Luminescent Pt(ii) complexes featuring imidazolylidene-pyridylidene and dianionic bipyrazolate: from fundamentals to OLED fabricationsElectronic supplementary information (ESI) available: Synthetic procedures for various imidazolium-pyridinium salts. X-ray crystallographic data file (CIF) of Pt(ii) complexes 1, 2 and 5, photophysical and electrochemical data for all Pt(ii) complexes and computational data for complexes 1, 2, 5 and 8. CCDC 1519153-1519155. For ESI and crystallographic data in CIF

Pt( ii ) complexes bearing imidazolylidene-pyridylidene (impy) and dianionic biazolate chelates were synthesized, for which the end products depend on the alkyl substituents of the impy chelate. Treatment of Pt(DMSO) 2 Cl 2 with dimethyl substituted imidazolium-pyridinium pro-ligand Me 2 impy(PF 6 ) 2 , followed by addition of 5,5′-(1-methylethylidene)-bis-(3-trifluoromethyl-1 H -pyrazole) (mepzH 2 ), 5,5′-di(trifluoromethyl)-3,3′-bis-pyrazole (bipzH 2 ), and 5,5′-di(pentafluoroethyl)-3,3′-bis-pyrazole (biepzH 2 ), afforded Pt( ii ) complexes [Pt(Me 2 impy)(mepz)] ( 1 ), [Pt(Me 2 impy)(bipz)] ( 2 ) and [Pt(Me 2 impy)(biepz)] ( 3 ), respectively. In contrast, reactions with ethyl and isopropyl substituted Et 2 impy(PF 6 ) 2 and Pr 2 impy(PF 6 ) 2 and with bipzH 2 gave [Pt(EtimHpy)(bipz)] ( 4 ) and [Pt(PrimHpy)(bipz)] ( 5 ) respectively, where notable alkyl-to-hydrogen transformations on the pyridylidene fragment took place. The reaction of Pt(DMSO) 2 Cl 2 with Et 2 impy(PF 6 ) 2 followed by addition of (biepzH 2 ) gave two products [Pt(Et 2 impy)(biepz)] ( 6 ) and [Pt(EtimHpy)(biepz)] ( 7 ). Single crystal X-ray diffraction analyses of 1 , 2 and 5 revealed negligible intermolecular Pt Pt interactions. Hybrid-DFT and TD-DFT computations were carried out on 1 , 2 and 5 to model the observed crystal structures and explain the photophysical data successfully. Organic light emitting diodes (OLEDs) were fabricated from complexes 4 or 5 using a multiple layered device architecture. The associated OLED performances ( i.e. η max = 12.5%, 11.2%, η L = 44.0 cd A −1 , 40.6 cd A −1 , and η P = 28.0 lm W −1 , 25.8 lm W −1 for 4 and 5 ) confirmed their suitability in serving as potential OLED phosphors. The intriguing structural-photophysical behaviors of [Pt(Me 2 impy)(biepz)] ( 3 ) and related luminescent Pt( ii ) derivatives are described in this study.