Photoreactions of Porphyrins Initiated by Deep Ultraviolet Single

May 30, 2017 - The newly built 177 nm all-solid-state deep ultraviolet (DUV) laser photoionization mass spectrometer finds a unique advantage to ident...
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Photoreactions of Porphyrins Initiated by Deep Ultraviolet Single Photons Jing Chen, Zhixun Luo,* Hongbing Fu, and Jiannian Yao* State Key Laboratory for Structural Chemistry of Unstable and Stable species, and Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China S Supporting Information *

ABSTRACT: The newly built 177 nm all-solid-state deep ultraviolet (DUV) laser photoionization mass spectrometer finds a unique advantage to identify porphyrins that bear ionization energies close to 7.0 eV. We observed dramatic selectivity of tetraphenylporphyrins (TPPs) pertaining to varied photochemical processes initiated by the DUV laser excitation. Single-photon ionization was found dominant for 2H-TPP resulting in a fragmentation-free mass spectrum; photoinduced dehydrogenation was observed for zinc TPP, but both dehydrogenation and demetalation are noted for copper TPP. Along with first-principle calculations, we demonstrate how the photoinduced reactions vary with residual energies of photoionization, highest occupied molecular orbital− lowest unoccupied molecular orbital gaps, donor−acceptor orbital overlaps, single-step barriers, and whether or not there is a major process of structural rearrangement. It is demonstrated that the rotation of benzene ring under proper laser radiation prompts dehydrogenation process; also, metallo-TPPs do not support direct demetalation, but it is selectively accomplishable along with dehydrogenation and successive hydrogenation processes. These findings not only provide insights into the hydrogen atom transfer in porphyrins initiated by ultraviolet laser but also suggest promising applications of the DUV laser in designed synthesis and chemical modification of porphyrins.

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molecule electronics due to their tunable diode-like behavior.18 Also TPPs and their derivatives have long been used as supersensitive spectrophotometric color reagents for the detection of a few ions (e.g., Cu+), but the mechanism is still not fully unraveled.19 It is desirable that the development of precise chemistry enables to control the selectivity in such photochemical applications as well as porphyrin synthesis associated with C−C formation and C−H bond activation.11,20,21 The use of laser to control selective chemical reactions is highly attractive and has been recognized of importance from early on.22 Along with reasonable research interest behind general photochemical reactions,23 UV light has initiated many fascinating biological processes and applications such as photodissociation,24 charge transfer,25 proton transfer,26 photodynamic therapy, and photosensitization.5 However, considering that under strong UV laser radiation porphyrins readily end in photodissociation, the application of UV laser technique in such organic compounds appeals to high single-photon energy and luminous flux so that small energy intensity is operative for efficient excited transition.

INTRODUCTION Photoreactions are key steps for many catalytic synthesis and biological processes where the direct transformation of chemical bond is a highly attractive strategy with wide applicability to general hydrocarbons, complex macromolecules, and biological polymers.1,2 Known as organic macrocycle compounds with four pyrrole subunits interconnected via methine bridges, porphyrins readily attach side groups or host central metal atoms,3,4 giving rise to novel porphyrin chemistry with wide applications in medicine, biomimetic catalysis,5,6 supramolecular materials,7−9 etc. In particular, porphyrins allow for dramatic (de)hydrogenation and metalation,4,10,11 and the metalation of free-base porphyrins was found to be initiated by “sitting-atop” (SAT) complexes of 2H-metalloporhyrins as indicated by density functional theory (DFT) studies and several experimental findings in gas phase.3,12−16 Among others, recent studies also demonstrated that metalation of porphyrins on solid surface could be initiated by interface hydrogen exchange.17 In particular, it was found that conformation changes of tetraphenylporphyrins (TPPs) could occur in a direct dehydrogenation process, where the rotation of phenyl rings relative to the tetrapyrrole plane could facilitate the hydrogen molecule release without other reactants.11 Note that TPPs are easy to synthesize, and they bear applications in photodynamic therapy of cancer and photosensitizer for the production of singlet oxygen,5 as well as potentials in single© XXXX American Chemical Society

