Application of Near-IR Absorption Porphyrin Dyes Derived from Click Chemistry as Third-Order Nonlinear Optical Materials.

Recently, third-order nonlinear properties of porphyrins and porphyrin polymers and coordination compounds have been extensively studied in relation to their use in photomedicine and molecular photonics. A new functionalized porphyrin dye containing electron-rich alkynes was synthesized and further modified by formal [2+2] click reactions with click reagents tetracyanoethylene (TCNE) and 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ). The photophysical properties of these porphyrin dyes, as well as the click reaction, were studied by UV/Vis spectroscopy. In particular, third-order nonlinear optical properties of the dyes, which showed typical d-π-A structures, were characterized by Z-scan techniques. In addition, the self-assembly properties were investigated through the phase-exchange method, and highly organized morphologies were observed by scanning electron microscopy (SEM). The effects of the click post-functionalization on the properties of the porphyrins were studied, and these functionalized porphyrin dyes represent an interesting set of candidates for optoelectronic device components.

Introduction

Materials with nonline<span class="Chemical">ar optical (NLO) properties and fast response to laser irradiation, as well those as with merits such as small optical loss, high optical quality, good stability, low cost and ease of preparation, have attracted increasing attention owing to their potential applications in ultrafast optical switching, optical communication, optical modulators, and optical limiting.1, 2, 3, 4, 5 The chemist's goal in this work is to design molecules and materials with high nonlinear coefficients and develop models that can predict these ch<span class="Chemical">aracteristics from the molecular structure.6, 7 Discovering organic molecules with large nonlinear responses is an active pursuit, and properties are often manipulated by making structural modifications to donor and acceptor building blocks, as well as to conjugated linking π‐units.8, 9, 10

n class="Chemical">Porphyrinsn> are comprised of four pyrrole units linked together through their α‐positions by methane bridges; the highly delocalized aromatic 18 π‐electron system of porphyrins can give rise to a strong NLO response.11 Recently, third‐order NLO properties of porphyrins and porphyrin polymers and coordination compounds have been extensively studied in relation to their use in photomedicine and molecular photonics.12, 13, 14, 15, 16, 17, 18

Although continuous optimization was explored previously, some <span class="Chemical">porphyrin derivatives were obtained through the fast, high‐yielding, and catalyst‐free [2+2] <span class="Chemical">click reaction,19 However, very little rese<span class="Chemical">arch has been done on the porphyrin dyes modified by [2+2] click chemistry with high third‐order optical nonlinearities. In particular, innovative [2+2] cycloaddition of strong electron acceptors, such as tetracyanoethene (TCNE) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ), to electron‐rich alkynes provides efficient access to nonplanar push–pull chromophores featuring intense intramolecular charge‐transfer (CT) and optical properties.20, 21, 22

In this paper, we use n class="Chemical">clickn> chemistry to aid the synthesis of extraordinary porphyrin derivatives, which provides the porphyrin derivatives with a widened absorption spectra and improved CT properties. These derivatives had d‐π‐A systems that contain a middle acceptor and peripheral multi‐donors in contrast to the conventional linear type of d‐π‐A compounds, and were prepared by quite short and high‐yielding synthetic routes. It is expected that the concept reported here can be expanded to other functional groups and may impact optoelectronic applications in the future.

Results and Discussion

Design and synthesis

A new n class="Chemical">ethynyln>‐bridged porphyrin intermediate (named Por−Zn−N) was designed and synthesized on the basis of Sonogashira coupling reactions (Scheme 1). Hence, alkynylpyrene derivative Por−Zn−N, which consisted of porphyrin as acceptor, N,N‐didodecyl aniline as donor, and an ethynyl group as a bridge, was firstly prepared as a click precursor. The alkoxy groups were added in order to improve solubility and decrease aggregations of the porphyrin derivatives. The products were obtained in high yields, and these porphyrin derivatives have good solubility in dichloromethane and tetrahydrofuran (THF).

Scheme 1

Molecular structures and synthetic routes of Por−Zn−N. Reagents and conditions: a) trimethylsilylacetylene (TMSA), THF, Et3N, PdCl2(PPh3)2, CuI, 30 °C, 8 h, 13 %; b) K2CO3, MeOH, rt, 4 h, 93 %; c) 1) pyrrole, TFA, CH2Cl2, rt, 20 h, 2) Zn(OAc)2, 93 %; d) NBS, CH2Cl2, rt, 1 h, 82 %; e) Pd(PPh3)2Cl2, PPh3, CuI, THF, Et3N, 80 °C, 12 h, 83 %.

