Correlation of molecular assembly and interactions in crystals and Langmuir-Blodgett films of N-(2,4-dinitrophenyl)-n-octadecylamine.

Correlation of molecular organization in crystals and in ultrathin films is of fundamental interest in the design of molecular materials based on thin films. We have chosen as a test case, N-(2,4-dinitrophenyl)-n-octadecylamine (DNPOA), a potential candidate for the fabrication of Langmuir-Blodgett (LB) films for quadratic nonlinear optical applications. Like several other 4-nitroaniline derivatives, DNPOA does not form stable monolayers at the air-water interface. This has precluded investigations of their organization in LB films. We have stabilized composite Langmuir films of DNPOA with the phospholipid molecule DSPC and fabricated their LB films. Successful growth of single crystals of DNPOA allowed structure determination and detailed analysis of molecular associations in the solid state. Electronic absorption spectra of DNPOA in solution, in the solid state and in the LB film are investigated. Modeling of the various spectral signatures by semiempirical computations on molecular clusters extracted from the crystal lattice provides insight into the correlation between the molecular organization in crystals and in LB films.