White-light emission in donor-acceptor systems usually requires relatively high acceptor content and/or multiple acceptors to "neutralize" the primary color of donors. Herein, a cyanostilbene-bridged ditopic ureidopyrimidinone donor (CSU) was designed and synthesized, which can self-assemble into dispersed nanoparticles in water. Fascinatingly, efficient white-light emission can be realized by co-assembling 0.1% DBT into the nanoparticles through a light-harvesting strategy. This new system is further demonstrated for use in white-light encryption materials.