Photochromic Rhenium-Based Molecular Rectangles: Syntheses, Structures, Photophysical Properties, and Electrochemistry

Structures, Photophysical Properties, and Electrochemistry

Article

Photochromic Rhenium-Based Molecular Rectangles: Syntheses,

Guo-Xia Jin, Teng Wang, Yanyan Sun, Yu-Long Li, and Jian-Ping Ma*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c01845

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sı Supporting Information

ABSTRACT: Two novel fac-Re(CO) -based rectangles {[(CO) Re-

(

μ-Cl) Re(CO) ] (μ-L) } (1) and {[(CO) Re(μ-OC H ) Re-

2 3 2 2 3 4 9 2

CO) ] (μ-L) }(2) based on new photochromic dithienylethene-

containing ligand 2,7-di(pyridin-4-yl)-9,10-bis(5-chloro-2-methyl-

thien-3-yl)-phenanthrene (L) were prepared. They displayed varying

photochromic properties both in solution and in the single-crystal

state. Through a judicious choice of the bridging ligands along the

short sides of the rectangles, the photophysical and electrochemical

properties of the complexes could also be readily tuned.

INTRODUCTION

Over the last two decades, much attention has been paid to fac-

on new photochromic dithienylethene-containing 4,4′-bipyr-

idyl ligand 2,7-di(pyridin-4-yl)-9,10-bis(5-chloro-2-methyl-

thien-3-yl)-phenanthrene. The photochromism of the new

molecules is preliminarily investigated by electronic absorption

and emission spectroscopy and cyclic voltammetry.

■

Re(CO) -based supramolecules that are assembled from 4,4′-

bipyridyl ligands and display discrete two- and three-dimen-

sional structures owing to their application prospects in the

ﬁelds of host−guest chemistry, photocatalysis, bioactivity, and

−7

functional molecular devices.

This continuing interest is

RESULTS AND DISCUSSION

■

evidenced by numerous fac-Re(CO) -based supramolecular

Synthesis of Ligand L. The synthesis route to the new

photochromic ligand is shown in Scheme 2. The character-

ization of L and its intermediates S3 and S4 was accomplished

assemblies such as triangles, rectangles, squares, prisms, and so

on. For example, Hupp, Lu, and other groups have prepared a

series of rectangular tetrarhenium molecules. Some of the

Re(I) rectangles feature alternating pyrazine and 4,4′-bpy

via the H NMR spectrum, IR spectrum, and elemental

analysis. The H NMR spectrum of L shows two signals for the

10,11

edges. Some of the Re(I) rectangles have thiolates,

methyl groups (δ, 2.09 and 2.04 ppm) and the protons located

on the thiophene rings (δ, 6.60 and 6.56 ppm) as well as two

signals for the protons located on the phenanthrene ring (δ,

13−16

alkoxides, or 2,2′-bisbenzimidazolate

and chloranilic

acid hydroxyl group along the short edges as the bridging

ligands and rigid or semirigid 4,4′-bpy linkers along the other

.90 and 7.86 ppm) (Figure S1 ). Irradiation with 313 nm UV

9,20

two edges. Lees

and Lin reported a number of

light led to the appearance of a third signal (δ, 2.69 and 2.70

ppm for the methyl group and 7.05 ppm for the thiophene

ring) belonging to the closed form (Scheme 2). According to

the signal integrals before and after irridiation, the peaks at

luminescent square molecules [ClRe(CO) (μ-4,4′-bpy)] .

Some of these Re-based assemblies have been demonstrated

13,17,20

to exhibit sensing properties for volatile molecules.

However, to the best of our knowledge, there have been no

examples of rhenium metallocycles incorporating a photo-

switching ligand reported to date. Tunable Re-based metallo-

cycles that incorporate a switching ligand are potentially useful

in optoelectronics as well as in chemical reactivity. It is well

known that switching molecules would be able to modulate the

chemophysical properties of molecular devices because they

can interconvert between two thermally stable forms when

.09, 6.56, and 7.86 ppm should be assigned to the parallel

isomer and the peaks at 2.04, 6.60, and 7.90 ppm should be

attributed to the antiparallel isomer. This observation is similar

to that of previously reported 9,10-bis-[5-phenyl-2-methyl-

thien-3-yl]-phenanthrene in Walko’s paper. The solution

simultaneously changed from colorless to red-purple. After

irradiation for 20 min, the closed form of L accounted for

irradiated with UV and visible light. In this regard,

photoresponsive 1,2-dithienylethene (DTE) derivatives are

particularly attractive due to the dramatic steric and electronic

diﬀerences between the photosensitive isomers and display

promising application prospects in optical memory and

Received: June 23, 2020

3−30

switches.

