Langmuir and Langmuir−Blodgett Films of NLO Active 2-(p-N-Alkyl-N-methylamino)benzylidene-1,3-indandioneπ/A Curves, UV−Vis Spectra, and SHG Behavior

We study 2-(p-N-hexadecyl-N-methylamino)benzylidene-1,3-indandione (1a) as a model compound for the preparation of nonlinear optically (NLO) active Langmuir−Blodgett (LB) layers. The pressure−area (π−A) isotherm of (1a) at the air−water interface is investigated. A limiting area of 0.60 ± 0.02 nm2 per molecule is found. The alternate-layer LB deposition of compound (1a) and an inert spacer, cadmium stearate, at different surface pressures is performed. The effects of temperature and delay time between spreading of the Langmuir film and the deposition of the LB films are studied. An increase of collapse pressure from 20 to 30 mN/m is observed as the delay time increases. UV−vis spectra indicate a uniform transfer of (1a) and show compression-induced changes as a function of the deposition conditions. A split of the absorption maximum is observed for LB films deposited at higher pressures and lower temperatures. The two bands can result from two different molecular electronic transitions, affected by the al...