Over the past decade, iron(II) polypyridines have gained a lot of attention as potential chromophores and sensitizers due to the low cost and high abundance of iron. Unfortunately, most iron(II) polypyridines are poor chromophores since their initially excited, photoactive metal-to-ligand charge transfer (MLCT) states quickly decay into non-photoactive metal-centered (MC) states. Many strategies to increase their lifetime have been pursued, built mainly around increasing the ligand field strength of these complexes and thus destabilizing the MC states. In this work, we aim to design a new class of Fe(II) complexes by stabilizing the energies of their MLCT states. To this end, we employ density functional theory (DFT) and time-dependent DFT to investigate a series of Fe(II) complexes, [Fe(L/X) 2,4 (N^N)] 2+/2− where L/X represents either cyanide, isocyanide, or bipyridine ligands and N ̂N stands for bidentate-extended π-conjugated ligands derived from the bipyridine. The L/X ligands tune the energetics of the Febased t 2g molecular orbitals, while the amount of π-conjugation on the N^N ligand impacts the energies of its π and π* orbitals, thus tuning the energetics of the MLCT and the ligand-centered (LC) states. Overall, our results suggest that the use of N^N ligands with the extended π-conjugation is a viable strategy to tune the relative energies of MLCT, LC, and MC states.
Small molecule organic dyes have many potential uses in medicine, textiles, forensics, and light-harvesting technology. Being able to computationally predict the spectroscopic properties of these dyes could greatly expedite screening...
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We have prepared a series of complexes of the type [Ir III (ppy) 2 (L] n+ complexes (1−4), where ppy is a substituted 2phenylpyridine and L is a chelating phosphine thioether ligand. The parent complex (1) comprises an unsubstituted phenylpyridine ligand, whereas complex 2 contains a nitro substituent on the pyridine ring, complex 3 features a diphenylamine group on the phenyl ring, and 4 has both nitro and diphenylamine groups. Crystallographic, 1 H NMR, and elemental analysis data are consistent with each of the chemical formulae. DFT (density functional theory) computational results show a complicated electronic structure with contributions from Ir, ppy, and the PS ligand. Ultrafast pump−probe data show strong contributions from the phenylpyridine moieties as well as strong panchromatic excited state absorption transitions. The data show that nitro and/or diphenylamine substituents dominate the spectroscopy of this series of compounds.
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