BODIPY–pyrene donor–acceptor sensitizers for triplet–triplet annihilation upconversion: the impact of the BODIPY-core on upconversion efficiency. Issue 6 (27th January 2022)

• Record Type: Journal Article
• Authors: Kiseleva, Natalia; Filatov, Mikhail A.; Fischer, Jan C.; Kaiser, Milian; Jakoby, Marius; Busko, Dmitry; Howard, Ian A.; Richards, Bryce S.; Turshatov, Andrey
• Is Part Of: Physical chemistry chemical physics. Volume 24:Issue 6(2022)
• Page Start: 3568
• Page End: 3578
• Publication Date: 2022-01-27
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp05382e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : BODIPY–pyrene heavy-atom-free donor–acceptor dyads are effective sensitizers for TTA-UC, with the highest TTA-UC quantum yield of 6.9% observed for the dyad with an unsubstituted BODIPY scaffold. Abstract : Triplet–triplet annihilation upconversion (TTA-UC) is an important type of optical process with applications in biophotonics, solar energy harvesting and photochemistry. In most of the TTA-UC systems, the formation of triplet excited states takes place via spin–orbital interactions promoted by heavy atoms. Given the crucial role of heavy atoms (especially noble metals, such as Pd and Pt) in promoting intersystem crossing (ISC) and, therefore, in production of UC luminescence, the feasibility of using more readily available and inexpensive sensitizers without heavy atoms remains a challenge. Here, we investigated sensitization of TTA-UC using BODIPY–pyrene heavy-atom-free donor–acceptor dyads with different numbers of alkyl groups in the BODIPY scaffold. The molecules with four and six alkyl groups are unable to sensitize TTA-UC in the investigated solvents (tetrahydrofuran (THF) and dichloromethane (DCM)) due to negligible ISC. In contrast, the dyad with two methyl groups in the BODIPY scaffold and the dyad with unsubstituted BODIPY demonstrate efficient intersystem crossing (ISC) of 49–58%, resulting in TTA-UC with quantum yields of 4.7% and 6.9%, respectively. The analysis of the elementary steps of the TTA-UC process indicates that heavy-atom-free donor–acceptor dyads are less effective than their noble metal counterparts, but may equal them in the future if the right combination of solvent, donor–acceptor sensitizer structure, and new luminescent molecules as TTA-UC emitters can be found.