New quiolinium polymorph with optimal packing for maximal off-diagonal nonlinear optical response

The influence of polymorphism on the nonlinear optical properties of HMQ-MBS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methoxybenzenesulfonate) crystals is investigated. By changing the solvent for crystal growth, a new polymorph has been found. While the previously reported alpha-phase of HMQ-MBS, having monoclinic Pc space group symmetry exhibits an optimal molecular packing for maximizing the diagonal component of the second-order nonlinear optical response, the beta-phase of HMQ-MBS has monoclinic Psi space group symmetry and exhibits an optimal molecular packing for maximizing the off-diagonal response. HMQ-MBS is therefore a very interesting compound for a wide range of second-order nonlinear optical applications. (C) 2012 Elsevier Ltd. All rights reserved.