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The fluorescence of cyclotetrasilanes with an extremely large Stokes shift (up to 13700 cm-l) has been observed in rigid matrices at 77 K. The large Stokes shift is interpreted in terms of variation in potential energy for the S, and So states as a function of the ring Si-Si bond distance. Fluorescence properties are dependent on the molecular structures (planar and bent forms) of the compounds ; the fluorescence quantum yield, lifetime, and Stokes shift for the former are greater than those for the latter.