Molecular orientation effects on two-photon absorption spectra of dimer systems

J-type dimer a exhibits a significant enhancement ratio of two-photon absorption (TPA) peak (Iimag(θ)/ Iimag(π/2) ∼ 275 around θ = π/6), while H-type dimer b also exhibits an enhancement ratio (∼4.8 at θ = 0). Such enhancements of Im γ(−ω; ω, ω, −ω) are caused by the double resonance effect, which is controlled by adjusting the relative monomer orientations.