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 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 language | English |
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Pages (from-to) | 6990-6995 |
Number of pages | 6 |
Journal | Chemical Science |
Volume | 11 |
Issue number | 27 |
DOIs | |
Publication status | Published - 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 Yut for solving single crystal XRD structures. A. T. T. acknowledges an EPSRC DTG. A.
Publisher Copyright:
© The Royal Society of Chemistry.