Photoactive materials are actively researched, piloting breakthroughs that have enriched fundamental understanding of science, and have led to real applications. Tetraphenylethene, a photoactive molecule that is of interest from fundamental and applied perspectives, features photochemical properties that are not exploited in the design of photoactive, dual-emissive materials. Here, tetraphenylethene-based, dual-emissive dendrimers are constructed via a synthetic approach that involves a photochemical reaction that exploits the photochemistry of tetraphenylethene. These dendrimers are emissive in solution and in the aggregate state with tunable dual emissions at 368 and 469 nm. The photochemical reaction also tunes the size of the aggregates, increasing the size after UV irradiation. The reported synthetic strategy is a direct and facile approach to accessing dual-emissive macromolecules, especially tetraphenylethene-based systems for real applications.