Study of UV-Vis absorption spectra of magnetic molecule tripyridinium bis[tetrabromidoferrate(III)] bromide with density functional formalisms

The Ultraviolet-Visible (UV-Vis) absorption spectra of discrete magnetic molecules [py.H]3[FeBr4]2Br were measured based on density functional theory with B3LYP exchange-correlation functional in acetonitrile solution. The molecule was dissolved dilutely in acetonitrile to ensure that its experimental response could be attributed to a single dispersed molecule without signicant interaction with other molecules. The experimental UV-Vis absorption spectra exhibited four typical peaks in the UV region and three peaks in the visible region. A number of different basis sets were employed to compare the experimental data with the theoretical absorption spectra on different levels of basis sets. The comparison between experimental data and theoretical computation demonstrated that choosing 6-311++G** improved computational results mainly in the visible region and made minor differences between the results associated with Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) in other wavelength do-mains, especially in UV wavelengths. The simulated results are of importance in simulating the response of these molecular magnets as a discrete asymmetric unit to applied light.