Here, we report the design and syntheses of

two photoresponsive rectangular tetrarhenium molecules based

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

acetate were analyzed by X-ray diﬀraction (Figure 1 ). There

Article

Scheme 1. Synthesis Route to New Photochromic Ligand L

Reagents and conditions: (i) K CrO , H SO , AcOH, H O. (ii) (1) SOCl ; (2) AlCl , CH Cl , 2-chloro-5-methylthiophene. (iii) TiCl , Zn, THF,

reﬂux. (iv) 4-Pyridyl boronic acid, Pd(PPh ) , K CO (aq), reﬂux.

Scheme 2. Photochromic Reaction of Ligand L

polymeric MOFs. The Suzuki coupling reaction of the 2,7-

positions of the phenanthrene unit aﬀords eﬃcient synthesis

strategies for the design of photochromic ligands because this

would lead to many other rigid ditopic linkers with carboxylate

and amino binding groups suitable for photoresponsive MOFs.

Self-Assembly and Characterizations of Molecular

Rectangles. Chloride-bridged molecular rectangle

{

[(CO) Re(μ-Cl) Re(CO) ] (μ-L) } (1) was obtained un-

3 2 3 2 2

about 12% of the total. The low photocyclization conversion

might be related to the absence of donor substituents or a

expectedly by reacting Re

acid (H CA) in a toluene−acetone mixture in the dark and

separated as yellow-brown crystals (Scheme 3). When

Re (CO)10 was treated with L in 1-butanol in the dark,

butoxy-bridged rectangle {[(CO) Re(μ-OC H ) Re-

(CO)10, ligand L, and chloroanilic

conjugated system on the thiophene rings, Additionally,

single crystals of L, grown by slow evaporation from ethyl

9 2

(

CO) ] (μ-L) }(2) was obtained as yellow crystals. These

3 2 2

two compounds are air- and moisture-stable. Complex 1 is

soluble in very polar solvents such as N,N′-dimethylformamide

(

DMF) and dimethyl sulfoxide (DMSO) but not soluble in

dichloromethane, chloroform, acetone, and tetrahydrofuran.

Complex 2 is soluble in dichloromethane and DMF and

sparingly soluble in DMSO.

Single crystals of 1 and 2 were studied by an X-ray

diﬀraction technique. The ORTEP diagrams of 1 and 2

(

Figures 2 and 3) revealed a similar rectangular structural

motif, where two planar ligands were coordinated to four

rhenium atoms that were bridged by four chloride atoms or by

four butoxyl groups. Four Re atoms are located at the four

corners of a rectangle. Each metal center is coordinated to one

N_p_y_r_i_d_y_latom of ligand L, two chloride/oxygen atoms, and three

C atoms of CO groups. Two face-to-face pyridine rings are

almost parallel, and the dihedral angles between them are

Figure 1. ORTEP representation of L with 30% thermal ellipsoids.

.205° (for 1) and 4.537° (for 2), respectively. Two

are two molecules in the unit cell, and the distance between

two pyridyl N atoms is ca. 15.6 Å. In the crystal structure, L

adopts an antiparallel (racemic) conﬁguration, as Fraysse and

co-workers observed for the related perﬂuoro-1,2-bis(2-iodo-5-

methylthien-4-yl)cyclopentene. This conformation is adap-

ted for the cyclization reaction that can occur with relatively

small movements. Irradiating the single crystals of L with 313

nm UV light resulted in an apparent color change from

colorless to red-purple, which indicated that photocyclization

also occurred in the single-crystal state. Thus, a rigid ditopic

linker suitable for the fabrication of light-responsive MOFs was

obtained by incorporating 4-pyridyl groups on the phenan-

threne units. As we know, the 4,4′-bipyridyl linker is one of the

most versatile building units for constructing discrete and

phenanthrene planes are antiparallel, and the dihedral angles

between them are nearly 0° (for 1) and 2.948° (for 2),

respectively. The centroid−centroid distances between two

pyridine units are ∼3.75 Å (for 1) and ∼3.55 Å (for 2), and

the distances between two pairs of parallel benzene rings on

the phenanthrene units are ∼3.67 Å (for 1) and 3.63 Å (for 2),

suggesting strong π···π stacking interactions between two

ligands. Further comparison of the two structures showed that

the sizes of rectangles 1 (ca. 20.126 × 3.794 Å ) and 2 (ca.