Moleculn class="Chemical">arn> structures and synthetic routes of Por−Zn−N. Reagents and conditions: a) trimethylsilylacetylene (TMSA), THF, Et3N, PdCl2(PPh3)2, CuI, 30 °C, 8 h, 13 %; b) K2CO3, MeOH, rt, 4 h, 93 %; c) 1) pyrrole, TFA, CH2Cl2, rt, 20 h, 2) Zn(OAc)2, 93 %; d) NBS, CH2Cl2, rt, 1 h, 82 %; e) Pd(PPh3)2Cl2, PPh3, CuI, THF, Et3N, 80 °C, 12 h, 83 %.

n class="Chemical">Clickn> chemistry provides efficient, reliable, and selective reactions for synthesizing new compounds and generating combinatorial libraries. In particular, typically thermal [2+2] cycloadditions by reacting “electronically confused” alkynes with TCNE and TCNQ are considered to be novel examples. These meso‐extended tetraarylporphyrin chromophores PY−Zn−TCNE and PY−Zn−TCNQ were obtained through the high‐yielding [2+2] click reactions between alkynes and TCNE and TCNQ as shown in Scheme 2. The structures and purities of newly prepared products were confirmed by 1H NMR, Fourier‐transform infrared (FT‐IR), and mass spectrometry.

Scheme 2

Molecular structures and synthetic routes of the click reaction products.

Molecul<span class="Chemical">arn> structures and synthetic routes of the <span class="Chemical">click reaction products.

The reactions with the <n class="Chemical">span class="Chemical">click reagent <spn>an class="Chemical">TCNE could be conducted under ambient temperature, and enhancement of temperature to 100 °C was just for higher efficiency. However, the click reactions of TCNQ required heating up to 100 °C and holding at reflux for 1 h to generate significantly high yields ranging 96 %. Furthermore, in all click reactions, metal catalysts were unnecessary, and purifications were done more easily in contrast with other reactions for the absence of by‐products. Moreover, the porphyrin derivatives were stable in the air at room temperature, and could be dissolved in common organic solvents such as dichloromethane, THF, and acetone, which were beneficial for further processing.

Photophysical properties

The photophysical properties of organic materials n class="Chemical">arn>e essential parameters that provide important information on their conformations and electronic structures. The UV/Vis absorption properties of Por−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ were characterized by UV/Vis spectroscopy in dilute dichloromethane solutions at 298 K, as shown in Figure 1. The UV/Vis spectra of these compounds exhibit features typical of a porphyrin ring, with an intense Soret band in the range 400–500 nm and less intense Q bands in the range 600–1200 nm.

Figure 1

UV/Vis absorption spectra of Por−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ in CH2Cl2 solutions.

UV/Vis absorption spen class="Chemical">ctra of Por−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ in CH2Cl2 solutions.

It is worth noting that the strongest absorption peaks of both n class="Gene">Porn>−Zn−TCNE (433 nm) and Por−Zn−TCNQ (453 nm) showed an obvious blue‐shift relative to Por−Zn−N (474 nm), which was attributed to the cyano group as strong acceptors decrease the electronic cloud density of the porphine ring.23 Meanwhile, Por−Zn−TCNQ is red shifted by 20 nm compared with Por−Zn−TCNE, resulting from the effective π‐extended conjugation caused by the hexatomic rings.

In compn class="Chemical">arn>ison with Por−Zn−N, both clicked products showed end absorptions (λend) reaching into the near infrared (900 nm for Por−Zn−TCNE and 1200 nm for Por−Zn−TCNQ) which was ascribed to the electronic effect between the donor (porphyrin) and acceptor (cyano group). Another fact worth mentioning is that the λend of the products also showed obviously bathochromic shifts between Por−Zn−TCNE and Por−Zn−TCNQ, concomitantly with increased conjugation lengths.

