Molecular orientation of all-trans-beta-carotene in spin-coated film and in Langmuir-Blodgett film as detected by polarized optical absorption and reflection spectroscopies

Time molecular orientation and spatial arrangement of all-trans-beta-carotene in a spin-coated (SC) film and in a mixed Langmuir-Blodgett (LB) film with barium stearate (1:10) were studied by the use of polarized optical absorption and reflection spectroscopies at non-normal incidences. The newly applied analyses of these spectra show that the SC film is an amorphous film with density p = 0.835 g/cm(3), refractive index n = 1.38 and extinction coefficient kappa = 1.09 at 445 nm. Based on the axis model proposed by Schmidt and Reich [Ber. Bunsenges. Phys. Chem. 76 (1972) 1202], the angle of the molecular axis in the LB film relative to the plane of the substrate was determined to be 27 degrees. The relative strengths of the molecular interaction of beta-carotene were compared for the n-hexane solution, LB film, SC film, and single crystal. It was shown that the molecules in the LB film are weakly aggregated, although the size of the aggregate is so small that it can be identified as a 'monomer'. The Davydov splitting ED of the single crystal is obtained as 170 +/- 60 cm(-1).