Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato Complexes: Synthesis, Characterization, and Photophysical, Electrochemical, and Computational Studies

Abstract

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)3 (N^N)(CNBR3 )], where N^N=bpy, 4,4'-Me2 bpy, phen, 4,7-Me2 phen, 2,9-Me2 phen, 3,4,7,8-Me4 phen; R=C6 F5 , C6 H5 , Cl, 4-ClC6 H4 , 3,5-(CF3 )2 C6 H3 , with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X-ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD-DFT calculations have been performed, which revealed that the lowest-energy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π*(N^N)] and LLCT [π(CNBR3 )→π*(N^N)] transitions.

Excited State Dynamics of Isocyano Rhenium(I) Phenanthroline Complexes from Time‐Resolved Spectroscopy

“…A brief summary of the calculated frontier orbitals are shown in Figure and Table S4 of the supporting information. The HOMO and HOMO‐1 are mainly d π (Re) orbital in character with some contribution of p π (CO/CNR); while the LUMO and LUMO+1 are π* orbitals of the phen ligand, which is similar to the previous compuational results on the [Re(CO) 3 (phen)(CNR)] +[23] and [Re(CO) 3 (phen)(CN)] complexes . The calculated vertical electronic transitions of 1–4 by TD‐DFT calculations are summarized in Tables S5–S8 in the Supporting Information.…”

Chromophore-Functionalized Phenanthro-diimine Ligands and Their Re(I) Complexes

“…The values of observed lifetimes (3.9–4.7 μs) are close to that determined for 1 - CN in solution, which indicates a certain similarity of their emissive excited states (i.e., significant mixing of 3 CT and 3 LC characters). Destabilization of the 3 CT state due to a phase transition (solution → solid) that accounts for a change in the lowest lying excited state (or efficient 3 IL– 3 CT coupling) for 1 and 2 is not uncommon for Re(I) phosphors 87 , 90 and confirms the small energy gap Δ E ( 3 IL– 3 CT) suggested above.…”

“…620 nm (Φ em = 2%) and lifetimes of 0.19 ( 1 )/0.14 ( 2 ) μs ( Table 4 ); the latter values are comparable to those of other Re(I) diimine tricarbonyl compounds. 37 , 38 , 67 , 89 , 90 The intensity of the LE band appreciably decreases in aerated solution, which suggests a triplet origin of the excited state (i.e., 3 ML′LCT likely mixed with some 3 LC). Higher energy excitation (λ exc 330 nm) results in appearance of an HE band with a maximum at 392 nm, particularly pronounced for complex 2 ( Figure 9 B), in addition to low-energy 3 CT emission.…”

“…It is known that the ancillary X ligand in [Re(CO) 3 X(NN)] compounds (X = pseudohalide or neutral L) can strongly affect the 3 MLCT/ 3 ML′LCT levels. 31 , 35 , 103 For the complexes with small energy separation between the ML′LCT and LC triplet states the variation in X nature (e.g., substitution of Cl for pyridine) 35 or its electronic characteristics (protonation or boronation of −CN) 90 , 104 can rise the energy of a triplet charge transfer level so that it becomes comparable to or exceeds that of the 3 LC transition. Furthermore, a better π-accepting ability of CN – vs Cl – simultaneously to increasing the energy of the 3 ML′LCT state is expected to stabilize the ground state of 1 - CN , causing a hypsochromic shift in emission and a decrease in radiative rate constant.…”

Influence of the Nucleophilic Ligand on the Reactivity of Carbonyl Rhenium(I) Complexes towards Methyl Propiolate: A Computational Chemistry Perspective

“…and neutral or anionic monodentate ligands (e.g., halides, pyridines, aqua, phosphines, alkyls, etc.) are functional molecules with applications in several important areas, such as catalytic reduction of CO 2 [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ], luminescence [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], medicinal chemistry [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ], supramolecular chemistry [ 47 ], etc. We reported, among others, the synthesis of the complexes [ReY(CO) 3 (N-N)] (Y = alkoxo [ 48 , 49 ], amido [ 50 , 51 ], hydroxo […”