Q-bands

The purity and the depth of the color of phthalocyanines arise front an isolated band (Q band) in the far-red end of the visible spectrum of light near 670 nm, with a molar absorption often exceeding 10s cm2 mol-1.77 321 A second absorption (B band), near 340 nm, extending to the blue of the visible spectrum is generally much less intense. Absorption spectra of 1,4-oc-tahcxyl-substitutcd PcNi322 and 1,4-octahexyl-substituted PcH2,323 both dissolved in chloroform, are shown below. 

Fe Q-band ENDOR study of the isotopically enriched Ni-C state of D. gigas and D. desulfuricans hydrogenases and Ni-B state of D. desulfuricans revealed a weak coupling between the Fe and the nickel atoms when the enzyme was in the Ni-A forms while no coupling was observed for the Ni-B form (186). A careful analysis of linewidth of Ni-A and Ni-B EPR signals detected in Fe enriched and nonenriched hydrogenase samples indicated that hyperfine interactions are lost in the spectral linewidth and, hence, nonde-tectable. 

The set of Mo(V) EPR signals detected in D. gigas and D. desulfuricans AORs shows close homology with the molybdenum-containing hydroxylase group. Mossbauer and X/Q-band EPR spectroscopic studies 208, 216) complemented the UV/visible and CD studies and the assignment of the [2Fe-2S] arrangement of the iron-sulfur cores. 

Fig. 12b). Since practically the same spectral shape is obtained at Q-band (35 GHz) (Fig. 12c), the commonly used criterion stating that the shape of an interaction spectrum is frequency-dependent fails to apply in this case. Actually, outer lines arising from the exchange interaction are visible on the spectrum calculated at Q-band (Fig. 12c), but these lines would be hardly detectable in an experimental spectrum, because of their weak intensity and to the small signal-to-noise ratio inherent in Q-band experiments. In these circumstances, spectra recorded at higher frequency would be needed to allow detection and study of the spin-spin interactions. 

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. ... 

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. ... 

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. 

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.)... 

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... 

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. 

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. 

Figure 4.1 Powder spectrum of [VO(mquin)2] in [GaCl(mquin)2] (bottom) 9.25 GHz (X-band), (top) 34.99 GHz (Q band).

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