A self-assembled monolayer (SAM)-based fluorescent film
was designed and prepared by chemical immobilization of a novel oligo(<i>p</i>-phenylene- ethynylene) (OPE) with cholic acid moieties
at the ends of its side chains (Film 1). As a control, a similar film,
Film 2, of which OPE brings no side chains, was also prepared. The
structures of the films were characterized by contact angle, XPS,
ATR-IR and fluorescence measurements. Fluorescence studies revealed
that the emission of Film 1 is sensitive to the presence of trace
amount of some inorganic acids in acetone, such as HCl, H<sub>2</sub>SO<sub>4</sub>, HNO<sub>3</sub>, and H<sub>3</sub>PO<sub>4</sub>,
etc., whereas the acids as studied showed little effect on the emission
of Film 2. The difference in the sensing performances of the two films
have been rationalized by considering presence or absence of a possible
cavity, a substructure appearing above the OPE adlayer which is something
like a dimer of cholic acid (CholA) formed at specific environment