Open Access
Add to BibSonomy
Abstract
The nonlinear absorption effect in a Fe-porphyrin metal-organic framework (Co-TCPP(Fe) MOF) was studied using the nanosecond Z-scan technique, which showed an enhanced reverse saturation absorption (RSA) compared with TCPP(Fe) ligand. By femtosecond transient absorption (fs-TA) measurements, the charge transfer dynamics of MOF are unveiled. Compared with TCPP(Fe) ligand, the ultrafast formation of charge separation states (CSSs) with extra-long lifetime (> 3.5 ns) detracts the recombination of electron-hole pairs, resulting in an enhanced excited state absorption (ESA). Based on the strong ESA caused by CSSs absorption, the MOF nanosheets showed an excellent optical limiting (OL) effect with the OL threshold of 0.89 J/cm2.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Porphyrins, as one of the vital molecules in many biological processes, have been received lots of attentions in many fields such as anti-cancer drugs [1], catalysis [2], semiconductors [3], electronic materials [4], DNA-binding or cleavage agents [5] and surface-enhanced Raman scattering [6,7]. Due to the specific optical properties of the tetrapyrrole macrocycle, porphyrins are also ideal targets for applications in nonlinear optics [8]. Comparing with porphyrins, metalloporphyrins are widely and intensely investigated due to their unique properties benefiting from the introduction of metal ions in porphyrins centers, such as high thermal and photostability, broad spectral response, long-lived excited-states, and high excited-state redox-potential [9]. The applications of metalloporphyrins were often in the homogeneous phase [10], however, the exist of singlet oxygen atoms can easily deactivate metalloporphyrins by redox-reaction. To overcome the quenching process, an efficient way is immobilization by using metalloporphyrins as components for the construction of porphyrin frameworks.
Metal-organic frameworks (MOFs), which are constructed by coordinating metal or metal-oxo clusters acting as nodes and organic building blocks referred to linkers or ligands, have been developed for many applications such as gas storage [11], gas separation [12], sensing [13], and catalysis [14] due to their unique advantages of porous structures, tunable surface properties and good stability by precisely designing their building blocks and nodes [15]. Porphyrin based MOFs, which use porphyrin or metalloporphyrin as building blocks, have become an essential part in MOFs family owing to the versatile functional molecules of porphyrins [16–19]. It is indicative that porphyrin-based MOFs can not only act as catalysts but also support or confine other molecular or atom level catalysts [20]. For example, H2TCPP[AlOH]2 MOF, has the visible-light photocatalytic activity for the sacrificial hydrogen evolution from water [21]. Moreover, introduction of metal atoms provides extra highly efficient electron transfer channels leading photo-excited electrons from MOF to single metal atoms [22]. Except the application in photocatalysis, the nonlinear optical properties of some porphyrin-based MOFs were also studied recently for applications such as optical limiting (OL) and saturable absorbers (SA). For instance, the Ni-MOF was used in microfiber-based SA for ultrafast pulse generation in fiber lasers [23]. And the nonlinear optical absorption of porphyrin-based surface-supported MOF can be modulated from saturable absorption to reverse saturable absorption with the increase of laser intensity [24].
However, most of the porphyrin-based MOFs with the 3D structure have inherently low carrier mobility. The emergence of 2D MOFs can help to alleviate the difficulty of extracting the charge from the interior of the material and prolong the lifetime of photoinduced electron-hole pairs [25,26]. In nonlinear optics, the prolonged carrier lifetime can be contributed to enhancing the nonlinear absorption response. For example, nonlinear absorption effects have been observed in several 2D materials like graphene [27], transition metal dichalcogenides [28] and MXene [29]. To modulate the nonlinear effect in the materials, different heterostructures have been synthesized such as metal nanoparticles/graphene [30] and MoS2/graphene [31]. The formation of heterojunction facilitates the charge interface migration and effectively suppresses the recombination of photogenerated electron-hole pairs, leading to the enhanced nonlinear optical absorption effects. In these years, 2D MOFs have gained a considerable interest as an emerging nonlinear optical material [32,33]. However, their nonlinear optical applications are rare and the relation between nonlinear optical properties and charge transfer dynamics is still needed to be further investigated. Due to the importance of Fe-porphyrin systems in photochemistry and photobiology [34], and the ability to form 2D MOF structures [35], the Fe-porphyrin based MOFs is considered having a great potential in nonlinear optical applications.
