Photocatalyzed and photosensitized
chemical processes have seen
growing interest recently and have become among the most active areas
of chemical research, notably due to their applications in fields
such as medicine, chemical synthesis, material science or environmental
chemistry. Among all homogeneous catalytic systems reported to date,
photoactive copper(I) complexes have been shown to be especially attractive,
not only as alternative to noble metal complexes, and have been extensively
studied and utilized recently. They are at the core of this review
article which is divided into two main sections. The first one focuses
on an exhaustive and comprehensive overview of the structural, photophysical
and electrochemical properties of mononuclear copper(I) complexes,
typical examples highlighting the most critical structural parameters
and their impact on the properties being presented to enlighten future
design of photoactive copper(I) complexes. The second section is devoted
to their main areas of application (photoredox catalysis of organic
reactions and polymerization, hydrogen production, photoreduction
of carbon dioxide and dye-sensitized solar cells), illustrating their
progression from early systems to the current state-of-the-art and
showcasing how some limitations of photoactive copper(I) complexes
can be overcome with their high versatility.