20.172 × 3.379 Å ) measured from the rhenium centers are

also diﬀerent, where the short sides of 2 decreased by 0.41 Å

compared to those of 1 due to the smaller oxygen bridges.

Both structures give rise to strong crystallographic disorder of

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Scheme 3. Synthesis Routes to New Molecular Rectangles 1 and 2

Figure 2. ORTEP plot of rectangle 1 with hydrogens excluded for clarity. Thermal ellipsoids are drawn to 50% probability.

the 5-chloro-2-methylthiophene groups probably due to the

coexistence of two parallel and antiparallel isomers.

solution. The doublets at 9.28 and 8.28 ppm and the singlet at

7.89 could be assigned to the protons on the phenanthrene

units. The two singlet peaks at 6.99 and 6.82 ppm could be

attributed to the protons on thiophene rings, and the peaks at

2.09 and 2.03 ppm could be assigned to methyl groups on

thiophene rings, indicating that there exist parallel (photo-

chemically inactive) and antiparallel (photochemically active)

isomers of ligand in rectangle 1. This spectrum showed a

highly symmetrical species, consistent with the rectangular

crystal structure. By comparison, it is found that the protons on

phenanthrene units in 1 all shifted downﬁeld relative to those

in ligand L. We concluded that the framework remained intact

throughout the solvation process. The photochromic reaction

There exist three characteristic bands of fac-Re(CO) at

043, 2026, and 1907 cm⁻in the IR spectrum of 1, while the

−

IR spectrum of 2 showed bands at 2020, 2006, and 1889 cm ,

shifted ca. 20 cm in the carbonyl stretching frequencies

−

(Figures S3 and S4 ). On the basis of the above studies, it

showed that the subtle geometric and electronic structures of

the two rectangles varied by changing the bridging groups

along the shorter sides, which would be expected to have an

eﬀect on their photophysical and electrochemical properties.

To verify that no signiﬁcant framework decomposition

occurred during solvation, a sample of crystal 1 was dissolved

in DMSO-d , analyzed by H NMR spectroscopy, and

of the rectangle was also monitored by H NMR spectra

compared with the proton spectrum of ligand L (Figure S5).

As the spectrum of the open form of 1 shows, there are two

sets of doublet peaks at 8.87 and 7.95 ppm that could be

assigned to H_αand H_βon pyridyl rings. The downﬁeld

chemical shifts (0.19 and 0.28 ppm) of protons on pyridyl

rings should indicate that the coordination is retained in

(Figures 4 and S6). When irradiated with 365 nm light, the

nearly colorless solution turned red-purple, the spectrum

showed that the signals at 6.82 and 2.09 ppm decreased to

almost zero, and the new signals at 7.44 and 2.61 ppm

belonging to the closed forms of the complex appeared. This

observation indicated that the ditopic 4,4′-pyridyl ligand

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Figure 3. ORTEP plot of rectangle 2 with hydrogens excluded for clarity. Thermal ellipsoids are drawn to 30% probability.

Article

Figure 4. H NMR (400 MHz) of 1 in DMSO-d before and after irradiation at 365 nm (left) and the color changes in the solution and crystal.

The signals corresponding to the antiparallel (●) and parallel (⧫) conformations of the open form and the closed form (★) are labeled.

maintained photochromic activity when incorporated into a

tetrarhenium rectangle. The relative integration of the new

signals showed that a photostationary state was reached after

irradiation for 50 min, and the concentration of the closed

form of 1 reached ca. 35% of the total.

state was suppressing the ring-opening reaction, as observed in

other dithienylethene- or azobenzene-derivatized MOFs.

34,35

Electronic Absorption and Emission Spectroscopy.

UV−vis absorption maxima and corresponding molar

absorption coeﬃcients of L, 1, and 2 are listed in Table 1.