Herein, the 2D Co-TCPP(Fe) MOF nanosheets are synthesized and dispersed into N,N-Dimethylformamide (DMF) for studying the nonlinear absorption and charge transfer dynamics by 532 nm nanosecond Z-scan method and fs-TA technique, respectively. Compared with TCPP(Fe) ligands, the Co-TCPP(Fe) MOF has an enhanced RSA effect with an excellent OL threshold of 0.89 J/cm2. This outstanding OL performance is attributed to the ultrafast formation of long-lived CSSs in Co-TCPP(Fe) MOF which is observed by coexistence of broadband ESA and ground state bleaching (GSB) in fs-TA spectra. The formation time of CSSs is within 1 ps and the lifetime of CSSs is longer than 3.5 ns.
2. Experiments
Cobalt nitrate hexahydrate (Co(NO3)2⋅6H2O), pyrazine, PVP, DMF, ethanol and TCPP(Fe) powders were of analytical grade and purchased from companies without further purification. The detailed synthesis procedures can be found elsewhere [35]. Briefly, 16 mL ethanol and DMF mixture solution (volume ratio 1:3) was prepared and 12 mL was used to dissolve 3.0 mg of Co(NO3)2⋅6H2O (0.01 mmol), 0.8 mg of pyrazine (0.01 mmol) and 20.0 mg of PVP. The obtained solution was then mixed with the solution of 4.4 mg of TCPP(Fe) (0.005 mmol) dissolved in another 4 mL mixture of ethanol and DMF (volume ratio 1:3). The final obtained solution was kept in a capped vial and sonicated for 10 min. After the sonication the vial was heated to 80 °C and kept for 24 hours. The dark brown products were washed twice with ethanol and collected by centrifuging at 8000 r.p.m for 10 minutes. Finally, the obtained Co-TCPP(Fe) MOF nanosheets were dispersed in DMF.
The morphology and structure of the sample were investigated by 200 kV field emission high-resolution electron microscope (HR-TEM) JEOL JEM-2100 Plus. The surface chemical composition was determined by X-ray photoelectron spectroscopy (XPS, Thermo Fisher ESCALAB Xi+). PL and UV-vis absorption spectra of the MOF nanosheets were obtained using the FLS920 (Edinburgh) and UV-2600 spectrometers.
The fs-TA measurements were conducted by our home-built setup to study the carrier dynamics of TCPP(Fe) ligands and Co-TCPP(Fe) MOF. The femtosecond laser output (Vitesse, Coherent, 800 nm center wavelength, 100 fs pulse width, 1 kHz repetition rate) was divided into two beams; the powerful one was frequency-doubled to produce a 400 nm pump beam, and the other one was focused on a sapphire window to produce a wideband supercontinuum probe beam. The average pulse width of white-light continuum probe is about 130 fs. The transmitted probe light was collimated and focused onto the sample with the pump beam, and the transmitted probe light was recorded by a fiber spectrometer. By changing the delay time between pump and probe beams, the TA spectra changed with delay time can be obtained.
The nanosecond Z-scan measurements were used to study the nonlinear optical absorption of samples. A Q-switched Nd3+: YAG laser operating at the second harmonic of 532 nm (pulse width: 10 ns, repetition rate: 10 Hz) was focused into the sample by a convex lens with a focal length of 20 cm. The nonlinear transmittance was recorded simultaneously when the distance between the sample and the focus of the laser beam was changed by a translation stage. The incident laser power density was controlled by an attenuator and kept lower than the damage threshold of samples. Both Co-TCPP(Fe) MOF and TCPP(Fe) were dispersed in DMF and kept in 1 mm thick optical quartz cuvette with 60% linear transmittance for fs-TA and Z-scan experiments.
3. Results and discussion
We firstly checked the morphology and chemical components of the synthesized Co-TCPP(Fe) MOF nanosheets. Figure 1(a) and (b) are the TEM and HR-TEM results of the sample. Figure 1(a) shows the sheet-like structure with a size distribution ranging from few hundred nanometers to micrometers. The HR-TEM in Fig. 1(b) indicates that some lattice fringes of Co-TCPP(Fe) can be observed, showing MOF nanosheets with good crystallinity. The XPS results are showed in Fig. 1(c) and (d) for Fe and O elements, respectively. The Fe XPS pattern has two peaks located at 709.0 eV and 720.8 eV, which can be assigned to Fe3+ 2p3/2 and Fe3+ 2p1/2, respectively. Two peaks given in Fig. 1(d) at 530.6 eV and 531.6 eV are attributed to the O 1s of the C = O and C-OH groups, respectively. These XPS features were also found in the TCPP(Fe) ligand and consistent with previous results given by Zhang et.al, proving the successful preparation of 2D Co-TCPP(Fe) nanosheets [35].
