequences on the sensitivity and selectivity of the sensors and that porphyrins and corroles can positively cooperate to enhance the performance of sensor arrays.

Photophysical properties of Sn(IV)tetraphenylporphyrin-pyrene dyad with a β-vinyl linker

A Sn (IV)tetraphenylporphyrin (T) has been functionalized with a β-vinyl pyrene (P) and the photophysical properties of the formed dyad (T-P) with its corresponding precursors were studied in three solvents with different polarities using steady-state and time-resolved measurements in ps and fs timescales. When the pyrene moiety is excited at λex = 340 nm, the fluorescence spectroscopy experiments indicate in all the studied solvents, an efficient quenching of the pyrene emission. When excited at either λex = 340 nm or λex = 405 nm, where porphyrin absorbs, a new emissive excited state complex (T-P)* is observed at wavelenghts close to the parent porphyrin emission. The emission is more pronounced in nonpolar hexane showing a mono-exponential decay, but bi-exponential decays are observed in more polar dicloromethane and acetonitrile. When the porphyrin moiety is excited at λex = 425 nm, the fs transient absorption analysis shows two different intermediate species (~ 7–11 ps and 80–100 ps) with broad absorption in the near-IR region. This implies either the existence of two different excited conformers (T-P)*, which decay to the ground state via a charge separated state (CSS), or the formation of the (T-P)* state via the second excited state of the porphyrin moiety, yielding first an excited emissive v(T-P)* state, with a lifetime of 80–100 ps.

Atomic structure and physical properties of fused porphyrin nanoclusters

The atomic and electronic structures, mechanical properties and potential barriers of formation of a set of meso–meso β–β fused porphyrin/metalloporphyrin nanopages, nanotapes, nanotubes and 2D nanofabrics were studied by GGA LC-DFT technique using cluster and PBC models. The porphyrin pages of the nanoclusters are connected with each other by graphene fragments formed by meso–meso β–β links. Fusion of all the edges of six porphyrin/metalloporphyrin units produces a novel ~ 1 nm sized molecule of cubic symmetry with a hollow cage inside. It was found that all studied nanoclusters are metastable with formation energies 0.36–7.57 kcal/mol per atom. Under applied mechanical stress, the nanoclusters exhibit superelastic and ultrastrong properties with binding graphene fragments being the weakest links for mechanical rupture. Depending on the spin-dependent reaction pathways, the hollow caged nanoclusters exhibit almost zero or low potential energy barriers (1–10 kcal/mol) during the initial stages of self-assembly. All nanoclusters exibit the main features of the electronic structures of the parent porphyrins, in particular the nature of HOMO/LUMO states and the relative energetic positions of the metal d states. The induced curvature of the hollow cage nanoclusters leads to admixture of more than 2% of the dπ⊥ states to the dσ energy region and formation of vacant superatomic molecular orbitals of d character in cubic ligand field. The Fe -derived hollow-caged nanoclusters reveal extremely high spin states with small energy differences between ferromagnetic and antiferromagnetic configurations, which can be utilized for quantum holonomic computations.

Electron-Deficient Porphyrin-Fullerene Cocrystallates: Effect of Fullerene on the Porphyrin Ring Conformation

A new family of electron-deficient porphyrin-fullerene cocrystallates were examined by single crystal X-RD. Solvatedcocrystallates of 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrin, {[H2(TPP)(CN)4]3•C60, 1, [Cu(TPP)(CN)4]3•C60, 2 and [H2(TPP)(CN)4]•C70, 3} were examined to elucidate the influence of fullerene on the stereochemistry of the porphyrin macrocycle and the extent of intermolecular interactions in the solid-state. The C60 units are encapsulated into the triporphyrin capsule and intermolecular interactions are dominated by mainly porphyrin…C60 and porphyrin…porphyrin π…π type of interactions. Both the cocrystallates revealed the formation of hexagonal honeycomb layer-like structure with 10 Å cavity filled with lattice solvates. On changing the fullerene to C70, co-crystallate, 3 showed essentially one-dimensional chain structure. Cocrystallates, 1-3 showed considerable distortion of the porphyrin ring as evidenced from root-mean square (r.m.s.) deviation which is the deviation of the 24-atoms of the macrocycle from their least square plane (0.25 Å) relative to that observed in nearly planar (0.046 Å) parent free base porphyrin, H2(TPP)(CN)4 structure. Another less electron rich porphyrin-fullerene cocrystallate, H2(TPP)Br4•(C60)2•(TCE)2, 4 revealed corrugated layer-structure mediated by solvent and porphyrin…C60 interactions. The macrocycle in the cocrystallate, 4 shows slightly higher distortion than that observed in the reported structure, H2(TPP)Br4. In these cocrystallates, the intermolecular close contact distances between the porphyrin…fullerene was found to be (por)C…C(C60) = 3.185(16) Å and (C70)C…N(por) = 3.03 (3) Å. The normal coordinate structure decomposition analysis of the macrocycle for out-of-plane distortion in the cocrystallates, 1-3 revealed considerable saddling (69-71%) with very minimal ruffled (2-8%) and domed (10-15%) distortions. Cocrystallate, 4 shows enhanced of wave distortion than that observed in the parent porphyrin, H2(TPP)Br4. The nonplanar distortion of the porphyrin ring in the cocrystallates has been ascribed mainly to intermolecular interactions.

