The rotational spectra of three isotopologues of the isopropanol dimethyl ether molecular complex have been measured with pulsed jet Fourier transform microwave spectroscopy. In the complex, isopropanol acts as a proton donor and takes a gauche conformation. The H -> D isotopic substitution of the hydroxylic hydrogen participating in the O-H center dot center dot center dot O hydrogen bond produces an increase of the B and C rotational constants, according to the shrinkage of the O center dot center dot center dot O distance of about 7 m angstrom, underlying and sizing the associated Ubbelohde effect.