## 3 Solid-Supported Eosin Y
### Functionalized Eosin Y Materials in Photocatalytic Applications  
A straightforward way of supporting Eosin Y is the exploitation of the fact that it readily generates an anion. The **EY3** and **EY4** anionic forms of Eosin Y can be tethered by ionic interactions to a positively charged ion-exchange resin. In this sense, very recently, [PERSON] and co-workers reported the realization of a polystyrene-supported Eosin Y (PS-eosin Y, **15**) through an anion-exchange reaction (Scheme 10a) as a reusable photocatalyst for visible light-mediated organic transformations such as the oxidation of thioethers to sulfoxides and phenylboronic acids to phenols under open atmospheric air [32]. In the first case, sulfoxides are generally obtained with modest-to-good yields; thioanisole bearing both electron-donating groups and electron-withdrawing groups underwent selective oxidation, leading to the formation of the corresponding sulfoxides with 64-88% yield when treated with 3 mol% of PS-eosin Y upon irradiation with 3 W green LEDs for 6 h at room temperature. Higher results were obtained when the alkyl chain of the sulfide was increased (Scheme 10b). In the same manner, substituted phenylboronic acids irradiated using a 14 W household CFL lamp in the presence of 5 mol% of PS-eosin Y and triethylamine (TEA) as a sacrificial electron donor gave the desired phenols with 56-87% yield after 36 h (Scheme 10c). In both cases, the reaction requires only atmospheric air as an oxidant, and the functionalized resin can be recycled and reused up to six times without exhibiting a drop in chemical efficiency. In a completely different approach, [PERSON] and [PERSON] [33] and [PERSON] and [PERSON] [34] used the four bromine atoms of the Eosin Y backbone to create different porous organic polymers characterized by an extensive \(\pi\)-network, which have been employed in dehydrogenase aza-Henry reactions and in the photoreduction of CO\({}_{2}\) under light activation. Many porous organic polymers were synthetized, and high levels of efficiency were observed when POP-(**17**) and POP-(**19**) materials were used. These functionalized polymers were, respectively, synthetized by a palladium-catalyzed Sonogashira-Hagihara cross-coupling reaction between Eosin Y and 1,3,5-triethynylbenzene (**16**) and 1,4-diethylnylbenzene (**18**) (Scheme 11a). Morphological investigations confirmed that these polymers are microporous materials in which the Eosin Y monomer skeleton is perfectly embedded into the polymer network. POP-(**17**) material has been successfully employed in the photocatalytic aza-Henry reaction of tetrahydroroisoquinolines with nitroalkanes, leading to the formation of desired products with good-to-excellent yields after 24 h of irradiation with a 14 W fluorescent lamp. After reaction completion, the material was recovered and recycled twelve times without any significant loss of catalytic efficiency (Scheme 11b). POP-(**19**) material consists of a dark-red powder, which was employed to promote the photoreduction of CO2 to CO in the presence of gaseous H2O under visible-light irradiation under ambient conditions (Scheme 11c). CO was produced with a production rate of 33 umol g-1 h-1 and selectivity of 92%, which decreased to 73.5% after five runs. In 2019, taking advantage of magnetic nanoparticle properties, [PERSON] and [PERSON] reported the use of Eosin Y-functionalized nanoparticles to promote C-C and C-P coupling reactions under irradiation with green light [35]. As illustrated in Scheme 12, 15 nm magnetite silica core-shell nanoparticles were chemically modified with a benzyl linker bearing a quaternary ammonium-ion salt to ionically tether Eosin Y to the magnetic nanoparticle. The catalytic nanoparticles (NPs) Eosin Y-(**20**) were then used in the photoredx catalytic generation of an iminium ion derived from different tetrahydroisoquinolines, which undergoes the nucleophilic addition of different nucleophiles such as nitroalkanes, malonomitrile, dimethylmalonate and phosphites.