The Importance of Vibronic Coupling for Efficient Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules.

ABSTRACT: Factors influencing the rate of reverse intersystem crossing (k_rISC ) in thermally activated delayed fluorescence (TADF) emitters are critical for improving the efficiency and performance of third-generation heavy-metal-free organic light-emitting diodes (OLEDs). However, present understanding of the TADF mechanism does not extend far beyond a thermal equilibrium between the lowest singlet and triplet states and consequently research has focused almost exclusively on the energy gap between these two states. Herein, we use a model spin-vibronic Hamiltonian to reveal the crucial role of non-Born-Oppenheimer effects in determining k_rISC . We demonstrate that vibronic (nonadiabatic) coupling between the lowest local excitation triplet (³ LE) and lowest charge transfer triplet (³ CT) opens the possibility for significant second-order coupling effects and increases k_rISC by about four orders of magnitude. Crucially, these simulations reveal the dynamical mechanism for highly efficient TADF and opens design routes that go beyond the Born-Oppenheimer approximation for the future development of high-performing systems.

SUBMITTER: Gibson J 

PROVIDER: S-EPMC5096030 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature