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

A series of chiral cyclometalated platinum­(II) complexes, [Pt((−)-L₁)­(Dmpi)]Cl ((−)-1), [Pt­((+)-L₁)­(Dmpi)]­Cl ((+)-1), [Pt((−)-L₂)­(Dmpi)]Cl ((−)-2), [Pt­((+)-L₂)­(Dmpi)]Cl ((+)-2), [Pt₃((−)-L₂)₂(Dmpi)₄]­(ClO₄)₄ ((−)-3), and [Pt₃((+)-L₂)₂(Dmpi)₄]­(ClO₄)₄ ((+)-3) [(−)-L₁ = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L₁ = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine), (−)-L₂ = (−)-1,3-bis­(2-(4,5-pinene)­pyridyl)­benzene, (+)-L₂ = (+)-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 Pt···Pt, π–π, 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.