Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis(thiocyanato)(2,2′‐bipyridyl)platinum(II)

Abstract

AbstractThis paper presents a Density Functional or Time Dependent Density Functional (DFT/TDDFT) study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers:bis(isothiocyanato‐S)(2,2′‐bipyridyl) platinum(II) ([Pt(SCN)2(bpy)]), (isothiocyanato‐S)(thiocyanato‐N)‐(2,2′‐bipy‐ ridyl) platinum(II) ([Pt(SCN)(NCS)(bpy)]), and bis(thiocyanato‐N)(2,2′)‐bipyridyl)platinum(II) ([Pt(NCS)2(bpy)]), in which different coordination ligands based on the N‐ and S‐coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries were compared to the experimentally observed structures. TDDFT calculation was carried out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model (PCM) to account for solute‐solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agreement with the experimental determinations. The first two absorptions were found to originate from mixed platinum‐SCN (or NSC) to bipyridyl‐π* transitions rather than pure metal‐to‐ligand‐charge‐transfer (MLCT) transitions, whereas the higher‐energy bands arose from intraligand π→π* transitions. The stretching frequencies of C≡N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper.