Ethylenediamine control of the supramolecular chemistry of magnesium phthalocyanine

Abstract

The two axially ligated magnesium phthalocyanine derivatives, MgPc(EDA) and MgPc(H2O), were obtained directly by thermal reaction of MgPc in ethylenediamine (EDA) solution. Both complexes, MgPc(EDA) and MgPc(H2O), co-crystallize with the water molecule yielding good-quality single crystals 1. Presence in the crystals 1 the MgPc(H2O) results from the high affinity of MgPc to trace of water in the solvent as well as due to the high affinity of MgPc to moisture in air. The axially substituted magnesium phthalocyanine derivatives, MgPc(EDA) and MgPc(H2O), are, as expected, non-planar MPcs and interact with each other through a solvated water molecule to form supramolecular aggregates linked by NH…O and OH…N hydrogen bonds. Supramolecular arrangement of the non-planar MgPc-derivatives in crystal is characterized by a reduction of π···π interactions and an improvement in inter-system crossing in relation to parent MgPc, which results in increase its solubility and improved photophysical and photochemical properties. The aggregation behavior of the MgPc(EDA) and MgPc(H2O) complexes building crystals 1 in EDA and ethanol solutions was investigated. The MgPc(EDA) and MgPc(H2O) complexes building crystals 1 in an ethanol solution are stable, while in the EDA solution, one of them undergoes demetallation with formation of a metal-free phthalocyanine, since the UV–vis absorption spectrum versus time shown additional electronic absorption band in the region known as the Q-band which is typical for the spectrum of H2Pc. Besides, the UV–Vis spectroscopic characterization of the crystals 1 in solutions, the diffuse reflectance spectroscopic (DSR) characterization on the solid sample of 1 was performed. The DSR spectra of 1 exhibit broad bands with a small blue-shift that might be attributed to a larger exciton coupling resulting from closer contacts between the molecules than in solution. In order to support and verify the experimental results, the DFT and time-dependent (TD) DFT calculations were performed.