Excited State Dynamics Govern Emission Properties of Unique Silsesquioxane-Salphen-Based Zinc Compounds

TL;DR

This paper describes the synthesis and study of new zinc compounds with unique structures that show improved light-emitting properties, potentially useful for medical treatments like photodynamic therapy.

Contribution

A novel mechanochemical method in silsesquioxane chemistry and the design of new ligands for Zn2+ coordination with enhanced photophysical properties.

Findings

The compounds show improved photophysical properties due to aggregation in solution.

Excited state dynamics significantly influence the emission properties of the compounds.

The complexes can generate singlet oxygen, relevant for photodynamic therapy applications.

Abstract

This study aims to
develop a synthetic protocol for preparing salphen-based
hybrid compounds with silsesquioxane T8 cages anchored
at the molecule’s periphery. Three types of coordination compounds
featuring κ4-N2O2-donating atoms
were obtained via a sequence of reactions. These compounds differ
in the arene linker between the salphen and silsesquioxane fragments.
An individual synthetic pathway was developed for the preparation
of aldehydes, followed by a tailored strategy for the synthesis of
the final complexes employing both solution-based and mechanochemical
methods in the solid state. The latter represents a novel technique
in silsesquioxane chemistry. The newly designed ligands were used
for the coordination of Zn2+ ions to evaluate their ligation
properties and to determine the photophysical properties of the resulting
complexes in comparison to their bare ligand molecules. Using absorption
and emission spectroscopy, combined with advanced time-resolved spectroscopic
methods, we demonstrated that the photochemical efficiency of these
compounds is influenced by their tendency to aggregate in solution,
which positively affects their photophysical properties and enhances
their potential for photodynamic therapy (PDT). Additionally, we explored
the ability of these complexes to generate singlet oxygen (1O2) depending on the architecture of the designed ligands.
The results indicate that the excited state dynamics plays a crucial
role in determining the emission properties of the studied compounds,
which may have significant implications for their applications in
medicine and materials science.

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