ChemRxiv
These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
1/1
0/0

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

preprint
submitted on 20.04.2020 and posted on 22.04.2020 by Andrew T. Turley, Andrew Danos, Antonio Prlj, Andrew P. Monkman, Basile F.E. Curchod, Paul R. McGonigal, Marc K. Etherington
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. 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.

Funding

HyperOLED Horizon 2020 project no. 732013

EPSRC Doctoral Training Grant

History

Email Address of Submitting Author

marc.k.etherington@northumbria.ac.uk

Institution

Northumbria University, Ellison Place, Newcastle upon Tyne, NE1 8ST

Country

UK

ORCID For Submitting Author

0000-0003-2101-5757

Declaration of Conflict of Interest

The authors declare no conflict of interest

Exports