Time‐resolved transient absorption spectra of porphyrins in dichloromethane at room temperature were taken at various delay times after the excitation pulse. The spectral trace of Por−Zn−N is shown in Figure 2, which displays broad negative signals in the range of 400–500 nm and 630–700 nm, corresponding to the bleaching of the strongly allowed S 0→S n absorption band upon excitation and also shows a buildup of a strong transient absorption signals in the region of 500–600 nm. The latter peak was associated with the S 1→S n transition.24, 25 Compared with Por−Zn−N, the click products Por−Zn−TCNE and Por−Zn−TCNQ didn′t show any signals under the same conditions, which were due to the increments of π‐conjugations and introduction of electron‐withdrawing cyano groups.

Figure 2

Picosecond time‐resolved transient spectra of compound Por−Zn−N excited at 532 nm.

Picosecond time‐resolved transient spen class="Chemical">ctra of compound <span class="Gene">Por−<span class="Chemical">Zn−N excited at 532 nm.

Hereafter, the reaction of <n class="Chemical">span class="Gene">Por−<spn>an class="Chemical">Zn−N was initially investigated by UV/Vis spectroscopic titration experiments by adding the click reagent TCNE in chlorinated solvents. As shown in Figure 3, Soret bands blue‐shifted to 400–450 nm and increased with the increasing amount of the TCNE, finally leading to completely reddish‐brown solutions. The presence of the isosbestic points at 410, 451, and 512 nm for Por−Zn−N indicated no side reactions during the TCNE click reaction. The position of the charge‐transfer (CT) bands (at 437 nm) was obviously blue‐shifted compared with the precursor Por−Zn−N (at 479 nm) during the experiments, suggesting that the electronic cloud density of porphyrin ring was decreased by the introducing of strong electron‐withdrawing groups (cyano group). Porphyrin derivative Por−Zn−N displayed a significantly advantages that the products featured strong CT interactions in the visible absorption‐region‐related properties. Furthermore, the controlled introduction of these click products into porphyrin was useful for optimization of the electronic states, thereby leading to the enhanced performance of various properties of optoelectronic materials. If the side‐chain chromophores did not interact with each other, the peak top values should be constant. This result suggested that this click‐type reaction could affect the electronic states of the whole conjugated compounds, and thus could be employed for tuning the energy levels of the conjugated materials.

Figure 3

UV/Vis spectral changes of Por−Zn−N upon titration with TCNE (0–1.0 equiv) in dichlorobenzene at 20 °C.

UV/Vis spen class="Chemical">ctral changes of Por−Zn−N upon titration with TCNE (0–1.0 equiv) in dichlorobenzene at 20 °C.

Nonlinear optical (NLO) properties

The NLO properties corresponding to Por−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ were measured by means of the Z‐scan technique, of which several recordings were acquired. All of the samples were measured at 10−6  m solution in THF (spectral pure, SP), and the solvent itself did not show any third‐order nonlinearities under the experimental conditions. The nonlinear absorption coefficient β and the nonlinear reflective index n 2 would be available under measurements, and the third‐order nonlinear susceptibility could be calculated (detailed calculation methods are listed in the Supporting Information).

Figure 4 shows the “open‐aperture” Z‐scan data and the normalized transmittance curves of all products, which could be fitted perfectly with respect to equations reported by references.19 In Figure 4 a,b, profound transmittance valleys can be seen around the focal plane, which was characteristic of reverse saturable absorption (RSA)‐type behavior of Por−Zn−N and Por−Zn−TCNE. Materials showing RSA became more opaque on exposure to high photon fluxes due to the high absorption from the excited state, and this property has been exploited in the field of optical limiting for laser protection. However, Figure 4 c shows a typical transmittance peak of compound Por−Zn−TCNQ, which exhibits saturable absorption (SA)‐type behavior. It could be observed that compared with Por−Zn−N and Por−TCNE, Por−Zn−TCNQ clearly exhibited reverse saturable absorption–saturable absorption (RSA‐SA) transition by click reaction with TCNQ. The reason for conversion from the RSA to SA phenomenon for Por−Zn−TCNQ is the threshold intensity26 determined by the parameters such as absorption cross section and level lifetime, and the saturation intensity declined dramatically. Once the incident light intensity crossed the threshold intensity, conversion from RSA to SA happened.

Figure 4

Open‐aperture Z‐scans measured in the THF solutions of a) Por−Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ.

