N-Hydroxyalkyl and 4-Substituted-N-(hydroxyhexyl)-1,8-naphthalimides: Synthesis and Impact of Molecular Structure on Electrochemical and Photophysical Properties

Two series of N-hydroxyalkyl-1,8-naphthalimide derivatives were synthesized to investigate the influence of structural variables on their electrochemical and photophysical properties. The first series includes compounds containing N-hydroxyalkyl substituents of various chain lengths and branches. The second series includes derivatives functionalized in the naphthalene core with electron-donating or electron-withdrawing groups. Cyclic voltammetry, UV–Vis spectroscopy and fluorescence measurements were supported by theoretical DFT calculations. Branched hydroxyalkyl chains enhanced photoluminescence quantum yields by up to 19%, compared to less than 4% for linear chains. Functionalization of the naphthalene core at the C4 position strongly affected optical band gaps, electrochemical properties and photoluminescence quantum yields. DFT calculations revealed significant changes in the energies of the frontier orbits: the HOMO energy varied from −6.95 eV to −5.51 eV, while the LUMO energy varied from −3.24 eV to −1.94 eV. Preliminary tests have demonstrated the suitability of the selected derivatives as cathode materials in lithium-ion batteries, achieving an initial capacity of 47 mAh/g.