Experimental and Computational Study of Isomerically Pure Soluble Aza-phthalocyanines and Azasubphthalocyanines of Varying Number of Aza Units

TL;DR

This study investigates how increasing aza units in soluble azaphthalocyanines affects their physical and photophysical properties, using experimental and computational methods, and introduces a new efficient synthesis for a key building block.

Contribution

It provides new insights into the electronic effects of aza substitution and presents a novel, highly efficient synthesis method for a phthalocyanine building block.

Findings

Increasing aza units lowers HOMO levels and influences absorption energies.

New synthesis method for tetramethyltetraline phthalocyanine is highly efficient.

Crystals of specific azaphthalocyanines were successfully obtained.

Abstract

Herein, we present a series of isomerically pure, peripherically alkyl substituted, soluble and low aggregating azaphthalocyanines as well as their new, smaller hybrid homologues, the azasubphthalocyanines. The focus lies on the effect of the systematically increasing number of aza building blocks [-N=] replacing the non peripheral [-CH=] units and its influence on physical and photophysical properties of these chromophores. The absolute and relative HOMO-LUMO energies of azaphthalocyanines was analyzed using UV-Vis, CV and compared to density functional theory calculations (B3LYP, TD-DFT). Crystals of substituted subphthalocyanine, N2-Pc*H2 and N4-[Pc*Zn$\cdot$H2O] were obtained out of DCM. For the synthesis of the valuable tetramethyltetraline phthalocyanine building block a new highly efficient synthesis involving a nearly quantitative CoII catalyzed aerobic autoxidation step is introduced replacing inefficient KMnO4/pyridine as oxidant. The lowering of the HOMO level is revealed as the determining factor for the trend in the adsorption energies by electronic structure analysis.