A novel amphiphilic Pt complex containing 2,6-bis(1-octadecylbenzimidazol-2-yl)pyridine (L18), [Pt(L18)Cl](PF6), has been synthesized. The complex exhibits concentration-dependent absorption and emission spectra in solution. With increasing the concentration of the Pt complex, we observed a new absorption band centered at 550 nm derived from a metal-metal d sigma* to ligand pi* charge transfer (MMLCT) transition and the corresponding broad emission centered at 650 nm. The Pt complex is surface-active, and the surface pressure-area isotherm reveals three phase transitions. The three phases correspond to one liquid-expanding phase and two solid-condensed phases, respectively, with different intermolecular overlap in the "flat-on" orientation at the air-water interface. Without additives such as fatty acids, the complex 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. Instead, the emission at 600 nm arising from the ligand-ligand pi-pi interacted excited state became dominant. The results would provide the insight into the control of molecular ordering for planar Pt complexes from the viewpoint of characteristic excited states.

Two novel fluorene derivatives having cationic substituents were synthesized. Two-photon absorption (TPA) properties of the derivatives were evaluated using the fluorescence-based technique with a femtosecond pulse emitted from a Ti:sapphire laser. Maximum TPA cross-sections of the compounds were estimated from the TPA spectra. TPA cross-sections of compounds with cationic substituents were found to be significantly larger than those of the compounds without cationic substituents.

We have designed a series of bis(cinnamylidene)cycloalkanone derivatives as two-photon absorption (TPA) compounds that possess a much stronger two-photon absorption induced fluorescence (TPF) than common organic dyes when excited with near-infrared laser radiation. The TPF intensity of the saturated solution of 2,5-bis(p-dimethylaminocinnamylidene)cyclopentanone (DMACCP) excited using a Q-switched Nd:YAG laser at 1064 nm was found to be 11 times larger than that of the most promising TPF compounds. The TPA cross section of the present compounds, as estimated by a fluorescence-based technique, varied from 5 Â 10 À50 cm 4 s/photon for 2,6-bis[3-(9-ethyl)carbazoyl-3-ylidene]cyclohexanone (DMACCH) to 20 Â 10 À50 cm 4 s/photon for DMACCP at an excitation wavelength of 1064 nm.