Process for the realization of polymeric materials with second order nonlinear electro-optical properties comprising the following steps: - mixing of a chromophore with nonlinear optical properties and two or three hydroxy groups in a non-reactive solvent toward isocyanate groups containing an isocyanate compound with at least two isocyanate groups in order one or more bi- or tri-isocyanate NLO chromophores to be obtained; - isolation of said pure bi- or tri-isocyanate NLO chromophores obtained according to the above step; - dissolution of said bi- or tri-isocyanate NLO chromophores obtained according to the above step in one or more non-reactive solvents toward isocyanate groups containing reactive substances consisting of acyl- substituted or unsubstituted formamides and/or acylamides bearing as nitrogen substituents, independently, one or more hydrogen atoms, one or more alkyls substituted or unsubstituted with isocyanate moiety not reactive groups, one or more phenyl groups substituted or unsubstituted with non-reactive groups toward isocyanate groups, in order to obtain a prepolymer mixture consisting of said not reactive solvents and reaction products of said NLO bi- or tri-isocyanate chromophores and said reactive substances; - coating of a thin layer of said prepolymer mixture on a substrate and evaporation of said not reactive solvents; - cross-linking and poling of said thin layer on substrate, by means of heating and application of an electric field, in order a cross-linked and poled thin layer to be obtained; - cooling of said thin cross-linked and poled layer at ambient temperature maintaining the applied poling electric field; - switching off the poling electric field. - mixing of a chromophore with nonlinear optical properties and two or three hydroxy groups in a non-reactive solvent toward isocyanate groups containing an isocyanate compound with at least two isocyanate groups in order one or more bi- or tri-isocyanate NLO chromophores to be obtained; - isolation of said pure bi- or tri-isocyanate NLO chromophores obtained according to the above step; - dissolution of said bi- or tri-isocyanate NLO chromophores obtained according to the above step in one or more non-reactive solvents toward isocyanate groups containing reactive substances consisting of acyl- substituted or unsubstituted formamides and/or acylamides bearing as nitrogen substituents, independently, one or more hydrogen atoms, one or more alkyls substituted or unsubstituted with isocyanate moiety not reactive groups, one or more phenyl groups substituted or unsubstituted with non-reactive groups toward isocyanate groups, in order to obtain a prepolymer mixture consisting of said not reactive solvents and reaction products of said NLO bi- or tri-isocyanate chromophores and said reactive substances; - coating of a thin layer of said prepolymer mixture on a substrate and evaporation of said not reactive solvents; - cross-linking and poling of said thin layer on substrate, by means of heating and application of an electric field, in order a cross-linked and poled thin layer to be obtained; - cooling of said thin cross-linked and poled layer at ambient temperature maintaining the applied poling electric field; - switching off the poling electric field. - isolation of said pure bi- or tri-isocyanate NLO chromophores obtained according to the above step; - dissolution of said bi- or tri-isocyanate NLO chromophores obtained according to the above step in one or more non-reactive solvents toward isocyanate groups containing reactive substances consisting of acyl- substituted or unsubstituted formamides and/or acylamides bearing as nitrogen substituents, independently, one or more hydrogen atoms, one or more alkyls substituted or unsubstituted with isocyanate moiety not reactive groups, one or more phenyl groups substituted or unsubstituted with non-reactive groups toward isocyanate groups, in order to obtain a prepolymer mixture consisting of said not reactive solvents and reaction products of said NLO bi- or tri-isocyanate chromophores and said reactive substances; - coating of a thin layer of said prepolymer mixture on a substrate and evaporation of said not reactive solvents; - cross-linking and poling of said thin layer on substrate, by means of heating and application of an electric field, in order a cross-linked and poled thin layer to be obtained; - cooling of said thin cross-linked and poled layer at ambient temperature maintaining the applied poling electric field; - switching off the poling electric field.