Enaminone‐Based Push–Pull Chromophores: Synthesis, Optical Properties, and Computational Insights

Abstract Chromophores incorporating enaminone units were efficiently synthesized using click‐type [2 + 2] cycloaddition‐retroelectrocyclization (CA‐RE) reactions. The preparation of electron‐rich alkynes necessary for these reactions initiated with the synthesis of alkynones via Sonogashira cross‐coupling, followed by nucleophilic conjugate addition to yield the target substrates. Subsequent reactions of these substrates with tetracyanoethylene (TCNE) through [2 + 2] CA‐RE achieved product yields of 85%–93%, while employing the bulkier tetracyanoquinodimethane (TCNQ) produced the desired chromophores with yields ranging from 48% to 97%. These chromophores exhibited strong intramolecular charge transfer (ICT) absorption bands, with λ max values between 460 and 695 nm as determined by UV/Vis studies. Furthermore, the chromophores demonstrated positive solvatochromism as an additional support for the ICT mechanism. Protonation–neutralization experiments were performed to analyze the low‐energy absorption bands, verifying that they originate from ICT transitions. Computational techniques were applied to gain deeper insight into the ICT characteristics and linear and nonlinear optical properties of the obtained compounds. The study involved geometry optimizations, TD‐DFT analyses, visualizations of frontier orbitals and electrostatic potential maps, as well as the calculation of parameters like, quinoid character, average polarizability, and first hyperpolarizability.