Synthesis and Photophysical Properties of Cycloplatinated(II) Complexes Bearing Isocyanide and Alkynyl Ligands

Abstract

Cyclometalated platinum(II) complexes havegained increasing interest during the last yearsdue to their rich chemistry and uniqueluminescent properties, making them suitablefor light emitting diodes (OLEDs),photocatalysis, bioimaging or chemicalsensors. However, there are very scarceantecedents of heteroleptic cycloplatinated(II)compounds with isocyanide and alkynylligands.1To expand this research, we aimed to prepare anew family of luminescent cycloplatinatedcomplexes with 2-(2,4-difluorophenyl)pyridine(dfppy, a) and 4-(2-pyridyl)benzaldehyde(ppy-CHO, b) as cyclometalating ligands. Thealkynyl/tert-butyl isocyanide complexes[Pt(C^N)(C≡CR)(CNtBu)], bearing 4-ethynylanisole (2) and 2-ethynylthiophene (3)have obtained from the chloride derivatives[Pt(C^N)Cl(CNtBu)] (C^N = dfppy 1a, ppy-CHO 1b) using the Sonogashira protocol.These systems have been designed by takinginto account features that could make thesecomplexes interesting in biological studies.The complexes have been fully characterizedusing NMR spectroscopy together with X-raydiffraction. Their optical properties have beenstudied in detail and interpreted with the helpof TD-DFT calculations. The dfppy derivativesexhibit a mechanochromic behaviour, relatedto their strong tendency to form stackingstructures or aggregates by Pt···Pt and/or π···πinteractions.