The spectral properties of a series of styryl dyes containing the aza-
15-crown-5 macrocycle are investigated. Using absorption UV-Vis spectr
oscopy the protonation and aggregation processes are studied and the c
orresponding pK(a) values and dimerization constants K-D determined. O
ligomer formation occurs in the presence of HClO4 or CIO42-, and a sch
eme describing these processes is suggested.