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

Andrew T. Turley, Andrew Danos, Antonio Prlj, Andrew P. Monkman, Basile F.E. Curchod, Paul R. McGonigal, Marc Etherington
2020 unpublished
Charge transfer in organic fluorophores is a fundamental photophysical process that can be either beneficial, e.g., facilitating thermally activated delayed fluorescence, or detrimetnal, e.g., mediating emission quenching. <i>N</i>-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. <i>N</i>-Alkylation causes changes in its emission that mirror
more » ... on 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 <i>N</i>-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 <i>N</i>-alkylation approach can be applied broadly in the discovery of emissive materials by tuning charge-transfer states.
doi:10.26434/chemrxiv.12159114.v1 fatcat:ekgutnzk2zdwnac3v7oye4sp3y