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

Abstract

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 ΔE_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 °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 °C and could therefore potentially serve as a sensor in temperature-sensing devices.