AGGREGATION CONTROL BY VAPOR-PHASE AND HEAT-TREATMENTS IN LANGMUIR-BLODGETT-FILMS OF AMPHIPHILIC HETEROARYLAZO DYES

The effects of heat treatment (HT), and acidic- and basic-vapour-phase treatments (AT and BT, respectively) have been studied on Langmuir-Bl odgett (LB) films of decylamino)-1-naphthylazo]-N-methylbenzothiazoliu m perchlorate (azo V) and decylamino)-1-naphthylazol-N-methylbenzothia zolium perchlorate (azo VI). The as-deposited films for azo V and azo VI exhibit an H-like aggregate band at 419 and 427 nm, respectively. A fter HCI vapour treatment, the H-like band for azo V disappears to pro duce monomeric (M) band at 563 nm. The film, which dissociated under A T treatment, exhibited an H-like band (at 480 nm) that differed from the original H-like band after HT, and also exhibited a band at ca. 42 9 nm after BT (exposure to NH3 vapour). A combination of two different treatments, i.e. AT --> HT gives a reversible change between M and H -like states. Similar optical changes were also obtained for azo VI fi lms. Comparison of infrared (IR) spectroscopic measurements with trans mission and reflection-absorption spectra of azo V in the LB films aft er AT and HT gave characteristic information due to the H- and H-like aggregations and the monomer state. Apart from evidence for gas-vapou r penetration into the LB films under the employed conditions, the IR spectra of the films correlate closely with the corresponding visible absorption spectra.