Phthalocyanine absorption spectra

Porphyrin [125-128] and phthalocyanine [129] derivatives are also employed as photosensitizers in DSSCs. A nanocrystalline Ti02 solar cell sensitized by Cu chlorophyllin produced 2.6% efficiency (./ . = 9.4 mA/cm2 and Voc = 0.52 V) under 100 mW/cm2 [127]. In order to develop new, efficient, metal dye photosensitizers, both an increase in the absorption coefficient of the metal complex and a greater red shift of the absorption spectrum is required. 

Perylenediimides represent another class of photoactive dyes which are characterized by their strong fluorescence emission and facile electrochemical reduction. Recently, a supramolecular bis(phthalocyanine)-perylenediimide hetero-triad (compound 42) has been assembled through axial coordination [47]. Treatment of perylenediimide 43, which has two 4-pyridyl substituents at the imido positions, with 2.5 equiv. of ruthenium(II) phthalocyanine 44 in chloroform affords 42 in 68% yield (Scheme 3). This array shows remarkable stability in solution due to the robustness of the ruthenium-pyridyl bond. Its electronic absorption spectrum is essentially the sum of the spectra of its molecular components 43 and 44 in... 

The photophysical properties of the self-assembled dimer [54]2 have been studied in detail with various spectroscopic and computational methods [53,54], In the lowest excited singlet (Si) state, the excitation delocalizes over the two macrocycles, and the non-radiative decay is enhanced by dimerization. By contrast, the exciton interaction is very weak in the lowest excited triplet (Ti) state. In the excited-state absorption spectrum recorded in 1-decane, two sharp bands at 658 and 694 nm are observed, which can be attributed to the Q bands of the Tx self-assembled phthalocyanine dimer. 

Figure 7 Complete set of 45 bands required to fill the absorption and MCD band envelopes of the phthalocyanine-rmg-reduced radical anion species [ZnPc(—3)] . The absorption spectrum was recorded at 77K, and the MCD spectrum at 40K. The bands were fitted using Gaussian-shaped bands with the identical band centers and bandwidths for pairs of absorption and MCD bands. A weak, Faraday term located at 14 860cm is due to a residual 1% impurity of neutral ZnPc(—2). Experimental data (sohd fine) fitted data (broken line). (Reproduced with permission from J. Mack, Y. Asano, N. Kobayashi, M. J. Stilhnan (2005) J. Am. Chem. Soc. 127 17697-17711. 2005 American Chemical Society)...

There are many examples of phthalocyanine derivatives, given the general designation azaphtha-locyanines, in which one (or two) of the carbons in each benzo unit is replaced by a nitrogen. The synthesis and properties of such macrocycles has been the subject of a detailed review.65 The physical properties of azaphthalocyanines differ from those of phthalocyanines. For example, they form hydrates readily, which complicates purification and they are protonated by, and soluble in, dilute acids. In addition, the Q-band in the UV/visible absorption spectrum is blue shifted relative to that of phthalocyanine.65 Importantly, the aza moiety can be quaternerized to give water-soluble or amphiphilic derivatives.66 Thus, the cyclotetramerization of symmetrical 2,3-dicyanopyrazines provides a route to isomerically pure 1,4,8,11,15,18,22,25-octaazaphthalocyanines. 

Phthalocyanines that contain four benzo units fused to the ring are termed naphthalocyanines. If the benzo units are fused to the 1,2,8,9(10,11),15,16(17,18),22,23(24,25)-positions, the parent compound is termed 1,2-naphthalocyanine alternatively, if fused to the 2,3,8,9,16,17,23,24-positions, it is called 2,3-naphthalocyanine (4). The linear benzoannulation of 2,3-napthalocya-nines results in a bathochromic shift of the Q-band in the absorption spectrum of lOOnrn as compared to phthalocyanine.36,69 In addition, their enhanced ability to generate singlet oxygen makes them candidates for photodynamic therapy. Most synthetic routes to 2,3-naphthalocyanines... 

