In
this work, for the first time, the comparative use of P-, As-,
and Sb-based ligands in phosphorescent coordination compounds is reported
toward new coordination chemical concepts in the design and realization
of tailored triplet emitters with nonconventional elements. By means
of spectroscopic, X-ray diffractometric, and quantum-chemical methods,
we reconstructed the nature of the chemical bonds as well as the influence
of the increasingly heavy elements on the photoexcited state properties,
which were correlated with the hybridization and polarizability of
the pnictogen atoms (Pn). In particular, we elucidated
the structural and photophysical properties of a series of homologous
Pt(II) complexes with monodentate ancillary ligands based on group
15 elements, namely P, As, and Sb. Six coordination compounds bearing
tridentate dianionic 2,6-bis(1H-1,2,4-triazol-5-yl)pyridine
luminophoric pincer ligands bearing either CF
3
or
t
Bu moieties on the triazole rings along with triphenylpnictogens
(PnPh
3
) as monodentate ancillary
ligands ([CF
3
/Pn] or [
t
Bu/Pn], respectively) have been investigated. The electron
donating or withdrawing effect of the peripheral substituent (
t
Bu vs. CF
3
, respectively) and its influence on the
bonding, crystal packing as well as the excited state energies and
lifetimes was assessed in fluid solutions, frozen glassy matrices,
amorphous solids, and crystalline phases. A progressively red-shifted
phosphorescence was observed with increasing atomic number along with
a growing compensation of hybridization defects upon coordination
of the Pn atom to the Pt(II) center. The change of molecular
geometry of the PnPh
3
unit upon
complexation was extrapolated to predict the structural and excited
state characteristics of the Bi-based analogues, which according to
DFT calculations should be stable species and are the subject of ongoing
synthetic efforts. In general, we envisage the use of these ligands
for the relativistic enhancement of radiative deactivation rate processes,
especially if Bi-based s-orbitals participate on the bond with the
metal center, paving the road toward novel coordination compounds
using abundant elements with high spin–orbit coupling for sustainable
electroluminescent devices.