Comparisons on isomeric 1,10-phenanthroline aromatic heterocyclic derivatives with triphenylamine and thiophene donors before and after rhenium(I) carbonyl complexation

We have described herein a series of unsymmetric 1,10-phenanthroline (phen) based aromatic heterocyclic derivatives with triphenylamine (TPA) and thiophene donors (L1–L5) and their respective neutral tricarbonyl rhenium(I) complexes (6a–6e). Comparisons between isomeric compounds L1/L2 and 6a/6b as well as L3/L4/L5 and 6c/6d/6e have been made on their 1H NMR and UV/Vis spectra, single-crystal structures and density function theory (DFT) calculations. The alterations of conjugated system of the whole molecules, originating from the introduction of 2-, 3- or 3,8-substituted TPA and thiophene groups of phen, are responsible for the structural and spectral discrepancy of these structural isomers. In particular, the introduction of TPA and/or thiophene donors at 2-postion of phen (L1 and L3) leads to smaller band gaps than their respective 3-substituted isomers (L2 and L4). In addition, rhenium(I) ion complexation could slightly lower the highest occupied molecular orbital (HOMO) energy levels but significantly decrease the lowest unoccupied molecular orbital (LUMO) energy levels of the molecular system.