Aggregation induced phosphorescent N-oxyde-2,2′-bipyridine bismuth complexes and polymorphism-dependent emission

Abstract

Unprecedented bismuth complexes, based on the rarely used ditopic ligand N-oxide-2,2'-bipyridine (bp2mo), crystallizing as three polymorphs, α- (), β- () and γ-[BiBr3(bp2mo)2] (), exhibit phosphorescence with a quantum yield up to 17% for the crystal phase (), while the complex displays a weak fluorescence in solution. A study of the luminescence properties combined with DFT/TDDFT calculations reveals that the lighting phenomenon originated by aggregation induced phosphorescence correlated with the weak intermolecular interactions present in the different crystal phases.

Aggregation Induced Phosphorescence in the Main Group

“…[41] While complexes 40 and 44 were nonemissive as solids, complexes that contained bismuth coordinated to the Hbp4mo + cations through BiÀO interactions were found to exhibit phosphorescence (l em = 560 nm for 41, and 530 nm for each 42 and 43). [42] Only weak fluorescence was observed for 45 in THF solution (l em = 442 nm, F = 0.01 %, t = 258 ps), however in the solid state three phosphorescent crystalline polymorphs complexes could be obtained, a-(45), b- (45), and g-[Br 3 Bi(bp2mo) 2 ] (g-45). The same group prepared a 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 bismuth(III) tribromide complex of N-oxide-2,2'-bipyridine (bp2mo), [Br 3 Bi(bp2mo) 2 ] (45, Figure 3b).…”

“…The same group prepared a 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 bismuth(III) tribromide complex of N-oxide-2,2'-bipyridine (bp2mo), [Br 3 Bi(bp2mo) 2 ] (45, Figure 3b). [42] Only weak fluorescence was observed for 45 in THF solution (l em = 442 nm, F = 0.01 %, t = 258 ps), however in the solid state three phosphorescent crystalline polymorphs complexes could be obtained, a-(45), b-(45), and g-[Br 3 Bi(bp2mo) 2 ] (g-45). The three polymorphs afford similar absorbance spectra (l max = 392-395 nm), assigned on the basis of TD-DFT as HOMO (BiBr 3 centered) to LUMO (ligand) transitions.…”

“…As for 37-39 (vide supra), the yellow phosphorescence in compounds 41-43 is thought to arise from metal-to-ligand charge transfer processes and 41 was shown to have a respectable quantum yield of 11 %, which was explained by the presence of a packing arrangement in 41 that reduces intermolecular contacts between neighboring organic moieties. [42] It was noted that the moderately phosphorescent a and g polymorphs of 45 have stronger intermolecular CÀH-O and CÀH-p hydrogen bonds in relation to the b form, thus leading to a more rigid environment in the former complexes. [42] Only weak fluorescence was observed for 45 in THF solution (l em = 442 nm, F = 0.01 %, t = 258 ps), however in the solid state three phosphorescent crystalline polymorphs complexes could be obtained, a-(45), b- (45), and g-[Br 3 Bi(bp2mo) 2 ] (g-45).…”

“…In the 1 : 1 complex [Br 3 Bi(bp4mo)] (47), a density packed interconnected structure is found, mediated by close bp4mo-Bi contacts (Figure 5b). [42] Very weak blue fluorescence (F = < 0.1 %, t = ca. 20-25 nm blue-shifts when these species are dissolved in CH 2 Cl 2 .…”

“…Polymorph b-45 shows only very weak phosphorescence (F < 0.5 %, l max 516 nm). [42] It was noted that the moderately phosphorescent a and g polymorphs of 45 have stronger intermolecular CÀH-O and CÀH-p hydrogen bonds in relation to the b form, thus leading to a more rigid environment in the former complexes.…”