Single-Molecular White Emission of Organic Thianthrene-Based Luminophores Exhibiting Efficient Fluorescence and Room Temperature Phosphorescence Induced by Halogen Atoms

Because of the contradiction of the efficiencies of fluorescence
(FL) and room temperature phosphorescence (RTP) under ambient conditions,
achievement of the molecular design of efficient monomolecular white
emission resulting from the overlapping of FL and RTP is attractive
but very challenging. With the aim of obtaining efficient white emission
from a single organic molecule, phenyl(thianthren-2-yl)methanone and
its tan derivatives with halogen atoms are developed. Single-molecular
white emitters are investigated by experimental and theoretical approaches
including steady-state and time-resolved spectroscopy, X-ray analyses,
and density functional theory calculations. Photoluminescence quantum
yields (PLQYs) of white emission of the molecular dispersion of phenyl(thianthren-2-yl)methanone
in the rigid host ZEONEX at room temperature are significantly enhanced
from 19 to 84% after the removal of oxygen. Based on the results of
X-ray analysis of the single crystal, the high PLQY values are partly
attributed to the absence of π–π intermolecular
interactions and the low number of weak van der Waals intermolecular
stacking due to the strong bending of heterocyclic thianthrene moiety
and the high dihedral angle between thianthrene and benzoyl groups.
The structural peculiarities of the newly synthesized thianthrene
derivatives may result in the development of even more efficient organic
monomolecular white emitters.