Fig. 1. (a) TEM and (b) HR-TEM of Co-TCPP(Fe) MOF. (c) High resolution Fe and (d) O XPS spectra of Co-TCPP(Fe).
The UV-vis spectra of both TCPP(Fe) and Co-TCPP(Fe) MOF were obtained and showed in Fig. 2. The peak intensity was normalized for better comparison. The main absorption peak of TCPP(Fe) locates at 418 nm and few peaks at 500-700 nm range are contributed to the Soret and Q bands of porphyrins, respectively. The Co-TCPP(Fe) MOF also shows two typical porphyrin absorption bands corresponding to the transition from ground state (S0) to the second and first excited state (S2 and S1) [36]. The broadening and redshift of two bands in MOF compared with TCPP(Fe) are due to the expanded π-conjunction of porphyrins in the ordered MOF structure. The photoluminescence spectroscopy of excitation wavelength from 300 nm to 800 nm showed no obvious emission in both TCPP(Fe) and MOF. Indicating our Fe-porphyrin coordinated systems did not generate PL under visible wavelength excitation, which is consistent with some other Fe-porphyrin coordinated MOFs like PCN-222(Fe), PCN-600(Fe) and In−FenTCPP-MOF [37–39].
The nonlinear optical properties of both TCPP(Fe) and Co-TCPP(Fe) MOF were studied by 532 nm nanosecond Z-scan technique. Figure 3(a) and 3(b) show the normalized nonlinear transmittance as a function of Z-position for both TCPP(Fe) and Co-TCPP(Fe) under different pulse energy. The decrease of the transmittance with increasing incident nanosecond laser intensity could originate from different kinds of mechanisms, including nonlinear absorption, and nonlinear scattering induced by thermal effect. To check whether the nonlinear scattering effect existed in our experiments, we applied another detector located around the sample at several different angles with transmitted beam during Z-scan measurements and no obvious nonlinear scattering signal was observed when the incident light intensity was increased. The results indicated that, the nonlinear response of the materials was mainly attributed to the RSA effect, and the contribution of nonlinear scattering effect could be ruled out. Compared with TCPP(Fe), the normalized transmittance of Co-TCPP(Fe) MOF has an increase about 10% then decreases more drastically with increasing the incident laser density, indicating enhanced SA and RSA effects.
Usually, the dominant mechanisms of nonlinear optical effects are attributed to the third-order nonlinear optical effects in Z-scan measurements. The nonlinear absorption coefficient α(I) can be expressed as [30,40,41]:
where ${\alpha _0}$ represents linear absorption coefficient, I and ${I_s}$ represents the incident light intensity and saturation intensity, and β indicates the RSA coefficient. The normalized transmission can be written as:
Table 1. The comparison of the nonlinear absorption coefficients
Figure 4 shows the normalized transmittance changed with pulse energy density, which can be expressed by $I/\mathrm{\pi}\omega _0^2({1 + {z^2}/z_0^2} )$. The OL threshold, defined by the corresponding laser pulse density when normalized transmittance decreases to 50%, is estimated to be about 0.89 J/cm2 for Co-TCPP(Fe) and 7.50 J/cm2 for TCPP(Fe) due to its weak RSA effect. Table 2 shows the comparison of OL threshold with other similar porphyrin-based systems including metal porphyrin [45], PCN-222 MOF loaded carbon nanodots (CND) [46] and 2D MOFs ZnTPyP(Cu) [33]. The relatively low OL threshold of Co-TCPP(Fe) MOF nanosheets shows the potential to fabricate practical OL devises such as MOFs/PDMS films [47].
Table 2. Comparison of OL threshold with similar structures
To understand the origin of the enhanced nonlinear absorption effects in Co-TCPP(Fe) MOF, fs-TA experiment was applied on both TCPP(Fe) ligands and Co-TCPP(Fe) MOF. Figure 5(a) is the fs-TA spectra of TCPP(Fe) ligands under 400 nm laser excitation with different delay time. The two negative peaks are corresponding to the bleaching of the absorption from the ground state (S0) to the first excited state (S1). And the positive peaks are related to the absorption of Q bands. When pumped by 400 nm laser, the sample was excited from S0 to the second excited state (S2), corresponding to the Soret band absorption in Fig. 2. The excitation from the ground state to the Soret band will cause the population reduction in the ground state as well as the decrease of the absorption from the ground state to Q and Soret bands, forming the two negative peaks in the TA spectra.
