1,6,7-Trisubstituted perylene bisimides with tunable optical properties for colorimetric and “turn-on” fluorescence detection of HCl

To elucidate the effect of different substituents on the optical and redox properties of perylene bisimide (PBI), a novel series of 1,6,7-trisubstituted PBIs (1–6) with a highly twisted perylene core was synthesized and characterized. By substituting the hydrogen atoms at the bay-positions with various substituents (dihexylamino, piperidinyl, morpholinyl, hexoxy, and bromo), the absorption and fluorescence wavelengths of 1–6 in cyclohexane were extensively tuned within the ranges of 551–646 and 586–720 nm, respectively, simply by harnessing the electron-donating strength of the substituents. Varying the substituents generated a new family of long-wavelength absorbing and fluorescent dyes. Moreover, PBI 2 exhibited colorimetric and “turn-on” fluorescence responses in extremely acidic medium (pH 1.0 to −0.6). Low-cost test strips containing 2 were easily prepared and could be used to detect HCl.