Second-order susceptibility tensors of partially ordered molecules on surfaces

Abstract

The shape of the macroscopic second-order susceptibility tensor of molecules bound to a surface depends upon both the molecular tensor and the distribution of orientations. The details of these dependencies are discussed in general and in the special case of two photon electronic resonance enhancement. Using the results of an orientation averaging procedure, experiments, based upon variation of the angle of incidence, the input polarization, the output polarization, or the frequency, can be devised to determine the shape of a molecular tensor or the orientation distribution. Specific examples are given for interfacial phenol and cinnamic acid.

Molecular Origins of the Remarkable Chiral Sensitivity of Second‐Order Nonlinear Optics

“…The generation of macromolecular chiroptical activity in chiral assemblies of achiral chromophores (referred to as structural rotary power) is reasonably well-understood in absorbance measurements of chiral media, [71,72] but has only relatively recently been applied to the interpretation of chiroptical effects in SHG and SFG of oriented systems. [7,8,42,43,45,46,62] Although predictions of possible chiroptical effects in SHG from oriented assemblies of planar chromophores with C 2v symmetry were reported as early as 1987, [73] most of the work in characterizing the role of molecular orientation in driving chiroptical phenomena in SHG and SFG of uniaxial films and interfaces has been performed within the last few years. [7,8,42,43,45,46,62] In both planar chromophores with C 2v symmetry and in "two-state" chromophores, in which the nonlinear optical properties of the chromophore are reasonably well-described by considering interactions between the ground state and a single excited state, only four elements within the molecular tensor are significant in electronically resonant SHG and SFG: b zzz , b zxx , b xzx , and b xxz .…”

Characterization of the Myosin-Based Source for Second-Harmonic Generation from Muscle Sarcomeres

“…(Note that the susceptibility tensor for this case also possesses Kleinman symmetry, even though we have not assumed that b is off-resonance: the susceptibility tensor may still be dependent on frequency.) Such an arrangement may be obtained by having molecules randomly distributed in a monolayer (56) or by having them form ordered structures such as helices.…”

On probing conformation of microtubules by second-harmonic generation

“…The second-order susceptibility (and also hyperpolarizability) tensor contains a total of 27 elements, but the number of independent elements is much less in the presence of symmetry [27]. For the process of SHG where the input wavelengths are degenerate, 18 tensor elements are independent.…”