Narrow Results

The reaction with sodium cyanide of the μ-oxo-bridged complex of tetra-4-tert-butyl-substituted iron phthalocyanine (form ‘690’) and that of the product of its treatment with organic bases such as Py, Im, etc. (form ‘627’) result in the formation of the same ferrous bis-cyanide complex Na₂[Pc^tFe^II(CN)₂] which can be readily oxidized to the analogous ferric complex Na[Pc^tFe^III(CN)₂]. Form ‘690’ has been oxidized to the corresponding ferric μ-oxo complex (form ‘630’). Data for all μ-oxo-bridged complexes (chemical behavior; electronic, NMR, Mössbauer, X-ray photoelectron and ESR spectra; magnetic susceptibility) are discussed, and based on them, the following structures are proposed: (HPc^tFe^II)₂O (form ‘690’), H₂[(LPc^tFe^II)₂O] (form ‘627’) and (Pc^tFe^III)₂O (form ‘630’).

Series of 5,10,15,20-tetraarylporphyrins 1 and 5,10,15,20-tetrakis[4-(arylethynyl)phenyl]porphyrins 2 were prepared via condensation of pyrrole with the appropriate benzaldehyde or 4-(arylethynyl)benzaldehyde derivative (3). Condensation of meso-phenyldipyrromethane with mixtures of benzaldehyde and 4-(trimethylsilyl-ethynyl)benzaldehyde gave a separable mixture of mono- (6), bis- (both cis-7 and trans-8) and tris[4-(trimethylsilylethynyl)phenyl]porphyrin (9). Following removal of the trimethylsilyl groups of 6–9, the 4-ethynylphenyl groups of 11–14 were coupled to 1-iodo-3,5-di(trifluoromethyl)benzene with Pd(OAc)₂ to give 15–18 bearing one, two (both cis- and trans-) and three 4-[bis-3,5-(trifluoromethyl)phenylethynyl]phenyl groups respectively. Coupling of 11 and 1-iodo-4-nitrobenzene with Pd(OAc)₂ gave porphyrin 19 with one 4-(4-nitrophenylethynyl)phenyl group. Porphyrin 24 with a p-quinone linked to the porphyrin core via a phenylethynyl group was prepared via similar chemistry. The absorbance spectra, emission maxima, excited-state fluorescence lifetimes, quantum yields of fluorescence, rates of fluorescence and rates of non-radiative decay were measured for each of the porphyrins. Absorbance spectra and emission maxima were nearly identical for all the porphyrins of this study, which suggests that the aryl groups and 4-(arylethynyl)phenyl groups are not strongly coupled to the porphyrin core in these metal-free compounds. Fluorescence quantum yields and rates of radiative decay were larger for porphyrins bearing 4-(arylethynyl)phenyl groups, while excited-state fluorescence lifetimes were somewhat shorter. These effects were additive for each additional 4-(arylethynyl)phenyl group.

Molecular orbital (MO) calculations of more than 60 porphyrinic π conjugated structures have been performed within the framework of the Pariser–Parr–Pople approximation. The results of a series of compounds are introduced and summarized in order to show how they vary depending on the systematic change in molecular structure. These are shown schematically or itemized. Our results are compared with the spectra of the corresponding known compounds and with the MO results reported by previous workers, if available. In addition, the results have continually been compared, where possible, with those of tetraazaporphyrin or phthalocyanine systems. In naphthalene- or anthracene-fused compounds, these molecule-centered orbitals often appear, and these are indicated using either triangles or circles in figures if they appear between HOMO – 3 and LUMO + 3 orbitals.

