Effect of carbazole functionalization with a spacer moiety in the phenanthroimidazole bipolar ligand in a europium(iii) complex on its luminescence properties: combined experimental and theoretical study

Abstract

The functionalization of carbazole with a spacer in the C1 position and fluorine in the N1 position in the imidazole phenanthroline based bipolar ligand has been designed, synthesised and utilized to make a Eu(TTA)₃Phen-Fl-O-CBZ complex. The absorption spectrum of the ligand shows the expected absorption due to the π–π* transition of the aromatic ring and this was verified by theoretical calculation. The PL emission spectra of the complex clearly indicates that the complete energy transfer occurs from ligand to the Eu(III) metal ion, and this was confirmed by DFT and TD-DFT calculations. It is found that the spacer molecule can decrease the energy gap of the HOMO–LUMO energy levels (2.6 eV) with respect to the case without a spacer molecule. In addition, an increase in the singlet and triplet energy levels was observed, the consequence of efficient energy transfer from the ligand to the Eu(III) ion. The complex has also been incorporated into the PMMA matrix and its PL properties analysed. The enhanced quantum efficiency observed by 1% doping with PMMA was found to be 14.2% and improved intensity ratios as well as FWHM were also observed. Electrochemical analysis has also been carried out for a better understanding of the energy levels. These results are indicate that the synthesized complex shows potential.