The paper aims at characterizing the excited state of a pyrrolyl-isoxazole derivative containing, apart from these two fragments with electron donor (D) - pyrrolyl - and acceptor (A) - isoxazole - character, a third one - methylenephthalydyl - having also an A character. They are single bonded in an A-D-A arrangement. It is shown that the presence of the second A fragment in the molecule modifies the photophysical properties comparing to D-A pyrrolyl-isoxazole derivatives: lower Stokes shift, band width practically independent on the polarity of the solvent, linear dependence of the Stokes shift on the solvent polarity function. The spectral study of the inclusion complex of the studied compound in beta-cyclodextrin reveals a decrease in the emission intensity in the presence of cyclodextrin. These experimental findings are consistent with the lack of a twisted intramolecular charge transfer (TICT) excited state, which in turn is present for pyrrolyl-isoxazole derivatives of the D-A type. The lack of a TICT state is further ascertained by theoretical calculations of sections through the potential energy surfaces along both possible A to D rotation dihedrals. The stable conformations are quasiplanar, while the orthogonal conformations are unstable.     «

The paper aims at characterizing the excited state of a pyrrolyl-isoxazole derivative containing, apart from these two fragments with electron donor (D) - pyrrolyl - and acceptor (A) - isoxazole - character, a third one - methylenephthalydyl - having also an A character. They are single bonded in an A-D-A arrangement. It is shown that the presence of the second A fragment in the molecule modifies the photophysical properties comparing to D-A pyrrolyl-isoxazole derivatives: lower Stokes shift, ba...     »