Two-dimensional second-order nonlinear optical spectra: landscape of second-order nonlinear optics

The landscape of second-order nonlinear optical (2nd NLO) responses of a system can be depicted as two-dimensional second-order nonlinear optical spectra in a range of external fields, and this is difficult to be realized in experiment for a wide range of external fields. In the present study, an efficient method for application of sum-over-states model to simulate electronic two-dimensional NLO (2DNLO) spectra has been developed, and techniques to analyze NLO response–structure correlation have been proposed. This 2DNLO method has been applied to simulate the 2DNLO spectra of a series of typical electron push–pull chromophores under external fields of up to 5.00 eV. The correlation between the NLO properties and structure has been disclosed, and a further strategy to enhance the NLO properties of push–pull chromophores has been proposed.