AGGREGATION OF PSEUDOISOCYANINE CHLORIDE IN AQUEOUS-SOLUTIONS AT HIGH-PRESSURES

The aggregation behavior of pseudoisocyanine chloride (=PIC) (1,1'-die thyl-2,2'-cyanine chloride) in dilute aqueous solutions was observed u p to 375 MPa by absorption spectroscopy. From the pressure dependence of the dimerization constant the change in volume associated with the dimerization, Delta V-D = -12.6 cm(3) . mole(-1), could be obtained. B y means of this value of Delta V-D the interplanar spacing of the quin oline rings in the dimer was estimated to 3.0 . 10(-8) cm. At higher c oncentrations the pressure dependence of the pressure-induced absorpti on-band (Scheibe-band) yields the volume contraction (Delta V-S) cause d by the aggregation. Evaluation of Delta V-S/Delta V-D allows a rough determination of the mean aggregation number n of monomer units per S cheibe-aggregate. n increases with increasing concentration of PIG. Th e values of n lie between 5 to 29.