Determination of the Orientation of Guest Molecules in the Host Lattice of Organic Crystals

Abstract It is a well known fact that the rate constant for mutual triplet annihilation in organic crystals depends on the magnitude of the magnetic field and on its direction relative to the crystallographic axes. The dependence of the delayed fluorescence on the magnetic field direction displays resonance minima, which are caused by energy level crossings of, the annihilating triplet pair. For the annihilation between free excitons (homofusion) in undoped crystals this has been first observed and theoretically explained by Johnson, Merrifield et al.1,2 The theory has been further extended by Suna.3