Received: April 18, 2017 Revised: May 23, 2017 Published: May 30, 2017 A

DOI: 10.1021/acs.jpca.7b03635 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A Recently scientists have developed a 177.3 nm all-solid-state deep ultraviolet (DUV) laser system by frequency-doubling of 355 nm laser through a KBBF-CaF2 prism coupled device,27 where unique advantages are found upon high photon flux, narrow bandwidth, good beam quality, and coherence compared to other DUV laser sources.28,29 Utilizing such a DUV laser (15.5 ps pulse duration, ∼10 μJ pulse energy, and luminous flux ∼1 × 1014/s), we developed a high-resolution and high-sensitivity time-of-flight mass spectrometry (TOFMS) instrument that allows for single-photon ionization (SPI) of numerous organic compounds.30 The importance of SPI has been recognized in attaining high ionization efficiency and lowfragmentation mass spectra without matrix or solvent interference.30−32 It is important to note that porphyrins bear ionization energies close to 7.0 eV (energy of a single photon of DUV laser), providing us a unique opportunity to set foot into the novel porphyrin photochemistry and subsequent applications. This is in sharp contrast to multiphoton ionization processes such as by 532 nm laser as applied in previous studies,32 where severe fragmentation may perplex the identification and distinction from usual organic molecules. Here we report a finding of dramatic selectivity of photoionization and photoinduced reactions of three TPPs, namely, 2H-tetraphenylporphyrin (2HTPP), zinc tetraphenylporphyrins (ZnTPPs), and copper tetraphenylporphyrins (CuTPPs). Interestingly, we obtained SPI mass spectra for 2HTPP, photoinduced dehydrogenation for ZnTPP, but both dehydrogenation and demetalation for CuTPP. Along with first-principles calculation analysis, we unraveled the reaction mechanisms of dehydrogenation and demetalation processes under the DUV laser radiation and illustrated the dependence of photochemical activities of TPPs upon their ionization energies, enthalpy changes, intramolecular interactions, and structural rearrangement. It is notable that direct demetalation of metallotetraphenylporphyrins (MTPPs) is not easy to achieve at room temperature, but it is accomplishable under proper laser excitation associated with dehydrogenation and successive hydrogenation processes.

(ECP’s) basis set (LANL2DZ)3,38 for Cu and Zn atoms. All the energies are corrected with zero-point-vibrations. The calculated ionization energy values (Table S1, Supporting Information) of these porphyrins are consistent with the previously reported studies.39−41 All transition states (TSs) are checked and confirmed by intrinsic reaction coordinate (IRC) calculations. The reaction paths for dehydrogenation and demetalation are optimized at both low-spin and high-spin states. Natural bond orbital (NBO) analysis is performed with the DFT calculations in Gaussian 09, and the orbital overlap patterns are given with multiwfn software.42

MATERIALS AND METHODS The experiments were performed on a customized Re-TOF-MS instrument based on the all-solid-state DUV laser photoionization strategy (177.3 nm wavelength, 15.5 ps pulse duration, and pulse energy at ∼10 μJ, a repeating rate of 10 Hz), along with a thermal evaporation source (Figure S1, Supporting Information).30 The powder samples of 2HTPP, CuTPP, and ZnTPP (99.5% purity, Alfa Aesar) were put in a customized quartz container, respectively, and heated to a certain proper temperature (150 °C for 2HTPP; 160 and 180 °C for CuTPP and ZnTPP) that could produce enough vapor to form a stable molecular beam. Regarding the proper evaporation temperature, thermogravimetric analysis of each material was performed to ensure the stability of samples without thermal decomposition (Figure S2, Supporting Information). Also, comparable experiments were conducted utilizing the photoionization of 355 nm pump laser. All the optimization, frequency, and energy calculations are performed on a basis of density functional theory (DFT) embedded in Gaussian 09 program package. Geometries of all species are fully optimized at the gradient-corrected BeckePerdew (BP86) exchange-correlation functional level of theory,33−35 by utilizing a valence triple-ζ-type basis set (TZVP)36,37 for C, H, N atoms and an effective-core-potentials