Open‐aperture Z‐scans measured in the n class="Chemical">THFn> solutions of a) Por−Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ.

From a plethora of recordings, the Imχ (3) (the imagery pn class="Chemical">arn>ts of the third‐order nonlinearities) value of Por−Zn−N was found to be 1.0×10−11 esu, which corresponds to a nonlinear absorption coefficient of β=4.8×10−10 m W−1. The Imχ (3) values of Por−Zn−TCNE and Por−Zn−TCNQ were 1.7×10−14 esu and 3.6×10−14 esu, while the nonlinear absorption coefficients β were 7.9×10−13 m W−1 and −1.7×10−13, respectively. Comparing to other organic molecules measured by Z‐scan, the third‐order nonlinear values of our compounds were relatively good.27, 28

“Closed‐aperture” Z‐scan data of n class="Gene">Porn>−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ are shown in Figure 5. In this figure, the normalized transmittance curve of Por−Zn−N could be fitted well according to the equation reported by reference and the real part of third‐order nonlinearity, Reχ , was found to be −1.1×10−11 esu, which corresponds to a nonlinear refractive index n=−2.3×10−17 m2⋅w−1. However, click products Por−Zn−TCNE and Por−Zn−TCNQ didn′t show closed‐aperture curves, and a plausible explanation could be that the nonlinear absorption is much stronger than the refraction. The properties of these products that we developed made it relatively important for new molecule synthesis used in NLO applications.

Figure 5

Closed‐aperture Z‐scans measured in the THF solution of Por−Zn−N.

Closed‐aperture Z‐scans measured in the <span class="Chemical">THFn> solution of <span class="Gene">Por−<span class="Chemical">Zn−N.

Self‐assembly properties

To develop novel organic optoelectronic materials, the hier<n class="Chemical">span class="Chemical">archical self‐assembly of multivalent components through the concerted action of multiple noncovalent interactions turns out to be one of the most promising approaches, as it allows the simultaneous organization of discrete molecules, long‐range order, and inherently defect‐free structures. Taking this into account, the introduction of an activated cyano group as acceptor and <spn>an class="Chemical">metal ions into the discoid porphyrin core could enhance multiple noncovalent interactions. The solventexchanging method was used to form regular self‐assembly structures in the solution phase, and SEM images of selfassembled morphologies are shown in Figure 6. A discoiddistinct‐like morphology shown in the Figure 6 a was observed for compound Por−Zn−N because of the cooperation of the π–π interactions and the metal ions coupling between the layers (here mainly brickwork‐type H‐aggregates). The upper right corner of Figure 6 a is a schematic diagram of molecular permutations of the discoid‐distinct‐like structure at the micron scale. By introducing click reagents TCNE and TCNQ substituents into the discoid cores, the degree of self‐assembling order of the compounds was likely to worsen due to the increasing steric hindrance. Products Por−Zn−TCNE and Por−Zn−TCNQ did not exhibit regular discoid‐distinct‐like morphologies; rather, spherical morphologies as shown in Figure 6 b,c. As the diagram shows, between Figure 6 b and c, the morphologies could not be classified as pure J‐ or H‐aggregates, but their combination. In addition, due to the greater steric hindrance effect, the size of the self‐assembled spheres of Por−Zn−TCNQ was smaller than that of Por−Zn−TCNE. For most materials, J‐aggregates of organic dyes are of significant interest for the development of advanced photonic technologies for their abilities to delocalize and migrate excitonic energy over a large number of aggregated dye molecules.29

Figure 6

SEM images of self‐assembled morphologies of compound a) Por−Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ; the yellow arrows are pointing to the aggregation mode of different self‐assembling morphologies.

SEM images of self‐assembled morphologies of compound a) n class="Gene">Porn>−Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ; the yellow arrows are pointing to the aggregation mode of different self‐assembling morphologies.

Density functional theory (DFT) calculations

As shown in Figure 7, the DFT‐optimized model structure of compound <n class="Chemical">span class="Gene">Por−<spn>an class="Chemical">Zn−N is close to planar. Both BP86 and TPSS calculations yielded similar results. According to the TPSS/RI/TZVP calculated results, the bond length of Zn−N is about 2.053 Å, and the four bond angles of N−Zn−N are 90.19. 89.88, 90.16, and 89.78 °; the sum of four N−Zn−N angles is almost 360 ° (360.01 °). Compared with the experimental results,30 the bond length of Zn−N in compound ZnTPP is 2.045(2) Å, and the four bond angles are about 90.16, 80.84, 90.16, and 80.84 °. The DFT‐calculated results agreed well with the experimental data.

