A phenylbenzoxazole-amide-cyclen linkage (L) behaves as a ratiometric fluorescent receptor for Zn2+ in water. The receptor dissolved in water at neutral pH shows fluorescence at 383 nm. The addition of Zn2+, however, leads to a decrease in this emission, along with an appearance of red-shifted emission at 445 nm. This thus facilitates ratiometric water Zn2+ sensing. Other metal cations do not promote such spectral change. Complexation of L with Zn2+ involves the coordination with four cyclen nitrogens and amide oxygen. IR and potentiometric analysis revealed that strong coordination of Zn2+ with amide oxygen leads to a deprotonation of the amide moiety and creates red shifted fluorescence. Ab initio calculation indicated that the deprotonation of the amide moiety allows rotational motion of the benzoxazole moiety in the excited state and stabilizes the twisted intramolecular charge transfer (TICT) excited state. This results in the creation of red shifted fluorescence from the TICT excited state.