The fluorescence sensing in the molecular recognizing system is very useful in biomimetic research, since the resulting output signal of fluorescence could be highly sensitive for analysis. Recently, many fluorophore-hosts were reported to recognize a number of guests such as alkali metals, alkaline earth metals, transition metals, etc.. In this session, we wish to discuss about the logical cation AND anion recognition caused by a novel crown ether armed pyrido[1 2 :1,2]imidazo[4,5-b]pyrazine (PIP) fluorophore-host.The PIP host having 12-crown-4-methyl carboxylate was prepared by the following route. By the addition of alkali and alkaline earth metal thiocyanates or the corresponding perchlorates to an acetonitrile solution of PIP host, only the emission of PIP was quenched, with no change in the emission and absorption wavelength and absorption intensity. The fluorescence intensity changes are summarized in Table, together with those of other simple aromatic fluorophore-hosts. The PIP host is clearly quenched only in the presence of the alkaline earth metal cation AND the thiocyanate anion. These results demonstrate that the logical cation AND anion recognitions are attained by one receptor site (crown ether) of PIP host.Moreover, we wish to report the application of the PIP host to the anion recognition.