Fig. 5. (a) Fs-TA spectra of TCPP(Fe) at certain different delay times. (b) Time-resolved TA spectra of TCPP(Fe) at certain wavelengths.
The time-resolved TA signal of 513 nm and 568 nm are extracted and showed in Fig. 5(b). It is found that the relaxation of ESA at 513 nm tends to have a fast and slow process. A bi-exponential decay function ΔA(t)=A1·exp(-t/τ1)+A2·exp(-t/τ2) is used to obtain the time constants during the relaxation. In the function, A1 and A2 refer to the amplitudes of each decay component, while τ1 and τ2 are two parameters used to describe decay processes with different decay lifetimes. The fitted fast relaxation time τ1 is about 3.5 ± 0.2 ps corresponding to the fast decay process of Soret band electrons. The slow relaxation time τ2 of 733.5 ± 15.9 ps is considered as the decay time of Q band electrons. For 568 nm ground state bleaching (GSB) signal of Q band, a single exponential decay function ΔA(t)=A1·exp(-t/τ1) was used for fitting the decay process and decay time τ1 of 747.8 ± 6.7 ps is consistent with slow relaxation part of 513 nm, indicating the S1 lifetime and no triplet states absorption in TCPP(Fe) during our experiment.
Figure 6 shows the ideal energy diagram and dynamics processes of TCPP(Fe) under 400 nm laser excitation. The ground state electrons were excited to Soret band (S2) then experienced a fast decay to Q band (S1). As there are many discrete energy levels in both Q band and Soret band, strong ESA can occur due to the absorption from lower energy levels of S1 to higher energy levels of S2, showing a broadband absorption from 480 nm to 750 nm. On the other hand, when the electrons in S0 are excited to S2, the bleaching of ground state leads to the weaken absorption in Q band, showing negative peaks from 550 nm to 610 nm and 601 nm to 615 nm.
Therefore, the RSA mechanism of TCPP(Fe) ligands under 532 nm nanosecond laser irradiation in Fig. 3(a) can be properly explained. The 532 nm wavelength is in Q band absorption of TCPP(Fe) in Fig. 2, indicating the electrons excited from S0 to S1. Due to the observed ESA at 532 nm in Fig. 5(a), after the S1 are fully occupied with excited electrons, the ESA starts to take place and keeps absorbing photons leading to the final RSA effect.
The fs-TA results of Co-TCPP(Fe) MOF are more complicated compared with TCPP(Fe) ligands. Figure 7(a) shows the TA spectra of MOF nanosheets at some certain delay times. With the limit length of delay stage, the longest delay time between pump and probe beam is about 3.5 ns. Similar with TCPP(Fe) ligands, the TA spectra of MOF also show negative peaks at around 540 nm and 608 nm, corresponding to the bleaching of Q band absorption in the MOF. Different from the ligands, the MOF TA kinetics at 540 nm (Fig. 7(b)) shows a short (about 1 ps) positive peak followed by the long-lived negative signal without apparent sign of relaxation in our detecting range, indicating the long-lived bleaching effect of the MOF ground state. We also analyze the TA kinetics at 632 nm, locating far from the GSB peaks (Fig. 7(c)), and a transition from ESA to GSB then back to ESA after 2.75 ns is observed. The same transition is also obtained in the whole wavelength range from 615 nm to 750 nm.
Fig. 7. (a) fs-TA kinetics of Co-TCPP(Fe) at different delay time points. (b) Time-resolved TA dynamics of probe wavelength at 540 nm. (c) Time-resolved TA dynamics of probe wavelength at 632 nm. (d) Time-resolved TA kinetics of different wavelengths 470 and 632 nm. The dash lines are used to mark the peak position of each curves. Inset in (b) and (c): TA dynamics at early decay time.
