Luminescent Complexes Tridentate Complexes of Palladium(II) and Platinum(II) Bearing bis-Aryloxide Triazole Ligands: A Joint Experimental and Theoretical Investigation Georges Dahm, [a] Etienne BorrØ, [a, b] Changkan Fu, [a] StØphane Bellemin-Laponnaz,* [a, c] and Matteo Mauro* [b, c] Abstract: A novel class of palladium(II) and platinum(II) com- plexes bearing tridentate bis-aryloxide triazole ligands was prepared by using straightforward and high-yielding syn- thetic routes. The complexes were fully characterized and the molecular structures of four derivatives were unambi- gously determined by single-crystal X-ray diffractometric analyses. For the most promising luminescent Pt II derivatives, further experimental investigations were carried out to char- acterize their photophysical features and to ascertain the nature of the emitting excited state by means of electronic absorption, steady-state, and time-resolved emission tech- niques in different conditions. In degassed fluid solution the complexes displayed broad and featureless photolumines- cence with l em = 522–585 nm, excited-state lifetime up to few microseconds and quantum yield (PLQY) up to 17 %, de- pending on the nature of both ancillary ligand and substitu- ent on the tridentate ligand. Computational investigation using density functional theory and time-dependent DFT were performed to gain insight into the electronic processes responsible for optical transitions and structure–photolumi- nescence relationship. Jointly, experimental and theoretical characterization indicated that the radiative transition arises from an excited state with admixed triplet-manifold metal- to-ligand charge transfer and ligand-centered ( 3 MLCT/ 3 LC) character. We elucidated the modulation of the photophysi- cal properties upon variation of substituents for this new family of complexes. Introduction Luminescent complexes have attracted growing attention in the recent past due to their potential application as active spe- cies in optoelectronics, [1] bio-imaging, [2] sensing, [2c, 3] solar- energy conversion [4] and photo-catalysis. [5] Amongst all differ- ent complexes, those based on second and third row transition metals such as octahedral d [6] Ir III , Ru II and Re I as well as square- planar d [8] Pt II showed the most interesting photophysical fea- tures so far in terms of PLQY, emission color modulation and quantum efficiency when employed as active species in solid- state devices. [1, 3, 6] Generally, their great efficiency stems from the sizeable spin-orbit coupling (SOC) effect exerted by the heavy atom that allows mixing of both singlet and triplet manifolds and, consequently, population of formally spin-for- bidden triplet-manifold excited states through intersystem crossing (ISC) processes with nearly unity efficiency. Hence, ra- diative coupling of the lowest-lying triplet excited state with the singlet ground state becomes highly allowed yielding to phosphorescence. In order to access efficient phosphorescent complexes, other key factors are represented by the molecular rigidity of the emitter and the presence of strong s-donating ligand-metal bonds, such as formally anionic (cyclo-)metalating phenyl rings and neutral carbene-based ligands. Indeed, the increased ri- gidity yields a sizeable decrease of the nonradiative deactiva- tion channels through radiationless coupling (internal conver- sion processes) with the electronic ground state. Whilst, the latter allows, on one hand, a better admixing of orbitals locat- ed on metal and ligand and, on the other hand, to locate the quenching metal centered (MC) d-d states much higher in energy with respect to the lower-lying emitting excited state. To accomplish such requirements and reduce the possibility of geometrical D 2d distortion processes upon excitation, several research groups have moved their attention towards the prep- aration of platinum(II) complexes bearing multidentate ligands, [a] Dr. G. Dahm, Dr. E. BorrØ, C. Fu, Dr. S. Bellemin-Laponnaz DØpartement des MatØriaux Organiques Institut de Physique et Chimie des MatØriaux de Strasbourg (IPCMS) UniversitØ de Strasbourg, CNRS UMR 7504 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2 (France) E-mail : bellemin@unistra.fr [b] Dr. E. BorrØ, Dr. M. Mauro Laboratoire de Chimie et des BiomatØriaux SupramolØculaires Institut de Science et d’IngØnierie SupramolØculaires (ISIS) UniversitØ de Strasbourg, CNRS UMR 7006 8 allØe Gaspard Monge, F-67083 Strasbourg (France) E-mail : mauro@unistra.fr [c] Dr. S. Bellemin-Laponnaz, Dr. M. Mauro University of Strasbourg Institute for Advanced Study (USIAS) 5 allØe du GØnØral Rouvillois, F-67083 Strasbourg (France) Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/asia.201500600. Chem. Asian J. 2015, 00,0–0  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 && These are not the final page numbers! ÞÞ Full Paper DOI: 10.1002/asia.201500600