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.