# Synthesis and Spectroscopic Characterization of Bis(thiadiazolo)benzoporphyrinoids: Insights into the Properties of Porphyrin-Type Systems with Strongly Electron-Withdrawing β,β’-Fused Rings

## TL;DR

This paper describes the synthesis and analysis of new porphyrin-like compounds with unique fused rings that alter their light absorption and electronic properties.

## Contribution

The study introduces bis(thiadiazolo)benzoporphyrinoids with strongly electron-withdrawing fused rings and their spectroscopic behavior.

## Key findings

- The compounds show large bathochromic shifts and strong absorption above 600 nm.
- NMR and computational methods confirmed global aromaticity and disconnected π-systems in the fused units.
- Metal complexes exhibit absorption shifts with increasing atomic number of the metal cations.

## Abstract

A series of porphyrinoids fused to highly electron-withdrawing bis(thiadiazolo)benzene units have been prepared and spectroscopically characterized. These structures have modified chromophores and exhibit large bathochromic shifts. The nickel(II), copper(II) and zinc complexes of a bis(thiadiazolo)benzoporphyrin were prepared, and these showed strong absorptions above 600 nm that shifted to longer wavelengths with increasing atomic number for the coordinated metal cations. Although the investigated porphyrinoids were poorly soluble, proton NMR data could be obtained, and these demonstrated that the structures possess global aromatic character. This was confirmed with nucleus-independent chemical shift (NICS) calculations and anisotropy of induced current density (AICD) plots. The AICD plots also demonstrate that the fused heterocyclic unit is disconnected from the porphyrinoid π-system, and in this respect, it differs from phenanthroline-fused porphyrinoids as it shows the presence of extended conjugation pathways.