Controlling and Fine-Tuning Charge-Transfer Emission in 2,6-Dicyanoaniline Multichromophores Prepared through Domino Reactions: Entry to a Potentially New Class of OLEDs

Substituted
2,6-dicyanoanilines are versatile electron donor–acceptor
compounds, which have recently received considerable attention, since
they exhibit strong fluorescence and may have utility in the synthesis
of fluorescent materials, non-natural photosynthetic systems, and
materials with nonlinear optical properties. The majority of known
synthetic procedures are, however, “stop-and-go” reaction
processes involving time-consuming and waste-producing isolation and
purification of product intermediates. Here, we present the synthesis
of substituted 2,6-dicyanoanilines via atom-economical and eco-friendly
one-pot processes, involving metal-free domino reactions, and their
subsequent photochemical and photophysical measurements and theoretical
calculations. These studies exhibit the existence of an easily tunable
radical ion pair-based charge-transfer (CT) emission in the synthesized
2,6-dicyanoaniline-based electron donor–acceptor systems. The
charge-transfer processes were explored by photochemical and radiation
chemical measurements, in particular, based on femtosecond laser photolysis
transient absorption spectroscopy and time-resolved emission spectroscopy,
accompanied by pulse radiolysis and complemented by quantum chemical
investigations employing time-dependent density-functional theory.
This chromophore class exhibits a broad-wavelength-range fine-tunable
charge recombination emission with high photoluminescence quantum
yields up to 0.98. Together with its rather simple and cost-effective
synthesis (using easily available starting materials) and customizable
properties, it renders this class of compounds feasible candidates
as potential dyes for future optoelectronic devices like organic light-emitting
diodes (OLEDs).