W0249

Crystallographic Studies of Phase Transition in the Complex of a Nonlinear Optical Molecule with Beta-Cyclodextrin. Ali Rashid, John Stezowski, G. Harbison, Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304 USA

Organic molecular crystals are of great interest due to their large nonlinear optical properties and their large damage threshold. It has been shown that organic molecules having conjugated [Sigma] electron systems and a donor acceptor pair posses large second order polarizabilities. However, most aromatic molecular crystals such as paranitroanaline (p-NA) pack in a centrosymetric fashion which forbids second harmonic generation (SHG). A method of removing crystalline centrosymetric geometry using host-guest inclusion complexation has been reported.

Single crystals of p-NA [Sigma]-Cyclodextrin inclusion complex have been obtained and data has been collected at room temperature and at 20K. Upon cooling a change in space group was detected (C2 to P21) which is indicative of a phase transition. In order to understand the mode of inclusion, the effects of temperature on the packing and the effect of the guest on the nonlinear optical properties on p-NA a number of methods will be applied to this system. The methods employed include crystallographic studies, measurements at room and low temperature, differential scanning calorimetry to track the phase transition temperature, solid-state NMR to look at the dynamics involved upon cooling, single crystal SHG to examine the nonlinear optical properties at low temperature and molecular modeling techniques such as molecular dynamics in order to simulate the phase transition.