New Multifunctional Bipyrimidine‐Based Chromophores for NLO‐Active Thin‐Film Preparation**

Abstract New synthesized bipyrimidine‐based chromophores presenting alkoxystyryl donor groups carrying aliphatic achiral and chiral chains in the 4 position, connected to electron‐accepting 2,2‐bipyrimidine cores have been synthesized. Their linear and nonlinear optical (NLO) properties were investigated as well as their mesomorphic properties by various techniques (light‐transmission measurements, polarized‐light optical microscopy, differential scanning calorimetry measurements and two‐photon excited fluorescence). The derivatives with achiral linear carbon chains were found to exhibit liquid‐crystal properties with the formation smectic phases over large temperature ranges, which were confirmed by small‐angle X‐ray scattering analysis via stacking models. The nonlinear optical properties in the solid state for derivatives with C14 and the citronellol chains have been studied by wide‐field second‐harmonic generation and multi‐photon fluorescence imaging, confirming centrosymmetry for these achiral mesogens and their excellent third‐order nonlinearity whereas the chiral compound exhibits non‐centrosymmetric organization resulting in a strong Second Harmonic Generation at the crystal state.