Intramolecular donor–acceptor complexes: N-(aminoalkyl)phthalimides

Abstract

The u.v. absorption spectra of N-(aminoalkyl)phthalimides (1)–(3) show that they form intramolecular charge-transfer complexes. Compounds (1; n= 1–4), (2), and (3; n= 2) show intramolecular charge-transfer fluorescence in solution and quantum yields of fluorescence are given. Charge-transfer fluorescence can be observed when the compounds are contained in rigid cyclohexane, acetonitrile, and ethanol matrixes at 77 K. It could not be proven whether the fluorescence is from inter- or intra-molecular complexes. Phosphorescence from the imide group is observed when an ethanol matrix is used. Intermolecular charge-transfer fluorescence from complexes of NN-dimethylaniline with N-butylphthalimide and N-butyl-3,4,5,6-tetrachlorophthalimide was detected in solution and in rigid matrixes at 77 K. Freezing cyclohexane and acetonitrile solutions of the amine containing the imides aids complex formation. Imides (1; n= 0) and (3; n= 0) exhibit charge-transfer absorption bands but do not fluoresce. An X-ray analysis of (1; n= 0), showed the aniline and the imide group to be nearly orthogonal to each other. The charge-transfer band is, therefore, proposed as arising from an orbital system in which the π-system of the aniline group is coupled to the n-orbitals of the oxygen atoms of the imide group via the σ-bonded framework. Compounds (4a) and (4b) do not show charge-transfer absorption or emission bands. Phosphorescence from the imide group is observed.