STUDIES OF CHAIN CONFORMATIONAL KINETICS IN POLY(DI-N-ALKYLSILANES) BY SPECTROSCOPIC METHODS .4. PIEZOCHROMISM IN SYMMETRICAL POLY(DI-N-ALKYLSILANES)

The effect of elevated pressure on backbone conformation in a series of symmetrically substituted poly(di-n-alkylsilanes) has been investigated using UV - vis, Raman, and FTIR spectroscopy. Initially at low pressures, lateral compression occurs, which gives rise to gross changes in conformation, e.g., a change from a helical to a planar zigzag structure. This is manifested by a dramatic red shift of UV absorption bands by as much as 50 nm. At high pressures axial compression occurs, which leads to a geometrical distortion of the sigma-conjugated backbone, which in turn causes a reversible continuous blue shift of UV absorption bands. Raman measurements at ambient and elevated pressures support these results.