Electronic structure and first hyperpolarizability of triple helicene compounds

•Photophysical properties of triple helicene compounds were firstly studied.•The electron transition properties of the studied compounds were assigned.•The relation between substitutions and photophysical properties was established.•Triple helicene compounds are the potential second-order NLO materials. Density functional theory (DFT) investigations on the reported triple helicene and four new substituted compounds are employed to aid in the design of nonlinear optical (NLO) materials with large first hyperpolarizability βHRS. The influences of different substituents were analyzed in terms of geometric and optoelectronic parameters such as energy gap, UV–vis absorption spectra, and electronic absorption energies. The investigation shows that the combination insertion of the donor unit and acceptor unit, especially the combination introduction of NH2 units at the R1 and R2 positions and NO2 units at the R3 and R4 positions, effectively reduces the band gap, makes the FMOs obvious spatial charge separation, broadens the absorption spectrum and produces a larger red shift, and obtains a larger βHRS value. Considering their strong NLO response, the studied compounds have the probability to be candidates used as excellent second-order NLO materials. The nonlinear optical properties of the studied compounds were studied with the help of the DFT calculations. [Display omitted]