I-Methylphenanthro[3,4-blthiophene was prepared by the photocyclization of 1-(4'-methyl-2'-thicnyl)-2{2"­naphthyl)ethene. The 1H and 13C-nmr spectra were assigned using two-dimensional 1H/13C heteronuclear chemical shift correlation and relayed coherence transfer (RELAY) experiments. From nuclear Overhauser difference spectra, the H11-C1 methyl-H intramolecular distance was determined to be 2.10Å. The molecule crystallized front chloroform in the monoclinic system, space group P21/c. A total of 3536 unique reflections were measured and the structure was solved by direct methods and refined to a final R = 0.049. The mole­cule is helical with both chiral forms observed in the crystal. The H11-C1 methyl-H distance in the crystal was 2.12(3)Å in excellent agreement with the distance measured in solution by NOE techniques.