ULTRA-VIOLET SPECTRA OF BENZ[F]INDAN IMPURITY IN A FLUORENE CRYSTAL

Because of its site symmetry, fluorene is an extremely useful matrix for the study of electronic spectra of aromatic molecules in polarized light. Unfortunately, fluorene contains a number of persistent impurities. Benz[f]indan is such an impurity giving rise to a weak absorption system at 3200 Å, at slightly lower energy than the first transition of the matrix itself. Not recognizing the presence of the impurity, previous workers have ascribed the transition at 3200 Å to the fluorene matrix. The 3200 Å system of benz[f]indan has been fully characterized and corresponds to an 1A1 ← 1A1 assignment, active along the long axis of the molecule, in analogy with the corresponding transition of naphthalene. A vibrational analysis of the polarized fluorescence and absorption spectrum is included and a comparison between corresponding fundamentals of the ground and excited electronic states is made. © 1969.