# Crystallization-Induced Coordination Diversity of Cu(I)-Pyridine Halide Complexes Resulting in Optical Tunability

## TL;DR

This paper explores how crystallization can create diverse copper(I) complexes with tunable optical properties, useful for luminescent and photoactive applications.

## Contribution

The study introduces crystallization-induced coordination diversity in Cu(I)-pyridine halide complexes for optical tunability.

## Key findings

- Crystallization leads to various coordination motifs in copper(I) complexes with different halides.
- Solid-state phosphorescence can be tuned from sky blue to deep red with high quantum yields and radiative rates.
- DFT/TD-DFT calculations reveal structure–property relationships controlling photophysical behavior.

## Abstract

Copper­(I) derivatives have emerged as a versatile class
of luminescent
and photoactive materials, combining earth abundance, structural adaptability,
and rich excited-state dynamics that enable their application in luminescent
devices, photocatalysis, and sensing technologies. Herein, we report
a family of copper­(I) pyridine halide complexes supported by a 4-(N,N-dimethylamino)­pyridine (DMAP) ligand, featuring crystallization-induced
diversity of coordination motifs. The variation of halides and stoichiometry
of [Cu­(NCMe)4]­BF4/CuX (X = Cl, Br, I) precursors
enabled the selective isolation of a series of cationic/neutral mono-
and multinuclear hybrid species, namely, [(DMAP)2Cu]­BF4, [(DMAP)­CuCl], [(DMAP)4Cu2(μ2–X)]­BF4 (X = Cl, Br), [(DMAP)4Cu4(μ2-Br)2(μ3-Br)2]­[(DMAP)2Cu]2(BF4)2, and [(DMAP)2Cu2(μ2–I)2]2[(DMAP)2Cu]3(BF4)3. Single-crystal X-ray diffraction
revealed that the bridging mode of halides is decisive in governing
packing topology, nuclearity, and structural arrangement of metal/cluster
centers. Photophysical studies demonstrated tunable solid-state phosphorescence
spanning from sky blue (478 nm) to deep red (640 nm), with quantum
yields and radiative rates reaching 0.41 and 7.3 × 104 s–1, respectively. Advanced photophysical studies
combined with DFT/TD-DFT calculations facilitated the untangling of
structural characteristics responsible for control over photophysical
properties such as triplet formation and its (non)­radiative decay
or the nature of luminescent excited states, defining multiple structure–property
relationships. These results establish an effective strategy to unlock
new coordination motifs in copper­(I) halide chemistry and to achieve
broadband optical tunability in earth-abundant photoactive materials
by means of crystallization tools.