spectrometer utilizing the all-solid-state DUV laser as photoionization source (7 eV single photon energy, 15 ps pulse width, 10 μJ energy per pulse). For 2HTPP, a strong molecular ion peak appears in the mass spectrum (Figure 1a) indicating the fragmentation-free advantage of DUV-SPI-MS, which is in sharp contrast with the intense fragments caused by 355 nm laser photoionization (Figure S3, Supporting Information), also more identifiable comparing with the mass spectra acquired with other methods where the solvent interference or matrix interference makes it difficult to identify chemical reactions.32 Similar low-fragmentation mass spectra were also obtained for ZnTPP and CuTPP under the DUV laser ionization conditions. Overall, the appearance of low-fragmentation is reasonable considering the ionization energies of these TPPs (6.0−6.5 eV)39−41 close to the single photon energy of 177 nm laser (7.0 eV). However, instead of the molecular ion peaks for all, dominant dehydrogenation products are observed for ZnTPP and CuTPP in the mass spectra, respectively; and interestingly, H+ ions appear in the mass spectra of ZnTPP but not in the mass spectra of CuTPP; instead, Cu+ ions are observed in the mass spectrum of CuTPP. To interpret this selectivity, by utilizing first-principles calculations we first checked: (1) vertical ionization energies (VIEs), which are the lowest energies required to ionize the

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RESULTS AND DISCUSSION Figure 1 displays the mass spectra of 2HTPP, ZnTPP, and CuTPP respectively, collected by the customized Re-TOF mass

Figure 1. TOF mass spectra of tetraphenylporphrins collected under radiation of 177 nm laser. (a) 2HTPP, (b) ZnTPP, and (c) CuTPP. (insets) HOMOs of neutral 2HTPP, ZnTPP, and CuTPP, respectively. The molecular formula of major molecular ion peaks and fragment ion peaks are given aside the peaks. To avoid thermal and laser damage to the TPPs, both reduced laser power and evaporating temperature are considered.

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B

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Figure 2. Optimized geometries of (a) [2HTPP]+, (b) [ZnTPP]+, and (c) [CuTPP]+. The possible dehydrogenation sites and the values of distances between C atoms and H atoms at these sites are given beside virtual lines. The sites of the same type are indicated in the circles of the same color.

[ZnTPP]+ and [CuTPP]+ reveal a point accounting for the varied HAT processes of the three TPPs. However, both our DFT calculations and previous photoelectron spectroscopic studies show that the three TPPs have very similar ionization energies (Table S1, Supporting Information),41 and also the enthalpy changes for dehydrogenation of tetraphenylporphyrins are quite close to each other (eqs 1−3). So, what is the determining role responsible for the diversity and selectivity of dehydrogenation from experimental observation?

