Understanding vibronic coupling in spin–flip dynamics of two-coordinate Cu(i) thermally activated delayed fluorescence (TADF) complexes for electroluminescence and photocatalysis

Abstract

Two-coordinate Cu(I) complexes featuring a carbene–Cu(I)–amine general structure have been developed as efficient thermally activated delayed fluorescence (TADF) materials for electroluminescent and photocatalytic applications. Revealing the underlying photophysical dynamics of this series of compounds allows proper tuning of deactivation pathways and excited state lifetimes. In this context, a complementary TADF mechanism involving vibronic coupling between triplets has been discussed. Both experimental and theoretical analyses provide insights to fully understand the spin-vibronic coupling in the spin–flip process between singlet and triplet excited states. By a rational design of the excited state energetic alignment, TADF decay lifetimes (τ_TADF) can be tuned in a wide range from 1.9 to 67 μs, enabling the propitious applications as luminescent dopants in organic light-emitting diodes (OLEDs) with short τ_TADF and as photosensitizers in photocatalysis with long τ_TADF.