Electronic absorption spectra chlorin

Although the formation of a bacteriochlorin resulted in further red shift in the electronic absorption spectrum, with long-wavelength absorption near 750 nm, these molecules were generally found to be air sensitive. Among various chlorin analogs, m-THPC (Foscan ) 7 (Scheme 1) appears to be quite effective and is currently under Phase III human clinical trials (see Chapter 147). 

Fortunately, the ene-ynes are easily recognizable because of their peculiar electronic absorption spectra. In the past we have produced ene-ynes by dehydrohalogenation reactions of chlorinated paraffins [20-22], hence we have acquired a certain specific experience in the field. Furthermore, the spectra of ene-ynes are well known in literature [23-25] starting from the spectrum of mycomycin and its isomer isomycomycin. In the context of the spectra of Figure 18.7(B-D), particularly interesting is... 

Porphyrin complexes of certain metal ions have reduction potentials for the ligand and the metal center that are sufficiently close to lead to uncertainties in the site of reduction. The outcome of the reaction can be determined from the optical absorption spectrum of the product (transient or stable). The site of reduction is dependent on the electron affinity of the ligand and, therefore, complexes of pyridylporphyrins or TMPyP are more likely to be reduced at the ligand than complexes of TPP or OEP. This was found to be the situation with Ni -porphyrins, where several complexes were reduced to Ni P but the presence of a single we o-pyridyl group was sufficient to direct the reduction toward the ligand to form Ni P . However, all one-electron reduction products were unstable in water and decayed to form the Ni -chlorin or phlorin. 

The reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

The spectra of nitriles (R—C=N) are characterized by weak to medium absorption in the triple-bond stretching region of the spectrum. Aliphatic nitriles absorb near 2260-2240 cm"1. Electron-attracting atoms, such as oxygen or chlorine, attached to the carbon atom a to the C=N group reduce the intensity of absorption. Conjugation, such as occurs in aromatic nitriles, reduces the frequency of absorption to 2240-2222 cm"1 and enhances the intensity. The spectrum of a typical nitrile is shown in Figure 2.31. 

The flash photolysis of Br2-02 mixtures was examined by Burns and Nor-rish , who also observed the spectrum of BrO as an intermediate. When a Pyrex filter was used to exclude radiation below 3000 A, no BrO was produced. Since, under these conditions, Br atoms are produced, it was concluded that, contrary to the chlorine case, BrO does not result from the reactions of Br with O2 as postulated by Durie and Ramsay The principal mode of formation of BrO was through absorption of radiation near 1800 A by O2 to form either 0 or O atoms, both of which react further with O2 to produce O3. The Br atoms which are then present can react with O3 via reaction (81) to produce BrO. Up to 90% of the BrO is formed in this way. The remaining BrO results from the reaction of highly electronically excited Bt2 with O2, viz. 

The UV spectrum of ferrocene in CCl. contains a new strong and broad absorption band in the wavelength region from 300 to 390 nm (60,61). This new band is due to a charge-transfer complex formed between ferrocene and CCl (62,63) The iron atom serves as an electron donor and the chlorine atom as an electron acceptor. Under U7-irradiation the photochemical dissociation of this charge-transfer complex takes placet... 

Figure 2. Absorption spectra of aromatic cations in chlorinated alkane solvents, formed in pulse radiolysis. (a) Diphenyl in 1,2-di-chloroethane. The spectrum was obtained 2 yjsec. after the electron pulse. (b) p-Terphenyl in 1,2-dichloroethane. The spectrum was obtained 4 nsec, after the electron pulse. The band at 420 m may contain a small contribution from a long-lived species produced by the radiolysis, (c) trans-Stilbene in 1,2-dichloroethane, in 1,1,2-tri-chloroethane, and in 1,1,2,2-tetrachloroethane. Spectrum was obtained 1 fisec. after the electron pulse...

Acyl chlorides have C=0 stretching absorptions at higher wavenumber (1800 cm ) than esters, and amides have C=0 stretching absorptions at lower wavenumber (1650—1655 cm ). These different values reflect the contribution of inductive and resonance effects in the stabilization of the Lewis structure of a carbonyl group compared to the dipolar resonance form. The chlorine atom of acyl chlorides inductively withdraws electrons from the carbonyl carbon and destabilizes the dipolar resonance form, thus leading to an increase in the double bond character of the carbonyl group. Figure 21.5 shows the infrared spectrum of acetyl chloride. 

The POAC-i-PSt micelles also oxidized A,A,A ,A -tetramethyl-l,4-phenylenediamine (TMPD) to produce Wurster s blue chloride. As 1 equivalent of TMPD relative to the VTEMPO imit was added to the micellar solution prepared by 1.94 equivalents of chlorine, the solution with orange colored micelles immediately turned piuple. Figiue 1-1-13 shows the UV spectrum of the micellar solution after the reaction. The characteristic absorption of Wurster s blue [48] was confirmed at 536, 574, and 624 nm. It was suggested that the Wurster s blue chloride was generated in the micellar cores by a one-electron transfer from TMPD to the OAC, because the insoluble Wurster s blue chloride was dissolved into carbon tetrachloride. 

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