TPPs prior to structural rearrangement, (2) the adiabatic ionization energies (AIEs) referring to the differences between the neutral and positive TPPs, and (3) highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO−LUMO) gaps (Table S1, Supporting Information). First, from the VIEs of these TPP molecules, the 177.3 nm DUV laser can easily excite electrons from their HOMOs to LUMOs or directly ionize them through a single photon process,43,44 but CuTPP bears an especially small HOMO− LUMO gap (almost half of the gaps of 2HTPP and ZnTPP, Table S1, Supporting Information) due to its open-shell electron configuration. In comparison, both ZnTPP and 2HTPP bear closed electron shell configurations, and the electrons on their HOMOs mainly distribute on tetrapyrrole ring and phenyl ring. There is also an important difference between ZnTPP and CuTPP, as the Zn-atom center rarely contributes to the HOMO of ZnTPP; after ionization, the unpaired electrons lead to a spin density surface having a similar shape with the HOMO, indicating that the Zn center may not be involved in a single-photon ionization process (Figure 1a,b and Figure S5, Supporting Information). For CuTPP, as indicated by the HOMO pattern and spin density surface, the unpaired electron distribution is mainly on the Cuatom center and tetrapyrrole rings (Figure 1c and Figure S5, Supporting Information). Therefore, the removal of an unpaired electron from CuTPP must bring forth changes relating to the Cu center. These DFT calculations suggest consistency with the experimental observation of dissociative Cu+ ions in the mass spectrum. To provide further insights why a molecule ion is attained for 2HTPP while dehydrogenation peaks [ZnTPP-H2]+ and [CuTPP-4H2]+ show, respectively, under the same DUV radiation, we reexamined the optimized structures of the three TPPs. It is found that chirality exists in their cations pertaining to phenyl ring rotation, as indicated by the different distances between two C atoms (one on phenyl ring and the other on tetrapyrrole ring), as shown in Figure 2. In [2HTPP]+ and [ZnTPP]+, at symmetric positions there are four pairs of different equivalent active sites (each type indicated by the same color of circle, Figure 2a,b). However, there are two and only two sites displaying the smallest intramolecular H···H atom distance at 2.667 Å (H1−H2), as shown in Figure 2b, corresponding to the smallest C−C atom distance at 3.140 Å (C1···C5), whereas [CuTPP]+ displays two kinds of active sites (each has four equivalent active sites at symmetric positions) among which one of the four equivalent active sites displays the smallest H···H atom distance at 2.674 Å (H1−H2) and smallest C···C atom distance at 3.106 Å (C1−C5), as addressed in Figure 2c. Different number of active sites and their positions in

hv(177)

[2HTPP]+ ⎯⎯⎯⎯⎯→ [TPP]+ + H 2 (ΔH = 0.47 eV)

(1)

hv(177)

[ZnTPP]+ ⎯⎯⎯⎯⎯→ [ZnTPP − 2H]+ + H 2 (ΔH = 0.49 eV) (2) hv(177)

[CuTPP]+ ⎯⎯⎯⎯⎯→ [CuTPP − 2H]+ + H 2 (ΔH = 0.56 eV) (3)

We then optimized the dehydrogenation product of [2HTPP]+, [ZnTPP]+, and [CuTPP]+ (Figure S7, Supporting Information) and found that tetrapyrrole ring of [2HTPP]+ is obviously distorted simply by noting the distance between N atom and H atoms, even with a hydrogen bond formed between N1 and H1 (Figure S7a, Supporting Information), whereas, in [ZnTPP-H2]+ and [CuTPP-H2]+, no apparent distortion of tetrapyrrole ring shows up, simply because the metal−N coordinate bonds facilitate the stabilization of tetrapyrrole rings (Figure S7c,e). The large structure relaxation of the tetrapyrrole ring needed for the dehydrogenation of 2HTPP may largely lower the reaction rate (even preventing the occurrence of dehydrogenation in [2HTPP]+ in view of the limited time and space of the TOF ionization and acceleration zone) and hence a dominant SPI process without suffering from fragmentation or (de)hydrogenation. Following, we endeavor to probe into the reaction mechanisms for the dehydrogenation and likely demetalation processes of [ZnTPP]+ and [CuTPP]+. As shown in Table S1 (Supporting Information), there are 0.72 and 0.52 eV residual energies (defined by subtracting VIEs from the single-photon energy of DUV, i.e., 7.0 eV) for ZnTPP and CuTPP after their SPI processes, which are close to the enthalpy changes of dehydrogenization. For ZnTPP, one pair of C−H bonds at the active sites (e.g., C1−H1, C5−H2) is readily activated via the rotation of phenyl ring and bending of relevant C−H bonds, resulting to a paralleled C−H pair and reduced C1···C5 distance (1.909 Å; 1→TS1, Figure 3). The distance between C1 and C5 is further shortened to 1.545 Å at the formation of C−C bond in intermediate 2 (also inferred by the emergence of C4−N2 stretching mode at 1555 cm−1, IR activity in Figure C

