Structural Features from Reflection Spectra: Orientation of 1, 3,-bis-(Dimethylamino) trimethinium Perchlorate Molecules in the Crystal

Abstract

If the orientation of a molecular electronic transition moment with respect to the molecular framework is known, reflection spectra of crystalline samples on various faces may be used to locate the molecules in question. This can be done through projection of the transition moment on the faces, or through use of the optical indicatrix. The two methods are briefly compared, and the preferred indicatrix method is applied to crystals of the dye 1,3-bis-(dim-ethylamino)trimethinium perchlorate. Along each principal axis of the indicatrix, best fit values for reasonant frequency, plasma frequency, and damping constant are obtained in the frequency range of the first singlet. Parameters of the crystal structure having to do with the orientation of the dye molecules are then deduced from this information.