# Photoinduced Tautomerisation of ESIPT-Capable Iridium(III) Complexes with Rationally Designed Acyclic Diaminocarbene Ligands

## TL;DR

This paper describes iridium complexes that emit light through a unique proton transfer process involving the metal center, resulting in orange emission.

## Contribution

The study introduces the first metal–organic luminophores where the metal center directly participates in the ESIPT mechanism.

## Key findings

- Pyrazine-derived complexes show a 100 nm redshift in phosphorescence compared to pyridine analogues.
- The ESIPT process is facilitated by the iridium center enhancing the basicity of the pyrazine ring.
- Density functional theory calculations support the solvatochromic emission behavior.

## Abstract

A series
of ESIPT-capable IrIII-(acyclic diaminocarbene
species) (ESIPT = Excited-state intramolecular proton transfer) exhibiting
strong photoluminescence properties is described. The emission profile
is strongly influenced by the nature of the azaheterocyclic fragment
in the diaminocarbene ligand: pyrazine-derived species display phosphorescence
bands red-shifted by approximately 100 nm compared to their pyridine
analogues. This redshift is attributed to the luminescence of tautomerized
species formed via an ESIPT process, wherein the iridium center enhances
the basicity of the pyrazine ring, facilitating proton transfer from
the Ccarbene–NH groups. This interpretation is supported
by the solvatochromic emission behavior of complexes prepared and
corroborated by density functional theory calculations. Prepared IrIII-(acyclic diaminocarbene species) complexes represent the
first example of metal–organic luminophores in which the ESIPT
mechanism involves direct participation of the metal center, resulting
in orange emission.