Synthesis, structure, Hirshfeld surface analysis and photophysical studies of red emitting europium acetylacetonate complex incorporating a phenanthroline derivative

Two new octa-coordinated red emitting complexes of the type [Ln(acac)(3)(Br-2-phen)] [acac: acetylacetonate, Br-2-phen: 4,7-dibromo-1,10-phenanthroline, Ln: Sm(III) and Eu(III)] have been synthesized and characterized. Single crystal X-ray diffraction (SCXD) of [Eu(acac)(3)(Br-2-phen)] and [Eu(acac)(3)(H2O)(2)](H2O) revealed distorted square antiprism structure for both complexes. 2D fingerprint plots and Hirshfeld surface analyses signify important interactions in crystal packing [H center dot center dot center dot H (72.2%), O center dot center dot center dot H/H center dot center dot center dot O (18.9%) and C center dot center dot center dot H/H center dot center dot center dot C (6.7%) contacts for [Eu(acac)(3)(H2O)(2)](H2O), while [Eu(acac)(3)(Br-2-phen)] showed H center dot center dot center dot H (40.5%), Br center dot center dot center dot H/H center dot center dot center dot Br (12.9%) and O center dot center dot center dot H/H center dot center dot center dot O (6.5%)] contacts]. Photophysical measurements gave quantum yield (Q(Ln)(L)) of 1.1 and 13% with corresponding luminescence lifetime (tau(obs)) of 38.76 +/- 0.61 mu s and 790 +/- 1.53 mu s for [Sm(acac)(3)(Br-2-phen)] and [Eu (acac)(3)(Br-2-phen)], respectively. We have further evaluated photophysical properties of [Eu(acac)(3)(Br-2-phen)] theoretically from the optimized sparkle structure and steady-state emission spectrum of Eu(III) complex. The intramolecular energy transfer (W-ET) and back-energy transfer (W-BT) rate predicted from the calculated singlet (S-1) and triplet (T-1) levels to the emissive D-5(1) and D-5(0) states for Eu(III) follow the path S-0 -> S-1 -> T-1 -> D-5(1) -> D-5(0) -> F-7(0,4). The Eu(III) complex showed large stimulated emission cross-section (sigma((0 -> 2)) = 1.27 x 10(-20) cm(2)) similar to Nd-glass laser (1.6-4.5 x 10(-20) cm(2)) and offers promise for high-power laser medium.