Langmuir−Blodgett Films of a New Pyridinium−Dicyanomethanide Dye and Their Potential Optical Applications

We report on Langmuir−Blodgett (LB) characterization of 4-[5-(dicyanomethanidyl)thien-2-yl]- N -cetylpyridinium (C 16 H 33 −PDCNT). Surface pressure−area isotherms of monolayers were investigated at T = 291 K. LB films of Y- and Z-type were characterized by means of UV−vis and FTIR spectroscopies. The compound is photobleachable and undergoes a change in molecular structure in monolayer and in solution. The molecule strongly absorbs in the visible region due to a charge transfer band both in homogeneous solution and LB films. Depending upon dipping conditions, a sharp absorption band appears at about 422 nm that could be attributed to molecular aggregates, probably of H-type. Both the 422 nm band and the broad charge transfer band at longer wavelength are photobleachable, and the former could have potential applications for optical data storage. The molecule seems to possess a large second-order hyperpolarizability, and non-centrosymmetric Z-type LB films could have promising nonlinear optical properties.