The effects exerted by fused aromatic rings on the UV-vis spectra of porphyrins are surveyed. Modified porphyrin chromophores with fused benzene, 1,2-naphthalene, 9,10-phenanthrene or phenanthroline rings are surprisingly little affected even when a maximum number of ring fusions are incorporated. Linearly annealed naphtho- or anthraporphyrins show large red shifts to the Q bands but the Soret absorptions are weakened and undergo only minor bathochromic shifts. Fluoranthoporphyrins give multiple bands in the Soret region, but the Q band region is virtually unaffected by this tetracyclic ring system. On the other hand, metal chelates of fluoranthoporphyrins show surprisingly strong bands near 600 nm. Benzothiadiazole rings split and weaken the Soret band, but the Q bands region is unexceptional. However, metal coordination again produces relatively intense bands near 600 nm. The most significant results were obtained for porphyrins with fused acenaphthylene rings. Monoacenaphthoporphyrins (41) have three Soret bands at 387, 431 and 454 nm, and the longest wavelength Q band is shifted to 658 nm. opp-Diacenaphthoporphyrin (43) further shifts these bands with two Soret absorbances at 443 and 470 nm, and an additional strong peak is observed at 692 nm. The metal complexes of these systems also show strong bands between 602 and 656 nm. Still larger effects are produced by tetraacenaphthoporphyrin (47), the dication for which in trifluoroacetic acid (TFA)–chloroform has a Soret absorption at 528 nm. Tetraaryltetraacenaphthoporphyrins (48) are even more red shifted, showing Soret bands between 556 and 570 nm for the free bases and 565 to 588 nm for the related dications. The lead(II) chelate for tetraphenylporphyrin (48a) shows an additional 'hyper' spectral shift that brings the Soret band to 604 nm, and this effect can also be achieved by introducing four meso-phenylethynyl substituents onto the tetraacenaphthoporphyrin nucleus (49). In addition, by combining these two factors for the lead(II) chelate of 49, a record-breaking value for the Soret band of 642 nm can be achieved. Spectral shifts due to ring annelation in porphyrin analogues are also discussed, including those for oxybenziporphyrins, oxypyriporphyrins, carbaporphyrins and sapphyrins.

Phthalocyaninatosilicon(IV), germanium(IV) and tin(IV) dihydroxides react with potassium hydroxide in o-xylene in the presence of crown ether 15-cr-5 initially forming paramagnetic compounds of dark-blue color with absorption bands at 580–590 nm and 620–625 nm and then diamagnetic compounds of red color with an absorption band at 518–523 nm. The red compounds are very reactive towards proton donors, restoring the initial phthalocyanines, and oxidation agents under decomposition of the phthalocyanines. The color changes are due to the formation of the mono- and dianions, (PcMO₂)^2- and (PcMO₂)^-, accompanied with transfer of electrons from oxygen atoms to the tetrapyrrol macrocycle.

The hydrogen-bonding dynamics in both singlet and triplet excited states of the trans-acetanilide (AA) in methanol (MeOH) solvent was investigated using the time-dependent density functional theory (TDDFT) method. Geometric optimizations of the hydrogen-bonded AA–MeOH complexes considered here as well as the isolated AA and MeOH molecules were performed using density functional theory (DFT) method. At the same time, the TDDFT method was performed to calculate the electronic transition energies and corresponding oscillation strengths of all the compounds in the low-lying electronically excited states. In this study, only the intermolecular hydrogen bonds C=O⋯H–O and N–H⋯O–H can be formed. A theoretical forecast that changes of hydrogen bonds in the low-lying electronic excited states was proposed. We discussed not only ground-state geometric structures and electronic excitation energies but also frontier molecular orbitals and electron density transition. The intermolecular hydrogen bonds between AA and MeOH molecules play an important role in the geometric structures and electronic excitation energies. Zhao et al. have put forward the relationship between the electronic spectra and hydrogen bonding dynamics for the first time. According to Zhao's rule, a redshift of the relevant electronic spectra will appear if hydrogen bond is strengthened, while the hydrogen bond weakening can make an electronic spectra shift to blue.

Electronic spectra of uracil, thymine, adenine, guanine, and cytosine in the gas phase and aqueous solution have been studied by extensive time-dependent density functional calculations. Calculations show that the Quantum mechanics/molecular mechanics (QM/MM) geometry optimization based on the molecular dynamics (MD) equilibrated configuration can locate an optimal solvated cluster for the base solvation, and the combined QM/MM and cluster-continuum computational protocol is capable of handling the solvent effect on the excited states of nucleic acid bases and providing realistic absorption spectra in water environment with relatively low computational costs. Generally, the vertical excitation energies in aqueous solution by PCM/TD-X3LYP calculations show excellent agreement with the experimental observations and the maximum deviation is less than 0.2 eV. The present results reveal that the hydrogen bond network around the excited-state base and its dipole moment change may remarkably modify the absorption spectra of nucleic acid bases in aqueous solution.

