Intramolecular triplet–triplet energy transfer enhanced triplet–triplet annihilation upconversion with a short-lived triplet state platinum(ii) terpyridyl acetylide photosensitizer

Abstract

A model of a dendritic compound (Pt–DPA) with two Pt-complex photosensitizer chromophores and two 9,10-diphenylanthracene (DPA) acceptor groups covalently attached to the periphery and the core of the poly(aryl ether) dendrimer of generation 1 was prepared. A triplet–triplet annihilation upconversion (TTA-UC) system (Pt–DPA/DPA–OH) was constructed in deaerated DMF by combining Pt–DPA with a dissociative acceptor (DPA–OH). Although the lifetime of the triplet state of the Pt-complex is only 52 ns, the upconversion fluorescence from DPA (400–460 nm) in the Pt–DPA/DPA–OH system was observed with a quantum yield of 0.22% upon selective excitation of the Pt-complex with a 473 nm laser, which is due to the efficient intramolecular triplet–triplet energy transfer (Φ_TTET > 0.81) from the Pt-complex photosensitizer to the DPA acceptor within Pt–DPA. The acceptor covalently linked with the photosensitizer acts as an energy-relay to transfer the harvested energy to the dissociative acceptor which further undergoes the TTA process. The efficient intramolecular triplet–triplet energy transfer process between the photosensitizer and the acceptor plays an important role in the TTA-UC system building with a short-lived triplet state photosensitizer, which facilitates the production of the triplet state of the acceptor, thus advancing the TTA-UC process. This work presents a new strategy for construction of efficient TTA-UC systems utilizing short-lived triplet state photosensitizers.