Cycloreversion of EPOs to their corresponding parent compounds was monitored in DMSO using (Figure ): UV-Vis monitoring was performed over a period of 75 minutes at different set temperatures: 25, 37.5, 45 and 50 °C. At 25 °C, only DIPA-O2 was found to partially start the conversion, while at 45 and 50 °C all the newly synthesized EPOs were found to significantly release O2. At physiologically relevant temperature, 37.5 °C (Figure ), detectable amount of parent compounds PFPA and PCPA could be observed while PABA-O2 did not show any release. However, DIPA-O2 outperformed the other candidates showing nearly quantitative conversion to parent DIPA in 75 minutes.