The present work aims at a better and deeper insight into the forces that govern the intramolecular charge transfer (ICT) and photo injection processes in dyes for dye sensitized solar cells (DSSC). The geometry, electronic structure, electron density distribution, and absorption spectra, for a selected donor-$\pi$-acceptor (D-$\pi$-A) dye for DSSC were computed and analyzed at a high level of DFT theory. The coplanar geometry of the studied dye (D1) indicates a strong conjugation which facilitates ICT. NBO analyses reveal that this ICT amounts to 0.8e, which is localized on the acceptor and anchoring groups resulting in a marked total delocalization interaction energy. The origin of this stabilization is two-fold; first the $\pi$-charge transfer (CT) interaction from donor to acceptor orbitals and the hyperconjugative interactions involving Rydberg states. The effect of fluorine substituents, in the $\pi$-spacer, on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state life time, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

In this work, we theoretically investigate the properties of excited state process for a novel salicylidene sal-3,4-benzophen (Sal-3,4-B) system, which contains two intramolecular hydrogen bonds (O1-H2$\cdots$N3 and O4-H5$\cdots$N6). Based on the density functional theory (DFT) and time-dependent DFT (TDDFT) methods, we find these two hydrogen bonds should be strengthened in the S₁ state, while the O4-H5$\cdots$N6 one could be largely affected upon the excitation process. Analyses about infrared (IR) vibrational spectra about hydrogen bond moieties also confirm this viewpoint. Frontier molecular orbitals (MOs) depict the nature of electronic excited state and support the excited state intramolecular proton transfer (ESIPT) reaction.Two kinds of stepwise potential energy curves of Sal-3,4-B in the S₁ state demonstrate that only one proton could be transferred. Also based on constructing potential energy curves, the synergetic situation could be eliminated. Due to the specific ESIPT mechanism for Sal-3,4-B, we successfully explain the previous experiment and provide a reasonable attribution to the second emission peak of experiment.

The reaction of bis(trimethylsiloxy)triphthalocyaninatosilicon, Me₃Si(OSiPc)₃OSiMe₃ (Pc₃) with KOH in o-xylene in the presence of 15-crown-5 in vacuum at 200°C has been studied by means of UV-vis, EPR and ¹H NMR spectroscopy. Upon gradual removal of H₂O, the formation of mono- and dianions of Pc₃ with absorption bands positioned at 575-590 nm was observed. An EPR spectroscopic study revealed that both monoanionic and dianionic of Pc₃ are paramagnetic in solution. ¹H NMR spectra have shown the absence of a ring current in the π-electron system of dianion. The reaction of Pc₃ with KOH or metal Na led to degradation of the Si-O-Si- backbone happened.

A novel low symmetry sulfur-containing porphyrazine, 5,23,28,32-octabutoxy-10,11,17,18-tetrahydro-[9,12,16,19]-tetrathiino-33H, 35H-dinaphtho-porphyrazine (OTTDP), was synthesized by mixed condensation and characterized by NMR, FAB-MS and UV-visible spectra; this complex was found to be low aggregation in organic solvents and can interact with the serum albumin at several binding sites.

Electronic absorption spectra of divalent metal (Ni(II) and Cu(II)) complexes of 2,3,7,8,12,13,17,18-octa(bromo/chloro)-5,10,15,20-tetraphenylporphyrins (MOXTPP; X = Br, Cl) were examined in various solvents. M(II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large red-shift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu(II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M(II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle.

Bicyclo[2.2.2]octadiene (BCOD)-fused porphyrins with no other substituents were prepared by [2 + 2] and [3 + 1] porphyrin syntheses from ethanodihydroisoindole derivatives in fairly good yields. Thermal retro-Diels-Alder reactions of BCOD-fused porphyrins gave the corresponding benzoporphyrins with no substituent in quantitative yields. Their UV-vis spectra and crystal structures were carefully examined in terms of π-system expansion of the porphyrin ring current. In the cases of monobenzo- and adj-dibenzo-porphyrins, a single Soret band in their UV-vis spectra and no bond alteration in the benzene rings of their crystal structures were observed, while the split Soret bands and the obvious bond alteration in their benzene rings were recorded in the case of opp-dibenzoporphyrin.

Three approaches to the synthesis of reduced derivatives of tetraazaporphine such as tetraazachlorin, tetraazabacteriochlorin, and tetraazaisobacteriochlorin are reviewed. The first synthesis of alkyl-substituted tetraazachlorins was achieved by the catalytic hydrogenation of magnesium complexes of tetraazaporphines. Two other synthesis approaches for reduced tetraazaporphines based on the mixed condensation of the precursors with different hydrogenation levels and β–β addition reactions have been developed in the last decade. The use of tetramethylsuccinonitrile as the saturated component in the mixed condensation with derivatives of aromatic and heteroaromatic dicarboxylic acids enable the synthesis of oxidation-resistant benzo-; 1,2- and 2,3-naphtho-; pyrazino-; 2,3- and 3,4-pyridino-fused tetraazachlorins, tetraazabacteriochlorins, and tetraazaisobacteriochlorins. Fullerene conjugates of reduced tetraazaporphine derivatives were obtained using 1,2-dicyanofullerene as the source of the hydrogenated sites. Tetraazaporphine can act as dienophile in Diels-Alder reaction with dienes of the anthracene and cyclopentadiene series and also as dipolarophile in 1,3-dipolar cycloadditions with azomethine ylides and nitrones. In addition, the effect of the reduction of peripheral double bonds in tetraazaporphine macrocycle alone, and in combination with annelation of benzene or heterocyclic rings on the absorption spectra is discussed.

