Fluorescent 4-amino-1,8-naphthalimide Tröger’s bases possessing conjugated 4-amino-1,8-naphthalimide moieties and their potential fullerenes Host-Guest complexes

Abstract

The synthesis and characterisation of two new 1,8-naphthalimide Tröger’s bases (TBNaps) 1 and 2 is described from the commercially available 4-chloro-1,8-naphthalic anhydride. These structures possess two additional 4-amino-1,8-naphthalimide (Naps) units, each of these ‘terminal’ Naps units have either 1-(2-aminoethyl)-pyrrolidine or 1-(2-aminoethyl)-piperidine moieties, that are conjugated to the TBNaps units via a short propyl spacer. The ground and the excited state properties of 1 and 2, as well as the bis-Nap precursor 10, were evaluated in a range of solvents that varied by polarity and hydrogen bonding ability. The UV–Vis absorption and the fluorescence emission spectra, demonstrated that all three compounds possess Internal Charge Transfer (ICT) excited state properties. Both 1 and 2 were designed as potential receptor molecules for the detection of C60 (buckminsterfullerene) where it was anticipated that C60 could possibly bind within the orthogonal cavity of the Tröger’s base’s, through additional interactions with the terminal Naps. While the titrations of 1 and 2 with C60 in a chlorobenzene:DMF (86:14) solvent mixture showed only minor changes in the absorption spectra, significant fluorescence quenching was observed for both 1 and 2. Analysis of the fluorescence data in terms of a Stern-Volmer plot, showed that the quenching involves a combination of both static and dynamic mechanisms.

Keywords

• Fluorescence
• 1,8-naphthalimide Tröger’s bases
• Chemosensors
• C60 buckminsterfullerene
• Fullerene