Communication: Molecular sensors can be used to monitor the polymerization of linear precursors and also the formation of epoxy networks. The synthesis and properties of a novel fluorescence probe, tris(p-isocyanatophenyl)amine (TIPA), which acts both as a crosslinking site and as a chemical sensor, are described. A dramatic change of fluorescence intensity coupled with the high second-order hyperpolarizability of TIPA and its urethane derivative make it promising for the synthesis of nonlinear optical thermosets whose degree of curing and the mobility of the crosslink points can be measured by luminescence.