Porphyrin molar extinction coefficients

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 beautiful colors associated with porphyrin and chlorophyll systems are manifest in their characteristic electronic absorption spectra. The most intense band in the spectra, around 400 nm, is known as the Soret band it is intrinsic to the large macrocyclic conjugated pathway and has molar extinction coefficients usually between 150 000-400 000. This extinction value is lower in chlorins than in porphyrins, and the band is absent in porphyrinogens (6) and ring-opened bile pigments. 

As usual, the content of porphyrins in copolymers were determined by UV-Vis spectroscopy taking the molar extinction coefficient of the non-aggregating monomers as reference. 

Due to their extended conjugated 7r-system, porphyrins and their derivatives as well as corrins are deeply coloured and show characteristic electronic absorption spectra which vary with the saturation of the chromophoric system, with the central metal ions of the macrocycles, and the various substituents attached to the chromophores (7, 19). Thus, the different porphyrin derivatives can be easily distinguished from each other. The most intense absorption of prophyrins occurs at Amax 400 nm with a molar extinction coefficient of e 400000. This band is named after its discoverer (1883) the Soret band. Other bands with lower intensity than the Soret band occur in the long-wave length... 

Fio. 3. GeneraUsed spectra of porphyrins and their reduction products. The abscissas are molar extinction coefficients, and ordinates are wavelengths in roit. 

The electron absorption spectrum of the chlorophylls and their derivatives is very characteristic and is attributed to the system of conjugated double bonds making up the basic porphyrin structure. Electron transitions in the chlorophyll molecules, detected by photosensitive optical equipment, produce absorption bands [8,64,65], The intensity of a particular absorption band is normally expressed by its molar specific coefficient of extinction s), which, according to the Beer-Lambert law, depends on the optic density (A), the molar concentration (C), and the optical pathway of the light beam through the solution, expressed in centimeters (L). 

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