Q-bands

Chlorophylls c have characteristic bands between 578 and 630 nm and between 443 and 450 mn that correspond to the Q-band and the Soret band, respectively.  

Comparative studies of the widely employed spectrophotometric readings at the Soret and Q bands (405 and 630 nm, respectively) and the elemental analysis of copper and nitrogen showed that the spectrophotometric assay based only on the Soret band can overestimate the purity of a preparation. Erroneous data were attributed to an increase in absorptivity at the Soret band when other colored compounds like metal-free analogs and carotenoids are present. Indeed, copper-free chlorin e6 exhibits a specific absorbance 3.6 times greater than that of its coppered counterpart. Therefore, measurements at the Q band (630 mn) and the establishment of the S Q ratio are preferred. 

The spectral characteristics of bacteriochlorophyUs differ from each other, depending on their peripheral side chains, and the Q band varies between 646 and 795 nm, while the Soret band ranges between 365 and 456 mn. BacteriochlorophyUs absorb in the infrared, in addition to the blue part of the spectrum.  

Jeevarajan, A. S., L. D. Kispert et al. (1996b). Role of excited singlet state in the photooxidation of carotenoids a time resolved Q-band EPR study. J. Phys. Chem. 100 669-671. 

Optical spectra of the Ni11 complex (189) show close similarity to those of Ni-phtalocyanines in the low-energy spectral region where the first 7r-7r transition (Q band) occurs.5 9,600 A reduction 

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. 

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