The photochromic behavior of L was studied by irradiation

with UV light at selected wavelengths and monitored by UV−

vis spectroscopy. The absorption maxima of the open form

appeared at wavelengths of 221 and 288 nm corresponding to

In the single-crystal state, the Re(I) rectangles also

underwent photocyclization, which was veriﬁed by the fact

that irradiating single crystals of 1 and 2 with 365 nm light

resulted in apparent changes in the crystal color (for 1, yellow-

brown to red-purple; for 2, yellow to red-brown) (Figures 4

and S7). However, X-ray diﬀraction experiments based on the

fully irradiated crystals showed only the presence of the open-

form structure of the complex, which was likely due to the low

conversion to the closed form. Although the photochromism of

Re(I) complexes 1 and 2 was fully reversible in solution (the

red solutions of the closed photoproduct returned to the initial

yellow state upon irradiation with >500 nm visible light), their

crystals did not completely go back to their initial state when

irradiated with visible light. After more than 2 h of irradiation

with visible light, the red coloration did not change much,

probably because the local chemical environment in the solid

Table 1. Major Absorptions in the UV−Vis Spectra of L, 1,

and 2 before and after Irradiation

compound

open form

221 (39.7);

288 (76.6)

photostationary state

258 (38.2); 303 (70.4); 338 (52.0);

544 (3.4); 584 (2.9)

293 (73.3);

327(82.9); 549 (4.2); 588 (3.7)

38(62.6)

295(94.4);

33(64.2)

310(84.0);; 545(2.7); 560(2.0)

The values correspond to λ

(nm), and values in parentheses

max

−1

correspond to ε (× 10 cm M ) measured in methanol or DMF.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 5. (a) UV−vis absorption and (b) emission spectral changes of L (1.30 × 10 M in MeOH) (λ_e_x^m^a^x= 341 nm at 298 K) upon irradiation at

−5

13 nm.

Figure 6. (a, c) UV−vis absorption and (b, d) emission spectral changes of 1 (1.30 × 10⁻⁵M) and 2 (1.20 × 10⁻⁵M) in DMF using excitation

wavelengths of 345 and 366 nm, respectively, at 298 K upon irradiation at 365 nm.

n−π* and π−π* transitions of the 2,7-di(4-pyridyl)-phenan-

threne moiety and the thiophene moiety. Upon irradiation at a

wavelength (313 nm) near their absorption maxima, the

colorless solution of L turned to red-purple and the UV−vis

spectrum showed one new additional absorption band at ca.

solution was irradiated with light of λ > 500 nm. Thus, the

reversible interconversion between the open form and closed

form modulates the intensity of the emitted light at this

particular wavelength.

The UV−vis absorption spectra of 1 and 2 in DMF showed

two absorption bands at ca. 293, 338 nm and 295, 333 nm,

respectively, which were largely red shifted in comparison to

the free-ligand bands, which are assigned to a ligand-centered

π−π* transition in the high-energy region and a metal-to-

ligand charge transfer (MLCT) [dπ(Re)-π*(L)] transition in

50−630 nm in the visible region. This new absorption band

might be assigned as an absorption of the ring-closing isomer,

as observed for 9,10-bis-[5-phenyl-2-methylthien-3-yl]-phe-

nanthrene in Walko’s paper. (Table 1 and Figure 5). The

photostationary state was reached after exposure to UV light

for ca. 10 min. Irradiation with visible light (>500 nm) resulted

in a photochemical ring-opening process and the restoration of

the original spectrum of L, showing the good reversibility of

the ligand (Figure S8 ).

,20,36

the low-energy region,

respectively. Upon irradiation, the

light yellow-brown solution of complex 1 changed to red-

purple and the yellow solution of complex 2 changed to red.