Towards Matched Pairs of Porphyrin–ReI/99mTcI Conjugates that Combine Photodynamic Activity with Fluorescence and Radio Imaging

We recently prepared two novel water soluble porphyrins bearing a single peripheral chelator, either diethylenetriamine (1) or bipyridyl (2), tethered to one meso position. The preparation of their conjugates with a fac-{(99m) Tc(CO)3 }(+) fragment and the potential of these resulting conjugates as fluorescence and radio imaging tools were also described. In this work, we focused on the corresponding non-radioactive analogues that bear the fac-{Re(CO)3 }(+) fragment (diethylenetriamine 3 and bipyridyl 4). We report on the uptake, in vitro PDT activity, and cellular localization of Re(I) conjugates 3 and 4 in comparison to the parent porphyrins 1 and 2. Compounds 1-4 have modest or negligible cytotoxicity in the dark against HeLa human cervical cancer cells but become remarkably cytotoxic after exposure to moderate doses of red visible light (590-700 nm). This phototoxicity was found to be directly proportional to the total light dose. Although the four compounds show distinct uptake patterns, they have comparable PDT activity. Confocal fluorescence measurements showed that porphyrin 1 and its Re(I) conjugate 3 have different cellular localization patterns in HeLa cells.

Enhanced Singlet Oxygen Generation from a Porphyrin–Rhodamine B Dyad by Two‐Photon Excitation through Resonance Energy Transfer

Mitochondrial-targeting photosensitizers have been associated with effective photodynamic responses. However, most photosensitizers absorb light between 400 and 700 nm, where light penetration through tissues is limited. Two-photon excitation is a rational approach to improve light penetration through tissues. In this report, the two-photon photophysical properties of a porphyrin-rhodamine B conjugate (TPP-Rh), previously demonstrated to target the mitochondria, were evaluated. The properties studied included: two-photon absorption (TPA) cross sections (σ2 ); resonance energy transfer (RET) kinetics and dynamics; and singlet oxygen generation. The conjugation of Rh B to TPP-OH approximately doubled the σ2 of TPP-Rh at 800 nm (40 ± 4 GM) compared with the parent porphyrin, TPP-OH (16 ± 4 GM). Furthermore, the rate of DPBF oxidation by singlet oxygen generated from TPP-Rh was twice as fast compared with that from TPP-OH (73 % versus 33% in 10 min) following two-photon excitation at 800 nm. In addition, a significantly stronger luminescence signal was detected from TPP-Rh, than from TPP-OH at 1270 nm, following two-photon excitation. This study indicates that conjugating photosensitizers to Rh B could provide greater TPA at the near-infrared range in addition to preferential mitochondrial accumulation for improved photodynamic responses.

