Theoretical study on the influence of twist Angle on the rate of reverse
intersystem crossing (RISC) in D-A molecule
Abstract
Abstract:Efficient reverse intersystem crossing (RISC) is one of the
most effective ways to achieve high exciton utilization of pure organic
electroluminescent materials. There are two factors affecting the RISC
rate (kRISC): the energy difference between the singlet and triplrt
excited states (ΔES-T) and the spin-orbit coupling (SOC) between the
excited states. In this article, based on the theoretical calculation
method which can accurately and quantitatively describe the excited
state of the molecule, the typical D-A molecule TPA-NZP is used as a
template to study the change of the ΔES-T and the SOC by adjusting the
twisting angle of the donor and acceptor in the molecule. By studying
the relationship between the excited state transition properties and the
SOC, we find that different transition states have a great influence on
the coupling. The two excited states are both LE states, but if the
phase of the electron cloud are different, which will cause the SOC
between them increased greatly; when the transition is the CT state, the
SOC matrix elements between the LE state and the CT state both very
small; when the singlet and triplet transitions occur in the same part,
but the direction of the transition is changed may lead to a huge
increase in the SOC.