4-(1H-Phenanthro[9,10-d]imidazol-2-yl)benzaldehyde (P-1) was prepared as a new ratiometric optical probe for hydrogen sulfite. Upon the addition of HSO3?, it displayed large emission wavelength shift (120 nm) and the detection limit was determined to be as low as 2 M. In addition to its high selectivity for hydrogen sulfite rather than other common anions, P-1 was successfully applied to the detection of hydrogen sulfite in HeLa cells with ratiometric fluorescent methods.
