Tuning of emitting colors and mimicking advanced Boolean logic functions via stimuli-responsive luminescence behavior of bimetallic lanthanide complexes comprising a TADF-active ligand.

Syntheses, characterizations and detailed investigations on the photophysical behaviors of a new array of four homobimetallic LnIII-complexes of type {(Ln2(hfa)6 (phen-Hbzim-tpy)} are undertaken in this work, where Ln = LaIII (1), EuIII (2), SmIII (3) and TbIII (4); hfa = hexafluoroacetylacetonate and phen-Hbzim-tpy = 2-[4-(2,6-dipyridin-2-yl-pyridin-4-yl)phenyl]-1H-imidazole[4,5-f][1,10]phenanthroline. Substantial improvement in terms of absorption, emission and sensitization efficacy is achieved herein compared to our related monometallic as well as homobimetallic complexes based on 2-thenoyltrifluoroacetone (tta). Interestingly, all the complexes, including the La(III), are found to inherit the thermally assisted delayed fluorescence (TADF) property of the phen-Hbzim-tpy bridging ligand and display excellent luminescence thermometric properties. DFT calculations of a representative complex (LaIII) also support the occurrence of the TADF event. The Eu(III) and Tb(III) complexes exhibit remarkable thermochromic behavior. The luminescence spectral characteristics of the complexes are also modulated to a significant extent upon varying the excitation wavelengths, which, in turn, appears instrumental in terms of generating various emitting colors in Sm(III) and Tb(III) complexes. Additionally, these stimuli-responsive luminescence behaviors of the complexes are employed to mimic the operations of two combinational logic gates to complement their practical utility in the field of advanced optical security.