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infrared spectrum (Figure S10B, spectrum No. 5). Subsequently, C1−H1 and C5−H2 bonds are cleaved, accompanied by a strengthened C1−C5 bond (1.535 Å) (5→TS4). The reaction finally arrives at a complex of dehydrogenation product ions with C1−C5 of 1.460 Å and a released hydrogen molecule. At the formation of a new five-member ring, the stretching vibrations of C−C in tetrapyrrole rings and phenyl rings become elaborate (spectrum 6, Figure S10B). It is worth mentioning that fully dehydrogenized product of CuTPP (i.e., [CuTPP-4H2]+) was also optimized and the lowest-energy structure (Figure S8, Supporting Information), which is consistent with that in previously reported calculations.4,17 We then offer a comparative discussion for the demetalation of ZnTPP and CuTPP. Repeated calculation results reveal that direct demetalation by splitting the metal−nitrogen bond in CuTPP and ZnTPP or their cations (i.e., [ZnTPP]+ and [CuTPP]+) are largely endothermic reactions having enthalpy changes above 7 eV; for instance, [CuTPP]+→Cu+ + TPP0 (ΔH = 9.1 eV), [ZnTPP]+→Zn+ + TPP0 (ΔH = 9.5 eV). Regarding to the functionalization of metallic TPPs, previous studies have proposed an SAT complex model for the metalation of free-base porphyrins and also observed such a dehydrogenation process after the demetalation.3,11−16,45−48 Herewith, it is reasonable to infer that the demetalation process may be also associated with the formation of a [2HMTPP]+ intermediate via a thermodynamics allowed reaction pathway. That is, a hydrogen molecule released from [CuTPP]+ by dehydrogenation could adsorb again to [CuTPP]+ and form [2HCuTPP]+ intermediate which may then pluck out a Cu+ ion, as described by the following equations.

Figure 3. Energy profiles for reaction pathways of dehydrogenation of [ZnTPP]+. Low-spin and high-spin pathways are represented in black and red, respectively. The energies are given in electronvolts.

S10A, Supporting Information). The C−H bonds at active sites are then elongated from 1.117 to1.461 Å allowing for cleavage along with the shortening of C1−C5 bond (2→TS2, Figure 3). At last, a hydrogen molecule is released, accompanied by the formation of a five-membered carbon ring (3). The rotation of phenyl ring (1→TS1, energy barrier of 2.37 eV) is a ratecontrolling step as previously proposed for the dehydrogenation of MTPP at vacuum−solid interface.10,11 As a reference, also provided is the high-spin state reaction pathway. Similarly in [CuTPP]+, the rotation of a phenyl ring to form a pair of paralleled C−H bonds at active sites (4→TS3) is also a rate-controlling step (energy barrier of 2.59 eV), as shown in Figure 4. Through the rotation of phenyl ring, the C1···C5 distance is sharply reduced from 3.106 to 1.951 Å. After the formation of intermediate 5, the C1···C5 distance further decreases to 1.548 Å, as also indicated by the appearance of C4−N2 stretching mode at 1560 cm−1 in the calculated

hv(177)

[CuTPP]+ ⎯⎯⎯⎯⎯→ [CuTPP − 8H]+ + 4H 2 h v(177)

[CuTPP]+ + H 2 ⎯⎯⎯⎯⎯→ [2HCuTPP]+ hv(177)

[2HCuTPP]+ ⎯⎯⎯⎯⎯→ Cu+ + [2HTPP]0

(4) (5) (6)

DFT calculations reveal that the enthalpy changes (∼0.4−0.6 eV) for the formation of [2HMTPP]+ are small enough to be overcome by the minor residual energies of SPI processes under the 177 nm DUV laser. In addition to the lower energy of reactant [2HCuTPP]+ with respect to the product in hydrogenation of [CuTPP]+ (Figure 5), the lower mole number of H2 required by hydrogenation to form [2HCuTPP]+ than that released by previous dehydrogenation of [CuTPP]+ also prompts the shift of reaction equilibrium toward the direction of [2HCuTPP]+ formation. Moreover, the splitting of [2HCuTPP]+ to “Cu+ + [2HTPP]0” is a barrierless process. In this regard, a combined reaction equation for CuTPP can be expressed as [CuTPP]+ + [CuTPP]0 h v(177)

