Molecular aggregation, orientation, and structure in Langmuir-Blodgett films of 2-(4'-(ethyloctadecylamino)phenylazo)-N-methylbenzothiazolium perchlorate and 2-(4'-(dioctadecylamino)phenylazo)-N-methylbenzothiazolium perchlorate studied by infrared, visible absorption, and resonance Raman spectroscopies