The kinetics of all wavelength are a combination of ESA signal and GSB signal which indicates the coexistence of ESA and GSB in 400 nm excited Co-TCPP(Fe) MOF nanosheets. At early delay time (from several ps to hundreds of ps for different wavelengths), the ESA is the main process before the excited electrons are transferred. However, those excited electrons are trapped or transferred to other states rather than relaxing to ground state of MOF, leading to the domination of GSB in TA kinetics. Then the absorption of those trapped states electrons results in the kinetics transition from GSB back to ESA again after several ns delay time. For MOF structure, the charge transfer from light harvest ligands to metal clusters can lead to the separation between electrons and holes to form CSSs where electrons are ‘trapped’ for longer time. The absorption of electrons from CSSs could also make contribution to the broadband fs-TA spectrum of Fig. 7(a). For example, the strong absorption peak at 470 nm occurs at early decay time. The UV-Vis result of Fig. 2 shows the Co-TCPP(Fe) MOF has a strong steady states absorption at 470 nm, corresponding to the negative GSB peak in fs-TA spectrum. However, the strongest ESA positive peak was found in Fig. 7(a) at early decay time, indicating the strong absorption of CSSs electrons could happened at 470 nm. Therefore, we attribute the broadband coexistence of ESA and GSB to the formation of CSSs which have been found in other MOF structures including TCPP based MOFs [48,49].
To further study the generation of CSSs, time-resolved TA dynamics are extracted at few wavelengths with apparent ESA at early delay time. Figure 7(d) is the time dependent TA signals with probe wavelength of 470 and 632 nm within 10 ps decay time. The results were corrected by chirp elimination. Two dash lines are used to mark the peak positions of absorption curves. The absorption of 470 nm has a longer formation time of about 1.12 ps, near 3 times of 0.36 ps which is the formation time of 632 nm absorption. By fitting the fast decay of 632 nm dynamics from 0.36 ps to 2 ps with single exponential decay function A(t)=A1·exp(-t/τ1), the decay time τ1 = 0.38 ps was obtained. Considering the instrument repose time of about 100 fs, the decay time should be <380 fs. This fast ESA decay time associated with the longer establishment time of 470 nm wavelength absorption, indicating the existence of ligand to cluster charge transfer which leads to the ultrafast formation of CSSs [49]. Therefore, the dynamics of Co-TCPP(Fe) MOF show the fast generation time of CSSs within 1 ps. Compared with TCPP(Fe) ligand, the Co-TCPP(Fe) MOF consist of Co metal nodes interconnected by TCPP(Fe) organic linkers, has a more adjacent porphyrinic groups between two individual frameworks to form abundant π-π interactions. The strengthened π-π interactions increase the electron delocalization and transfer, leading to electron transfer from organic linkers to the cobalt metal clusters, causing the formation of CSSs. The generated CSSs provides another efficient channel for electrons transfer and detracts the relaxation of excited electrons to ground state, which could influence the nonlinear absorption of MOF structure.
With above analyzation in mind, we then try to explain the Z-scan result of Co-TCPP(Fe) MOF at 532 nm in Fig. 3. When pumped by laser pulses, the MOF can absorb 532 nm laser and electrons are pumped to excited states. Besides the ESA and GSB effects, the transition of electrons from ligands excited states to metal clusters forming CSSs could also take place. As the CSSs has a longer lifetime, the relaxation of excited electrons to ground state is detracted, and the absorption of the incident light is weakened, causing a SA effect with a 10% increase of the transmittance. As we keep increasing the laser fluence, more CSSs are formed and absorption of electrons in CSSs could lead to further laser absorption, inducing an enhanced RSA effect of MOF under 532 nm laser irradiation.
4. Conclusion
In this paper, the Fe porphyrin based Co-TCPP(Fe) MOF nanosheets were prepared and the nonlinear absorption properties was studied by 532 nm nanosecond Z-scan technique. Compared with TCPP(Fe) ligand, the Co-TCPP(Fe) MOF has an enhanced RSA effect with an excellent OL threshold of 0.89 J/cm2. The fs-TA results show that the long-lived (>3.5 ns) CSSs in Co-TCPP(Fe) MOF provides another charge transfer channel and detracts the recombination of electrons and holes. Absorption of electrons in CSSs could lead to further laser absorption, inducing an enhanced RSA effect, which could be used to enhance the OL performance of MOFs materials. The study on the carrier dynamics in the OL process could provide references for the further design and synthesis of effective MOF-based OL materials.