⎯⎯⎯⎯⎯→ [CuTPP − 8H]+ + Cu+ + [2HTPP]0 + 3H 2 + e−

(7) +

In comparison, [2HZnTPP] is even less stable than [ZnTPP]+ (Figure S9, Supporting Information), which could explain why we did not observe Zn ions in mass spectrum of ZnTPP. Figure 5 shows that the adsorption of H atoms on [CuTPP]+ results in weakened H−H bonds and initiates the adhesion of the two H atoms onto a N and a Cu atom, respectively (7→ TS5), where an energy barrier of 1.50 eV is the rate-controlling

Figure 4. Energy profiles for reaction paths of dehydrogenation of [CuTPP]+. Low-spin and high-spin pathways are represented in black and red, respectively. The structures given are all at low-spin state. The energies are given in electronvolts. D

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formation of [2HCuTPP]+. In contrast, the adsorption of H2 on [ZnTPP]+ only suppresses the overlaps between hydrogenbound N atoms (N1 and N3) and p-type LP*(Zn) (Figure 7a−

Figure 5. Energy profiles for formation of SAT [2HCuTPP]+ complexes. Low-spin and high-spin pathways are represented in black and red, respectively. The structures given are all at low-spin state. The energies are given in electronvolts.

Figure 7. Donor−acceptor overlaps in the reactant 10 and product 12 of formation of [2HZnTPP]+ (low-spin state). Isosurfaces of donor and acceptor orbitals are plotted in green/blue and brown/purple, respectively. spn gives the hybridization type of LPN.

step. Then, there forms a N1−H bond (1.042 Å) and a Cu−H bond (1.536 Å), accompanied by the cleavage of H−H bond and elongation of N1−Cu bond (2.495→2.678 Å) in intermediate 8 (Figure 5 and Figure S10C). The H atom adsorbed on the Cu center then migrates toward N3 giving rise to the formation of SAT complex of 2HCuTPP (TS6→9; Figure 5). Reaction paths for the formation of [2HZnTPP]+ and related IR activities are provided in Supporting Information (Figures S9 and S10). In addition, utilizing NBO analysis we depicted the donor− acceptor overlaps between the metal center and N atoms (Figure 6) to reveal the role of interactions between central

d). The different weakening degree of metal−N interactions by H-adsorption clarifies why CuTPP allows the formation of 2HCuTPP and subsequently Cu ions release but ZnTPP does not. Overall, on the one hand, the weakening of interactions between metal center and tetrapyrrole ring by the adsorption of H atoms on N atoms supports the previous proposal of SAT complex intermediate during the demetalation of MTPPs. On the other hand, the removal of H2 from such MTPPs mostly causes changes of hybridization of LPN (Figures S11 and Figure S12). There emerges an “(s)LP*Cu→RY*C” in the new fivemember carbon ring of [CuTPP-H2]+, while full dehydrogenation leads to a high symmetric [CuTPP-4H2]+ with four “LP*Cu→RY*C” overlaps (Figure S13). In contrast, no such orbital overlaps are found for ZnTPP (Figures S11 and Figure S12, Supporting Information), which again verifies the determining role of metal atoms themselves during the dehydrogenation and likely subsequent hydrogentation/demetalation processes.

