# Positional Fluorination of Phenylpyridine: Unexpected Electronic Tuning in Bis-Cyclometalated Iridium(III) Acetylacetonate Complexes

## TL;DR

This paper shows how fluorination at different positions on a ligand can change the electronic properties and emission color of iridium complexes, useful for technologies like OLEDs.

## Contribution

The study reveals that positional fluorination nontrivially tunes HOMO and LUMO levels, affecting emission color in iridium complexes.

## Key findings

- Para fluorination results in the most red-shifted emission compared to non-fluorinated complexes.
- Meta and ortho fluorination lead to progressively bluer emission, supported by electrochemical and computational data.
- An asymmetric complex shows intermediate properties between symmetric counterparts.

## Abstract

We report a systematic study on the effect of positional
fluorination
of 2-phenylpyridine (Hppy) cyclometalating ligands in neutral iridium­(III)
complexes of general formula [Ir­(Fppy)2(acac)], where Fppy
= 2-(fluorophenyl)­pyridine and acac = acetylacetonate. Five complexes
(C1–C5) were synthesized, including
a nontrivial asymmetric derivative. The archetypal complexes [Ir­(ppy)2(acac)] (C6) and [Ir­(dFppy)2(acac)]
(C7) were also prepared, to serve as reference. We demonstrate
that fluorination does not simply induce a general blue shift, but
that the specific substitution site on the phenyl ring of the cyclometalating
ligands tunes HOMO and LUMO levels in a nontrivial fashion. Indeed, para fluorination (as in C3) affords the most
red-shifted emission of the series, even compared to the fluorine
free C6 complex. On the other hand, meta and ortho substitutions (as in C4 and C2, and C1, respectively) result in progressively
bluer emission, in line with electrochemical and computational data.
The asymmetric complex (C5) exhibits intermediate properties,
reflecting the averaged contribution of the two parent symmetric complexes
(C1 and C3). This work establishes positional
fluorination as a powerful design tool for tuning the electronic structure
and emission color of cyclometalated iridium­(III) complexes, with
relevance for photocatalytic applications, OLED development, and other
photonic technologies.