Halogen Bonding to Amplify Luminescence: A Case Study Using a Platinum Cyclometalated Complex

Abstract

The cocrystallization of aw eakly luminescent platinum complex [Pt(btpy)(PPh 3 )Cl] (1)( Hbtpy = 2-(2benzothienyl)pyridine;e mission quantum yield F em = 0.03) with fluorinated bromo-and iodoarenes C 6 F 6-n X n (X = Br,I; n = 1, 2) results in the formation of efficient halogen-bonding (XB) interactions Pt À Cl···X À R. An up to 22-fold enhancement (F em = 0.65) in the luminescence intensity of the cocrystallized compound is detected, without as ubstantial change of the emission energy.B ased on crystallographic,p hotophysical, and theoretical investigations,t he contribution of the XB donors C 6 F 6-n X n to the amplification of luminescence intensity is attributed to the enhancement of spin-orbit coupling through the heavy-atom effect, and simultaneously to the suppression of the nonradiative relaxation pathwaysbyincreasing the rigidity of the chromophore center.Noncovalent attractive interactions,s uch as hydrogen, halogen, or metallophilic bonding as well as p-p stacking, are widely used for the design and fabrication of avariety of functional materials,c onstructed from organic, inorganic,o r organometallic building blocks.T hese diverse assemblies of different levels of complexity are capable of certain unique actions,such as adetectable response to an external physical or chemical stimulus,energy transfer,orenergy conversion. [1] In yet another approach, halogen bonding (XB) [2] has been recognized as an effective tool in crystal engineering. [3] A deeper understanding of XB-driven aggregation in the solid state led to an umber of supramolecular systems with attractive physical characteristics,w hich include modified surfaces, [4] organic gels, [5] charge-transfer electroactive species, [6] liquid crystals, [7] and optically active compounds. [8] Despite the considerable progress which has been achieved in the construction of XB-stabilized architectures,t he explo-ration of the XB phenomenon for the development of lightgenerating materials remains in its infancy. Thevast majority of reports on this topic deal with the activation of phosphorescence from purely organic compounds by cocrystallization with as uitable haloaromatic partner.[8] Cocrystallization induces XB formation, leading to an enhanced externalheavy-atom effect facilitating spin-orbit coupling and consequently intersystem crossing, resulting in efficient triplet emission.In contrast, very few studies on the effect of XB on the optical properties of transition-metal complexes,alarge class of luminophores,have been reported to date.Halogen bonds were used to construct supramolecular assemblies containing weakly luminescent cyanometallates [Ru(diimine)(CN) 4 ] 2À

Reactions of Cyclometalated Platinum(II) [Pt(N∧C)(PR3)Cl] Complexes with Imidazole and Imidazole-Containing Biomolecules: Fine-Tuning of Reactivity and Photophysical Properties via Ligand Design

“…Cyclometalating N ∧ CH precursors, 2-(benzofuran-3yl)pyridine, and 2-(benzothiophen-3-yl)pyridine, were obtained according the Suzuki reaction. 30,43 The 1PTA complex was synthesized using slightly modified literature procedure. 32 The platinum(II) precursors [Pt(C ∧ N)(DMSO)Cl], 44 complexes 1PPh 3 , 27 2PPh 3 , 45 and 3PPh 3 , 30 were prepared according to the published procedures.…”

“…30,43 The 1PTA complex was synthesized using slightly modified literature procedure. 32 The platinum(II) precursors [Pt(C ∧ N)(DMSO)Cl], 44 complexes 1PPh 3 , 27 2PPh 3 , 45 and 3PPh 3 , 30 were prepared according to the published procedures. The conjugates of 1PPh 3 −4PPh 3 complexes with HSA and 1PPh 3 with ubiquitin were obtained according to the procedure described earlier.…”

Metal-Involving Bifurcated Halogen Bonding C–Br···η2(Cl–Pt)

“…Halogen bonding (XB) is one of the most intensively studied types of noncovalent systems in modern science. 1 Along with other weak interactions such as hydrogen bonding (HB), 2 chalcogen bonding, 3,4 metallophilic, 5 and π−π interactions, 6 it has been recognized as a useful tool for crystal engineering, design of supramolecular systems 7 (featuring, in particular, thermochromic 8 or tunable phosphorescent properties 9 ), catalysis, 10 medicinal chemistry, 11 etc.…”

Studies of Nature of Uncommon Bifurcated I–I···(I–M) Metal-Involving Noncovalent Interaction in Palladium(II) and Platinum(II) Isocyanide Cocrystals

“…Noncovalent interactions (NCIs) are a powerful instrument applied in such fields as synthesis, 1 catalysis, 2 , 3 design of photoactive materials, 4 − 6 and biochemistry. 7 , 8 Halogen bonding (XB), in particular, has been found to be a very useful NCI, for example, in the synthesis of self-assembled polymers, 9 , 10 due to its high directionality and possibilities for fine-tuning.…”