Meso-Arylporpholactones and their Reduction Products

The rational syntheses of meso-tetraaryl-3-oxo-2-oxaporphyrins 5, known as porpholactones, via MnO(4)(-)-mediated oxidations of the corresponding meso-tetraaryl-2,3-dihydroxychlorins (7) is detailed. Since chlorin 7 is prepared from the parent porphyrin 1, this amounts to a 2-step replacement of a pyrrole moiety in 1 by an oxazolone moiety. The stepwise reduction of the porpholactone 5 results in the formation of chlorin analogues, meso-tetraaryl-3-hydroxy-2-oxachlorin (11) and meso-tetraaryl-2-oxachlorins (12). The reactivity of 11 with respect to nucleophilic substitution by O-, N-, and S-nucleophiles is described. The profound photophysical consequences of the formal replacement of a pyrrole with an oxazolone (porphyrin-like chromophore) or (substituted) oxazole moiety (chlorin-like chromophore with, for the parent oxazolochlorin 12, red-shifted Q(x) band with enhanced oscillator strengths) are detailed and rationalized on the basis of SAC-CI and MNDO-PSDCI molecular orbital theory calculations. The single crystal X-ray structures of the porpholactones point at a minor steric interaction between the carbonyl oxygen and the flanking phenyl group. The essentially planar structures of all chromophores in all oxidation states prove that the observed optical properties originate from the intrinsic electronic properties of the chromophores and are not subject to conformational modulation.

Novel nanostructural photosensitizers for photodynamic therapy: In vitro studies

Photosensitizing properties of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (p-THPP) functionalized by covalent attachment of one chain of poly(ethylene glycol) (PEG) with a molecular weight of 350, 2000, or 5000Da (p-THPP-PEG350, p-THPP-PEG2000, p-THPP-PEG5000) were studied in vitro. Dark and photo cytotoxicity of these photosensitizers delivered in solution or embedded in liposomes were evaluated on two cell lines: a human colorectal carcinoma cell line (HCT 116) and a prostate cancer cell line (DU 145), and compared with these treated with free p-THPP. The attachment of PEG chains results in the pronounced reduction of the dark cytotoxicity of the parent porphyrin. Cell viability tests have demonstrated that the phototoxicity of pegylated porphyrins is dependent on the length of PEG chain and p-THPP-PEG2000 exhibited the highest photodynamic efficacy for both cell lines. The encapsulation into liposomes did not improve the PDT effect. However, the liposomal formulation of p-THPP-PEG2000 showed a greater tendency to induce apoptosis in both cell lines than the parent or pegylated porphyrin delivered in solution. The colocalization of p-THPP, p-THPP-PEG2000 and p-THPP-PEG2000 enclosed in liposomes with fluorescent markers for lysosomes, mitochondria, endoplasmatic reticulum (ER) and Golgi apparatus (GA) was determined in the HCT 116 line. The p-THPP exhibited ubiquitous intracellular distribution with a preference for membranes: mitochondria, ER, GA, lysosomes and plasma membrane. Fluorescence of p-THPP-PEG2000 was observed within the cytoplasm, with a stronger signal detected in membranous organelle: mitochondria, ER, GA and lysosomes. In contrast, p-THPP-PEG2000 delivered in liposomes gave a distinct lysosomal pattern of localization.

New dyads using (metallo)porphyrins as ancillary ligands in polypyridine ruthenium complexes. Synthesis and electronic properties

Porphyrins bearing enaminoketones at their periphery have been used as ancillary ligands in ruthenium complexes. Free base, nickel and zinc porphyrins were successfully coordinated to Ru(bpy)(2)Cl(2) under microwave irradiation. The positive contribution of the ruthenium complex was demonstrated by the complexes' wide absorption domains that covered the 500-600 nm region where the parent porphyrins did not absorb. Electrochemical as well as computational data revealed an efficient electronic communication between the porphyrins and the ruthenium cation in the dyads.

Bridging the Gap between Porphyrins and Porphycenes: Substituent‐Position‐Sensitive Tautomerism and Photophysics in meso‐Diphenyloctaethylporphyrins

