Photofunctionalization of a Pentamethylcyclopentadienyl Ligand with the N-Phenylcarbazolyl Group To Prepare a Highly Luminescent Tb³⁺ Complex Having a Fast Radiation Rate

Abstract

Lanthanide(III) bent-metallocene complexes with a novel photofunctionalized pentamethylcyclopentadienyl ligand having an N-phenylcarbazolyl group (Cp PhCar =η 5 -C 5 Me 4 CH 2 -C 18 H 12 N), [Ln(Cp PhCar ) 2 I(THF)] (Ln = Tb (1), Gd (2)), were prepared and their molecular structures and luminescence properties were investigated. The f-f emission from the terbium metal center of 1 was efficiently sensitized by Cp PhCar (ε=0.88 Â 10 4 M -1 cm -1 at 331 nm, Φ = 0.67 at 330 nm excitation, k r = 1.68Â10 3 s -1 ). Additionally, the solid-state structure of potassium salts of C 5 -ring (η 5 -C 5 R 5 , R = Me, H) derivatives was uncommonly characterized in Cp PhCar .Ligand functionalization is a common approach to form metal complexes that have a desired structure and functionality. To date, various photofunctionalized ligands have been developed and successfully utilized as photosensitizers for transition-metal and lanthanide complexes. 1 Among them, macrocyclic polyamines such as cyclam (1,4,8,11-tetraazacyclotetradecane) and tacn (1,4,7-triazacyclononane), which are popular ligands in inorganic chemistry, are widely employed as useful frameworks to construct adaptable and efficient photofunctionalized ligands. 2,3 Although the anionic pentamethylcyclopentadienyl ligand (Cp* = η 5 -C 5 Me 5 ) is one of the most common and important ligands in organometallic chemistry, 4 photofunctionalized Cp* derivatives have been hitherto unknown because of troublesome synthesis and isolation of the ligand. 5 We believe that photofunctionalized Cp* ligands could open a new field of organometallic chemistry, including developments of novel photocatalysts and luminous materials. We have now found that a new class of photofunctionalized ligands, the N-phenylcarbazolyl-functionalized Cp* ligand (Cp PhCar = η 5 -C 5 Me 4 CH 2 C 18 H 12 N), serves as an efficient photosensitizer for the terbium(III) ion. Thus, a highly luminescent organolanthanide complex having a fast radiation rate was successfully prepared by proper combination of the metal ion and the photofunctionalized Cp* ligand (vide infra). Herein we report the synthesis, structure, and photophysical properties of a terbium(III) complex with Cp PhCar , [Tb(Cp PhCar ) 2 I(THF)] (1). The gadolinium(III) complex [Gd(Cp PhCar ) 2 I(THF)] (2) was also synthesized to gain insight into the photosensitization of the N-phenylcarbazolyl group. Furthermore, the solid-state polymeric structure of the THF-solvated Cp PhCar potassium salt, which is a key precursor for the preparation of 1 and 2, is presented. Solidstate structural information for the Cp* or Cp (η 5 -C 5 H 5 ) derivative alkali-metal salts is comparatively limited, even though their salts are widely used for preparing organometallic complexes. 4a,6 Quici, S.; Barigelletti, F.; Accorsi, G.; Bottaro, G.; Cavazzini, M.; Tondello, E. Coord. Chem. Rev. 2010, 254, 487. (2) (a) Prodi, L.; Maestri, M.; Ziessel, R.; Balzani, V. Inorg. Chem. 1991, 30, 3798. (b) Alexander, V. Chem. Rev. 1995, 95, 273. (c) DeRosa, F.; Bu, X.; Ford, P. C. I...

Lanthanide(III) Sandwich and Half‐Sandwich Complexes with Bulky Cyclooctatetraenyl Ligands: Synthesis, Structures, and Magnetic Properties

“…Incidentally, it is worth mentioning that the COT′′ ring retains the original 1,4‐bis(trimethylsilyl) substitution pattern upon treatment with AgI, and no isomerization took place as has been observed for various other transformations of Ln and An COT′′ complexes under oxidative conditions {see, e.g., [Ho 2 (µ‐1,5‐COT′′)(1,4‐COT′′) 2 ] and [Pu(1,4‐COT′′)(1,3‐COT′′)]}. In 4 , the three Tb–I distances are in a narrow range of 313.14(3)–314.51(3) pm, which is significantly longer than those of other iodido terbium(III) complexes {e.g., [TbI 2 {HC(Ph 2 P=NSiMe 3 ) 2 }(THF)]: Tb–I 299.48(5) and 301.92(5) pm; [(TbICp PhCar ) 2 (THF)]: Tb–I 303.08(4) pm, Cp PhCar = N ‐phenylcarbazolyl‐derived cyclopentadienyl}. This difference arises most likely from the fact that the I – ligands adopt a µ‐bridging coordination in 4 , whereas they are bonded terminally in the reference compounds.…”

A highly luminescent and highly oxygen-sensitive Tb(iii) complex with a tris-aryloxide functionalised 1,4,7-triazacyclononane ligand

“…S4, ESI †). 11,16 Thus, the energy gap (DE) between the lowest ligand-centred ( MeMe ArO À ) and metal-centred (Tb 3+ , 5 D 4 : 20 490 cm À1 , which is estimated from the luminescence spectrum of 1 in 2-MeTHF at 77 K (Fig. S5, ESI †)) levels in 1 is found to be 5970 cm À1 .…”

“…S3, ESI †): the radiative rate constant (k r = F/t) of 1 was calculated to be 1.08 Â 10 3 s À1 , which is relatively high among the highly luminescent lanthanide complexes. 11 Since the asymmetric environment of the lanthanide(III) ion is known to promote f-f radiative transition and thereby provide high quantum yield, 12 the seven-coordinate environment of the Tb 3+ ion in 1 (vide supra, Fig. 1) would dominantly contribute to the high quantum yield of 1.…”

Reversible Switching of the Luminescence of a Photoresponsive Gadolinium(III) Complex

“…Owing to the small Stokes shift and short emission lifetime (t), the blue emission can be assigned to the fluorescence from an intraligand excited state (l em max = 412 nm, t < 50 ms, quantum yield (F) = 0.01; Figure S3). The heavy-atom effect of the Gd 3+ ion (11). The obtained spectrum ( Figure S4 in the Supporting Information, black dots), in which the original fluorescence band (l em max = 412 nm) is still observed with the same F, is identical to the emission spectrum of 1 in degassed THF at room temperature (Figure 3 b, red).…”

“…Thus, the luminescence photochromism is based on the fluorescence and room-temperature phosphorescence of 1. The heavy-atom effect of the Gd 3+ ion (9), N1-Gd1-N3 = 68.58 (11), N2-Gd1-N3 = 66.56(11), O1-Gd1-O2 = 111.08(11), O1-Gd1-O3 = 118.34(9), O2-Gd1-O3 = 115.01 (11). [18] and the chelate effect of the ligand in 1 contribute to the observed rare room-temperature phosphorescence in solution.…”