# Synthesis and Intramolecular Charge Transfer Studies on meso-Tetracyanobutadine-Functionalized Diphenylporphyrin Complexes Incorporating Copper and Nickel Metals

## TL;DR

This paper describes the synthesis and study of new porphyrin complexes with copper and nickel, showing how they transfer charge efficiently when light is applied.

## Contribution

The paper introduces novel donor–acceptor porphyrin complexes with enhanced push–pull properties and reports their intramolecular charge transfer dynamics.

## Key findings

- The TCBD-functionalized porphyrin complexes were synthesized and characterized with moderate yields.
- Femtosecond studies showed charge-transfer lifetimes of 383.1 ps and 484.7 ps for NiDPP-TCBD and CuDPP-TCBD, respectively.
- DFT calculations and X-ray structures revealed the electronic and molecular configurations of the complexes.

## Abstract

This study presents the synthesis and electrochemical characterization of meso-tetracyanobutadiene (TCBD)-functionalized diphenylporphyrin (DPP) complexes incorporating copper (Cu) and nickel (Ni) metals. These push–pull metallo diphenylporphyrin–TCBD complexes were synthesized via a [2 + 2] cycloaddition–retroelectrocyclization reaction between 5-bromo-15-formyl-10,20-diphenylporphyrin metal(II) complexes (M = Cu, Ni) and tributyl(phenylethynyl)stannate, followed by tetracyanoethylene (TCNE) addition. The resulting TCBD-functionalized porphyrins were obtained in moderate yields (70–75%) and thoroughly characterized by 1H and 13C NMR, UV-Vis spectroscopy, MALDI-TOF-MS, and single-crystal XRD. Although the single-crystal X-ray structure of NiDPP was solved, DFT calculations were used to determine the structures of the donor–acceptor MDPP-TCBD systems and to visualize their electronic structures. HOMO on the porphyrin π system and LUMO on the TCBD entity were observed, and energy level diagrams clearly laid out the electron donor and acceptor parts of the molecular systems. As expected, these novel donor–acceptor porphyrinoid assemblies exhibited enhanced push–pull properties in both the ground and excited states. Femtosecond transient absorption studies revealed that both NiDPP-TCBD and CuDPP-TCBD populate the charge-transfer state upon photoexcitation, with lifetimes of 383.1 ps and 484.7 ps, respectively, in benzonitrile. The charge-transfer states populated the triplet or doublet states (in the case of CuDPP) before returning to the ground state.