Aroca and Loutfy report surface enhancement from phthalocyanine films with 15-nm silver overlayers. They estimate the enhancement at 1000, but give no details of their method of deriving it. Note, further, that the dye was investigated at a win-dow of its absorption spectrum. The dye in a film absorbs at 600 nm, while the surface studies reported were at 488 and 514.5 nm. 

Arsenic trichloride reacts with dilithium phthalocyanine in dimethyl-formamide to yield chloroarsenic phthalocyanine 808), which does not react with silver ions in pyridine. Its absorption spectrum has been recorded (Section V,B), but little else is known of the complex. 

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). 

In this review, we explain the SAC-CI applications to molecular spectroscopy with some examples. In Section 2, we briefly explain the theoretical and computational aspects of the SAC-CI method. Then, we show some SAC-CI applications to molecular spectroscopy the excitation and ionization spectra of tt-conjugated organic molecules (Section 3), collision-induced absorption spectra of van der Waals complex (Section 4), excitation spectra and NMR chemical shifts of transition metal complexes (Section 5), photofragmentation reaction of Ni(CO)4 (Section 6), absorption spectrum of free-base phthalocyanine (FBPc) and bacterial photosynthetic reaction center... 

Quite pronounced photovoltaic effects have been observed in Mx 1150 nm -chlorophyll a M2 sandwich cells, where Mx = A1 or Cr and M2 = Hg or Au.7e>77 These are ascribed to a Schottky barrier at the junction with metal Mx which has a lower work function than M2. If the Mi junction is the front (illuminated) electrode then the photovoltaic action spectrum is identical with the absorption spectrum of the chlorophyll. If it is at the rear, the action spectrum shows an inner filter effect, because only light absorbed in the region of the barrier is effective. Figure 11 shows the performance of a typical cell, which has a power conversion efficiency of ca. 10-3% at 745 nm. The best efficiency, 5 x 10-a%, was achieved by a Cr chlorophyll a Hg cell. Photovoltaic properties have also been reported in the cell A11 Mg phthalocyanine Ag, which has a Schottky barrier of height ca. 0.6 eV at the A1 junction.78 At 690 nm, the power conversion efficiency was ca. 10-2%. It has been shown that oxidized A1 contacts to Cu phthalocyanine are blocking.79... 

Why are phthalocyanines blue or green and not red like the porphyrins The phthalocyanines have a similar macrocyclic structure to porphyrins so you might expect the same light-absorbing properties. They are not and one look at the UV-visible absorption spectrum of a phthalocyanine will show how it differs from a porphyrin. 

Fig. 7. Photoresponse of copper phthalocyanine. Photocurrent units are arbitrary left scale refers to lower curve, which is the absorption spectrum. (From ref. 37)...

Band in the absorption spectrum of phthalocyanine lutetium form a thin layer is characterized by X, = 662 nm. This indicates that the sandwich complex is in neutral form. After treatment of the film an alcoholic solution happens recovery process. What does the reduction of the band intensity X = 662 nm, an increase in absorption X. = 618 nm and the appearance of the shoulder X = 708 nm. That the shape and position of the spectrum corresponds to phtlialocyanine blue forms. 

The absorption spectrum of the majority of metal phthalocyanines (e g., MgPc in DMF, see Fig. 13.2) in solvents has a narrow absorption band in the range 665-675 nm (depending on the cerrtral metal ion) characteristic for a monomer state of metal complex [16-19],... 

As it was merrtioned earlier, the aggregate state of metal phthalocyanines depends on the central metal ioa Figure 13.3 shows the absorption spectrum of metal-free phthalocyarrine in different supramolecular systems. Both for potymers and micellar solutions a broad absorption band at 600-650 nm was observed. Hence metal-free phthalocyarrine in these supramolecular systems is presented in the form of its H-aggregates. 

Fig. 26 a,b. Photoaction spectra of unsubstituted and substituted copper(II) phthalocyanines a) PcCu, b) MegPcCu (the dotted line represents the UV/VIS absorption spectrum)... 

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