Exciton Localization on Ru-based Photosensitizers Induced by Binding to Lipid Membranes

TL;DR

This study investigates how lipid membrane environments influence exciton localization in Ru-based photosensitizers, revealing environment-dependent electronic structure changes crucial for designing optogenetic tools.

Contribution

It demonstrates that the lipid membrane environment causes exciton localization changes in Ru complexes, highlighting the environment's role in tuning electronic properties for optogenetics.

Findings

Exciton size decreases and localizes at one site in lipid membranes.

The environment influences electronic structure despite unchanged absorption spectra.

Electrostatic interactions with membranes affect exciton localization.

Abstract

The characterization of electronic properties of metal complexes embedded in membrane environments is of paramount importance to develop efficient photosensitizers in optogenetic applications. Molecular dynamics and QM/MM simulations together with quantitative wavefunction analysis reveal an unforeseen difference between the exciton formed upon excitation of [Ru(bpy)2(bpy-C17)]2+ embedded in a lipid bilayer and in water, despite the media does not influence the charge-transfer character and the excitation energy of the absorption spectra. In water the exciton is mainly delocalized over two ligands and the presence of non-polar substituents induces directionality of the electronic transition. Instead, when the photosensitizer is embedded into a lipid membrane, the exciton size diminishes and is more localized at one bypyridyl site due to electrostatic interactions with the positively charged surface of the bilayer. These differences show that the electronic structure of metal complexes can be controlled through the binding to external species, underscoring the crucial role of the environment in directing the electronic flow upon excitation and thus helping rational tuning of optogenetic agents.