Inverse opaline photonic crystal structures are created from carbon precursor polymer networks derived from the thermal Bergman cyclopolymerization of bis-ortho-diynyl arene (BODA) monomers. A new hydroxy-functional BODA monomer was prepared that exhibited excellent compatibility with silica opal templates. Monomer melt infiltration of the template, in situ thermal polymerization, and pyrolysis, followed by removal of the silica with HF affords a carbon inverse opal structure that conserves the original dimensions of the template. The photonic crystal was characterized by the reflectance spectra, and the refractive index of the carbon was estimated. The functionality of the carbon opal as a sensor element was demonstrated with water/acetonitrile mixtures and reveals a bandstop shift of 13 nm over a refractive index change of 0.011.