Potential Switchable Circularly Polarized Luminescence from Chiral Cyclometalated Platinum(II) Complexes

A series of chiral cyclometalated platinum(II) complexes, [Pt((-)-L-1)(Dmpi)]Cl ((-)-1), [Pt((+)-L-1)(Dmpi)]Cl ((+)-1), [Pt((-)-L-2)(Dmpi)]Cl ((-)-2), [Pt((+)-L-2)(Dmpi)]Cl ((+)-2), [Pt-3((-)-L-2)(2)(Dmpi)(4)](ClO4)(4) ((-)-3), and [Pt-3((+)-L-2)(2)(Dmpi)(4)](ClO4)(4) ((+)-3) [(-)-L-1 = (-)-4,5-pinene-6'-phenyl-2,2'-bipyridine, (+)-L-1 = (+)-4,5-pinene-6'-phenyl-2,2'-bipyridine), (-)-L-2 = (-)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, (+)-L-2 = (+)-1,3-bis(2-(4,5-pinene)pyridyl)benzene, Dmpi = 2,6-dimethylphenyl isocyanide], have been designed and synthesized. In aqueous solutions, (-)-1 and (+)-1 aggregate into one-dimensional helical chain structures through PtPt, p-p, and hydrophobic-hydrophobic interactions. (-)-3 and (+)-3 represent a novel helical structure with Pt-Pt bonds. The formation of helical structures results in enhanced and distinct chiroptical properties as evidenced by circular dichroism spectra. Circularly polarized luminescence (CPL) was observed from the aggregates of (-)-1 and (+)-1 in water, as well as (-)-3 and (+)-3 in dichloromethane. The CPL activity can be switched reversibly (for (-)-1 and (+)-1) or irreversibly (for (-)-3 and (+)-3) by varying the temperature.