Chiral macrocyclic imine nickel(II) coordination complexes with diverse photophysical properties

Abstract

Chiral transition metal complexes are of great interest in the second-order nonlinear optical (NLO) field due to their intrinsic non-centrosymmetric structure and the combination advantage of both inorganic and organic compounds. Very recently, the chiral macrocyclic imine Ni(II) coordination complex 1 with outstanding photophysical properties has been reported. The understanding of the structure-property relationship at the microscopic level is very important to further improve its performance. Here, time-dependent density functional theory (TDDFT) calculations have been used to investigate linear, chiroptical, and second-order nonlinear optical (NLO) properties of the eleven complexes with different stereoisomers (e.g. SS and RS) and substituent groups. The simulated UV–Vis/CD spectra of the complex 1 are in good agreement with the experimental ones, which can be used to assign the electron transition properties and absolute configuration (AC) with high confidence. It is found that stereoisomers and different substituent groups have great effect on the photophysical properties such as electronic absorption wavelengths, electron transition properties, and NLO responses. In particular, the designed complex 6 (SS stereoisomer) has the largest β value (32.6 × 10−30 esu), which is about 187 times as large as the organic urea molecule. The analysis of electronic transition indicates that ML'CT/IL'CT charge transfer is mainly responsible for its NLO response. More interestingly, complex 3 with SS stereoisomer could act as NLO switching material because it exhibits obvious different NLO response values from neutral state to the cationic states (3+ or 32+). The effects of different functionals and solvent effects on the UV–Vis/CD spectra were also considered.