posted on 2024-01-26, 03:30authored byThomas Pope, Julien Eng, Andrew Monkman, Thomas J. Penfold
We present a detailed
investigation into the excited state properties
of a planar D3h symmetric
azatriangulenetrione, HTANGO, which has received significant interest
due to its high solid-state phosphorescence quantum yield and therefore
potential as an organic room temperature phosphorescent (ORTP) dye.
Using a model linear vibronic coupling Hamiltonian in combination
with quantum dynamics simulations, we observe that intersystem crossing
(ISC) in HTANGO occurs with a rate of ∼1010 s–1, comparable to benzophenone, an archetypal molecule
for fast ISC in heavy metal free molecules. Our simulations demonstrate
that the mechanism for fast ISC is associated with the high density
of excited triplet states which lie in close proximity to the lowest
singlet states, offering multiple channels into the triplet manifold
facilitating rapid population transfer. Finally, to rationalize the
solid-state emission properties, we use quantum chemistry to investigate
the excited state surfaces of the HTANGO dimer, highlighting the influence
and importance of the rotational alignment between the two HTANGO
molecules in the solid state and how this contributes to high phosphorescence
quantum yield.