Thiol-Activatable Triplet–Triplet Annihilation Upconversion with Maleimide-Perylene as the Caged Triplet Acceptor/Emitter

Efficient thiol-activated triplet–triplet annihilation (TTA) upconversion system was devised with maleimide-caged perylene (Py-M) as the thiol-activatable triplet acceptor/emitter and with diiodoBodipy as the triplet photosensitizer. The photophysical processes were studied with steady-state UV–vis absorption spectroscopy, fluorescence spectroscopy, electrochemical properties, and nanosecond transient absorption spectroscopy. The triplet acceptor/emitter Py-M shows week fluorescence (ΦF = 0.8%), and no upconversion (ΦUC = 0%) was observed. The quenching of fluorescence of Py-M is due to photoinduced electron-transfer (PET) process from perylene to maleimide-caging unit, which quenches the singlet excited state of perylene. The fluorescence of Py-M was enhanced by 200-fold (ΦF = 97%) upon addition of thiols such as 2-mercaptoethanol, and the ΦUC was increased to 5.9%. The unique feature of this thiol-activated TTA upconversion is that the activation is based on addition reaction of the thiols with the cage...