A new NLO-active polyurethane (T-g = 145 degreesC) based on a two-dimensional NLO chromophore has been investigated. Two ends of this lambda-shaped chromophore can be directly bound to the main chain of polyurethane. After poling, fast relaxation of the effective second harmonic (SH) coefficient was observed at temperatures higher than 122 degreesC. Moreover, excellent temperatures higher than 122 degreesC. Moreover, excellent temporal stability at 100 degreesC was obtained despite the operating temperature being very close to the fast relaxation temperature. This is due to the fact that embedding the rigid lambda-shaped chromophores into the polymer backbone effectively restricts molecular motion at temperatures close to T-g.