Optoelectronic properties for main group element-bridged ladder compounds

Ladder-type π-conjugated molecules with fully ring-fused structures have fascinating optoelectronic properties because the flattened π-conjugated framework can eliminate conformational disorder and effectively enhance π-conjugation. Their optoelectronic properties can be modified by incorporating main group elements into the ladder skeleton. Heteroatom-bridges not only stiffen the skeleton but also contribute to the electronic structure through orbital interaction between the main group elements and the π-conjugated skeleton. Herein, the structural, electronic, and optical properties of bisand tetrakis-bridged (C, Si or P-bridged) stilbene derivatives were investigated by density functional theory (DFT) and time-dependent DFT (TDDFT) to provide theoretical understanding and predictions for these compounds. The electronic structures of these π-conjugated skeletons could be tuned by the incorporated elements. Compared with bis-bridged analogs, tetrakis-bridged derivatives exhibited substantial red shifts in the absorption and shorter radiative lifetimes because of extended π-conjugation. In addition, the energy barrier for the injection and transport rates of the holes and electrons was evaluated using ionization potentials, electronic affinities, and reorganization energies (λ). Compared to bis-bridged analogs, tetrakis-bridged derivatives exhibit higher accepting abilities for both holes and electrons.