Q-Band absorption

The metal-free porphyrazine, H Pz (3), was prepared by treatment of MgPz with minimum amount of triflouraaceticacid. When metal ion is removed from the center of core system, two N atoms in pyrrole ring are protonated. That was proved by both IR and UVWIS spectra of the compound. In the IR spectram, the peak around 3,240 cm shows the presence N-H bonds in H Pz. There is splitting in the Q band absorptions of H Pz, because of the symmetry of molecule. The Q band... 

Electronic spectra are especially useful to establish the stracture of the porphyrazines (3-4). UV-Vis spectra of porphyrazine core are dominated by two intense bands, the Q band around 660 mu and the B band in the near UV region of around 355 mu, both correlated to n—m transitions [12, 13]. UV-Vis spectra of metallo-porphyrazines (3, 4 in CHCy prepared in the present work exhibited intense single Q band absorption of the transitions around 665 nm and B bands in the UV region around 341-373 nm. For metal-free derivative 4, Q band is split into two... 

Phthalocyanines 84 and 85 substituted with six optically active alkyl chains and one chiral diol have been synthesized by mixed cyclization of the two corresponding phthalonitriles [72], The self-organizing properties of these compounds in chloroform solution and thin film have been studied by a range of spectroscopic and physical methods. Both compounds show split Q-band absorptions at 678 and 694 nm in chloroform, and the emission (at 696 nm) is red-shifted compared with that of a non-diol-containing analog. Upon addition of 0.5% methanol, the absorption at 694 nm... 

Tetraazaporphyrin (3) (or porphyrazine) differs from Pc only in the absence of the four benzo units. The Q-band absorption of tetraporphyrins is found at shorter wavelengths ( 600 nm)69 and they are less prone to oxidation, which is advantageous for their use in catalysis. The cyclo-tetramerization of maleonitrile by the Linstead method, usually initiated by magnesium alkoxide, is by far the most important route to tetraazaporphyrins (Table l).70 The preparation and properties of substituted maleonitriles have been reviewed.71... 

The polarized optical absorption and luminescence spectra of [M(porphine)j (M = Pd, Ni, or Hj) doped in triphenylene host crystals have been reported. Other workers have also reported high-resolution Q-band absorption and emission spectra of [M(porphine)] (M = Pd, Pt, or Cu) in single crystals of n-octane at 4.2 The lifetimes determined from the 0-0 linewidths in the absorption spectra were also given. 

FBPc, the well-known pigment, has much larger Q-band absorption than FBP. FBPc has tetraza-substitution at the four meso-positions and the butadiene units are attached to the four pyrrole rings. Therefore, free-base tetrazaporphin (FBTAP) is the structure intermediate between FBPc and FBP. In Fig. 39.16, the experimental and SAC-Cl spectra of FBPc [106] are compared. The SAC-Cl calculations successfully reproduced the experimental spectrum, which realized the detailed assignment and interpretation of the electronic mechanism for the strong absorption in FBPc. 

It has already been established that aerobic samples at 277K are unstable when subjected to dye laser excitation [5,6]. Damaged samples lose the 37 ns component and this is accompanied by a significant increase in the yield of the 6.5 ns component. A shift in both the steady state absorption and fluorescence maxima to the blue accompanies the loss of the 37 ns component (see table 1). When the sample shows an absorption maximum of 670.0 nm, 98% of the fluorescence is due to uncoupled chlorophyll with a 6.3 ns lifetime. This indicates that one of the effects of damaging the complex is to decouple chlorophyll from the charge separation reaction. Samples which show a Qy band absorption maximum less than 673 nm are termed "inactive . Fluorescence decays from inactive samples are best represented by a sum of two exponentials with at least 90% of the emission coming from uncoupled chlorophyll. All of the fluorescence decays from active D1/D2 samples were best represented by a four exponential model [6]. All active samples showed a Q band absorption maximum of (675.9 0.2) nm before and after all measurements. 

Steady state absorption and fluorescence measurements were made using a Perkin-Elmer 554 spectrophotometer and a Perkin-Elmer MPF-4 fluorimeter. Fluorescence lifetimes were measured using time-correlated single photon counting [3]. All of the fluorescence decays from D1/D2 samples were best represented by a sum of four exponentials. Details of the analysis of the decays can be found in [5]. All samples showed a Q band absorption peak of (675.9 0.2) nm before and after all time resolved measurements. 

They are not soluble in common organic solvents and hence it is difficult to determine the molecular weights of the polymers by the usual methods. UV-vis spectra were used by some authors to determine the degree of polymerization [70]. An increase of conjugation length (TT-electron delocalisation) is expected to increase the extinction coefficient and cause a red shift in Q band absorption. UV-vis absorption spectra of polymeric phthalocyanine are comparable to those of low molecular-weight phthalocyanines and show blue shifts at 2 > 350 nm (Q and B bands) The IR spectrum... 

Core-Expanded Benzoporphyrins Core-expanded porphyrins had a variety of beautiful colors, and this was due to their characteristic electronic spectra showing a strong Soret-band absorption around 400-500 nm and several weak Q-band absorptions over 500 nm [94]. Hexapyrrolic macrocycles of red-colored rubyrin (hexaphyrin(l. 1.0.1.1.0)) [95] and amethyrin (hexaphyrin( 1.0.0.1.0.0)) [96] were named after their mby-Iike and amethyst-Uke colors of precious stones. Among the expanded porphyrins, sapphyrin (penta-phyrin(l.l.l.l.O)) was the first example, which was seren-dipitously discovered during the synthesis of vitamin B12 by Woodward and coworkers in 1966 [97]. These electronic spectra could be easily modified by 71-expansion by the rDA method. 

The Q-band absorption maximum with the lowest energy. 

---