Second-harmonic generation from thin films of mixtures of an aggregated chiral 4-nitroazobenzene dye and amylose acetate

Second-harmonic generation (SHG) from both Langmuir-Blodgett (LB) films and solvent-cast films of mixtures of a chiral nonlinear optical (NLO) dye, an ester of palmitic acid and 4-nitro-4'-[(3R)-hydroxypyrrolidinyl]azobenzene (KMES16) and amylose acetate is investigated. Results are discussed concerning the structure of the films. The NLO-active molecules form crystalline domains in which the molecules are aligned anti-parallel without a centre of symmetry (crystal point group P21). The dye domains behave like H aggregates. LB multilayer films show no significant SHG when measured “as deposited”. After heating and cooling down unexpectedly large SHG is measured. Cast films of the same mixtures also show SHG. The effect is attributed partly to a crystal-size effect and an enhancement of the SHG by H aggregates is suggested. In this paper, we describe SHG of thin layers without the execution of extended procedures to orient the molecules