A methodological survey of density functional theory (DFT) methods for the prediction of UV–visible (vis)–near-infrared (NIR) spectra of phthalocyanines is reported. Four methods, namely, full time-dependent (TD)-DFT and its Tamm–Dancoff approximation (TDA), together with their simplified modifications (sTD-DFT and sTDA, respectively), were tested by using the examples of unsubstituted and alkoxy-substituted metal-free ligands and zinc complexes. The theoretical results were compared with experimental data derived from UV–visible absorption and magnetic circular dichroism spectroscopy. Seven popular exchange-correlation functionals (BP86, B3LYP, TPSSh, M06, CAM-B3LYP, LC-BLYP, and ωB97X) were tested within these four approaches starting at a relatively modest level using 6-31G(d) basis sets and gas-phase BP86/def2-SVP optimized geometries. A gradual augmentation of the computational levels was used to identify the influence of starting geometry, solvation effects, and basis sets on the results of TD-DFT and sTD-DFT calculations. It was found that although these factors do influence the predicted energies of the vertical excitations, they do not affect the trends predicted in the spectral properties across series of structurally related substituted free bases and metallophthalocyanines. The best accuracy for the gas-phase vertical excitations was observed in the lower-energy Q-band region for calculations that made use of range-separated hybrids for both full and simplified TD-DFT approaches. The CAM-B3LYP functional provided particularly accurate results in the context of the sTD-DFT approach. The description of the higher-energy B-band region is considerably less accurate, and this demonstrates the need for further advances in the accuracy of theoretical calculations. Together with a general increase in accuracy, the application of simplified TD-DFT methods affords a 2–3 orders of magnitude speedup of the calculations in comparison to the full TD-DFT approach. It is anticipated that this approach will be widely used on desktop computers during the interpretation of UV–vis–NIR spectra of phthalocyanines and related macrocycles in the years ahead.

The complexes [Pt(tpp)] (H2tpp=tetraphenylporphyrin), [M(acac)2] (M=Pd, Pt, Hacac=acetylacetone), and [Pd(ba)2] (Hba=benzoylacetone) were co‐crystallized with highly electron‐deficient arene systems to form reverse arene sandwich structures built by π‐hole⋅⋅⋅[MII] (d8M=Pt, Pd) interactions. The adduct [Pt(tpp)]⋅2 C6F6 is monomeric, whereas the diketonate 1:1 adducts form columnar infinity 1D‐stack assembled by simultaneous action of both π‐hole⋅⋅⋅[MII] and C⋅⋅⋅F interactions. The reverse sandwiches are based on noncovalent interactions and calculated ESP distributions indicate that in π‐hole⋅⋅⋅[MII] contacts, [MII] plays the role of a nucleophile.

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Pd-catalyzed coupling reactions have been used to prepare meso-phosphorylporphyrins. A 2D metal-organic network formed via P horizontal lineO...Zn axial supramolecular coordination of 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin is the first example of a 2D framework based on phosphorylporphyrin derivatives.

Copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin was obtained and characterized by means of cyclic voltammetry, electron paramagnetic resonance, Fourier transform infrared, and UV-visible spectroscopy. Three crystalline forms were grown and studied by means of X-ray diffraction methods (single crystal and powder). The highly electron-withdrawing effect of phosphoryl groups attached directly to the porphyrin macrocycle results in a self-assembling process, with formation of a stable 2D coordination network, which is unusual for copper(II) porphyrins. The resulting 2D structure is a rare example of an assembly based on copper(II) porphyrins where the copper(II) central metal ion is six-coordinated because of a weak interaction with two phosphoryl groups of adjacent porphyrins. The other polymorph of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin contains individual (isolated) porphyrin molecules with four-coordinated copper(II) in a distorted porphyrin core. This polymorph can be obtained only by slow diffusion of a copper acetate/methanol solution into solutions of free base 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in chloroform. It converts to the 2D structure after dissolution in chloroform followed by consecutive crystallizations, using slow diffusion of hexane. A six-coordinated copper(II) porphyrin containing two axially coordinated dioxane molecules was also obtained and characterized by X-ray diffraction crystallography. The association of copper(II) 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrin in solution was also studied.