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CONCLUSIONS Utilizing newly developed all-solid-state DUV laser photoionization mass spectrometry, we have studied the photoreactions of TPPs that bear ionization energies close to the single-photon energy of the 177.3 nm DUV laser (i.e., 7.0 eV). High-resolution Re-TOF-MS analysis reveals dramatic reaction selectivity, although the TPPs bear comparable ionization energies. A single-photon ionization process was found dominant for 2HTPP, but photoinduced dehydrogenation for ZnTPP and even demetalation was observed for CuTPP. Along with first-principles calculations, we illustrate a rate-controlling step for the dehydrogenation involving benzene ring rotation under laser radiation. MTPPs do not support direct demetalation, but it is selectively accomplishable through the formation of 2HMTPP intermediates that weaken the bonding interactions between the metal center and pyrrole rings. The selectivity for the dramatic distinction between ZnTPP and CuTPP is associated with unpaired electron distributions, whether or not a structure rearrangement, thermodynamics and reaction kinetics, etc. These insights regarding (de)hydrogenation and (de)metalation of TPPs provide important

Figure 6. Donor−acceptor overlaps in the low-spin reactant 7 and product 9 of formation of [2HCuTPP]+. Isosurfaces of donor and acceptor orbitals are plotted in green/blue and brown/purple, respectively. spn gives the hybridization type of LPN.

metal atoms and tetrapyrrole ring (mostly nitrogen atoms) in determining the photochemical reactivity of TPPs. As seen from the typical donor−acceptor charge-transfer interactions before and after the reactions, the adsorption of two H atoms on N1 and N3 (9) causes suppression of LPN1→LP*Cu and LPN3→LP*Cu, as well as the backward (s)LP*Cu→RY*N (7). The decrease of charge-transfer interactions between Cu and tetrapyrrole ring (due to H2 adsorption) evidence the proposal that [CuTPP]+ releases a Cu+ though a path involving the E

