  In this work, we investigate thermodynamic properties of the one-dimensional
(1D) spin-crossover molecular chain being a subject of a constant external
pressure. Effective compressible degenerate Ising model is used as a
theoretical framework. Using transfer matrix formalism analytic results for the
low spin -- high spin crossover were obtained. We derive the exact expressions
for the fraction of molecules in the high spin state, correlation function and
heat capacity. We provide analysis of parameters region where the spin
crossover takes place and demonstrate how pressure changes location of the
crossover.
