Tetrazine Chromophore‐Based Metal–Organic Frameworks with Unusual Configurations: Synthetic, Structural, Theoretical, Fluorescent, and Nonlinear Optical Studies

Abstract

Three unusual three-dimensional (3D) tetrazine chromophore-based metal-organic frameworks (MOFs) {(Et4 N)[WS4 Cu3 (CN)2 (4,4'-pytz)0.5 ]}n (1), {[MoS4 Cu4 (CN)2 (4,4'-pytz)2 ]⋅CH2 Cl2 }n (2), and {[WS4 Cu3 (4,4'-pytz)3 ]⋅[N(CN)2 ]}n (3; 4,4'-pytz=3,6-bis(4-pyridyl)tetrazine) have been synthesized and characterized by using FTIR and UV/Vis spectroscopy, elemental analysis, powder X-ray diffraction, gel permeation chromatography, steady-state fluorescence, and thermogravimetric analysis; their identities were confirmed by single-crystal X-ray diffraction studies. MOF 1 possesses the first five-connected M/S/Cu (M=Mo, W) framework with an unusual 3D (4(4) ⋅6(6) ) topology constructed from T-shaped [WS4 Cu3 ](+) clusters as nodes and single CN(-) /4,4'-pytz bridges as linkers. MOF 2 features a novel 3D MOF structure with (4(20) ⋅6(8) ) topology, in which the bridging 4,4'-pytz ligands exhibit unique distorted arch structures. MOF 3 displays the first 3D MOF structure based on flywheel-shaped [WS4 Cu3 ](+) clusters with a non-interpenetrating honeycomb-like framework and a heavily distorted "ACS" topology. Steady-state fluorescence studies of 1-3 reveal significant fluorescence emissions. The nonlinear optical (NLO) properties of 1-3 were investigated by using a Z-scan technique with 5 ns pulses at λ=532 nm. The Z-scan experimental results show that the π-delocalizable tetrazine-based 4,4'-pytz ligands contribute to the strong third-order NLO properties exhibited by 1-3. Time-dependent density functional theory studies afforded insight into the electronic transitions and spectral characterization of these functionalized NLO molecular materials.

Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

“…The detailed intensity‐dependent open aperture Z‐scan data for all three samples are presented in the Supporting Information (Section S5, Figure S26–28). Moreover, the obtained NLO absorption coefficient, β , value is as high as 4470 cm/GW and 4170 cm/GW for Por‐COF‐ZnCu and Por‐COF‐ZnNi, respectively; these values are higher than those of other reported materials, such as metalated porphyrins ( β =132–366 cm/GW), MOFs ( β =0.28–0.46 cm/GW), graphene ( β =900 cm/GW), and so on (Table S2) . The switching behavior from SA to RSA is highly interesting in view of optical switching applications .…”

“…By comparison, in the case of Por-COF-ZnCu and Por-COF-ZnNi excited-state absorption leads to characteristic RSA behavior. [11,[16][17][18][19][20] Theswitching behavior from SA to RSA is highly interesting in view of optical switching applications. [14] In Figure 3, the red lines are the best theoretical fits to the experimental data at different input intensities.F rom the fit, we deduced the nonlinear absorption coefficient (b), ground-state absorption cross section (s o ), first excited state (s 1 ), and second excited-state absorption cross sections (s 2 ) for Por-COF-HH, Por-COF-ZnCu, and Por-COF-ZnNi (Table S1, Supporting Information).…”

Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks

“…Moreover,t he obtained NLO absorption coefficient, b,v alue is as high as 4470 cm/GW and 4170 cm/GW for Por-COF-ZnCu and Por-COF-ZnNi, respectively;these values are higher than those of other reported materials,s uch as metalated porphyrins (b = 132-366 cm/GW), MOFs (b = 0.28-0.46 cm/GW), graphene (b = 900 cm/GW), and so on (Table S2). [11,[16][17][18][19][20] Theswitching behavior from SA to RSA is highly interesting in view of optical switching applications. [21] Moreover,t he switchover from RSA to SA behavior may be applicable in optical limiting devices based on RSA behavior at higher intensities, as well as in mode-locked lasers,because it demonstrates SA behavior at low input intensities.…”

Auto-controlled fabrication of a metal-porphyrin framework thin film with tunable optical limiting effects

“…[16][17][18][19][20] A few cases of powder MOFs have been realized to investigate the third-order NLO properties. [21][22][23] However, such powder MOFs have large scattering and are usually required to be dispersed in solvents for investigating the third-order NLO properties. Thus it is difficult to avoid the inuence from solvents.…”