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(8) Jurow, M.; Schuckman, A. E.; Batteas, J. D.; Drain, C. M. Porphyrins as Molecular Electronic Components of Functional Devices. Coord. Chem. Rev. 2010, 254, 2297−2310. (9) Mohnani, S.; Bonifazi, D. Supramolecular Architectures of Porphyrins on Surfaces: The Structural Evolution from 1D to 2D to 3D to Devices. Coord. Chem. Rev. 2010, 254, 2342−2362. (10) Di Santo, G.; Blankenburg, S.; Castellarin-Cudia, C.; Fanetti, M.; Borghetti, P.; Sangaletti, L.; Floreano, L.; Verdini, A.; Magnano, E.; Bondino, F.; et al. Supramolecular Engineering through TemperatureInduced Chemical Modification of 2H-Tetraphenylporphyrin on Ag(111): Flat Phenyl Conformation and Possible Dehydrogenation Reactions. Chem. - Eur. J. 2011, 17, 14354−14359. (11) Röckert, M.; Franke, M.; Tariq, Q.; Ditze, S.; Stark, M.; Uffinger, P.; Wechsler, D.; Singh, U.; Xiao, J.; Marbach, H.; et al. Coverage- and Temperature-Dependent Metalation and Dehydrogenation of Tetraphenylporphyrin on Cu(111). Chem. - Eur. J. 2014, 20, 8948−8953. (12) Xiao, J.; Ditze, S.; Chen, M.; Buchner, F.; Stark, M.; Drost, M.; Steinrueck, H.-P.; Gottfried, J. M.; Marbach, H. TemperatureDependent Chemical and Structural Transformations from 2Htetraphenylporphyrin to Copper(II)-Tetraphenylporphyrin on Cu(111). J. Phys. Chem. C 2012, 116, 12275−12282. (13) Ditze, S.; Stark, M.; Drost, M.; Buchner, F.; Steinruck, H. P.; Marbach, H. Activation Energy for the Self-Metalation Reaction of 2HTetraphenylporphyrin on Cu(111). Angew. Chem., Int. Ed. 2012, 51, 10898−10901. (14) Diller, K.; Klappenberger, F.; Marschall, M.; Hermann, K.; Nefedov, A.; Woll, C.; Barth, J. V. Self-metalation of 2Htetraphenylporphyrin on Cu(111): An X-Ray Spectroscopy Study. J. Chem. Phys. 2012, 136, 13. (15) Buerker, C.; Franco-Canellas, A.; Broch, K.; Lee, T. L.; Gerlach, A.; Schreiber, F. Self-Metalation of 2H-Tetraphenylporphyrin on Cu(111) Studied with XSW: Influence of the Central Metal Atom on the Adsorption Distance. J. Phys. Chem. C 2014, 118, 13659−13666. (16) Doyle, C. M.; Krasnikov, S. A.; Sergeeva, N. N.; Preobrajenski, A. B.; Vinogradov, N. A.; Sergeeva, Y. N.; Senge, M. O.; Cafolla, A. A. Evidence for the Formation of an Intermediate Complex in the Direct Metalation of Tetra(4-bromophenyl)-Porphyrin on the Cu(111) Surface. Chem. Commun. 2011, 47, 12134−12136. (17) Rockert, M.; Franke, M.; Tariq, Q.; Lungerich, D.; Jux, N.; Stark, M.; Kaftan, A.; Ditze, S.; Marbach, H.; Laurin, M.; et al. Insights in Reaction Mechanistics: Isotopic Exchange during the Metalation of Deuterated Tetraphenyl-21,23D-porphyrin on Cu(111). J. Phys. Chem. C 2014, 118, 26729−26736. (18) Zoldan, V. C.; Faccio, R.; Pasa, A. A. n and p Type Character of Single Molecule Diodes. Sci. Rep. 2015, 5, 8350. (19) Yoshimura, K.; Nigo, S.; Tarutani, T. Ion-exchanger ColorimetryVIII Microdetermination of Copper in Natural Waters. Talanta 1982, 29, 173−176. (20) Hewage, D.; Silva, W. R.; Cao, W.; Yang, D.-S. La-Activated Bicyclo-oligomerization of Acetylene to Naphthalene. J. Am. Chem. Soc. 2016, 138, 2468−2471. (21) Ding, X.-L.; Wu, X.-N.; Zhao, Y.-X.; He, S.-G. C−H Bond Activation by Oxygen-Centered Radicals over Atomic Clusters. Acc. Chem. Res. 2012, 45, 382−390. (22) Letokhov, V. S. Use of Lasers to Control Selective Chemical Reactions. Science 1973, 180, 451−458. (23) Liu, Y. J.; De Vico, L.; Lindh, R.; Fang, W. H. Spin-orbit ab initio Investigation of the Ultraviolet Photolysis of Diiodomethane. ChemPhysChem 2007, 8, 890−898. (24) Parthasarathi, R.; He, Y.; Reilly, J. P.; Raghavachari, K. New Insights into the Vacuum UV Photodissociation of Peptides. J. Am. Chem. Soc. 2010, 132, 1606−1610. (25) Bucher, D. B.; Kufner, C. L.; Schlueter, A.; Carell, T.; Zinth, W. UV-Induced Charge Transfer States in DNA Promote Sequence Selective Self-Repair. J. Am. Chem. Soc. 2016, 138, 186−190. (26) Zhang, Y.; de La Harpe, K.; Beckstead, A. A.; Improta, R.; Kohler, B. UV-Induced Proton Transfer between DNA Strands. J. Am. Chem. Soc. 2015, 137, 7059−7062.

controllable and conversable strategies for metal−N and C−H bonds activation.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.7b03635. Instrumentation and sample characterization data; multiphoton ionization experimental data; DFT calculated energetic, structural, and vibrational data; reaction pathways for the formation of 2HZnTPP; and natural bond orbital (NBO) donor−acceptor overlaps (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. (Z.L.) *E-mail: [email protected]. (J.Y.) ORCID

Zhixun Luo: 0000-0002-9819-9155 Hongbing Fu: 0000-0003-4528-189X Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by Young Professionals Program in Institute of Chemistry, Chinese Academy of Sciences (Y3297B1261), the National Basic Research Program of China (973; Grant No. 2013CB933503), and the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. Y62A0412B1). In addition, we thank the National Thousand Youth Talents Program and financial support from CAS project with Grant Nos. Y31M0112C1 and Y5294512C1.

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