Effects of Peripheral Substituents on the Optical and Electrochemical Properties of Dibenzo‐5,10,15‐triazaporphyrins

In contrast to the great advances of phthalocyanine-based materials, the potential of 5,10,15-triazaporphyrins has not been realized because of the lack of fundamental information about their structure-property relationships. Here, we report new derivatives of dibenzo-5,10,15-triazaporphyrin (DBTriAP) with aryl or alkyl substituents at the meso and/or β positions. Freebases of DBTriAP were prepared by the condensation of two types of 1,9-dibromodipyrrins with 1,3-diiminoisoindoline and subsequent functionalization of the β-pyrrolic carbons. Zinc(II) complexes of DBTriAP were obtained by complexation of the corresponding freebases with zinc(II) acetate. The optical and electrochemical properties of the DBTriAP derivatives were studied by steady-state and transient ultraviolet/visible absorption/emission spectroscopy, magnetic circular dichroism spectroscopy, cyclic voltammetry (CV), and density functional theory (DFT) calculations. Replacing the β-pyrrolic hydrogens of the 5-mesityl-DBTriAP derivatives with aryl groups resulted in substantial red shifts of the low-energy absorption band because of the effective π-delocalization and/or charge-transfer interaction with the DBTriAP chromophore. The 2,3,17,18-tetraethyl-DBTriAP freebase exhibited split redox processes in its cyclic voltammogram, suggesting the rapid formation of a π-stacked dimer radical cation facilitated by the highly planar structure. Most of the DBTriAP derivatives emitted red fluorescence with quantum yields of 0.07-0.31, indicating their potential as luminescent materials.