Three polymorphs of 2-hydroxynaphthaldehyde semicarbazone (2-NOH-S) have been identified, and their mechano-responsive luminescent emissions and interconversions are discussed.

No abstract

Isomeric ortho, meta and para naphthalimide–urea derivatives ND‐2U, ND‐3U and ND‐4U were synthesized and characterized. Upon gentle mechanical stimulation, the weakly emissive ortho isomeric sample ND‐2U was transformed into a yellow‐green emissive material (λem=500 nm), with Δλ≈125 nm. The mechanoluminescent emission of this isomer could be “switched off” by exposing the sample to solvent vapour. Moreover, ND‐2U could respond to fluoride anions in solution with a dramatic enhancement of fluorescence at λ=446 nm. The sigmoidal nature of the binding isotherm suggested cooperative binding of fluoride to the ortho isomer. 1H NMR spectroscopic studies provided vital insights into the nature of ND‐2U/F−complexation, highlighting the role of the proximal 1,8‐naphthalimide motif.

Stimuli-responsive fluorescence modulation of two cystine-derived bis-naphthalimide gelators was demonstrated using fluoride/tetrafluoroborate anions as the chemical inputs.