Enhancement of quadratic nonlinearity via multiple hydrogen-bonded supramolecular complex formation

Abstract

The formation and quadratic nonlinearity of a multiple hydrogen-bonded 1:1 supramolecular complex 1.2 between the 2,6-diaminopyridine-based ?-shaped molecule, 1, and ferrocenyl barbituric acid, 2, in solution have been investigated by the hyper-Rayleigh scattering (HRS) and NMR techniques. A 6-fold increase in the molecular hyperpolarizability (β) of the complex 1.2 over the sum of the molecular hyperpolarizabilities of the components 1 and 2 is seen. Such a significant enhancement in β is attributed to the alignment of the molecular dipoles of 1 and 2 in the 2D plane leading to the creation of a large dipole moment in the plane of the supramolecular complex. Depolarized HRS experiments led to the determination of the in-plane polarization components of β of the supramolecular complex 1.2. The component of β in the direction of the dipole moment is large. This investigation exemplifies the role of multiple hydrogen bonds in stabilizing a 2D supramolecular architecture leading to a large enhancement of molecular nonlinearity.