Similar to the iridium complexes, the UV region of the absorption spectrum of reactive oxygen species causing a decomposition of the PC. Moreover, the UV-vis absorption spectrum of Eosin Y has previously been shown to be sensitive to pH. In a photoborylation reaction of diazonium salts using Eosin Y as the PC, no band between 450 -550 nm was present in the UV-vis absorption spectrum, while after the addition of base, this band appeared. This is presumably due to the formation of the dianonic form of Eosin Y that is associated with this band. Therefore, under the present reaction conditions, the loss of this band after irradiation suggests that the dianionic form of Eosin Y is no longer present, either because it resides back in the neutral form (although this seems unlikely due to the large excess of basic amine present), or the PC has degraded.