Ultralarge Hyperpolarizability, Novel Ladder-Type Heteroarenes Electro-Optic Chromophores: Influence of Fused Heterocyclic π-System and Push–Pull Effect on Nonlinear Optical Properties

A new series of ladder-type heteroarenes electro-optic (EO) chromophores based on unique fused oligothiophene, oligofuran, and oligopyrrole bridge with a strong push–pull effect were designed, and their distinctive electric structure and nonlinear optical (NLO) properties were investigated by multiple methods, including DOS analysis, CPKS method, SOS model, TSM model, and hyperpolarizability density analysis. Interestingly, it is found that the introduction of different strengths of donor and acceptor moieties, the nature of ladder-type heteroarenes bridge, and the medium polarity play critical roles in achieving ultra-large hyperpolarizabilities. Encouragingly, the DN1-6Fu-AS1 and DN1-6Py-AS1 both exhibit ultra-large β_prj values (up to 12965.5 × 10⁻³⁰ esu) and β_tot value (up to 13238.2 × 10⁻³⁰ esu), owing to their exceptionally low transitions energy and large variation of dipole moment. The DO2-6Fu-AO2, DO2-6Th-AO2, DO2-6Fu-AS1, and DO2-6Th-AS1, exhibit very deep HOMO levels, which are expected to have superior air stability and effectively prevent large leakage currents. Hirshfeld surface analysis and interaction region indicator analysis were employed to explore the noncovalent interactions in the dimer. The DO2-6Fu-AS1 and DO2-6Py-AS1 show the outstanding electro-optical Pockels effect, and DN1-6Fu-AO2 exhibit large SHG responses. These unique and brand-new push-pull ladder-type heteroarenes chromophores are promising candidates for chip-scale EO modulators, and electronic and photonic devices in emerging communication, energy, analog, and digital technologies.