Irradiation of 1-(1-benzocyclobutenylidene)benzocyclobutene gives indenoindene and its head-to-head photodimer nonacyclo[9.7.7.7^2,10.0^1,11.0^2,10.0^3,8.0^12,17.0^19,24.0^26,31]dotriaconta-3,5,7,12,14,16,19,21,23,26,28,30-dodecaene, C₃₂H₂₄. The molecule is built from four essentially planar indane units attached to an elongated cyclobutane ring. In the crystal, C—H...π interactions connect molecules into layers parallel to the bc plane.