Figure 7

Optimized model structures obtained with DFT (TPSS/RI/TZVP) calculations for compounds a) Por−Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ. Zn atoms: yellow, N atoms: blue, O atoms: red, H atoms: white, C atoms: brown.

Optimized model structures obtained with DFT (TPSS/RI/TZVP) calculations for compounds a) <n class="Chemical">span class="Gene">Por−<spn>an class="Chemical">Zn−N, b) Por−Zn−TCNE, and c) Por−Zn−TCNQ. Zn atoms: yellow, N atoms: blue, O atoms: red, H atoms: white, C atoms: brown.

The DFT‐optimized model structures of compounds <n class="Chemical">span class="Gene">Por−<spn>an class="Chemical">Zn−TCNE and Por−Zn−TCNQ are both crooked (bent) due to the large substituted groups introduced through click reactions with TCNE or TCNQ. As a result of these bent structures, spherical morphologies of compound Por−Zn−TCNE and Por−Zn−TCNQ could be observed by SEM (Figure 6)

Conclusion

In this work, a series of n class="Chemical">Znn>‐complexed d‐π‐A porphyrin derivatives, Por−Zn−N, Por−Zn−TCNE, and Por−Zn−TCNQ were designed and synthesized through [2+2] click reactions based on the aniline groups as donor units and cyano groups as acceptor units. Investigations of the photophysical properties by using UV/Vis spectroscopy showed that the charge‐transfer character of the d‐π‐A structures plays a key role in the absorption peak shifts, and the click products showed various bathochromic shifts. Most importantly, upon the introduction of electron acceptors by click reactions, the third‐order nonlinear absorption of the products showed typical RSA‐SA transition, and both the products revealed relatively good third‐order nonlinear optical susceptibilities. In addition, the discoid‐distinct‐like and spherical morphologies were observed through a phase‐exchange method for packing porphyrin molecules, and the results agreed well with DFT calculations. The structure–property relationships of these porphyrin derivatives were built and could help in promising applications in organic electronics.

Experimental Section

General conditions

Reagents were purchased from commercial sources (Aldrich) and used without further purification. <span class="Chemical">Triethylamine (<span class="Chemical">TEA) and <span class="Chemical">THF were distilled and purged with Ar before use. TCNE and TCNQ were purchased from Aldrich, and all other reagents were purchased from commercial sources and used as received.

n class="Chemical">1Hn> NMR spectra of the samples were recorded with a Varian 400 MHz instrument (Palo Alto, CA, USA) in CDCl3 using the residual solvent resonance of CHCl3 at 7.26 ppm relative to SiMe4 as internal reference. FT‐IR spectra were recorded in KBr pellets using a PerkinElmer LR‐64912C spectrophotometer (Waltham, MA, USA). Matrix‐assisted laser desorption ionization time‐of‐flight mass spectra (MALDI‐TOF‐MS) were recorded on a Shimadzu AXIMA‐CFR mass spectrometer (Kyoto, Japan). All UV/Visible spectra were recorded on a HITACHI U‐3010 spectrophotometer (Tokyo, Japan). SEM images were obtained on a Jeol JSM‐5400/LV (Tokyo, Japan) with accelerating voltage of 15 kV.

Synthesis

Synthesis of n class="Gene">Porn>−C: To a degassed solution of dipyrromethane (146.0 mg, 1.00 mmol), 4‐dodecyloxy‐benzaldehyde (290.2 mg, 1.00 mmol) in CH2Cl2 (100 mL) was added trifluoroacetic acid (TFA, 0.60 mmol, 44 μL). The mixture was stirred in the dark for 3 h, and then 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ, 0.90 mmol, 200.0 mg) was added. Afterwards, the solution was stirred at rt for another 1 h, and the solvent was removed under decreased pressure. The product was isolated by column chromatography (silica gel) using CH2Cl2/hexane 1:1 as eluent. Recrystalization from CH2Cl2/MeOH gave a red solid, Por−C, (0.065 mmol, 13 %); 1H NMR (400 MHz, CDCl3): δ=10.33 (s, 2 H), 9.42 (d, 4 H, J=6.4 Hz), 9.15 (d, 4 H, J=6.4 Hz), 8.20 (d, 4 H, J=8.0 Hz), 7.36 (d, 4 H, J=6.4 Hz), 7.29 (s, 2 H,), 4.30 (t, 4 H), 2.05 (m, 8 H), 1.51 (m, 30 H), 0.92 ppm (t, 6 H); FT‐IR (KBr): ṽ=2920, 2859, 1448, 1474, 1242, 784 cm−1; MALDI‐TOF‐MS (dithranol) m/z: calcd for C56H70N4O2: 830.5, found: 830.7.

