Rhodamine-diformyl p-cresol conjugate (L) has been developed as a novel Al3+-selective fluorometric and colorimetric sensor based on the FRET mechanism for the first time. L can selectively detect Al3+ through time-dependent PET-CHEF and FRET processes. This phenomenon is nicely reflected from H-1 NMR, fluorescence lifetime, and fluorescence cell imaging studies. The probe can detect Al3+ as low as 5 x 10(-9) M in HEPES-buffered EtOH:water (0.1 M, 4:1, v/v, pH 7.4). The probe shows pH-dependent emission properties viz. an intense red emission (585 nm) at acidic pH and an intense green fluorescence (535 nm) at basic pH. Thus, L can also be used as a pH sensor via tunable wavelength.