The effects of extended π-conjugation in bipyridyl ligands on the tunable photophysics, triplet excited state and optical limiting properties of Pt(ii) naphthalimidyl acetylide complexes.

Pt(II) complexes that exhibit long-lived triplet excited state lifetimes are promising for optical power limiting materials. The introduction of large pi-conjugated substituents can switch the triplet excited state to a long-lived 3 pi,pi* state. Herein, we report four Pt(II) diimine complexes with high pi-conjugation via inserting an aryl group on the diimine ligand. Their photophysical properties were investigated using spectroscopic techniques. All the complexes exhibit strong ground absorption bands in their UV-Vis absorption spectra (maximum peaks ranging from 370 to 530 nm) and long-lived emission and triplet excited states. The insertion of pi-conjugated substituents induces a pronounced red-shift in the ground state absorption and longer emission lifetime. Broadband transient absorption spectra in the visible-NIR region and Z-scan properties under 532 nm were carried out on the Pt(II) diimine complexes, resulting in a remarkably strong reverse saturable absorption at 532 nm for nanosecond laser pulses. Otherwise, the high pi-conjugation in the bipyridyl ligand increases the reverse saturable absorption. Therefore, these Pt(II) diimine complexes with high pi-conjugation are excellent candidates for devices that require strong reverse saturable absorption.