Aggregates of tetrakis(4-sulfonatophenyl)phthalocyanine were deposited on Au(111) from solutions of varying pH. The resulting surface species were studied by scanning tunneling microscopy (STM) under ambient and ultra high vacuum conditions. The pH of the solution from which the TSPc is deposited has profound effects on the adsorbed structures. We observed a diversity of surface structures. At low pH web like aggregates composed of vertically stacked coherent columnar assemblies averaging five molecules per stack were observed. Basic solutions yielded dense molecular monolayers.

An efficient synthetic route for the preparation of benzene or 1,2-naphthalene fused and phenyl substituted metal-free tetraazachlorins with yields up to 40% was developed using In(III) as a removable template. New substituted tribenzotetraazachlorins derivatives with tert-butyl and phenylsulfanyl groups in β and α position of fused benzene rings, correspondingly, were synthesized by novel approach and their spectral properties were investigated.

The mechanism of photoconductivity in a crystalline photoconductor synthesized from 1:1 ratio of meso-tetra(4-pyridyl)porphyrin (TPyP) and meso-tetra(4-sulfonatophenyl)porphyrin (TSPP) ionic tectons was examined. The rod-like crystals of TPyP:TSPP insulate in the dark but become photoconducting on illumination and a portion of the photoinduced current persists after the laser light is turned off. This persistent photoconductivity (PPC) is investigated as a function of laser illumination wavelength, laser power, and sample temperature. The primary charge carriers in the TPyP:TSPP upon photoexcitation are electrons and the charge recombination mechanism follows monomolecular kinetics. The number of electrons contributing to the photocurrent is directly proportional to the number of photons absorbed thus, the mechanisms of the photoconductivity resulting from excitations within the Soret band and the Q-band are the same. The PPC is interpreted to be the result of the formation of photoinduced metastable defects that allow for Miller–Abrahams-like hopping conductivity. The TPyP:TSPP has an incommensurately modulated crystal lattice and its proposed model structure is based on both ionic and neutral porphyrin tectons. The thermogravimetric analysis shows that the porphyrin crystals undergo dehydration on heating (˜50 ^∘C) by losing water molecules located in the crystalline channels. Temperature dependent XRD indicates that dehydration causes irreversible changes to the crystal structure. The loss of crystallinity observed with heating the TPyP:TSPP crystals above 90 ^∘C causes approximately 25% loss in photoconductivity but has little effect on the lifetime associated with the persistent photoconductivity.

A near planar macrocycle containing 2,3,12,13-tetraphenylethynyl-5,10,15,20-tetrakis-(4${}^{\prime }$-$n$-butylphenyl)porphyrin, H₂T(4${}^{\prime }$-$n$-Bu Ph)P(PE)₄ and a series of antipodally mixed substituted nonplanar porphyrins, 2,3,5,10,12,13,15,20-octaphenyl-7,8,17,18-tetra(2${}^{\prime }$-thienyl/phenylethynyl, PE)porphyrin, H₂OPP(2${}^{\prime }$-Th/PE)₄ and 2,3,12,13-tetramethyl-7,8,17,18-tetra(2${}^{\prime }$-thienyl/PE)-5,10,15,20-tetraphenylporphyrin, H₂TPP(CH${}_3{)}_4$(2${}^{\prime }$-Th/PE)₄were examined by electronic absorption spectroscopy in twenty different solvents. The presence of push-pull substituents at the antipodal $\beta$-pyrrole positions of the nonplanar macrocycle induces varying degrees of orthogonal dipole moments to the porphyrin ring. The influence of different solvents on the degree of nonplanarity and electronic nature of the macrocycle on their electronic absorption spectral properties were examined. Generally, free base porphyrins showed dramatic solvent dependent absorption spectral band shifts and follow the order: H₂OPP(PE)₄ > H₂OPP(2${}^{\prime }$-Th)${}_4\ge$ H₂TPP(CH${}_3{)}_4$(2${}^{\prime }$-Th)₄ >H₂TPP(CH${}_3{)}_4$(PE)₄ > H₂T(4${}^{\prime }$-$n$Bu Ph)P(PE)₄. Absorption spectral data in different solvents was analyzed using selected solvatochromic parameters, (${\eta }^2$ – 1)/(2${\eta }^2$ + 1), $E_T$ (30),${}^{}\beta$, and $\pi$*. The enhanced red-shift of the absorption bands of the mixed substituted porphyrins in polar solvents was influenced by solvent-core (porphyrin) interaction and is reflected from the ¹H NMR chemical shift of the core imino-hydrogens in polar solvents relative that observed in less polar solvents. The magnitude of the difference in chemical shift ($\mathrm{\Delta }\delta$, ppm) of imino-hydrogens in DMSO-d₆ relative to that in CDCl₃ follow the order: H₂TPP(CH${}_3{)}_4$(2${}^{\prime }$-Th)₄ (1.37 ppm) > H₂OPP(PE)₄ (1.17 ppm) > H₂TPP(CH${}_3{)}_4$(PE)₄ (0.57 ppm). The large red-shift in B and Q bands in polar solvents relative to apolar (or less polar) solvents has been possible due to the combined effect of the electronic nature of the macrocycle, its nonplanarity, and solvent-porphyrin core interactions.

