Porphyrins Q-bands

The absorption spectrum of 2 in dichloromethane is shown in Figure 3. It is similar to a superposition of the spectra of the carotenoid, porphyrin, and quinone components. The porphyrin Soret band at 420 nm dominates the spectrum. The porphyrin Q-bands in the 650, 590, and 550 nm regions are... 

FIG. 16 Photocurrent spectra corresponding to the photo-oxidation of DCMFc by ZnYPPC" at the water-DCE interface under chopped illumination and lock-in detection. The main features of the spectra coincide with the onset of the Soret band and the Q-bands of the porphyrin ring. (From Ref. 73. Reproduced by permission of the Royal Society of Chemistry.)... 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

Another class of red dopants, tetraphenylporphyrins (63), offer a direct energy transfer from blue to red [151], The absorption bands comprise the sharp porphyrin Soret band at 418 nm and the weaker Q bands at 512 and 550 nm. The photoluminescence shows two sharp transitions at 653 and 714 nm and can be induced from a blue emitting host by Forster transfer to the Soret band and internal conversion to the Q bands. 

The UV-Vis spectra of the polymers show signals in the regions of the Soret band (417 nm) and the Q-band (547,585 nm), a peak sphtting. Zinc porphyrin itself, along with the monomeric compounds, does not show such splitting. The... 

When the -C=C- unit is directly bonded to the zinc porphyrin unit (polymer of type B), the Soret and Q-bands are shifted to a longer wavelength, suggesting the formation of a highly 71-conjugated system along the main chain, due to the lack of steric hindrance around the zinc porphyrin ring. 

Al(HE), Ga(HE) as well as In(HE) porphyrin are typical porphyrins incorporated with a tervalent metal ion Characteristic Q and B bands in the visible and near-ultraviolet region, respectively, arise from the (7T,7T ) excitations in the porphyrin ring with only minor perturbation from the outershell electrons of the central metal ion. The Q band is of forbidden character, however, the Q band can borrow the intensity by vibronic couplings from the allowed B band (30). The intensity of the Q(1,0) band is much less sensitive to the peripheral substituents, the axial ligands and the central metal ions, while that of the Q(0,0) band without excitation in the skeletal vibrational modes is rather sensitive to various substituents. 

Ru (0)2(por " )] (for por = TMP and OEP) have been generated by oxidation of [Ru (0)2-(por)] with phenoxathiin hexachloroantimonate. The products show a broad Q band and a less intense and blue-shifted Soret band, consistent with the formation of the porphyrin cation radical. 

Tetrapyrroles contain an extended jt-conjugated system which is responsible for their use in a wide range of applications ranging from technical (pigments, catalysts, photoconductors) to medicinal (photodynamic therapy) uses. The electronic absorption spectra are governed by the aromatic 18 tt-electron system and typically consist of two main bands. In phthalocyanines the Q band around 660-680 nm is the most intense one accompanied by a weaker Soret band near 340 nm . In porphyrins the situation is reversed with an... 

The experimental studies of the MCD spectra of porphyrin and TPP complexes (134,137,138) have generally focused on the first two major bands. The first band, the Q band, appears near 2eV and is has low intensity in the absorption spectrum. The second band, the or Soret band, starts at around 3 eV and has greater intensity in the absorption spectrum. Both bands exhibit some fine structure that may indicate that more than one excitation contributes to each band. 

The qualitative details of the simple model are also reproduced in the band region of Ni porphyrin and NiTPP. The MCD is due to the A term of the 2Eu transition. While the Aj parameter of the band is larger than that of the Q band, the band AjtDj ratio is smaller. A third transition assigned as b2u— eg (3Eu) placed approximately 0.2 eV above 2Eu is found to contribute in a very small way to the MCD intensity. 

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