## 1 Introduction  
In 1912, Prof. [PERSON] envisioned a future in which chemical processes would be mostly run by a sustainable, abundant and never-ending energy source--photons coming from our Sun [1; 2]. More than 100 years later, we are still far from reaching that goal, but significant progress has been achieved in organic chemistry thanks to the advent of visible light photoredox catalysis. With this approach, chemical transformations (redox reactions) can be promoted in a catalytic way using energetic photons obtained from light. In contrast to non-catalyzed photochemistry, which employs powerful UV lamps, the chemical transformations of photoredox catalysis are usually achieved by photons of the visible light spectrum. For this to work efficiently, an absorbing sensitizer (photoredox catalyst) needs to be present. Photoredox catalysis possesses the intrinsic advantage of allowing chemical reactions to proceed that are otherwise difficult to realize. One of the first examples related to photoredox catalysis was published in 1978 from [PERSON] and co-workers, where a light-induced and dye-accelerated reduction of phenacyl sulfonium salts was performed in the presence of a Ru(II)(bipy)\({}_{3}\)Cl\({}_{2}\) catalyst and substituted 1,4-dihydroxyproyridine as a reducing agent [3]. A few years later, it was found that a similar ruthenium complex was able to catalyze the photo-oxidation of carbonyls to aldehydes when operating in the presence of visible light [4]. Starting from these seminal studies, many developments have been made in the field, and today, processes involving metal complexes, organic dyes and solid materials (semi-conductors or conjugated organic polymers) as molecular photoredox catalysts are known [5; 6; 7; 8; 9]. A typical photoredox catalytic cycle is shown in Scheme 1. Usually, the photoredox catalyst **PC** is excited with a photon of a suitable wavelength to generate the excited state **PC\({}^{\star}\)**. This new species can be then subjected to a reductive or oxidative step according to the nature of the reaction partners. In the first case, **PC\({}^{\star}\)** could receive a single electron from reactant **D** (\"donor\", _reductive quenching cycle_)to form a **PC\({}^{-}\)** species. This species, after a second single electron transfer process, can be oxidized to **PC** in the presence of reactant **A**. In this way, the initial photoredox catalyst is regenerated, closing the catalytic cycle. Conversely, in an _oxidative quenching cycle_, activated **PC\({}^{+}\)** species can be subjected to an abstraction of a single electron in the presence of reactant **A** (\"acceptor\"). This generates the oxidized species **PC\({}^{+}\)**, which can be reduced by reactant **D** to regenerate the photoredox catalyst **PC**. Independently of the quenching cycle involved, the net charge of the photoredox catalyst does not change, while formally, the radical cation and anion of reactants **A** and **D** recombine to form the product **P**. Most photoredox catalytic reactions employ heavy metal complexes as sensitizers, which are toxic, harmful to the environment, expensive and not sustainable for industrial processes. Organic dyes such as Eosin Y (EY) are very preferable compared to heavy metal complexes, since they can be obtained at low cost and present good availability since they can be synthesized from the live feedstock. Furthermore, organic dyes generally possess no toxic properties and are environmentally benign. Considering the numerous reviews published in the last few years in this very wide field [10; 11; 12], in the present contribution, only the most recent and significant applications of Eosin Y as an organo-photocatalyst in homogeneous reactions performed under fluidic conditions and in solid-supported catalyst reactions will be discussed. The most important employment of Eosin Y is related to its use as a filler in the production of dye-sensitized solar cells [13; 14; 15; 16] and as a photoredox catalyst in organic synthesis [10; 11].