Structure-dependent luminescence of tetra-(4-pyridylphenyl)ethylene: a first-principles study

Luminescent materials with tunable wavelengths have been attracting much attention due to their many promising applications. In the present work, the recently reported supramolecular coordination complexes of tetra-(4-pyridylphenyl)ethylene (TPPE) that produce variable-wavelength light emissions were investigated by time-dependent density functional theory (TDDFT) calculations. We discovered that variations in the luminescent wavelength of TPPE mainly depend on the structural deviations from molecular planarity, which affect the molecular orbital wavefunction distribution. An interesting trigonometric-functional relationship between the emission wavelength (the emission energy) and the dihedral angle defining deviations from molecular planarity was uncovered. The solvent effect was also considered to reveal the mechanism of the solvent-dependent fluorescence color. These findings may be helpful to rational molecular design for high-performance luminescent materials with tunable color.