New environment-sensitive bis-dansyl molecular probes bearing alkyl diamine linkers: Emissive features and interaction with cyclodextrins

Bis-dansyl fluorescent probes bearing aliphatic diamine linkers of increasing length (2DA1.n, n = 2, 4, 6, 8, 10, 12) were synthesized, and their emissive characteristics in solvents and in cyclodextrin solutions were discussed. Dual emission from locally excited (LE) and intramolecular charge transfer (CT) excited states was observed. The LE/CT relative magnitude is sensitive to solvent polarity and linker length. In water, the CT or LE state is favoured for short chain or long chain probes, respectively. The LE/CT relative magnitude also depends on the CD type: 2-hydroxypropyl-β-CD favours the CT state, while β- and γ-CD stabilise the LE state.