Heteroleptic [Cu(NN)P2]+‐type cuprous complexes and their structural modulation on phosphorescent color: Synthesis, structural characterization, properties, and theoretical calculations

• Published in: Applied organometallic chemistry 2020-04, Vol.34 (4), p.n/a
• Main Authors: Wang, Dan‐Dan, Song, Li, Wang, You‐Yu, Guo, Jia‐Yu, Shen, Hang‐Yan, Wang, Xiao‐Rong, Chai, Wen‐Xiang
• Format: Article
• Language: English
• Subjects: Absorption spectra; Angles (geometry); Charge transfer; charge transfer, heteroleptic cuprous complex, P–Cu–P angle, phosphorescence color, TD‐DFT calculation; Chemistry; Color; Density functional theory; Infrared analysis; Ligands; Mathematical analysis; Phosphines; Phosphorescence; Photoluminescence; Structural analysis; Time dependence; Wave functions; X-ray diffraction
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.5561

Four new heteroleptic [Cu(NN)P2]+‐type cuprous complexes—1‐TPP, 2‐POP, 3‐Xantphos, and 4‐DPPF—were designed and synthesized using a diimine ligand 2‐(2′‐pyridyl)benzoxazole (2‐PBO) and different phosphine ligands (TPP, triphenylphosphine; POP, bis[2‐(diphenylphosphino)phenyl]ether; Xantphos, 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene; DPPF, 1,1′‐bis(diphenylphosphino)‐ferrocene). All complexes were characterized using single‐crystal X‐ray diffraction, spectroscopic analysis (infrared, UV–Vis.), elemental analysis, and photoluminescence (PL). Single‐crystal X‐ray diffraction revealed complexes 1–4 as isolated cation complex structures with a tetrahedral CuN2P2 coordination geometry and diverse P–Cu–P angles. Their UV–Vis. absorption spectra exhibited a blue‐shift sequence in wavelength with an enlarged P–Cu–P angle from 4 to 2 then to 3 and then to 1. The PL emission peaks of 1–3 also exhibited a similar blue‐shift sequence (2 → 3 → 1). Their PL lifetime in microseconds (~7.5, 5.1, and 4.7 μs for 1, 2, and 3, respectively) indicated that their PL behavior represents phosphorescence. Time‐dependent density functional theory (TD‐DFT) calculation and wavefunction analysis revealed that S1 and T1 states of 1–3 should be assigned as metal–ligand and ligand–ligand charge‐transfer (ML + L'L)CT states. Their UV–Vis. absorption and phosphorescence should be attributed to the charge transfer from the P–Cu–P segment to the 2‐PBO ligand. Therefore, as the P–Cu–P angle increased (lower HOMO), the energy of S1 and T1 states also increased, following the change of PL color. Four new [Cu(NN)P2]+type complexes are constructed by 2‐PBOand different phosphine ligands, TPP(1), POP(2), Xantphos(3), and DPPF(4). Obvious wavelength shifts (color change) are observed in their UV and PL spectra of 1–3. TD‐DFT calculation and wavefunction analysis visually reveal their absorption and phosphorescence transitions should be assigned as 1(ML + LL)CT (S1) and 3(ML + LL)CT (T1) excited states, meanwhile, the wavelength shifts are successfully clarified using a positive correlation of P–Cu–P angle and excited‐state (S1/T1) state energy.