Vibrational spectroscopy of phthalocyanine and naphthalocyanine in sandwich-type (na)phthalocyaninato and porphyrinato rare earth complexes : Part 13. The Raman characteristics of phthalocyanine in unsubstituted and peripherally octa(octyloxy)-substitute

The Raman spectroscopic data in the range of 500–1800 cm−1 for two series of thirty homoleptic bis(phthalocyaninato) rare earth complexes M(Pc)2 and M[Pc(OC8H17)8]2 [M = Y, La–Lu except Pm; H2Pc = unsubstituted phthalocyanine, H2Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyanine] have been collected and comparatively studied using laser excitation sources emitting at 633 and 785 nm. Under both laser excitations, the marker Raman band of Pc2− and [Pc(OC8H17)8]2− in the Raman spectra of Ce(Pc)2 and Ce[Pc(OC8H17)8]2 appears as a strong scattering at 1498–1501 cm−1 with contributions from both pyrrole CC and aza CN stretches together with isoindole stretchings. This band has been found to upshift to 1502–1528 cm−1 in the Raman spectra of MIII(Pc)2 and MIII[Pc(OC8H17)8]2 as the marker Raman band of phthalocyanine monoanion radicals, Pc− or [Pc(OC8H17)8]−. With laser excitation at 633 nm, Raman vibrations derived from isoindole ring and aza stretchings in the range of 1300–1600 cm−1 for both series are selectively intensified. In contrast, when excited with laser radiation of 785 nm, the ring radial vibrations of isoindole moieties and dihedral plane deformations between 500 and 1000 cm−1 for M(Pc)2 and M[Pc(OC8H17)8]2 intensify to become the strongest scatterings. The present Raman results also reveal that the frequencies of Pc breathing, pyrrole stretching, isoindole stretchings, aza stretchings and coupling of pyrrole and aza stretchings depend on the rare earth ionic size, shifting to higher wavenumbers along with the lanthanide contraction due to the increased ring–ring interaction across the series. Moreover, under these laser excitations, in particular under 785 nm laser line, the Raman spectrum appearance, i.e., the pattern of relative intensities, also changes systematically depending on the rare earth ionic size.

Graphical abstractThe solid state Raman spectra of the series of double-decker sandwich complexes M(Pc)2 and M[Pc(OC8H17)8]2 were recorded with excitation at 633 and 785 nm. The energies and relative intensities of various characteristic bands vary systematically with the ionic radius of the rare earth ion.Figure optionsDownload full-size imageDownload as PowerPoint slide