The 2pn*-3dn interaction in the excited state of aromatic silanes has been studied by means of absorption and emission spectroscopy. Broad and structureless fluorescence spectra of phenyldisilanes and naphthyldisilanes with large Stokes shifts have been observed and they have been attributed to the emissions from the intramolecular charge-transfer (c. t.) states with large dipole moments. Evidence that the c.t. emission originates from the l(2pn, 3dz) state produced by the 2pn* (aromatic ring) 3d7t (Si-Si bond) intramolecular charge transfer is given by the effect of steric twisting on the emission. It is shown that the fast formation (d 1 ns) of the c.t. state from the locally excited state I(n, n*) 'B, (or ' L b ) of phenyldisilanes takes place, followed by rapid decay (d 1 ns) of the intersystem crossing I(2pn, 3dn) + 3(7t, x*). However, no c. t. emission has been observed for aromatic monosilanes and polycyclic aromatic disilanes (aromatic rings 2 3) even in fluid polar solvents. The 2pn* -+ 3dn intramolecular c.t. mechanism is discussed in comparison with that of the twisted intramolecular charge-transfer (t.i.c.t.) state.

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The relation between the mixed-valence state and crystal structure of 1 ', 1 "'-didecyl-and 1', 1 "'-bis(undecy1)-1,l "-biferrocenium triiodide has been studied by means of "Fe Mossbauer spectroscopy and X-ray powder diffraction. The salts with even numbers of carbon atoms in the alkyl chain show a phase transition between two types of layered structures, accompanied by a change in mixed-valence state. Iodine-129 Mossbauer spectroscopy was applied to determine the electronic state of the triiodide anion in the biferrocenium salts. A change in the electronic state accompanied by a phase transition was observed in the case of the 1 I , 1 "'-didecyl derivative.

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