posted on 2020-04-23, 18:33authored byAmbra Guarnaccio, Teng Zhang, Cesare Grazioli, Fredrik O. L. Johansson, Marcello Coreno, Monica de Simone, Giovanna Fronzoni, Daniele Toffoli, Elisa Bernes, Carla Puglia
The
present study is focused on the comprehensive gas phase electronic
structure characterization of 2,8-bis(diphenylphosphoryl)-dibenzo[b,d]thiophene
(PPT), a promising ambipolar phosphorescent host material recently
introduced in organic light-emitting diodes (OLEDs). This molecular
system can be considered ideally formed by two diphenylphosphine oxide
(dPPO) moieties functionalizing the small dibenzothiophene (DBT) core.
PPT is characterized by high triplet energy and is known as good vacuum
sublimable electron transporting material for blue OLEDs. The triphenyl
phosphine oxide (TPPO) molecule has been chosen as the model compound
of the dPPO groups in PPT. A combined experimental and theoretical
study by density functional theory of the gas phase electronic structure
of TPPO and PPT has been performed through X-ray photoelectron spectroscopy
and near-edge X-ray absorption fine structure spectroscopy measured
at the carbon and oxygen 1s regions. The study represents a detailed
characterization of the impact of the single building blocks on the
electronic structure of the whole PPT molecule. Moreover, it confirms
that the phosphine oxide groups act as breaking points of the π-conjugation
between the DBT core of PPT and the outer groups, leaving the electronic
structures of the compound practically matching those of the central
DBT moiety.