Synthesis, spectroscopy, electrochemistry, spectroelectrochemistry, Langmuir-Blodgett film formation, and molecular orbital calculations of planar binuclear phthalocyanines

Abstract

A planar binuclear phthalocyanine and its dizinc and dicobalt derivatives, in which two phthalocyanine units share a common benzene ring, have been studied by spectroscopy, electrochemistry, and spectroelectrochemistry. Their Langmuir-Blodgett film-forming properties have been examined, and the results of molecular orbital calculations on these and related systems are also presented. The properties are compared with those of the corresponding mononuclear control molecules. UV-visible-near IR absorption and magnetic circular dichroism spectroscopies and cyclic and differential pulse voltammetry indicate that, in these compounds, two relatively independent chromophore units interact and therefore that the two phthalocyanine planes are not completely planar in solution. The electrochemical and spectroelectrochemical measurements show the formations of various mixed-valence oxidation and reduction species in the binuclear compounds. The nonmetalated and dizinc complexes exhibit both Si and S2 emission. The radiative lifetimes (r) of the dizinc complex are smaller than those of the metal-free binuclear derivative for both Si and S2 emission, while the quantum yields ( fa) are larger. Furthermore, for S2 emission, the fa and t values of the binuclear compounds are larger than those of the corresponding mononuclear control molecules. Molecular orbital calculations within the framework of the Pariser-Parr-Pople approximation reproduce the splitting of the Q absorption band and further show that the splitting becomes larger the smaller the size of the shared common aromatic unit. In monolayers spread on water, the metal-free binuclear complex appears to have a slipped-stack conformation, tilted from the airwater interface normal plane. In Langmuir-Blodgett films, it may form a slipped-stack molecular arrangement with the stacking axis parallel to the substrate and/or a flat-lying conformation on the substrate surface.

Fluorescence Detected Induced Circular Dichroism Observed for Optically Active Binaphthyl-Linked Metal-Free and Zinc Phthalocyanines

“…Not only S1 but also S2 emission are reported from time to time for porphyrinoids, [10] although the latter may need to be re-evaluated on the basis of a recent study, which called into question whether S2 emission is actually the result of an impurity generated by photodegradation. [11] As for the other Pc ligands that have been reported to date, [12][13][14] the Stokes Shift of the S1 emission is very small, while that of the apparent S2 emission is large. Compared with Pcs with normal substituent groups, the S1 emission appears at somehow longer wavelength and the quantum yields (Φ F = 0.12) are slightly smaller than those reported previously, since non radiative decay becomes easier with increasing wavelength.…”

Synthesis and some spectroscopic properties of tetra-2,3-pyridoporphyrazinatosilicon involving bulky axial ligands

“…Molecular orbital calculations were performed for the pyrrole proton-deprotonated species within the framework of the Pariser-Parr-Pople (PPP) approximation [26,27], where the parameters and other conditions were exactly the same as those we used in our previous publications [15,16,22]. (OH) 2 SiPyD, 5.…”

“…Indeed, it is known that the Q band of the macrocycles prepared from 2,3-dicyanopyridine and 2,3-dicyanopyrazine appears at shorter wavelength and has weaker intensity than the Q band of Pcs [18]. From the values of configurations the contribution of the HOMO-LUMO transition in the Q band decreased from 87% of the Pc dianion [15] to 85% of 1's dianion and further to 83% of the PyZ dianion [16]. Thus the 'purity' of the Q band increases for compounds which show this band at longer wavelength.…”

“…nuclear species without aggregation in solution, they can be considered to be highly representative data for the Pc, PyD and PyZ skeletons. Accordingly, in order to enhance our understanding of these spectra, we have calculated the molecular orbitals (MOs) of the PyD dianion within the framework of the Pariser-Parr-Pople (PPP) approximation(Table 1)and compared these with the results for the Pc[15] and the PyZ[16] dianion. In calculations performed under exactly the same conditions, the Q and Soret bands of the dianions of Pc, 1 and PyZ are estimated to lie at 662 and 332 nm, 642 and 331 nm and 634 and 331 nm respectively, reproducing the experimental data and trends fairly correctly.…”

Binuclear metallophthalocyanine supported on treated silk fibres as a novel air-purifying material

“…The absorption peaks at 1134, 1093, 771, and 745 cm ÿ1 in Co 2 Pc 2 were assigned to phthalocyanine, and the strong absorption peak at 1704 cm ÿ1 was due to the carboxylic acid groups in Co 2 Pc 2 . Synthesized products were further confirmed according to the literatures [21]. …”