Pillar[5]arene-based Neutral Radicals with Doublet Red Emissions and Stable Chiroptical Properties

Abstract

Stable organic radicals with unique luminescence show great importance in photoelectromagnetic materials. We herein report two unusual radical-based systems (P5N-TTM and P5B-TTM) using the concerted effects of planar chiral pillar[5]­arenes and tris­(2,4,6-trichlorophenyl)­methyl (TTM) radicals. The steric effect and electronic doublet-spin character of these radicals allowed the optical resolution and the first red emissions (∼650 nm) for pillar[5]­arene derivatives. Notably, cross-coupling with macrocyclic pillar[5]­arene, in turn, considerably enhanced the configurational stability of TTM radicals.

Per-Arylation of Pillar[n]arenes: An Effective Tool to Modify the Properties of Macrocycles

“…The average tilt angle of benzene rings was measured to be 29° to the side faces of an ideal right prism, which was about 10° larger than that of a P5OEt crystal without guest inclusion (Table S3-2). In contrast, dihedral angles between benzene and benzofuran rings were around 38° (Table S3-3), being much smaller than those of partially aryl-substituted molecules with pillar shapes (typically 50–65°). , Thus, the solid-state structure of P5BFa was not very suitable for through-space interunit interactions but allowed conjugation within the π-units. To obtain information on stable conformations in solution, low-temperature 1 H NMR spectra were recorded in CD 2 Cl 2 (Figure S1-4).…”

“…Despite these merits of arylated derivatives, there have been many fewer reports on pillar­[ n ]­arenes arylated partially at one or two units , than those on per-alkoxy-substituted ones, probably owing to the difficulty in coupling reactions. Suzuki–Miyaura cross-coupling at one rim of pillar[5]­arene triflate worked well for a methoxy-substituted substrate ( 1a , Table , entry 1) but proceeded in less than 30% yield for a substrate with bulky cyclohexylmethoxy groups on the other rim ( 1b , entry 2) .…”

Tuning the Electro‐Optical Properties of Mixed‐Halide Trityl Radicals Bearing para‐Brominated Positions through Halogen Substitution

“…Unfortunately, TTM and PTM structures offer a poor chemical versatility due to the lower reactivity of chlorine atoms compared with bromine and iodine ones. Although some functionalization have been reported involving directly chlorinated substrates, [7,19] many efforts have been tried to increase the reactivity of polyhalogenated triphenyl methane adducts (radical precursors) by introducing bromine or iodine substituents in different positions (Figure 1). [4,5,[20][21][22] In fact, such substrates can be easily functionalized via transition-metal mediated cross-coupling reactions expanding their chemical versatility.…”

“…Inert triaryl methyl radicals are getting an increasing interest in several technological fields since they offer the possibility of combining several features within a single chemical species, representing the perfect building block in the design of multifunctional molecular materials. [1] Recently, they are getting noticed for their unique optical properties [2] such as: emission in the first biological window (650-950 nm), [3,4] circularly polarized luminescence (CPL), [5][6][7] two-photon absorption, [8,9] excimer formation and magnetoluminescence [10][11][12] and the possibility to obtain the 100 % of internal quantum efficiency in electroluminescence devices. [13][14][15] Due to this rising interest, the synthesis of new doublet emitters is of extreme relevance.…”

Iridium(III) Complex Radical and Corresponding Ligand Radical Functionalized by a Tris(2,4,6-trichlorophenyl)methyl Unit: Synthesis, Structure, and Photophysical Properties

“…In recent years, organic radicals with unpaired electrons have been widely used in the fields of organic optoelectronics − and molecular magnetism − due to their special open-shell character. Notably, organic radicals with the stable structure and good luminescence properties are mainly concentrated in tris­(2,4,6-trichlorophenyl)­methyl (TTM) radical derivatives, − perchlorotriphenylmethyl (PTM) radical derivatives, − pyridyl-containing triarylmethyl radicals (PyBTM), − and so forth. At present, the design strategy based on TTM radical luminescent materials mainly introduces some important organic functional groups, such as carbazole, pyridine, benzimidazole, and so forth, so as to facilitate the regulation and improvement of their optical performance.…”