To a solution of n class="Gene">Porn>−C (1.00 mmol) in CH2Cl2 (50 mL) was added a solution of Zn(OAc)2 (283.0 mg, 1.29 mmol) in MeOH (10 mL). After the mixture was stirred at rt for 1 h, the solvent was removed under decreased pressure. The residue was extracted with CH2Cl2. The solvent was dried over anhydrous Na2SO4 and removed under decreased pressure. The product was recrystallized from CH2Cl2/MEOH to give a red solid Por−C (0.93 mmol, 93 %);1H NMR (400 MHz, CDCl3): δ=10.33 (s, 2 H), 9.42 (d, 4 H, J=6.4 Hz), 9.14 (d, 4 H, J=6.4 Hz), 8.20 (d, 4 H, J=8.0 Hz), 7.37 (d, 4 H, J=6.4 Hz), 4.31 (t, 4 H), 2.04 (m, 8 H), 1.68 (m, 8 H), 1.55 (m, 24 H), 0.93 ppm (t, 6 H); FT‐IR (KBr): ṽ=2920, 2859, 1449, 1474, 784 cm−1; MALDI‐TOF‐MS (dithranol) m/z: calcd for C56H68N4O2Zn: 892.5, found: 892.3.

Synthesis of brominated n class="Chemical">porphyrinn>. To a solution of Por−C (1.00 mmol) in CH2Cl2 (100 mL) was added a solution of N‐bromosuccinimide (NBS, 712.0 mg, 4.00 mmol) in CH2Cl2 (10 mL). After the mixture was stirred at rt for 1 h, the solvent was removed under decreased pressure. The brown solid product Br−Por−C was purified by column chromatography (silica gel) using CH2Cl2/hexane 1:1 as eluent (0.82 mmol, 82 %);1H NMR (400 MHz, CDCl3): δ=9.42 (d, 4 H, J=6.4 Hz), 9.12 (d, 4 H, J=6.4 Hz), 8.22 (d, 4 H, J=8.0 Hz), 7.47 (d, 4 H, J=6.4 Hz), 4.28 (t, 4 H), 2.06 (m, 8 H), 1.66 (m, 8 H), 1.45 (m, 24 H), 0.93 ppm (t, 6 H); FT‐IR (KBr): ṽ=2922, 2859, 1508, 1448, 1242 and 788 cm−1; MALDI‐TOF‐MS (dithranol) m/z: calcd for C56H66Br2N4O2: 1048.3, found: 1048.2.

Hagihn class="Chemical">arn>a–Sonogashira cross‐coupling procedure. Synthesis of the Por−Zn−N: Pd(PPh3)2Cl2 (17.0 mg, 0.0240 mmol), CuI (4.73 mg, 0.0240 mmol), and PPh3 (16.2 mg, 0.0600 mmol) were added to a degassed solution of triethylamine (6 mL) and THF (10 mL) under Ar. Meanwhile Br−Por−C (0.556 g, 0.600 mmol) was added. While stirring, the reaction mixture was heated to 60 °C, and (4‐ethynyl‐phenyl)‐dioctyl‐amine (1.64 g, 4.80 mmol) was injected to get Por−Zn−N. After 15 min of stirring at this temperature, the reaction was heated to 80 °C and stirred o/n under Ar atmosphere. The cooled reaction mixture was diluted with CH2Cl2 and extracted with water. The organic phase was dried over MgSO4, and the solvent was removed under decreased pressure. The crude product was purified by column chromatography (silica gel, petroleum ether) to afford the purple powder Por−Zn−N (0.871 g, 83 %); 1H NMR (400 MHz, CDCl3): δ=9.00 (m, 8 H), 8.11 (m, 8 H), 7.29 (d, 4 H, J=6.4 Hz), 7.22 (d, 4 H, J=6.4 Hz), 4.28 (t, 4 H), 3.36 (t, 8 H), 2.01 (m, 16 H), 1.65 (m, 16 H), 1.52 (m, 32 H), 1.40 (m, 36 H) 1.34 (m, 32 H), 0.94 ppm (m, 6 H); FT‐IR (KBr): ṽ=2934, 2182, 1668, 1522, 1245, 822 cm−1; MALDI‐TOF‐MS (dithranol) m/z calcd for C120H174N6O2Zn 1795.3, found 1795.7.