Funding
National Key Research and Development Program of China (2019YFA0706402); National Natural Science Foundation of China (62027822).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. H. Han and L. H. Hurley, “G-quadruplex DNA: a potential target for anti-cancer drug design,” Trends Pharmacol. Sci. 21(4), 136–142 (2000). [CrossRef]
2. B. S. Lane and K. Burgess, “Metal-catalyzed epoxidations of alkenes with hydrogen peroxide,” Chem. Rev. 103(7), 2457–2474 (2003). [CrossRef]
3. H. Eichhorn, “Mesomorphic phthalocyanines, tetraazaporphyrins, porphyrins and triphenylenes as charge-transporting materials,” J. Porphyrins Phthalocyanines 04(01), 88–102 (2000). [CrossRef]
4. A. S. Sandanayaka and O. Ito, “Photoinduced electron transfer in supramolecules composed of porphyrin/phthalocyanine and nanocarbon materials,” J. Porphyrins Phthalocyanines 13(10), 1017–1033 (2009). [CrossRef]
5. H. A. Wagenknecht, “Helical Arrangement of Porphyrins along DNA: Towards Photoactive DNA-Based Nanoarchitectures,” Angew. Chem. Int. Edit. 48(16), 2838–2841 (2009). [CrossRef]
6. H. Sun, S. Cong, Z. Zheng, Z. Wang, Z. Chen, and Z. Zhao, “Metal-organic frameworks as surface enhanced Raman scattering substrates with high tailorability,” J. Am. Chem. Soc. 141(2), 870–878 (2019). [CrossRef]
7. Y. Fu, J. Cao, K. Yamanouchi, and H. Xu, “Air-laser-based standoff coherent Raman spectrometer,” Ultrafast Sci. 2022, 9867028 (2022). [CrossRef]
8. M. O. Senge, M. Fazekas, E. G. Notaras, W. J. Blau, M. Zawadzka, O. B. Locos, and E. M. Ni Mhuircheartaigh, “Nonlinear optical properties of porphyrins,” Adv. Mater. 19(19), 2737–2774 (2007). [CrossRef]
9. G. McLendon and D. S. Miller, “Metalloporphyrins catalyse the photo-reduction of water to H2,” J. Chem. Soc., Chem. Commun. 11(11), 533–534 (1980). [CrossRef]
10. S. Takagi, M. Eguchi, D. A. Tryk, and H. Inoue, “Porphyrin photochemistry in inorganic/organic hybrid materials: Clays, layered semiconductors, nanotubes, and mesoporous materials,” J. Photochem. Photobiol., C 7(2-3), 104–126 (2006). [CrossRef]
11. M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe, and O. M. Yaghi, “Systematic design of pore size and functionality in isoreticular MOFs and their application in methane storage,” Science 295(5554), 469–472 (2002). [CrossRef]
12. J.-R. Li, J. Sculley, and H.-C. Zhou, “Metal-organic frameworks for separations,” Chem. Rev. 112(2), 869–932 (2012). [CrossRef]
13. L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van Duyne, and J. T. Hupp, “Metal-organic framework materials as chemical sensors,” Chem. Rev. 112(2), 1105–1125 (2012). [CrossRef]
14. J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen, and J. T. Hupp, “Metal-organic framework materials as catalysts,” Chem. Soc. Rev. 38(5), 1450–1459 (2009). [CrossRef]
15. T. Zhang and W. Lin, “Metal-organic frameworks for artificial photosynthesis and photocatalysis,” Chem. Soc. Rev. 43(16), 5982–5993 (2014). [CrossRef]
16. I. Bhugun, D. Lexa, and J.-M. Savéant, “Catalysis of the electrochemical reduction of carbon dioxide by iron (0) porphyrins. Synergistic effect of Lewis acid cations,” J. Phys. Chem. 100(51), 19981–19985 (1996). [CrossRef]
17. H. Shinokubo and A. Osuka, “Marriage of porphyrin chemistry with metal-catalysed reactions,” Chem. Commun.1011–1021 (2009).
