First hyperpolarizabilities of Pt(4-ethynylbenzo-15-crown-5)2(bpy) derivatives with the complexation of mono-cations (Li+, Na+, K+) and di-cations (Mg2+, Ca2+): development of a cation detector

Square-planar platinum(II) compounds containing two crown ethers play an important role in the development of nonlinear optical (NLO) materials, liquid crystals, luminescent materials and also in supramolecular chemistry owing to their diverse charge transfer excited states. The coordination of mono-cationic (Li+, Na+, K+) and di-cationic (Mg2+, Ca2+) metals onto the crown seems to be advantageous for the design of NLO-based cation detectors. Pt(4-ethynylbenzo-15-crown-5) 2(bpy) (L) and its cation derivatives have been investigated by the density functional theory. The binding of alkali metal cations obviously shrinks the crown ethers due to their strong interaction energies and distorts the crown ethers perpendicular to the bipyridine and Pt plane. Significantly, as compared with L, an obvious decrease appears in the first hyperpolarizability after cation complexing. This can be explained by their variable charge transfer transitions along the y-axis in conjunction with the distribution of holes and electrons. Thus, it can be noted that square-planar platinum(II) compounds merit the widespread use in the fields of optical detectors.