Mechanochromic and acidochromic response of 4H-pyran derivatives with aggregation-induced emission properties

Abstract

Several 1- and 2-position naphthylethylene-substituted 4H-pyran derivatives comprising two different end groups were synthesized. These two pairs of positional isomers with aggregation-induced emission properties exhibit different stimuli-responsive solid-state fluorescent properties. Both the linking position of the naphthylethylene and the electron-withdrawing end group have a significant impact on the mechanochromic properties of the compounds, whereas, the acidochromic properties are only related to the latter. The transformation between amorphous and crystalline states accounts for the mechanochromic properties and is attributed to loose molecular packing with weak intermolecular interactions, as revealed by crystallographic data. The reversible acidochromic properties are mainly ascribed to protonation/deprotonation of the carbonyl group, which is confirmed by 1H NMR experiments. Additionally, because the emission of these 4H-pyran derivatives in solid state can be tuned by external stimuli, several molecular logic gates were established by using appropriate stimuli operations as the inputs and fluorescent colors as the outputs.