# Role of Spacers in Molecularly Linked RuRh Dyads: A Comparative Synthetic and Ultrafast Spectroscopic Investigation

## TL;DR

This study explores how spacers in RuRh complexes affect their photocatalytic performance using synthetic and spectroscopic methods.

## Contribution

The paper introduces a comparative analysis of Ru(II)-based dinuclear complexes to understand the role of spacers in photocatalysis.

## Key findings

- Minor structural changes in the complexes significantly influence photocatalytic activity.
- The spacer choice determines photophysical and photochemical properties.
- Ultrafast spectroscopy and quantum calculations reveal electronic process dynamics.

## Abstract

Supramolecular photocatalysts consisting of photosensitizer
(PS),
bridging ligand (BL), and catalytic center (CAT) have garnered significant
attention in solar fuel applications. In this study, the photophysics
and photocatalytic properties of two Ru(II)-based dinuclear complexes,
specifically [(tbbpy)2Ru(p(Ph)np)Rh(Cp*)Cl]3+ (n = 0, 1; Ru(pp)Rh for n = 0 or Ru(p(Ph)p)Rh for n = 1; tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine,
Cp* = pentamethylcyclopentadienyl, Ph = phenyl, p = 1,10-phenanthroline),
are investigated. These complexes are studied as model complexes only
differing
by the distance between PS and CAT and thus allows a selective investigation
of the influence of spacers in light-driven catalysis. A joint synthetic,
spectroscopic, and theoretical approach, incorporating time-resolved
absorption and emission spectroscopy, resonance Raman (rR) spectroscopy,
density functional theory (DFT), and time-dependent (TD)DFT calculations,
allows for comprehensive structural, electrochemical, photophysical,
and photochemical characterization. Our findings suggest that minor
structural variations in the intramolecular photocatalytic system
significantly impact photocatalytic activity and system stability.

Ru(II)-based dinuclear complexes, specifically
[(tbbpy)2Ru(p(Ph)np)Rh(Cp*)Cl]3+ (n = 0, 1; Ru(pp)Rh for n = 0 or Ru(p(Ph)p)Rh for n = 1; tbbpy
= 4,4′-di-tert-butyl-2,2′-bipyridine,
Cp* = pentamethylcyclopentadienyl, Ph = phenyl, p = 1,10-phenanthroline),
were investigated in solution. The light-driven electronic processes
are investigated through a combination of ultrafast spectroscopy and
quantum chemical calculations. The choice of a spacer determines the
photophysical and photochemical properties and consequently the resulting
photocatalytic activity.