Soret phthalocyanines

Optical Spectra. The optical spectra of the unsymmetrical porphyrazines 65 and 66a-66d exhibit Soret bands between 330 and 375 nm and a split Q band, due to reduced symmetry between 650 and 700 nm. The peripherally metalated species 67d-67h do not have a split Q band, reflecting the extension of the pz n system into the five-membered chelate ring mediated by the bridging dithiolene. Table XVII compares the Q-band region of the optical spectra for 65, 66a-66c, 67b-67d to the symmetrical octa. V-bcnzyl porphyrazines 58, 59, 60a, 60b, 61a, and 61b to the analogous phthalocyanines (4). 

The dithionite reduction of the micelle encapsulated aqua (hydroxo) ferric hemes at pH 10 (in inert atmosphere) gives an iron (II) porphyrin complex whose optical spectrum [21] shows two well-defined visible bands at 524 and 567 nm and a Soret band split into four bands (Fig. 10). Such spectral features are typical of four-coordinate iron (II) porphyrins. The magnetic moment (p = 3.8 + 0.2 Pb) of this sample in the micellar solution is also typical of intermediate spin iron(II) system and is similar to that reported for four-coordinate S = 1 iron(II) porphyrins and phthalocyanine [54-56]. The large orbital-contribution (ps.o. = 2.83 p for S = 1) observed in this iron(II) porphyrin... 

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... 

All normal oxidation state phthalocyanines are characterized by an intense band near 28,000 cm-1 (Soret band), and another intense band near 14,000-15,000 cm-1. Metal-free phthalocyanine differs in having an intense doublet near 14,000-15,000 cm-1. The intensities are of the order of 106 (dipole strength 1-2 A2) (138). Films as thin as 30 A are reported, by virtue of their color, to be visible to the naked eye (165). Because of the 14,000-... 

With a few exceptions, the variation in the absorption spectrum with central metal ion is even less marked in the phthalocyanine series. This is particularly true of the position of the red band, which is almost independent of the central metal ion. There appears to be no obvious relationship between the electronegativity of the metal ion and the absorption maxima in the phthalocyanine series (214). This is readily understood since there is no metal orbital of biu or biu symmetry, and the metal e orbitals will, in general, have too low an energy to interact with the phthalocyanine e orbital involved in the transition. The small variations which do occur in the red band are therefore probably inductive rather than conjugative. The Soret band, in the blue, does vary slightly with metal ion, and it seems probable that the transition involves the a2u orbital admixed by configurational interaction (see also Section VII). 

An interesting path is using metal phthalocyanines as models for hemoproteins. In this direction it was tried to get a coordinative bond between Fe- and CoPc(S03Na)4 (12 a) at natural globin62). The interaction between globin or hemoglobin and the Pc led to green crystals after Sephadex gel separation. Spectroscopic methods shown that heme is partially displaced (Eq. 5) by MPc (disappearance of Soret band in VIS-spectra typical for porphyrins). 

In such Pc LB films, CuPc mainly exists as dimer. When the LB films were exposed to various organic vapors, the dimer absorbance band was blue-shifted from 625 nm initially to 624 (hexane), 622 (benzene), 620 (aniline), 620 (toluene), and 619 nm (pyridine), respectively (Figure 3.2). It is clear that the change becomes apparent when the films were exposed to the vapors of aromatic compounds. When such film was continuously exposed to benzene vapors, the dimer band was blue-shifted much more (Figure 3.3). However, the Soret bands have no change in their adsorption position. In all the cases, there is a hypochromic effect when exposed to the vapors. A same phenomenon was observed in LB films of bis(phthalocyaninate) rare earth compounds exposed to hexanal vapor [32]. These changes are associated with the formation of a charge-transfer (CT) complex between the phthalocyanine and the VOC [33,34]. 

CD study in THF solution shows Cotton effects at 700 and 370 nm in addition to the intense effects corresponding to the binaphthyl substituents. These effects, positive for the [(/ ) or (M)]-binaphthyl and negative for the [(5) or (P)]-ligand, arise from the Q (700 nm) and Soret (370 nm) bands of the conjugated system of the phthalocyanine. These electronic transitions are characteristic of the achiral planar chromophore of... 

A phthalocyanine may also have a chiral structure if the metallic centre coordinated by the nitrogen atoms is out of the plane defined by the Pc ligand. A subphthalocyanine (6.41) with C3 symmetry was resolved by HPLC. The CD showed dichroic effects at 560 and 570 nm (Qoo- band) and 280 and 300 nm (Soret band), being either positive or negative according to the enantiomer. Unfortunately, the authors were not able to assign configurations to the enantiomers. 

The incorporation of phthalocyanines into a multichromophore supra-molecular system was attempted by attachment to imidazolyl zinc porphyrin 65 (Fig. 28). A combination of strong absorption of the Soret band of porphyrin and of the Q-band of phthalocyanine makes compound 66 an attractive dyestuff similar to chlorophylls and covering the whole visible re-... 

Phthalocyanines show two distinct absorption bands in the visible range, namely the Q band around 650-700 nm and the B or Soret bands around 300-350 nm (Figure 4.7). These bands correspond to a transition from the HOMO to the LUMO... 

Fig. 3 Absorption spectra of some of the chromophores from Figs. 1 and 2. Upper part some natural chromophores. Pheo a stands for pheophytin a, the free base of Chi a after replacement of the magnesium ion by two protons Lower part some synthetic chromophores dark green trace - nickel tetrasulfonated phthalocyanine (PcS4) dissolved in a water DMSO mixture (note the shoulders at 640 and 600 nm due to dimers and H-aggregates, respectively) magenta trace - meso-tetratolyl-porphyrin cyan trace - zinc tetratoljd-porphyrin. Note the sharp 420 nm (Soret) bands of the porphyrins and their very low visible absorptions (the Q bands) in comparison to Chls and phthalocyanines.

Incorporation of electronegative flnorine atoms in benzene rings of phthalocyanine macrocycle has a considerable impact on its electronic structure and spectral properties. The electronic absorption spectra of fluorinated phthalocyanines are typical for symmetrical metal phthalocyanines (Table 3). They contain an intense Q-band in the visible region (650-715 nm) corresponding to the lowest degenerated it-it transition of the macrocyclic jt-chromophore, and a less intense and broader Soret band in the UV-region (300-380 nm). 

The perimeter model yields the standard Lb, La, Bb, and Ba labels for the excited states of molecules derived from an uncharged aromatic perimeter with 4N + 2 electrons, and the L, L2, Bi, and B2 labels for those of molecules derived from charged aromatic perimeters (some of the latter have structure-specific labels, e.g., in porphyrins and phthalocyanins the L states are called Q and the B states are called Soret). 

Phthalocyanines exhibit two absorption bands, one in the visible region at 600-700 nm (the Q-band) and the other in near-UV at 300-400 nm (the Soret) [74]. The vapor phase spectra are usually blue-shifted several hundred cm with respect to the solution spectra. While the spectrum of HaPc shows two clear vibronic bands at 698.5 and 663 nm in 1-chloronaphthalene solution, most phthalocyanines show only one absorption band and an absorption shoulder in the visible absorption. The visible absorption of phthalocyanine is not sensitive to the central metal ion. A summary of the absorption spectral data of phthalocyanines has been compiled in an earlier review by Lever [46]. 

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