Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

Sara Fuertes; Andrés J Chueca; Lorenzo Arnal; Antonio Martín; Umberto Giovanella; Chiara Botta; Violeta Sicilia

doi:10.1021/acs.inorgchem.6b02826

Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

Inorg Chem. 2017 May 1;56(9):4829-4839. doi: 10.1021/acs.inorgchem.6b02826. Epub 2017 Apr 7.

Authors

Sara Fuertes¹, Andrés J Chueca¹, Lorenzo Arnal¹, Antonio Martín¹, Umberto Giovanella², Chiara Botta², Violeta Sicilia³

Affiliations

¹ Departamento de Química Inorgánica, Facultad de Ciencias, Instituto de Síntesis Química y Catálisis Homogénea, CSIC, Universidad de Zaragoza , Pedro Cerbuna 12, 50009 Zaragoza, Spain.
² Istituto per lo Studio delle Macromolecole, Consiglio Nazionale delle Ricerche (CNR) , Via Corti 12, 20133 Milano, Italy.
³ Departamento de Química Inorgánica, Escuela de Ingeniería y Arquitectura de Zaragoza, Instituto de Síntesis Química y Catálisis Homogénea, CSIC, Universidad de Zaragoza , Campus Río Ebro, Edificio Torres Quevedo, 50018 Zaragoza, Spain.

PMID: 28387513
DOI: 10.1021/acs.inorgchem.6b02826

Abstract

New heteroleptic compounds of platinum(II)-containing cyclometalated N-heterocyclic carbenes, [PtCl(R-C^C*)(PPh₃)] [R-CH^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene (R-C = Naph; 1A), 1-[4-(ethoxycarbonyl)phenyl]-3-methyl-1H-imidazol-2-ylidene (R = CO₂Et; 1B), and [Pt(R-C^C*)(py)(PPh₃)]PF₆ (py = pyridine; R-C = Naph, 2A; R = CO₂Et, 2B], have been prepared and fully characterized. All of them were obtained as the trans-(C*,PPh₃) isomer in high yields. The selectivity of their synthesis has been explained in terms of the degree of transphobia (T) of pairs of ligands in trans positions. X-ray diffraction studies on both 2A and 2B revealed that only in 2A, containing a C^C* with a more extended π system, do the molecules assemble themselves into head-to-tail pairs through intermolecular π···π contacts. The photophysical properties of 2A and 2B and those of the related compounds [Pt(NC-C^C*)(PPh₃)L]PF₆ [NC-CH^C*-κC* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene; L = pyridine (py; 2C), 2,6-dimethylphenylisocyanide (CNXyl; 3C), and 2-mercapto-1-methylimidazole (MMI; 4C)] have been examined to analyze the influence of the R substituent on R-C^C* (R-C = Naph; R = CO₂Et, CN) and that of the ancillary ligands (L) on them. Experimental data and time-dependent density functional theory calculations showed the similarity of the electronic features associated with R-C^C* (R = CN, CO₂Et) and their difference with respect to R-C^C* (R-C = Naph). All of the compounds are very efficient blue emitters in poly(methyl methacrylate) films under an argon atmosphere, with QY values ranging from 68% (2B) to 93% (2C). In the solid state, the color of the emission changes to yellowish-orange for compounds 2A (λ_max = 600 nm) and 3C (λ_max = 590 nm) because of the formation of aggregates through intermolecular π···π interactions. 2C and 3C were chosen to fabricate fully solution-processed electroluminescent devices with blue-light (2C), yellow-orange-light (3C), and white-light (mixtures of 2C and 3C) emission from neat films of the compounds as emitting layers.