6-[(2E)-3-(4-Nitrophenyl)triaz-2-en-1-yl]-9H-purine (p-nitrophenyl triazenyl purine, PNTP) has been synthesized and evaluated for sensing the anions PF6-, HSO4-, ClO4-, and BF4- as their tetrabutylammonium salts in DMSO. This is the first example of any adenine-based anion sensor. The addition of 2 equivalents of PF6-, HSO4-, ClO4-, and BF4-to the 2 x 10(-5) mol dm(-3) DMSO solution of PNTP at room temperature produced visible color changes and perturbation of UV-vis spectral pattern of PNTP in terms of absorbance at 398 and 575 nm in reciprocal patterns. The sensing ability of PNTP was found to be best for PF6-among all the chosen anions.