Synthesis, Structure, Hirshfeld Surface Analysis and Photophysical Studies of Red Emitting Europium Acetylacetonate Complex Incorporating a Phenanthroline Derivative

Abstract

Two new octa-coordinated red emitting complexes of the type [Ln(acac) <inf>3</inf> (Br <inf>2</inf> -phen)] [acac: acetylacetonate, Br <inf>2</inf> -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) <inf>3</inf> (Br <inf>2</inf> -phen)] and [Eu(acac) <inf>3</inf> (H <inf>2</inf> O) <inf>2</inf> ](H <inf>2</inf> O) 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) <inf>3</inf> (H <inf>2</inf> O) <inf>2</inf> ](H <inf>2</inf> O), while [Eu(acac) <inf>3</inf> (Br <inf>2</inf> -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 <inf>Ln</inf> L ) of 1.1 and 13% with corresponding luminescence lifetime (τ <inf>obs</inf> ) of 38.76 ± 0.61 μs and 790 ± 1.53 μs for [Sm(acac) <inf>3</inf> (Br <inf>2</inf> -phen)] and [Eu(acac) <inf>3</inf> (Br <inf>2</inf> -phen)], respectively. We have further evaluated photophysical properties of [Eu(acac) <inf>3</inf> (Br <inf>2</inf> -phen)] theoretically from the optimized sparkle structure and steady-state emission spectrum of Eu(III) complex. The intramolecular energy transfer (W <inf>ET</inf> ) and back-energy transfer (W <inf>BT</inf> ) rate predicted from the calculated singlet (S <inf>1</inf> ) and triplet (T <inf>1</inf> ) levels to the emissive 5 D <inf>1</inf> and 5 D <inf>0</inf> states for Eu(III) follow the path S <inf>0</inf> → S <inf>1</inf> → T <inf>1</inf> → 5 D <inf>1</inf> → 5 D <inf>0</inf> → 7 F <inf>0,4</inf> . The Eu(III) complex showed large stimulated emission cross-section (σ <inf>(0→2)</inf> = 1.27 × 10 −20 cm 2 ) similar to Nd-glass laser (1.6–4.5 × 10 −20 cm 2 ) and offers promise for high-power laser medium. © 2019 Elsevier B.V.