Photoinduced electron-transfer reaction of cyclic oligosilanes and polysilanes in solution

Photoinduced electron‐transfer (PET) reactions were investigated for the cyclic oligosilanes and high molecular weight polysilanes in the presence of 9‐cyanoanthracene (CA), 9,10‐dicyanoanthracene (DCA), and triphenylpyrylium tetrafluoroborate (TPP+BF −4) using chemical and spectroscopic methods in solution. For the cyclic oligosilanes, the pyranyl radical (TPP·) and silane radical cation were observed as direct evidence of the PET from silanes to TPP+BF −4, and the reaction quantum yields showed that the ring opening of the radical cation of the cyclic oligosilane competed with the nucleophilic attack on the radical cation by the counter ion of the pyrylium salt and a back electron transfer (BET). For the high molecular weight polysilane, the observation of the transient absorptions of TPP· and the radical cation of polysilane is evidence of the PET, and the extremely long lifetime observed for the radical cation indicates the inefficient BET and reactivities. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:269–275, 2001