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.

Efficient shielding of phosphorescent transition metal complexes against diffusion-controlled collisional quenching by triplet molecular dioxygen as well as reduction of microenvironment-related radiationless deactivation pathways is crucial for their applications in bioimaging and optoelectronics. In this report, we present a straightforward yet efficient approach to safeguard emissive triplet states from external influences by adsorbing phosphorescent Pt(II) complexes onto a layered nanoclay, namely Laponite. These hybrids facilitate the dispersion of otherwise insoluble transition metal complexes in aqueous media while shielding them from physical quenching. Self-assembly of the nanoclay and intermolecular stacking between molecules adsorbed at different nanodisc units are mirrored in the photophysical, colloidal, and morphological properties of the hybrids, which were herein characterized by steady-state and time-resolved photoluminescence spectroscopy, dynamic light scattering, and atomic force microscopy. We also show that the hybrids are noncytotoxic and can be exploited as luminescent reporters in spectrally resolved phosphorescence lifetime imaging implemented by confocal optical microscopy.

Two isoleptic complexes involving Pd(II) and Pt(II) centres with a tetradentate luminophoric ligand were adsorbed onto Laponite (LAP), yielding H2O-dispersible nanohybrids with remarkable photoexcited state properties. The adsorption promoted rigidification of the coordination compounds and suppression of roto-vibrational deactivation pathways, thus enhancing the performance of the molecular species. Interestingly, room temperature phosphorescence was achieved in the case of the Pd(II)-containing nanohybrid along with a marked 3O2 sensitivity, whereas the photoluminescence of the Pt(II)-based material showed only a mild dependence on the presence of 3O2 while reaching up to 37% quantum yield.