Synthesis of n class="Gene">Porn>−Zn−TCNE. Compound Por−Zn−N (0.36 g, 0.20 mmol, 1 equiv) and TCNE (51.2 mg, 0.40 mmol, 2 equiv) were mixed in CH2Cl2 (10 mL). After stirring for 10 min, the solvent was removed under decreased pressure, and the crude product was purified by column chromatography (silica gel, ethyl acetate/petroleum ether 1:4) to give the final click‐type reaction product Por−Zn−TCNE as a dark green solid (0.36 g, 89 %); 1H NMR (400 MHz, CDCl3): δ=7.52 (12 H, d, J=8.0 Hz), 7.27 (2 H, d, J=8.0 Hz), 7.20 (4 H, d, J=8.0 Hz), 6.94 (4 H, d, J=8.0 Hz), 6.71 (4 H, d, J=8.0 Hz), 6.68 (2 H, d, J=8.0 Hz), 6.77 (2 H, d, J=8.0 Hz), 6.44 (2 H, d, J=8.0 Hz), 5.39 (2 H, d, J=8.0 Hz), 4.06 (4 H, m), 3.78 (8 H, m), 1.76–1.26 (120 H, m), 0.88 ppm (18 H, m); FT‐IR (KBr): ṽ=2923, 2863, 2220, 1738, 1596, 1285, 1184 cm−1; MALDI‐TOF‐MS (dithranol) m/z: calcd for C132H174N14O2Zn: 2051.3, found: 2049.6.

Synthesis of n class="Gene">Porn>−Zn−TCNQ. Compound Por−Zn−N (0.36 g, 0.20 mmol, 1 equiv) and TCNQ (0.08 g, 0.40 mmol, 2 equiv) were dissolved in dichlorobenzene (10 mL). Under stirring, the reactor was heated to 140 °C and maintained for 1 h. The solvent of the cooled reaction mixture was removed under decreased pressure, and the crude product was purified by column chromatography (silica gel, ethyl acetate/petroleum ether=1/4) to give the pure Por−Zn−TCNQ as a black solid (0.38 g, 87 %); 1H NMR (400 MHz, CDCl3): δ=7.52 (12 H, d, J=8.0 Hz), 7.27 (2 H, d, J=8.0 Hz), 7.20 (4 H, d, J=8.0 Hz), 6.94 (4 H, d, J=8.0 Hz), 6.71 (4 H, d, J=8.0 Hz), 6.68 (2 H, d, J=8.0 Hz), 6.77 (2 H, d, J=8.0 Hz), 6.44 (2 H, d, J=8.0 Hz), 5.84 (8 H, d, J=8.0 Hz)5.39 (2 H, d, J=8.0 Hz), 4.06 (4 H, m), 3.78 (8 H, m), 1.76–1.26 (120 H, m), 0.88 ppm (18 H, m); FT‐IR (KBr): ṽ=2922, 2864, 2219, 1739, 1594, 1285, 1184, 980 cm−1; MALDI‐TOF‐MS (dithranol) m/z: calcd for C144H182N14O2Zn: 2203.4, found: 2202.8.

Computational Methods

The all‐electron Kohn–Sham DFT calculations were performed with the quantum‐chemical program package TURBOMOLE.31 The functional BP8632, 33 and TPSS34 in combination with the resolution‐of‐the‐identity (“RI”) density fitting technique35, 36 and the TZVP basis sets37 were applied in all the DFT calculations. All geometry optimizations were performed in C1 symmetry. The molecul<span class="Chemical">ar structures were visualized with the program Molden.38

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