2,3,7,8,12,13,17,18-Octaethyl-5,15-diphenylporphyrin (1) is characterized by an inner cavity with a rectangular shape and small NH⋅⋅⋅N distances. It resembles porphycene, which is a constitutional isomer of porphyrin known for its strong intramolecular hydrogen bonds and rapid tautomerization. Such distortion of the porphyrin cavity leads to tautomeric properties of 1 that are intermediate between those of porphyrin and porphycene. In particular, a tautomerization in the lowest excited singlet state of 1 has been discovered, occurring with a rate three orders of magnitude lower than that in porphycene, but three to four orders of magnitude higher than that in porphyrin. An isomer of 1, 2,3,7,8,12,13,17,18-octaethyl-5,10-diphenylporphyrin (2), exhibits a different kind of geometry distortion. This molecule is nonplanar, but the inner cavity shape and dimensions are similar to those of the parent porphyrin. The same hydrogen-bonding strength as that in porphyrin is observed for 2. In contrast, the nonplanarity of 2 significantly influences the photophysics, leading to a decrease in fluorescence quantum yield and lifetime. Absorption, magnetic circular dichroism, and fluorescence spectra are similar for 1 and 2 and resemble those of parent porphyrin. This is a consequence of comparable energy splittings of the frontier orbitals, ΔHOMO≈ΔLUMO. The results demonstrate that judicious selection of substituents and their position enables a controlled modification of geometry, hydrogen-bonding strength, tautomerization rate, and photophysical and spectral parameters of porphyrinoids.

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 (A 4, B 4) and four hybrid porphyrins (A 3B, cis-A 2B 2, trans-A 2B 2, AB 3) which are isolated and characterized.

Quinoline-Annulated Porphyrins

Porphyrin-2,3-dione mono- and dioximes were used as starting materials for the efficient syntheses of mono- and bis-quinoline-annulated porphyrins and their corresponding N-oxides. Owing to an extended π-system, these novel porphyrinoid chromophores show significantly red-shifted UV-vis spectra compared to the parent porphyrins. A crystal structure exemplifies the nonplanar conformation of the macrocycle.

Porphyrin-fullerene, C60, cocrystallates: influence of C60 on the porphyrin ring conformation.

To examine the influence of fullerene on the macrocyclic ring conformation, crystal structures of a series of cocrystals of 2,3,5,10,12,13,15,20-octaphenylporphyrin, M(TPP)(Ph)(4) (M = 2H, Co(II), Cu(II)), and 2,312,13-tetramethyl-5,7,8,10,15,17,18,20-octaphenyl-porphinato copper(II), CuTPP(Ph)(4)(CH(3))(4), derivatives with fullerene, C(60), were elucidated. Furthermore, crystal structures of the parent porphyrins, M(TPP)(Ph)(4) (M = Co(II), Cu(II)) complexes, were also determined. All the cocrystals revealed one-to-one stoichiometry between the porphyrin and C(60) and were free of lattice solvates. Porphyrin rings in M(TPP)(Ph)(4)·C(60) cocrystals revealed significant distortion with the root-mean-square (rms) value as high as 0.265(2) A which is the average deviation of the 24 atoms core from the least-squares plane. Crystal structures of the parent M(TPP)(Ph)(4) (M = Co(II), Cu(II)) complexes indicated near planarity of the 24-atom core with the root-mean-square deviation value of 0.016(2) A. Molecular packing in the M(TPP)(Ph)(4)·C(60) cocrystals showed essentially one-dimensional chains interconnected by weak interporphyrin and porphyrin-fullerene close contacts. The N(porphyrin)···C(C(60)) shortest distances between the H(2)(TPP)(Ph)(4) (M = 2H, Co(II), Cu(II)) and fullerene in the cocrystals are 3.031(5) A, 3.062(4) A, and 3.059(3) A, respectively. Similarly, close contact M···C distances in the M(TPP)(Ph)(4)·C(60) (M = Co(II), Cu(II)) are 2.761(6) A and 2.886(3) A, respectively. In the Cu(TPP)(Ph)(4)(CH(3))(4)·C(60) cocrystal, the shift of macrocyclic ring toward planarity was evidenced from the rms value of 0.236(2) A relative to that observed in CuTPP(Ph)(4)(CH(3))(4)·CHCl(3) (0.391(2) A). The distortion of the macrocyclic ring in M(TPP)(Ph)(4)·C(60) complexes was examined by normal-coordinate-structure decomposition (NSD) analyses. Their out-of-plane displacement of the core atoms revealed predominant contribution being saddle (∼95-96%) and gentle domed distortions (3-4%). In the case of M(TPP)(Ph)(4)(CH(3))(4)·C(60) cocrystal, it showed mainly saddled (∼83%), minimal ruffled (8%) and domed (8%) distortions of the macrocyclic ring. In-plane displacement on the 24-atom core of the porphyrin in these cocrystallates features generally a varying degree of N-str (B(1g)) and bre (A(1g)) distortions.