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.

本研究合成并表征了两种新型两亲性铂(II)配合物：[Pt(2-(4-氟苯基)-5-(4-十二烷氧基苯基)吡啶)(acac)]（记为Pt-1）与[Pt(2-(4-十二烷氧基苯基)-5-(噻吩-2-基)-环戊烯并吡啶)(acac)]（记为Pt-2），其中acac为乙酰丙酮根（acetylacetonate）。除单分子常规磷光（单体发射（monomer emission），缩写ME）外，当嵌入磷脂囊泡时，Pt-1与Pt-2还会表现出激基缔合物发射（excimer emission，缩写EE），该发射被归属于具有发射特性的Pt–Pt激基缔合物。囊泡介质中的EE强度似乎取决于囊泡的黏度以及嵌入配合物的浓度。Pt-1与Pt-2的EE特性差异，与由环金属化苯基吡啶配体的分子设计所定义的π特征前沿轨道能级相关。更高的前沿π轨道（最高占据分子轨道（HOMO）与最低未占据分子轨道（LUMO））能级，自然会增强π–π相互作用，从而阻碍Pt(II)–Pt(II)相互作用。