The Peculiarities of the Optical Absorption of Monocrystalline Fluorene and Its Heteroanalogues in the Energy Range Between 3.5 eV and 8.5 eV

Abstract

Electronic absorption spectra of carbazole, dibenzofuran and fluorene were obtained in all three crystallographic directions (energy range 3.5-8.5eV). All electronic transitions with transition dipoles at oblique angles to a and b crystallographic axes can be traced to parental molecular states.

Crystal transitions with parallel transition dipoles can be traced to parental molecular states for thin (0.1-0.2μ) crystals, slow crystallized from melt under uniaxial pressure. For sublimation flakes and crystals fast crystallized from melt, these transitions cannot be traced to parental molecular states since their spectra have continuous, essentially uniform intensity distribution except for such transition at the onset of absorption.

Acknowledgments

The spectra were measured at the National Synchrotron Light Source, which is supported by the Office of Basic Energy of the U.S. Department of Energy. We wish to thank Mr. John Trunk for expert technical assistance; Dr. Nykypanchuk for helpful discussions and guidance in crystal thickness measurements; Ms. Tiffany Bowman for expert graphical work; Mr. Mike Sullivan for kind guidance and help with use of equipment in the sample preparation room; Dr. Jacob Padgug for expert language editing; and Ms. Lihi Avidan for help with preparing the manuscript for publication.