Flexible Luminescent MOF: Trapping of Less Stable Conformation of Rotational Isomers, In Situ Guest-Responsive Turn-Off and Turn-On Luminescence and Mechanistic Study

Abstract

Flexible and dynamic Cu I metal−organic framework [Cu(I)-MOF (1)] with well-defined nanoporous channel built with flexible terpyridine ligand offers a scaffold for the inclusion of different classes of guest molecules through a single-crystal-tosingle-crystal (SCSC) transformation in the vapor phase at ambient conditions with visual color change. Thus, Cu(I)-MOF (1) offers a potential platform for molecular recognition and undergoes guestresponsive structural dynamism that can be triggered by interfacial interactions. Despite having the stable conformation of the rotational isomers, it selectively encapsulates the less stable conformation (eclipsed and gauche) into its cavity from their vapor phases in the SCSC process. All of the guest-exchanged processes are reversible. It shows selectivity toward less polar guest in a class. The intermediate of all of the guest-exchanged processes appeared as a black material (H 2 O@Cu(I)-MOF) (1z) prior to the encapsulation of each guest that happens through the SCSC manner followed by encapsulation of the guests replacing H 2 O in situ at ambient conditions through SCSC transformation. This confirms that the process is a two-step process leading to a common intermediate. The MOF loses its luminescence behavior with H 2 O removing lattice solvents in situ and appears as a black material, and it regains its luminescence property with the guests replacing H 2 O. Thus, the MOF displays both luminescence "turn-off" and "turn-on" before and after incorporation of the guests, respectively, leading to a common turn-off mechanism. A fluorescence titration experiment shows selectivity toward aniline among benzene and its derivatives.

Terpyridine‐Based 3D Metal–Organic‐Frameworks: A Structure–Property Correlation

“…This p-assembled 2D geometry was further polycatenatedt of orma3D (3,6) interpenetrated network (Fig- Additional functionalities or substitutionsa tthe 4'-phenyl ring, coordinating (a-i)a nd non-coordinating (j-l). Note:W ehavegiven some short notation (in parenthesis) for three terpyridines as (2,2':6',2'') (O), (3,2':6',3'') (M), (4,2':6',4'') (P); we made ac ombination to understand all reported 4'-phenyl substituted terpyridines.a )(O, [21] M, [22] P [22a,.23] ); b) (O, [24] M, [25] P [26] ); c) (M, [25a] P [27] ); d) (O, [28] P [29] ); e) (O, [30] P [31] )f)(O, [32] M [33] ); g) (O, [34] M, [35] P [36] ), h) (O); [37] i) (O); [38] j) (P); [39] k) (P); [40] l) (O). [41] ure 2c).…”

“…This exceptional selectivity towards CHCl 3 could be described as a dimeric association of CHCl 3 molecules with two strong ‐C−H⋅⋅⋅Cl interactions with the two strong ‐C−Cl⋅⋅⋅π and two ‐C−H⋅⋅⋅I hydrogen‐bonding interactions between the framework core and CHCl 3 in the 1D channel. Notably, the exchange of these guest molecules affects the slippage of the interpenetrated 2D networks, which results in the small change in pore dimensions, depending on the strength of non‐covalent interactions, as well as the shape and size of the guest molecules [39f] . Because of such slippage, the diagonal length (hydrophilic corner (I 2 ⋅⋅⋅I 2 ) and hydrophobic corner (CH 2 ⋅⋅⋅CH 2 )) of the 1D nanopore of the solvent encapsulated complexes change from 9.197 Å and 9.358 Å to 8.954 Å and 10.369 Å (in CHCl 3 ); 8.767 Å and 9.957 Å (in CH 2 Cl 2 ); and 9.276 Å and 9.720 Å (in CCl 4 ), respectively (Scheme 6).…”

Mechanistic Insight into Charge and Energy Transfers of Luminescent Metal–Organic Frameworks Based Sensors for Toxic Chemicals

“…[158,159] Common mechanisms involve the transfer of energy or electronic charges between substrate molecules and photoexcited fluorophores, which can result in either "turn on-off" fluorescence responses, followed by fluorescence enhancement, or quenching. [160,161] Importantly, MOF materials with a fluorophore and central metal ions presenting emission properties are considered promising devices in sensing. [162] However, the whole optical sensing process, involving different transitions and energy or charge transfer from donor to acceptor through photophysical changes, might result from PET, PCT, CHEF, RET, FRET, coupled transitions, radiative transitions, radiationless transitions, TBET, DTBET, and ET (Figure 1).…”

Metal–organic frameworks based on a benzimidazole flexible tetracarboxylic acid: Selective luminescence sensing Fe3+, magnetic behaviors, DFT calculations, and Hirshfeld surface analyses

“…Metal-organic frameworks (MOFs) have received growing interest in recent years because of their large surface areas, tunable structure, and high porosity, which make them comprehensive and abundant for applications as functional materials in catalysis, [1][2][3][4][5] luminescence, [6][7][8] magnetism, [9][10][11] chemical sensors, [12,13] and especially gas storage/separation. [14][15][16][17] Generally, magnetic MOFs can be designed by incorporating transition metal ions containing unpaired electrons (Co 2+ , Ni 2+ ) and organic multidentate bridges.…”