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(Br2-phen)] [acac: acetylacetonate, Br2-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(Br2-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⋯H (72.2%), O⋯H/H⋯O (18.9%) and C⋯H/H⋯C (6.7%) contacts for [Eu(acac)3(H2O)2](H2O), while [Eu(acac)3(Br2-phen)] showed H⋯H (40.5%), Br⋯H/H⋯Br (12.9%) and O⋯H/H⋯O (6.5%)] contacts]. Photophysical measurements gave quantum yield ( Q L n L ) of 1.1 and 13% with corresponding luminescence lifetime (τobs) of 38.76 ± 0.61 μs and 790 ± 1.53 μs for [Sm(acac)3(Br2-phen)] and [Eu(acac)3(Br2-phen)], respectively. We have further evaluated photophysical properties of [Eu(acac)3(Br2-phen)] theoretically from the optimized sparkle structure and steady-state emission spectrum of Eu(III) complex. The intramolecular energy transfer (WET) and back-energy transfer (WBT) rate predicted from the calculated singlet (S1) and triplet (T1) levels to the emissive 5D1 and 5D0 states for Eu(III) follow the path S0 → S1 → T1 → 5D1 → 5D0 → 7F0,4. The Eu(III) complex showed large stimulated emission cross-section (σ(0→2) = 1.27 × 10−20 cm2) similar to Nd-glass laser (1.6–4.5 × 10−20 cm2) and offers promise for high-power laser medium.