Two series of diphosphoryl-substituted porphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The investigated compounds are 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrins (Ph)2(P(O)(OEt)2)2PorM and 5,15-bis(diethoxyphosphoryl)-10,20-di(para-carbomethoxyphenyl)porphyrins (PhCOOMe)2(P(O)(OEt)2)2PorM where M = 2H, Co(II), Ni(II), Cu(II), Zn(II), Cd(II), or Pd(II). The free-base and five metalated porphyrins with nonredox active centers undergo two ring-centered oxidations and two ring-centered reductions, the latter of which is followed by a chemical reaction of the porphyrin dianion to give an anionic phlorin product. The phlorin anion is electroactive and can be reoxidized by two electrons to give back the starting porphyrin, or it can be reversibly reduced by one electron at more negative potentials to give a phlorin dianion. The chemical conversion of the porphyrin dianion to a phlorin anion proceeds at a rate that varies with the nature of the central metal ion and the solvent. This rate is slowest in the basic solvent pyridine as compared to CH2Cl2 and PhCN, giving further evidence for the involvement of protons in the chemical reaction leading to phlorin formation. Calculations of the electronic structure were performed on the Ni(II) porphyrin dianion, and the most favorable atoms for electrophilic attack were determined to be the two phosphorylated carbon atoms. Phlorin formation was not observed after the two-electron reduction of the cobalt porphyrins due to the different oxidation state assignment of the doubly reduced species, a Co(I) π anion radical in one case and an M(II) dianion for all of the other derivatives. Each redox reaction was monitored by thin-layer UV-visible spectroelectrochemistry, and an overall mechanism for each electron transfer is proposed on the basis of these data.

The first synthesis and self-organization of zinc β-phosphorylporphyrins in the solid state and in solution are reported. β-Dialkoxyphosphoryl-5,10,15,20-tetraphenylporphyrins and their Zn(II) complexes have been synthesized in good yields by using Pd- and Cu-mediated carbon-phosphorous bond-forming reactions. The Cu-mediated reaction allowed to prepare the mono-β-(dialkoxyphosphoryl)porphyrins 1 Zn-3 Zn starting from the β-bromo-substituted zinc porphyrinate ZnTPPBr (TPP = tetraphenylporphyrin) and dialkyl phosphites HP(O)(OR)(2) (R = Et, iPr, nBu). The derivatives 1 Zn-3 Zn were obtained in good yields by using one to three equivalents of CuI. When the reaction was carried out in the presence of catalytic amounts of palladium complexes in toluene, the desired zinc derivative 1 Zn was obtained in up to 72% yield. The use of a Pd-catalyzed C-P bond-forming reaction was further extended to the synthesis of β-poly(dialkoxyphosphoryl)porphyrins. An unprecedented one-pot sequence involving consecutive reduction and phosphorylation of H(2)TPPBr(4) led to the formation of a mixture of the 2,12- and 2,13-bis(dialkoxy)phosphorylporphyrins 5 H(2) and 6 H(2) in 81% total yield. According to the X-ray diffraction studies, 1 Zn and 3 Zn are partially overlapped cofacial dimers formed through the coordination of two Zn centers by two phosphoryl groups belonging to the adjacent molecules. The equilibrium between the monomeric and the dimeric species exists in solutions of 1 Zn and 3 Zn in weakly polar solvents according to spectroscopic data (UV/Vis absorption and NMR spectroscopy). The ratio of each form is dependent on the concentration, temperature, and traces of water or methanol. These features demonstrated that zinc β-phosphorylporphyrins can be regarded as new model compounds for the weakly coupled chlorophyll pair in the photosynthesis process.

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