Two series of multibranched compounds with vinylenes attaching to the s-triazine core have been synthesized. The two-photon absorption cross section (sigma) increases significantly as the branch number increases, with the ratios of sigma between one-, two-, and three-branched compounds being 1.0:3.3:7.0 for series A and 1.0:3.7:7.0 for series B respectively, indicating remarkable cooperative enhancement.