Novel naphthalene diimides and a cyclophane thereof: synthesis, characterization, photophysical and electrochemical properties

Three novel naphthalene diimides (1-3) and a cyclophane (4) containing two naphthalene diimide moieties were synthesized and characterized. In contrast to the absorption spectra, the emission spectra were strongly dependent on the solvent polarity. The excimer-like emission and low fluorescence rate constant suggest the formation of ground state complexes in DMF. All the compounds have low fluorescence quantum yields (0.001-0.012). They undergo reversible electron reduction and oxidation while Delta E-p values depend strongly on solvent polarity. The LUMO energy values of 1 (3.76 eV), 2 (3.69 eV), and 3 (3.66 eV) vary with the substituent pattern. The structurally relatively rigid cyclophane 4 exhibits excellent thermal stability, a high glass transition temperature (t(g), 102 degrees C) and a low LUMO energy value (3.59 eV). Compound 2 is insoluble in DMF at room temperature, but begins to dissolve at 37 degrees C and could therefore potentially serve as a sensor in temperature-sensing devices.