Values of the conformation-dependent polymer-solvent interaction parameter V-D have been calculated for some simple polysilane model compounds using quantum-mechanically derived molecular polarizabilities coupled with London’s dispersion formula. The value V-D = 0.97 kcal mol(-1) obtained in the present study for the sigma-conjugated polysilanes nearly equals the V-D approximate to 1.1 kcal mol(-1) estimated by Schweizer for the analogous pi-conjugated carbon-backbone polymers, assuming similar physical conditions. The present results thus provide theoretical evidence in support of the pertinence of Schweizer’s theory of abrupt thermochromism to the polysilanes. The conformational flexibility and versatility of the backbone is much greater for the polysilanes compared with most pi-conjugated polymers, hence the conformational ’defect energy’ epsilon of the former should be small or even negative. The combination of large V-D (favouring the ’ordered’ backbone) and small epsilon (favouring the ’disordered’ backbone) predicted for the polysilanes would place the critical V-D/epsilon parameter well in excess of the limiting value V-D/epsilon greater than or equal to 0.37 required for onset of abrupt thermochromism according the Schweizer. The (Austin Model 1) AMI-calculated change in polarizability Delta alpha with respect to backbone rotation phi was 0.63 Angstrom(3) for the model polysilane but only 0.08 Angstrom(3) for the analogous non-conjugated carbon-backbone model polymer. This substantial difference substantiates the existence of strong coupling between the molecular polarizability and the backbone conformation in the polysilanes. Only the longitudinal polarizability alpha(xx) contributes substantially to Delta alpha, while the transverse polarizabilities alpha(yy) and alpha(zz) essentially combine with no net effect on Delta alpha (i.e. Delta alpha(yy) congruent to -Delta alpha(zz)). The variation of the calculated band-gap energy Eg with alpha for corresponding values of phi fits a second-order regression curve (correlation coefficient r = 0.98). As the silicon backbone approaches an all-trans conformation, the highest occupied molecular orbital (HOMO) energy increases while the lowest unoccupied molecular orbital (LUMO) energy decreases to reduce E(g). This increase in the HOMO energy is balanced by a nearly equal decrease in the HOMO-1 energy; likewise, the decrease in the LUMO energy is balanced by an increase in the LUMO+1 energy.