Optical absorption and magnetic circular dichroism studies of hydrogen, copper(II), zinc(II), nickel(II), and cobalt(II) crown ether-substituted monomeric and dimeric phthalocyanines

Abstract

Monomeric and dimeric species of phthalocyanines with four, 15-crown-5-ether (1,4,7,10,13-pentaoxacyclopentadecane) voids at the 2,3 positions (ML)(where M = H₂, Cu, Zn, Ni, or Co), have been studied using optical absorption and magnetic circular dichroism (m.c.d.) spectroscopies. The ready solubility of these crown ether-substituted complexes in chloroform allows the measurement of spectral data over a wide wavelength range. In particular, absorption and m.c.d. data are reported for H₂L between 250 and 750 nm. The contribution by individual bands to the absorption and m.c.d. spectral envelopes measured for the monomeric and dimeric species of H₂L and NiL, has been determined using deconvolution calculations carried out on pairs of related absorption and m.c.d. spectra. M.c.d. A terms have been used to identify the O, B₁, B₂, and Nπ→π* degenerate transitions in the spectra of the monomer of NiL, at 14 946 cm^–1(669 nm) in the visible region, and at 24 398 (410), 31 414 (318), and 36 286 cm^–1(276 nm) in the u.v. region. The deconvolution calculations were also used to find the pairs of bands that arise from the exciton splittings in the Q and B bands of the cofacial dimers. In the spectra of the dimer of NiL, two degenerate bands are required to fit the observed envelope in the Q-band region [at 14 887 (672) and 15 832 cm^–1(632 nm)], which indicates that the splitting is ca. 950 cm^–1, while the pair of B bands are separated by ca. 2 180 cm^–1. The deconvolution of the spectra of the H₂L complex gives a value of 1 925 cm^–1 for the separation of the two components in the B band region.