Poly(dendrimers) are an emerging class of fluorescent organic semiconductors that have been investigated for their ability to detect nitro-based explosives and taggants. In this work, the sensing chromophores were dendritic side chains attached to a norbornenyl-derived polymer backbone. The sensing chromophore of each poly(dendrimer) was based on fluorene and carbazole moieties, both of which have been shown to be sensitive toward nitro-containing explosives. The monomers, and corresponding polymers, were screened against 2,4-dinitrotoluene (DNT) and 2,3-dimethyl-2,3-dinitrobutane (DMNB) vapors and a range of household interferents such as mouthwash and ethanol. An important result of this work was the rapid and sensitive detection of DMNB, a taggant added to commercial plastic explosives, which is usually difficult to detect via fluorescence quenching due to its relatively low electron affinity and spontaneous diffusion out of the sensing film. Testing of the poly(dendrimer)s was also performed with a hand-held prototype detector for explosives. Selectivity was demonstrated with a range of interferents and explosive or taggant vapors, with the interferents giving an increase in fluorescence intensity and the explosive related materials a quenching of the luminescence. The results show that organic semiconductor poly(dendrimer)s are an interesting class of material for the detection of nitro-based explosives and taggants, especially DMNB.