A new family of luminescent compounds: platinum(ii) imidoylamidinates exhibiting pH-dependent room temperature luminescence

Abstract

The imidoylamidinate platinum(II) compounds [Pt{NH=C(R)NC(Ph)NPh}2] (R = CH2Ph 2, p-ClC6H43, Ph 4) were prepared by the reaction of the appropriate trans-[PtCl2(RCN)2] with 4 equiv of the amidine PhC(NH)NHPh giving 2-4 and 2 equivs of the salt PhC(=NH)NHPh.HCl. We also synthesized, by the double alkylation of 4 with MeOSO2CF3, complex [Pt{NH=C(Ph)N(Me)C(Ph)=NPh}2][CF3SO3]2 (5) which models the bis-protonated form of 4. The complexes were characterized by 1H, 13C NMR, and IR spectroscopies, FAB-MS and by C, H, N elemental analysis. The X-ray crystallography of 4.2CH2Cl2 enables the confirmation of the square planar coordination geometry of the metal center with almost planar imidoylamidine ligands, while in 5.2CHCl3 the planarity of the metallacycles is lost and and the central N atom is sp3-hybridized. The imidoylamidinate complexes represent a new family of Pt(II)-based luminescent complexes and they are emissive at room temperature both in solution and in the solid state, with an emission quantum yield ranging from 3.7 x 10(-4) to 6.2 x 10(-2) in methanol solution; the emission intensity is pH-dependent, being quenched at low pH. UV-visible and luminescence spectroscopies indicate that the lowest excited state of these compounds is 3MLCT or 3IL with significant MLCT character, with emission lifetimes of a few micros. A blue shift of both the absorption and emission with increasing solvent polarity and with decreasing pi-electron withdrawing properties of the ligand substituent was observed.

Platinum(iv)-mediated nucleophilic addition of 1,3-diphenylguanidine to propiononitrile

“…Complex 1a was separated and purified by silica gel column chromatography (Silicagel 60 F ν(C=N and/or C=C (Ar)); 756, 694 δ(C-H (Ar)). 1 11.57 (CH 3 ) (Et). Crystals suitable for X ray diffraction were grown by slow evaporation of a solution of complex 2 in a 3 : 1 hexane-chlo roform mixture.…”

“…The addition of imines and heteroimines to coordinated nitriles has been investigated in recent years. [5][6][7][8][9][10][11][12] In continuation of research on reactions of nitriles RCN coordinated to platinum with imines (hetero imines) HN=ER n (ER n = CPh 2 , 5 C(Alkyl)(OAlkyl), 7,12 * Dedicated to Academician B. A. Trofimov on the occasion of his 70th birthday.…”

Platinum(II)‐Mediated Double Coupling of 2,3‐Diphenylmaleimidine with Nitrile Functionalities To Give Annulated Pentaazanonatetraenate (PANT) Systems

“…To the best of our knowledge, the photophysical properties of platinum(II) -diketonates (Figure 1, A) and -diketiminates (B) have not been studied before, but their triaza analogues, namely TAPD platinum(II) complexes (C), exhibit luminescence in the visible region (450-600 nm) with substantial quantum yields (up to 0.74) in the solid state. [15,16,60] Concurrently, platinum(II) phthalocyanines (E), featuring four annulated TAPD systems, demonstrate luminescence from 750 to 900 nm, and this emission is characterized by relatively low quantum yields (0.0017-0.013). [62][63][64][65] 700-800 nm with low quantum yields, are closer to platinum(II) phthalocyanines (E).…”

“…their generation, [5,15,16,20] phosphorescence properties, [15,16] and application for studies of weak molecular interactions [23,24] ) and relevant phthalocyanines (E), [25] we focused our attention on an almost unexplored type of TAPD ligands that includes two annulated triazapentadiene rings, 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT; D). Indeed, to the best of our knowledge, only four examples of compounds with PANT ligands have been reported, and methods for the facile generation of PANT ligand systems have not been developed.…”

Highly luminescent imidoylamidinato platinum(ii) complexes formed by the coupling of 1H-pyrazole-1-carboxamidine with nitriles used as reaction solvents

“…12,13 Although the photophysical properties of some of them have also been reported, most of the data are limited to the solution state, in which the bis(imidoylamidinato) Pt(II) complexes exhibit weak luminescence. 13 We have succeeded in the synthesis of a series of Pt(II) complexes consisting of 2,2'-bipyridine (bpy) and imidoylamidinate {NH=C(pz)NC(R)=NH} (R = Me, Et, Ph), which exhibit drastic color change of luminescence upon grinding. This phenomenon is known as mechanochromism.…”