18. A. Harriman, “Luminescence of porphyrins and metalloporphyrins. Part 2.—Copper (II), chromium (III), manganese (III), iron (II) and iron (III) porphyrins,” J. Chem. Soc., Faraday Trans. 1 77(2), 369–377 (1981). [CrossRef]
19. G. Knoer and A. Vogler, “Photochemistry and photophysics of antimony (III) hyper porphyrins: activation of dioxygen induced by a reactive sp excited state,” Inorg. Chem. 33(2), 314–318 (1994). [CrossRef]
20. C. V. Reddy, K. R. Reddy, V. a. Harish, J. Shim, M. Shankar, N. P. Shetti, and T. M. Aminabhavi, “Metal-organic frameworks (MOFs)-based efficient heterogeneous photocatalysts: synthesis, properties and its applications in photocatalytic hydrogen generation, CO2 reduction and photodegradation of organic dyes,” Int. J. Hydrogen Energy 45(13), 7656–7679 (2020). [CrossRef]
21. A. Fateeva, P. A. Chater, C. P. Ireland, A. A. Tahir, Y. Z. Khimyak, P. V. Wiper, J. R. Darwent, and M. J. Rosseinsky, “A water-stable porphyrin-based metal-organic framework active for visible-light photocatalysis,” Angew. Chem. Int. Ed. 51(30), 7440–7444 (2012). [CrossRef]
22. X. Fang, Q. Shang, Y. Wang, L. Jiao, T. Yao, Y. Li, Q. Zhang, Y. Luo, and H. L. Jiang, “Single Pt atoms confined into a metal-organic framework for efficient photocatalysis,” Adv. Mater. 30(7), 1705112 (2018). [CrossRef]
23. Q. Zhang, X. Jiang, M. Zhang, X. Jin, H. Zhang, and Z. Zheng, “Wideband saturable absorption in metal-organic frameworks (MOFs) for mode-locking Er-and Tm-doped fiber lasers,” Nanoscale 12(7), 4586–4590 (2020). [CrossRef]
24. C. Gu, H. Zhang, P. You, Q. Zhang, G. Luo, Q. Shen, Z. Wang, and J. Hu, “Giant and Multistage Nonlinear Optical Response in Porphyrin-Based Surface-Supported Metal-Organic Framework Nanofilms,” Nano Lett. 19(12), 9095–9101 (2019). [CrossRef]
25. Q. Zuo, T. Liu, C. Chen, Y. Ji, X. Gong, Y. Mai, and Y. Zhou, “Ultrathin metal-organic framework nanosheets with ultrahigh loading of single Pt atoms for efficient visible-light-driven photocatalytic H2 evolution,” Angew. Chem. Int. Ed. 58(30), 10198–10203 (2019). [CrossRef]
26. M. Liu, K. Xie, M. D. Nothling, P. A. Gurr, S. S. L. Tan, Q. Fu, P. A. Webley, and G. G. Qiao, “Ultrathin metal-organic framework nanosheets as a gutter layer for flexible composite gas separation membranes,” ACS Nano 12(11), 11591–11599 (2018). [CrossRef]
27. Z. Liu, X. Zhang, X. Yan, Y. Chen, and J. Tian, “Nonlinear optical properties of graphene-based materials,” Chin. Sci. Bull. 57(23), 2971–2982 (2012). [CrossRef]
28. X. Wen, Z. Gong, and D. Li, “Nonlinear optics of two-dimensional transition metal dichalcogenides,” InfoMat 1(3), 317–337 (2019). [CrossRef]
29. T. Feng, X. Li, P. Guo, Y. Zhang, J. Liu, and H. Zhang, “MXene: two dimensional inorganic compounds, for generation of bound state soliton pulses in nonlinear optical system,” Nanophotonics 9(8), 2505–2513 (2020). [CrossRef]
30. Y. Yu, J. Si, L. Yan, M. Li, and X. Hou, “Enhanced nonlinear absorption and ultrafast carrier dynamics in graphene/gold nanoparticles nanocomposites,” Carbon 148, 72–79 (2019). [CrossRef]
31. Y. Xu, L. Yan, J. Si, M. Li, Y. Ma, J. Li, and X. Hou, “Nonlinear absorption properties and carrier dynamics in MoS2/Graphene van der Waals heterostructures,” Carbon 165, 421–427 (2020). [CrossRef]
32. Y. Zheng, F. Z. Sun, X. Han, J. Xu, and X. H. Bu, “Recent Progress in 2D Metal-Organic Frameworks for Optical Applications,” Adv. Optical Mater. 8(13), 2000110 (2020). [CrossRef]
33. D.-J. Li, Q.-h. Li, Z.-G. Gu, and J. Zhang, “Oriented Assembly of 2D Metal-Pyridylporphyrinic Framework Films for Giant Nonlinear Optical Limiting,” Nano Lett. 21(23), 10012–10018 (2021). [CrossRef]
34. M. Gouterman, “Study of the effects of substitution on the absorption spectra of porphin,” J. Chem. Phys. 30(5), 1139–1161 (1959). [CrossRef]
