Chiral Metal–Organic Cluster Induced High Circularly Polarized Luminescence of Metal–Organic Framework Thin Film

Abstract

Guest-induced host-guest assembly in metal-organic frameworks (MOFs) has become a critical strategy to achieve circularly polarized luminescence (CPL). Herein, chiral metal-organic clusters (MOCs) induced CPL of achiral MOF are reported. Enantiopure titanium-oxo clusters (R/S-TOCs) are effectively loaded into the pores of a fluorescent, highly stable MOF NU-901 thin film by using a liquid-phase epitaxial layer-by-layer encapsulation method. The resulting chiral TOCs@NU-901 MOF thin films exhibit strong chirality, intense photoluminescence, and excellent CPL performance with the highest dissymmetry factor (±0.025) reported so far for the downshifted MOF-based materials. Further, the comparison experiments and density functional theory (DFT) calculations demonstrate that the excellent performance benefited from the strong chirality and charge transfer caused by the significant π-π interactions between the host (MOF) and guest (R/S-TOCs). This novel chiral MOCs induced approach provides a powerful toolbox for new host-guest CPL thin film materials.

Chiral metal–organic frameworks for photonics

“…For example, chiral titanium-organic clusters Ti 4 (OH) 4 (R/S-BINOL) 6 (BINOL = 1,1 0 -bi-2-naphthol) were incorporated into thin films of the achiral MOF NU-901 ([Zr 6 (m 3 -OH) 4 (m 3 -O) 4 (OH) 4 (OH 2 ) 4 -(TBAPy) 2 ]; TBAPy = 1,3,6,8-tetra(4-carboxylphenyl)pyrene), whose pyrene-based ligands exhibit strong fluorescence. 59 The very similar sizes of the titanium-organic clusters (1.56 nm) and the MOF channels (1.57 nm) facilitates a strong chirality transfer from the chiral guest to the ligand, resulting in a large g lum of AE2.5 Â 10 À2 . When smaller chiral guests were loaded into the pores, the observed g lum was much weaker, again highlighting how size compatibility is important for enabling the chiral, hostguest interactions which underpin effective chirality transfer.…”

Charge transfer in metal–organic frameworks

“…chromophores) can be assembled in a crystalline and tailorable geometry/position. 1,[28][29][30][31][32] Further, the geometry and inter-molecular (chromophore) distances can be preconceived either by isoreticular chemistry principles or in silico. These advantages are truly remarkable compared with organic selfassembled materials in which structure prediction and property correlation are challenging.…”

Exploring Functional Photonic Devices made from a Chiral Metal-Organic Framework Material by a Multiscale Computational Method

“…In addition, the possibility to use virtually any organic molecule as a building block connecting metallic centers to design MOFs [16][17][18][19] has also drawn the focus to chiral MOFs. Furthermore, it is also possible to load achiral MOFs with chiral guest structures [20]. The exciting opportunity to control the chirality of highly porous structured materials [21,22] intrigued researchers to explore applications in the fields of enantioselective chemistry and catalysis [23][24][25], chiral molecules separation [26,27], optics [17,[28][29][30][31][32][33][34][35], and sensors based on chiral MOFs [36][37][38][39][40].…”