Manipulating Electroluminochromism Behavior of Viologen-Substituted Iridium(III) Complexes through Ligand Engineering for Information Display and Encryption.

Electrically controlling photoluminescence has attracted great research interest and offers many opportunities for technological developments. Electroluminochromic materials undergo redox reactions under low-voltage stimuli to achieve reversible luminescence switching. Till now, photoluminescence switching of a single molecule caused by electrical stimuli is restricted to intensity response because the redox-active moieties are good electron donors or acceptors and electrical stimuli can regulate the photoinduced electron-transfer and affect the luminescence intensity. In this work, the manipulation of the electroluminochromism behavior of a series of viologen-substituted iridium(III) complexes through the regulation of ligand orbital energy levels and electronic communication between the viologen pendants and the iridium(III) complex core is reported. Electrochemical redox reactions reversibly modulate either the luminescence quenching effect or the push-pull electronic effect of the viologen substituents, achieving multicolor "on-off" luminescence response toward electrical stimuli and luminescence manipulation between two emissive states with different wavelengths and lifetimes. To illustrate the promising applications of these electroluminochromic materials, recording and displaying luminescence information under electrical stimuli are demonstrated. Information encryption is realized by letting the electroluminochromism occur in the near-infrared region or in the time domain. Near-infrared camera or time-resolved luminescence analysis can be used to help read the invisible information.
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