inorganic chemistry

ABSTRACT

Rhenium(I) diimine carbonyl complexes have been well
investigated because of their functionalities, such as the intense
emission properties, capabilities as a building block for multinu-
clear complexes, and photocatalytic activities.
This chapter describes the following three topics of the rhe-
nium complexes including recent reported works: photophysics,
photochemical reactions, and photocatalyses.
After Section I, the photophysical processes of the rhenium
complexes are briefly summarized: the electronic structures, the
photophysical relaxation processes,and the effects of intramolecular
weak interaction between ligands on the photophysical properties.
The next section about photochemical reactions includes ligand
substitution, homolysis, and reactions of the ligand on the rhe-
nium complexes. This section also includes synthesis of emissive
multinuclear rhenium(I) complexes using the photochemical
ligand substitution.
The last section describes unique and high photocatalytic
activities of the rhenium(I) diimine carbonyl complexes, especially
for CO 2 reduction. The photocatalyses of mononuclear rhenium
complexes, multicomponent systems, supramolecular systems
with a Ru(II) complex as a photosensitizer, and a rhenium complex
with periodic mesoporous organosilica as a light-harvesting
system.

Keywords:Rhenium complex; Photophysics; Photochemistry;
Photocatalyst.

I. Introduction

The photophysics and photochemistry ofd^6 transition metal
complexes, such as Re(I), Ru(II), Os(II), and Ir(III), with
a-diimines as electron acceptor ligands have been widely
investigated during past four decades. These complexes have
been frequently used as photofunctional molecules because of
the following common properties( 1 – 16 ):

1. Quantum yields for the formation of stable triplet metal-to-
   ligand charge transfer (MLCT) and/orpp* excited states are
   very high, usually almost unity.


2. Many of the complexes are emissive even in solution at room
   temperature, and the lifetimes of the lowest excited state
   are long, typically several hundred nanoseconds.

138 HIROYUKI TAKEDAet al.