New push-pull ladder-type chromophores with large hyperpolarizability for nonlinear optical application

A novel series of ladder-type chromophores TA0-5 with strong donor and acceptor were designed and theoretically investigated for applications in nonlinear optics. Chromophores TA0-5 possess ladder-type bridges with different fused-ring structures. The influence of varying structures of ladder-type bridges and introduction of strong donor and acceptor on the first hyperpolarizabilities in this innovative push-pull fused system were analyzed by multiple methods, such as (hyper)polarizability density, coupled perturbed Kohn-Sham (CPKS) method, sum-over-states (SOS) model and two states model. Through density of states analysis, TA0-TA5 all show deep HOMO levels and low energy gaps, indicating the excellent air-stable property of them. Through tuning the number of thiophene rings in the bridge and introduction of strong push-pull architecture, the first hyperpolarizabilities of new chromophores are significantly enhanced. Importantly, TA5 exhibits remarkable first hyperpolarizability ( beta tot value is 5882.1 x 10-30 esu) in AN. The two-dimensional second-order nonlinear optical (NLO) spectra predicted by the SOS model show the strong NLO responses under external fields. All the designed chromophores exhibit outstanding electro-optical Pockels and optical rectification effects. The results reveal that this new series of push-pull ladder-type chromophores can be high-performance NLO materials and are expected to be prevalent for NLO and optoelectronic application.