Structure and photophysics of an old, new molecule: 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)]dodecane.
More than a century after its initial synthesis, the static and dynamic geometry of 1,3,6,8-tetraazatricyclo [4.4.1.1(3,8)]dodecane (TTD), a fully saturated cage-like molecule, is finally established. Detection and modeling of the supersonic jet fluorescence excitation and emission spectra show that the molecule undergoes interconversion between two S(4) symmetry minima. The barrier at the D(2d) symmetric conformation is only 105 cm(-1), i.e., approximately 0.3 kcal mol(-1), and is overcome along a carbon-carbon torsional mode of a(2) symmetry. The presence of an S(4) conformation is corroborated by a Raman investigation. When excited to the first excited singlet state, the 3s Rydberg state, the molecule adopts a geometry with D(2d) symmetry. The satisfactory description of the spectroscopy of TTD obtained by a combination of quantum chemical and quantum mechanical models is discussed, and the apparent conflict between the present results and nuclear magnetic resonance and X-ray diffraction experiments is solved. Because of the close analogy between a Rydberg state and the ground state of the radical cation regarding geometry and spectroscopic properties, it is concluded that the radical cation is also of D(2d) symmetry.
Zwier
Jurriaan M
JM
Institute of Molecular Chemistry, Faculty of Science, University of Amsterdam, Nieuwe Achtergracht 127-129, 1018 WS Amsterdam, The Netherlands.
Brouwer
Albert M
AM
Buma
Wybren Jan
WJ
Troisi
Alessandro
A
Zerbetto
Francesco
F