Tuning the Excimer Emission of Amphiphilic Platinum(II) Complexes Mediated by Phospholipid Vesicles

Two new amphiphilic
platinum­(II) complexes, [Pt­(2-(4-fluorophenyl)-5-(4-dodecyloxyphenyl)­pyridine)
(acac)] (Pt-1) and [Pt­(2-(4-dodecyloxyphenyl)-5-(thien-2-yl)-c-cyclopentenepyridine) (acac)] (Pt-2), where
acac is acetylacetonate, were synthesized and characterized. Apart
from conventional phosphorescence of single molecules (MEmonomer
emission), complexes Pt-1 and Pt-2 also
exhibit excimer emission (EE) when embedded into phospholipid vesicles,
that is assigned to emissive Pt–Pt excimers. The EE intensity
in vesicular media appeared to depend on the viscosity of the vesicles
and the concentration of the embedded complex. Differences in the
EE properties of complexes Pt-1 and Pt-2 are correlated with the energies of the π-character frontier
orbitals defined by the design of the cyclometalating phenylpyridine
ligand. Higher energies of the frontier π-orbitals (HOMO and
LUMO) naturally promote stronger π–π interactions,
thus obstructing the PtII–PtII interaction.