A series of new nonlinear optical chromophores based on configurationally locked polyenes (CLPs) with chiral pyrrolidine donors are synthesized. All CLP derivatives exhibit high thermal stability with decomposition temperatures T-d at least > 270 degrees C. Acentric single crystals of enantiopure D- and L- prolinol-based chromophores with a monoclinic space group P2(1) exhibit a macroscopic second-order nonlinearity that is twice as large than that of analogous dimethylamino-based crystal. This is attributed to a strong hydrogen-bonded polar polymer-like chain built by these molecules, which is aligned along the polar crystallo-graphic b-axis. Five alpha-phase CLP crystal with different donors grown from solution exhibit a reversible or irreversible thermally induced structural phase transition to a beta-phase. These phase transitions are unusual, changing the crystal symmetry from higher to lower at increasing temperature, for example, from centrosymmetric to non-centrosymmetric, enhancing their macroscopic second-order nonlinear properties.