35. Y. Wang, M. Zhao, J. Ping, B. Chen, X. Cao, Y. Huang, C. Tan, Q. Ma, S. Wu, and Y. Yu, “Bioinspired design of ultrathin 2D bimetallic metal-organic-framework nanosheets used as biomimetic enzymes,” Adv. Mater. 28(21), 4149–4155 (2016). [CrossRef]
36. J. Liu, W. Zhou, J. Liu, Y. Fujimori, T. Higashino, H. Imahori, X. Jiang, J. Zhao, T. Sakurai, and Y. Hattori, “A new class of epitaxial porphyrin metal-organic framework thin films with extremely high photocarrier generation efficiency: promising materials for all-solid-state solar cells,” J. Mater. Chem. A 4(33), 12739–12747 (2016). [CrossRef]
37. D. Feng, Z. Y. Gu, J. R. Li, H. L. Jiang, Z. Wei, and H. C. Zhou, “Zirconium-metalloporphyrin PCN-222: mesoporous metal-organic frameworks with ultrahigh stability as biomimetic catalysts,” Angew. Chem. Int. Ed. 51(41), 10307–10310 (2012). [CrossRef]
38. K. Wang, D. Feng, T.-F. Liu, J. Su, S. Yuan, Y.-P. Chen, M. Bosch, X. Zou, and H.-C. Zhou, “A series of highly stable mesoporous metalloporphyrin Fe-MOFs,” J. Am. Chem. Soc. 136(40), 13983–13986 (2014). [CrossRef]
39. S.-S. Wang, H.-H. Huang, M. Liu, S. Yao, S. Guo, J.-W. Wang, Z.-M. Zhang, and T.-B. Lu, “Encapsulation of single iron sites in a metal-porphyrin framework for high-performance photocatalytic CO2 reduction,” Inorg. Chem. 59(9), 6301–6307 (2020). [CrossRef]
40. B. Qu, Q. Ouyang, X. Yu, W. Luo, L. Qi, and Y. Chen, “Nonlinear absorption, nonlinear scattering, and optical limiting properties of MoS2-ZnO composite-based organic glasses,” Phys. Chem. Chem. Phys. 17(8), 6036–6043 (2015). [CrossRef]
41. X. Li, L. Yan, J. Si, A. Pan, Y. Xu, and X. Hou, “Tunable nonlinear absorption effect and carrier dynamics of perovskite quantum dots,” Opt. Mater. Express 11(2), 569–574 (2021). [CrossRef]
42. B.-W. Xu, R.-J. Niu, Q. Liu, J.-Y. Yang, W.-H. Zhang, and D. J. Young, “Similarities and differences between Mn (II) and Zn (II) coordination polymers supported by porphyrin-based ligands: synthesis, structures and nonlinear optical properties,” Dalton Trans. 49(36), 12622–12631 (2020). [CrossRef]
43. R.-J. Niu, W.-F. Zhou, Y. Liu, J.-Y. Yang, W.-H. Zhang, J.-P. Lang, and D. J. Young, “Morphology-dependent third-order optical nonlinearity of a 2D Co-based metal-organic framework with a porphyrinic skeleton,” Chem. Commun. 55(33), 4873–4876 (2019). [CrossRef]
44. R. Matshitse, S. Khene, and T. Nyokong, “Photophysical and nonlinear optical characteristics of pyridyl substituted phthalocyanine-detonation nanodiamond conjugated systems in solution,” Diamond Relat. Mater. 94, 218–232 (2019). [CrossRef]
45. M. B. M. Krishna, V. P. Kumar, N. Venkatramaiah, R. Venkatesan, and D. N. Rao, “Nonlinear optical properties of covalently linked graphene-metal porphyrin composite materials,” Appl. Phys. Lett. 98(8), 081106 (2011). [CrossRef]
46. Y.-H. Xiao, Z.-G. Gu, and J. Zhang, “Vapor-assisted epitaxial growth of porphyrin-based MOF thin film for nonlinear optical limiting,” Sci. China Chem. 63(8), 1059–1065 (2020). [CrossRef]
47. D.-J. Li, Q.-h. Li, Z.-R. Wang, Z.-Z. Ma, Z.-G. Gu, and J. Zhang, “Interpenetrated metal-porphyrinic framework for enhanced nonlinear optical limiting,” J. Am. Chem. Soc. 143(41), 17162–17169 (2021). [CrossRef]
48. S. Yang, W. Hu, J. Nyakuchena, C. Fiankor, C. Liu, E. D. Kinigstein, J. Zhang, X. Zhang, and J. Huang, “Unravelling a long-lived ligand-to-metal cluster charge transfer state in Ce-TCPP metal organic frameworks,” Chem. Commun. 56(90), 13971–13974 (2020). [CrossRef]
49. M. Gutierrez, B. Cohen, F. Sánchez, and A. Douhal, “Photochemistry of Zr-based MOFs: ligand-to-cluster charge transfer, energy transfer and excimer formation, what else is there?” Phys. Chem. Chem. Phys. 18(40), 27761–27774 (2016). [CrossRef]
