Crystal structure and optical property of a Cadmium(II) complex based on triphenylamine derivative—Theoretical and experimental investigation

Highlights: • The complex has excellent one- and two-photon excited fluorescence. • The "experimental Stokes shift vs. solvent polarity" is exactly the Boltzmann S-curve. • The geometry distortion of the complex is explained by computational method. • The OPA mechanism of complex is interpreted by hole-electron method. A triphenylamine derivative (E)-N,N-diphenyl-4-(2-(pyridin-2-yl)vinyl)benzenamine (L) was synthesized, and the corresponding cadmium complex CdI₂L₂ crystal was obtained and solved by single crystal X-ray diffraction analysis. The experimental resutls of one photon absorption (OPA) and one photon excited fluorescence (OPEF) indicate that coordination of CdI₂ only has slight effect on the spectrum peak position relative to the free ligand. Besides the Stokes shift, the full width half maximum of OPEF and the variation of the "peak span between solvents" from OPA to OPEF can also indicate the electron transition direction of the excitation process. The laser experiments show that both the ligand and complex have considerable two photon excited fluorescence (TPEF) emission. The experimental Stokes shift is correlated with the computational solvent polarity rMPI, and the results illustrate that the curve of "experimental Stokes shift vs. solvent rMPI" is exactly the Boltzmann S-curve. The computational results also indicate that the static interaction between the CdI₂L₂ molecules in crystal has strong effect on OPA properties. Considering the weak coordination bond strength of the complex CdI₂L₂, the S1→S0′ fluorescence emission may occur on both ligands, although the S0→S1′ excitation only occurs on the right ligand.