Re-examination of the emission properties of alkoxy- and thioalkyl-substituted phthalocyanines.

The role of n-->pi( *) transitions in the optical spectra of alkoxy- and thioalkyl-substituted phthalocyanines with peripheral substituents is re-examined, based on a detailed analysis of UV-visible absorption, magnetic circular dichroism (MCD) and fluorescence emission spectral data and the results of density functional theory (DFT) and time dependent-density functional theory (TD-DFT) calculations. The npi( *) excited states associated with the lone pairs of the peripheral heteroatoms have been proposed as the origin of a second emission peak observed in the 400-600nm region, which has been assigned as S(2) emission, since S(1) fluorescence associated with the Q band is observed in the near IR region. Our results demonstrate that emission from a photodecomposition product can fully account for this violet emission and that reports of S(2) emission for peripherally substituted phthalocyanines and porphyrazines should be treated with caution. Copyright 2009 Elsevier Inc. All rights reserved.