Luminescent Langmuir-Blodgett films of platinum(II) complex [Pt(L18)Cl](PF6) (L18=2,6-bis(1-octadecylbenzimidazol-2-yl)pyridine)

A novel amphiphilic Pt complex containing 2,6-bis(1-octadecylbenzimidazol-2 -yl)pyridine (L18), [Pt(L18)Cl](PF6), has been synthesized. The complex exh ibits concentration-dependent absorption and emission spectra in solution. With increasing the concentration of the Pt complex, we observed a new abso rption band centered at 550 nm derived from a metal-metal d sigma* to ligan d pi* charge transfer (MMLCT) transition and the corresponding broad emissi on centered at 650 nm. The Pt complex is surface-active, and the surface pr essure-area isotherm reveals three phase transitions. The three phases corr espond to one liquid-expanding phase and two solid-condensed phases, respec tively, with different intermolecular overlap in the "flat-on" orientation at the air-water interface. Without additives such as fatty acids, the comp lex forms a stable and reproducible Langmuir-Blodgett (LB) multilayer film above a surface pressure of 15 mN m(-1). Strong emission from the LB films, even monolayer, was observed. Comparing the relative emission intensity of the MMLCT band for transferred LB monolayer film with that for cast films, we concluded that Pt-Pt interactions are suppressed in the LB film. Instea d, the emission at 600 nm arising from the ligand-ligand pi-pi interacted e xcited state became dominant. The results would provide the insight into th e control of molecular ordering for planar Pt complexes from the viewpoint of characteristic excited states.