Modulation of Charge Transfer by N-Alkylation to Control Photoluminescence Energy and Quantum Yield

Turley, A.T.; Danos, A.; Prlj, A.; Monkman, A.P.; Curchod, B.F.E.; McGonigal, P.R.; Etherington, M.K.

Abstract

Charge transfer in organic fluorophores is a fundamental photophysical process that can be either beneficial, e.g., facilitating thermally activated delayed fluorescence, or detrimental, e.g., mediating emission quenching. N-Alkylation is shown to provide straightforward synthetic control of the charge transfer, emission energy and quantum yield of amine chromophores. We demonstrate this concept using quinine as a model. N-Alkylation causes changes in its emission that mirror those caused by changes in pH (i.e., protonation). Unlike protonation, however, alkylation of quinine’s two N sites is performed in a stepwise manner to give kinetically stable species. This kinetic stability allows us to isolate and characterize an N-alkylated analog of an ‘unnatural’ protonation state that is quaternized selectively at the less basic site, which is inaccessible using acid. These materials expose (i) the through-space charge-transfer excited state of quinine and (ii) the associated loss pathway, while (iii) developing a simple salt that outperforms quinine sulfate as a quantum yield standard. This N-alkylation approach can be applied broadly in the discovery of emissive materials by tuning charge-transfer states.

Citation

Turley, A., Danos, A., Prlj, A., Monkman, A., Curchod, B., McGonigal, P., & Etherington, M. (2020). Modulation of Charge Transfer by N-Alkylation to Control Photoluminescence Energy and Quantum Yield. Chemical Science, 11(27), 6990-6995. https://doi.org/10.1039/d0sc02460k

• Journal Article Type: Article
• Acceptance Date: Jun 8, 2020
• Online Publication Date: Jun 9, 2020
• Publication Date: Jul 21, 2020
• Deposit Date: Jun 9, 2020
• Publicly Available Date: Jun 9, 2020
• Journal: Chemical Science
• Print ISSN: 2041-6520
• Electronic ISSN: 2041-6539
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Issue: 27
• Pages: 6990-6995
• DOI: https://doi.org/10.1039/d0sc02460k
• Related Public URLs: https://chemrxiv.org/articles/Modulation_of_Charge_Transfer_by_N-Alkylation_to_Control_Photoluminescence_Energy_and_Quantum_Yield/12159114/1