Porphine. free base

Fig. 3. Molecular structures of free-base porphine, free-base chlorin, and Et-Pheo-a. Structures of the respective magnesium analogs, magnesium porphine, magnesium chlorin, and Et-Chl-a, are obtained by replacement of the NH hydrogen atoms by a magnesium atom at the center of the macrocycle (Reprinted with permission)...

In the first step, the fairly acidic proton on CIO of the red biladiene-ac salt 6 is abstracted and, even in solution in polar solvents, the salts are converted into the corresponding yellow bilatriene-u/ic salts 7. With a base such as piperidine, the salts 7 form the green bilatriene-a/>e free base. For further reaction to the porphyrin it is important that the salts 7 are oxidized to the bilatriene enamines 8 which cyclize via the electrophilic carbon of the terminal pyrrole ring by the loss of the leaving group X to 9. Porphin (10) is finally obtained by the loss of... 

Free-base porphyrins can be chlorinated with hydrogen peroxide-hydrochloric acid mixtures, but formation of mono- and di-substituted derivatives is not easy to control, the reaction preferring to produce the methine tetrachloro derivative. The magnesium(II) comptex of porphin (1) can be transformed into the 5,10,15,20-tetrabromo derivative with NBS, and no peripheral substitution is observed however, free-base porphin (1) is mono-brominated at a peripheral carbon under these circumstances. Treatment of deuteropor-phyrin-IX (Table 1) with pyridinium bromide perbromide gives the 3,8-dibromo derivative. 

The free base 5,10,15,20-tetraphenyl-21 A/,23//-porphine (H2tpp) may be prepared from pyrrole and benzaldehyde4 or purchased from Strem Chemicals, P.O. Box 108, Newbury Port, MA 01950 or Aldrich Chemical Co., 940 St. Paul Ave., Milwaukee, WI 53233. The material should be chlorin free, which can be effected either by dry column chromatography using alumina and chloroform or by oxidation of the chlorin to porphyrin using 2,3-dichloro-5,6-dicyano-... 

Interpretation of the Electronic Spectrum of Free Base Porphin... 

The electronic spectrum of free base porphin has been the subject of many experimental and theoretical studies. Because of the size of this molecule, obtaining meaningful ab initio calculations has been a significant challenge. Different calculations naturally give different numerical results, but they also give different... 

Gwaltney SR, Bartlett RJ (1998) Coupled-cluster calculations of the electronic excitation spectrum of free base porphin in a polarized basis. J Chem Phys 108 6790-6798. 

Nakatsuji H, Hasegawa J, Hada M (1996) Excited and ionized states of free base porphin studied by the symmetry adapted cluster-configuration interaction (SAC-CI) method. J Chem Phys 104 2321-2329. 

Figure 5,14. Luminescence of free-base porphine (12) in Ne (4 K) and Xe (12 K). The former is totally dominated by fluorescence (left) and the latter by phosphorescence (right) (by permission from Radziszewski et al., 1991).

Fig. 18.12 Frequency shift and broadening of the hole burnt in the Bj site of the 0-0 transition of free-base porphin in w-octane. Shown are excitation spectra of hole burnt at 1.6 K (the deeper hole) and 3.9 K. (Fig. 4 from S. Volker, Ann. Rev Phys. Chem. 40, 499-530 (1989).)...

Reports of gas-phase ultraviolet PES of porphyrins are available only for free-base porphine (H2P) and a number of highly substituted (usually, octaethyl and tetraphenyl) porphyrins and metalloporphyrins. 

Ab initio Electron Propagator Calculations Table 3.5 Free-base porphine ionization energies, eV... 

The similarity transformed EOM, STEOM-CC [183], approaches the problem somewhat differently, but it also provides an exponential ansatz for excited states, namely = exp(5) exp(7)l0), where exp(5) has a different meaning than before. The method decouples the contributions of higher cluster operators from the lower ones, by using the results for the (1,0) and (0,1) results to define the second similarity transformation, 5, leaving the excited states to be obtained now from a problem of the dimension of a Cl singles (CIS) calculation. This method is a kind of exact CIS for the excited states of molecules, at least those dominated by single excitations. It is very attractive for large-scale application as in our work for free-base porphine [184,185]. Extensions by Nooijen and Lotrich have been made for doubly excited states [186]. 

It seems worth mentioning here that Hesselink and Wiersma recently also have been successful in measuring the homogeneous linewidth of the Si -So transition of the -sites of Zn-porphin in n-octane. Also in this case over an extended temperature range, as shown in Fig. 11, an exponential activation of the linewidth is observed. The measured activation energy of 31 2 cm of these A-sites is in close agreement with the estimated 30 cm activation energy for the 4-sites of the free-base porphin in n-octane. 

In some cases the authors detected, using spectroscopic techniques, that the incorporation of metal ions in the phthalocyanine and porphyrin systems weakens their interaction with the nanotube sidewalls. For example, [Zn(porphyrin)] and [Cu(phthalocyanine)] showed a weaker binding ability to SWCNTs than that of metal-free molecules [82a], Similarly, the interactions of THPP [5,10,15,20-tetrakis(hexadecyloxyphenyl)—21/7, 23//-porphine] with CNTs were apparently specific to the porphyrin-free base and were hindered upon Zn chelation [82b],... 

The procedure above was used in a recent study of the lower excited states of free-base porphin [35]. This molecule has 24 tt orbitals and 24 it electrons. It is clearly impossible to have all these orbitals and electrons active. Therefore, an SDCI-type RASSCF calculation was first performed with the 24 tt orbitals active. The occupation numbers were then used as a guidance in a series of CASSCF/CASPT2 calculations on the excited states. It was possible to increase the active space in a systematic way until the computed excitation energies had converged. There is no guarantee that this is always possible, however. If not, the CASSCF/ CASPT2 method cannot be used to study the electronic spectrum. One... 

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