Modulation of charge transfer by: N -alkylation to control photoluminescence energy and quantum yield

Andrew T. Turley, Andrew Danos, Antonio Prlj, Andrew P. Monkman, Basile F.E. Curchod, Paul R. McGonigal, Marc K. Etherington

Research output: Contribution to journalArticlepeer-review


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 analogue 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.

Original languageEnglish
Pages (from-to)6990-6995
Number of pages6
JournalChemical Science
Issue number27
Publication statusPublished - 21 Jul 2020

Bibliographical note

Funding Information:
We thank the Royal Society for access to their archives to retrieve the introductory quote, which was transcribed by Melody Bishop. We thank Dr Dmitry Yut for solving single crystal XRD structures. A. T. T. acknowledges an EPSRC DTG. A.

Publisher Copyright:
© The Royal Society of Chemistry.

Cite this