Triplet exciton transport in the benzophenone-fluorene-naphthalene molecule

Abstract

Incoherent triplet-triplet energy transfer through the benzophenone-fluorene-naphthalene system is computationally investigated to determine triplet hopping rates. These rates have been previously measured experimentally and have also been estimated computationally. There are many complex steps associated with such a computational analysis, though, and earlier efforts resorted to a variety of semi-empirical modifications to the methods used in order to obtain results consistent with the experimental data. This has motivated an investigation in which best practice methods are applied to the system without any empirical adjustments. The calculation of triplet excitation energy and triplet-triplet electronic coupling are examined in detail using a range of computational methods from simple Density Functional Theory to the many-body Green function approach embodied in the Bethe-Salpeter Equation. This analysis includes an evaluation of the robustness of each method considered. Significantly, the investigation identifies the excited states of benzophenone as being extremely difficult to calculate using even the most advanced excitation methods, and a theory is presented as to why the molecule is both interesting and troublesome. The final rate estimates, without any empirical adjustments, are one to two orders of magnitude greater than those measured experimentally. This data, and the detailed methodological study supporting it, is expected to be helpful in future efforts to computationally scrutinize triplet exciton hopping.