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

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

^aDepartment of Chemistry, Durham University, South Road, Durham, DH1 3LE. UK

^bDepartment of Physics, Durham University, South Road, Durham. DH1 3LE. UK

^cDepartment of Mathematics, Physics and Electrical Engineering, Northumbria University, Ellison Place, Newcastle upon Tyne. NE1 8ST. UK

E-mail: marc.k.etherington@northumbria.ac.uk and paul.mcgonigal@durham.ac.uk

N-Alylkation provides a simple synthetic tool to engineer the charge transfer, fluorescence energy and quantum yield of tertiary amine systems. Using quinine as a model system we have deconvoluted the changes in emission spectra that are observed traditionally as a function of pH and provided a synthetic method to change one parameter at a time. The modification provides fundamental insight into the through-space charge-transfer state that molecular quinine forms and how it provides a loss pathway that can be turned on and off by modifying the lone pair on the quinuclidine nitrogen group [1,2]. By producing new quinine-based salts we have obtained control over their charge-transfer nature and have developed a pathway to superior blue-emitting fluorescence standards. Our preliminary compounds show emission colours that are independent of solvent polarity and pH and in the solid state. This modification is applicable to other tertiary amine-based compounds [3-5] and opens pathways to a new set of solid-state fluorescence standards and functional emitters that have uses in a wide range of photonic applications. Specific control of the charge transfer states in these compounds could mean these systems provide a new motif for thermally activated delayed fluorescence emitters and extend their uses further.

[1]      W. Qin, A. Vozza, A. M. Brouwer, J. Phys. Chem. C 2009, 113, 11790.

[2]      J. Qian, A. M. Brouwer, Phys. Chem. Chem. Phys. 2010, 12, 12562.

[3]      K.-L. L. Wang, W.-T. T. Liou, D.-J. J. Liaw, S.-T. T. Huang, Polymer (Guildf). 2008, 49, 1538.

[4]      J. Zhang, J. Chen, B. Xu, L. Wang, S. Ma, Y. Dong, B. Li, L. Ye, W. Tian, Chem. Commun. 2013, 49, 3878.

[5]      S. Achelle, J. Rodríguez-Lopez, C. Katan, F. Robin-Le Guen, J. Phys. Chem. C 2016, 120, 26986.