Alkynyl triphosphine copper complexes: synthesis and photophysical studies

Abstract

A rigid triphosphine PPh₂C₆H₄–PPh–C₆H₄PPh₂ (P³) reacted with Cu⁺ and a stoichiometric amount of terminal alkyne under basic conditions to give a family of copper(I) alkynyl compounds [Cu(P³)CCR]. The number of terminal –CCH groups in the starting ligand determines the nuclearity of the resulting complexes giving mono- (1, R = Ph; 2, R = C₆H₄OMe; 3, R = C₆H₄NO₂; 4, R = C₆H₄CF₃; 5, R = 2-pyridyl), di- (R = -(C₆H₄)_n-, n = 1 (6), n = 2, (7), n = 3 (2)) and trinuclear complexes (9, R = 1,3,5-(C₆H₄)₃-C₆H₃; 10, R = 1,3,5-(C₆H₄-4-C₂C₆H₄)₃-C₆H₃). In all the complexes the Cu(I) centers are found in a distorted tetrahedral environment that is achieved by tridentate coordination of the P³ ligand and σ-bonding to the alkynyl function. The crystal structures of 1, 3 and 5 were estimated by single crystal X-ray diffraction analysis. The ³¹P, ¹H and ¹H–¹H COSY NMR spectroscopy confirms that all the molecules remain intact in solution. The photophysical studies carried out in the solid state at 298 and 77 K revealed moderate to weak orange luminescence (Φ_em up to 19%), tentatively assigned to thermally activated delayed fluorescence for the mononuclear complexes. The quantum yields of emission of 1–10 demonstrated strong dependence on the nature of the alkynyl ligand, the role of which in the electronic transitions was elucidated by TD-DFT computational studies.