The selectivity of PB for Cr3+ over other metal ions was also explored
and only Cr3+ resulted in a pronounced fluorescence decrease
with an association constant (Ka) of PB for Cr3+ of 7.52 × 104 M−1.
to pH. As expected, the capture of Cr3+ by the receptor resulted
in reduced electron-donating ability for the phenanthroxazole moiety;
thus, the pyrene moiety showed a red shift of 160 nm for fluorescence
emission with high selectivity for Cr3+ over other heavy and transition
metal ions.