In this study, it is demonstrated
that the radiative
rate constant
of phosphorescent metal complexes can be substantially enhanced using
monodentate ancillary ligands containing heavy donor atoms. Thus,
the chlorido coligand from a Pt(II) complex bearing a monoanionic
tridentate C^N*N luminophore ([PtLCl]) was replaced by
triphenylphosphane (PPh3) and its heavier pnictogen congeners
(i.e., PnPh3 to yield [PtL(PnPh
3
)]). Due to the high tridentate-ligand-centered
character of the excited states, the P-related radiative rate is rather
low while showing a significant boost upon replacement of the P donor
by heavier As- and Sb-based units. The syntheses of the three complexes
containing PPh3, AsPh3, and SbPh3 were completed by unambiguous characterization of the clean products
using exact mass spectrometry, X-ray diffractometry, bidimensional
NMR, and 121Sb-Mössbauer spectroscopy
(for [PtL(SbPh
3
)]) as well as steady state and time-resolved photoluminescence spectroscopies.
Hence, it was shown that the hybridization defects of the Vth main-group atoms can be overcome by complexation with the Pt center.
Notably, the enhancement of the radiative rate constants mediated
by heavier coligands was achieved without significantly influencing
the character of the excited states. A rationalization of the results
was achieved by TD-DFT. Even though the Bi-based homologue was not
accessible due to phenylation side reactions, the experimental data
allowed a reasonable extrapolation of the structural features whereas
the hybridization defects and the excited state properties related
to the Bi-species and its phosphorescence rate can be predicted by
theory. The three complexes showed an interesting antiprotozoal activity,
which was unexpectedly notorious for the P-containing complex. This
work could pave the road toward new efficient materials for optoelectronics
and novel antiparasitic drugs.