Nitration of 2,7,12,17-tert-butylporphycene, leading mainly to meso-substituted 9-nitro- and 9,20-nitro- derivatives, also yielded a small amount of porphycene bearing three tert-butyl moieties and the nitro group at the $\beta$ position. The electronic absorption spectra of 2-nitro and 9-nitroporphycenes are similar, but the photophysical characteristics strongly differ. Unlike the meso-substituted derivative, 2-nitroporphycene emits intense, long-lived (ns) fluorescence. Strong enhancement of fluorescence intensity is due to the absence of steric interactions between tert-butyl and nitro moieties. The two porphycenes also differ in their tautomeric properties. 2-nitroporphycene exists in one trans-tautomeric form, whereas two trans-tautomers of similar energies coexist in the meso derivative. These results are well reproduced by quantum-chemical calculations. The possibility of changing photophysics and tautomerism by shifting the position of the substituent may be exploited while designing porphycenes targeted for specific applications, such as photodynamic therapy or building molecular switches.

Complexes of Al${}^{\mathrm{\text{III}}}$, Ga${}^{\mathrm{\text{III}}}$ and In${}^{\mathrm{\text{III}}}$ with peripherally chlorinated phthalocyanine (Cl₈PcM) and tetrapyrazinoporphyrazine (Cl₈TPyzM) were prepared and studied using spectral and electrochemical methods. DFT calculations were used to reveal the peculiarities of their molecular and electronic structure. Peripheral chlorination of phthalocyanine complexes increases their electron affinity and the first reduction of [Cl₈PcM] is observed at −0.25 – −0.35 V (by 0.2 – 0.3 V easier than for [PcM]). Additional azasubstitution further increases the acceptor properties of the macrocycle and [Cl₈TPyzM] are reduced at −0.16 V. Among [Cl₈PcM] only the Ga${}^{\mathrm{\text{III}}}$ complex is stable to photooxidation, while among [Cl₈TPyzPzM] it is the only one undergoing photoreduction. Fluorescence quantum yields (${\mathrm{\Phi }}_{\text{F}})$ and lifetimes (${\tau }_{\text{F}})$ as well as the ability to generate singlet oxygen (${\mathrm{\Phi }}_{\mathrm{\Delta }})$ were determined. The ${\mathrm{\Phi }}_{\text{F}}$ values show typical dependence on the central metal Al > Ga >> In and are decreased upon the introduction of chlorine atoms in the peripheral and especially in the axial position. At the same time, azasubstitution in the benzene ring has a minor influence on the ${\mathrm{\Phi }}_{\text{F}}$ values but strongly shortens ${\tau }_{\text{F}}$ (from ca 6 to ca 2 ns). The Ga${}^{\mathrm{\text{III}}}$ complexes have the highest ability to generate ¹O₂ and can be considered as effective photosensitizers, especially [Cl₈TPyzPzGa(OH)] (${\mathrm{\Phi }}_{\mathrm{\Delta }}$ = 0.87 in slightly acidified solution). Spectral properties in a strongly acid medium were also studied and it was observed that [Cl₈PcM] are consequently protonated on meso-nitrogens.