One-dimensional dielectric (N...H...N)(infinity) hydrogen-bonding chains of monoprotonated 1,4-diazabicyclo[2.2.2] octane (HDABCOdagger) were Introduced Into an electrically conducting 7,7,8,8-tetracyano-P-quinodimethane (TCNQ) salt as the countercation structure. Room-temperature electrical conductivity Was similar to10(-3) S cm(-1), with a semiconductive behavior. The temperature-dependent dielectric constants of (HDABCO(+))(2)(TCNQ)(3) indicated a dielectric transition at 306 K. A large deuterium Isotope effect for the dielectric transition (DeltaT = 70 K) was observed for the deuterated salt, (DDABCO(+))(2)(TCNQ)(3), Thermally activated order/disorder of the protons or deuteriums within the one-dimensional hydrogen-bonding chains of (HDABCO(+))(infinity) and (DDABCO(+))(infinity) affected the dielectric responses in the TCNQ-based semiconductors.