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.