The photostationary states of the solution of complexes of 1

and 2 were reached after exposure to 365 nm for about 3 min

(for 1) and 30 s (for 2), showing a faster photocyclization

conversion compared to that of the free ligand. The UV−vis

absorption spectra showed that two sets of new absorption

bands were generated at ca. 327, 549, and 588 nm and 310,

In the ring-open isomer of L, ﬂuorescence intensity was

max

observed at 402 and 417 nm when excited at λ_e_x= 341 nm

(Figure 5b). After a solution of L was irradiated at 313 nm, the

ﬂuorescence intensity at 402 nm decreased to almost zero. The

original emission spectrum was regenerated when the colored

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

45, 560 nm, respectively, after irradiation. These new

Article

absorption bands were assigned as metal-perturbed IL

transitions of the ring-closing isomers of the rectangles,

which were mixed with MLCT transitions in the low-energy

region, as observed for Zn O(TPDC) [TPDC = 9,10-bis(2,5-

dimethylthiophen-3-yl)-phenanthrene-2,7-dicarboxylate] in

Patel’s paper and some other coordination compounds with

photochromic ligands. The extent of π-conjugation in the

closed forms of rectangles 1 and 2 would be expanded upon

photocyclization. Figure 6a,c shows the UV−vis absorption

spectral changes of complexes 1 and 2 in solution. Irradiation

with visible light (>500 nm) resulted in a photochemical ring-

opening process, and the original spectra of 1 and 2 were

restored, showing the good reversibility of the complexes

Figure S9 ).

Excitation into either the intraligand (IL) or MLCT band of

the open form of complexes 1 (λ_e_x^m^a^x= 345 nm) and 2 (λ_e_x^m^a^x

366 nm) in DMF resulted in broad emissions with maxima at

50 and 592 nm, respectively. Upon irradiation with 365 nm

light in the open forms of complexes 1 and 2, the emission

intensities at ca. 550 and 592 nm were found to decrease and

the emission maxima were blue-shifted. Emission spectral

changes of 1 and 2 are shown in Figure 7b,d. According to the

spectroscopic studies on previously reported fac-Re(CO) -

pyridyl complexes, the emission of 1 and 2 could be assigned

as MLCT [dπ(Re)−π*(L)] phosphorescence.

Electrochemical Studies. The cyclic voltammetry (CV)

scan of L displayed three quasireversible reduction couples

Figure 7a). The ﬁrst two reduction couples at −1.73 and

1.94 V (vs SCE) overlap to some extent and could be

compound. The reduction couples at −2.57 V (vs SCE) are

ascribed to pyridine-based reduction. The ﬁrst two reductions

are one-electron events. On conversion to the closed form, two

new irreversible reduction waves, which also partially overlap,

were observed at less negative potentials (−1.18 and −1.34 V

vs SCE). This observation conﬁrms the thiophene-based

reduction because conversion of the thiophene rings in the

open form to the condensed thiophene units has more π-

conjugation and hence a better π-accepting ability, which

would be expected to lead to less negative potentials.

The CV curve of 1 is shown in Figure 7b. There are two

overlapping reduction couples near −1.41 V and one

irreversible oxidation wave at +1.57 V. When the negative

potential limit is set to −3.0 V, the CV curve shows another

reduction couple at −2.49 V and another irreversible oxidation

wave at +1.22. By comparison with the CV curve of the ligand,

the oxidation at +1.22 V may be ascribed to the ligand-

centered oxidation while the irreversible oxidation waves at

Figure 7. Cyclic voltammograms of (a) L, (b) 1, and (c) 2 before

(black solid and dashed lines) and after (blue lines) irradiation with

313 or 365 nm UV light in DMF (0.1 M Bu

mV s .

NPF

). Scan rate: 100

−

that in 1 the thiophene-based reduction potentials are 0.32 V

less negative than those observed for free ligands. This

observation indicates that the coordination of the ligand to the

Re Cl cluster stabilizes the π* level in the ligand and lowers

1.57 V can be assigned as the oxidation of Re to Re ,

according to the electrochemical studies of other Re(CO) -

based complexes. The ﬁrst overlapping reversible reduction

couple at −1.41 V is assigned as two closely spaced one-

electron thiophene-based reductions, which are less negative

compared to that of the free ligand. The second reduction

couple at −2.49 V is ascribed to pyridine-based reduction,

which is more negative compared to that of the ligand. On

conversion to the closed form, one new irreversible reduction

wave at a less negative potential (−1.05 vs SCE) was observed.

This observation conﬁrms the thiophene-based reduction.

There were no observable changes for the irreversible

oxidation wave for the Re(I) center. The CV studies show

the energy of the π* orbital. The greater overlap of the

thiophene-based reductions in 1 compared to that in the free

ligand implied a smaller electronic energy gap on coordination

to the Re Cl cluster center.

Rectangle 2 in DMF showed two distinct sets of reversible

reduction couples, one quasireversible reduction wave, and two

oxidation waves (Figure 7c). The ﬁrst two reversible reduction

couples at −1.36 and −1.84 V, two one-electron events, can be

assigned to thiophene-based reduction, and the third

quasireversible reduction wave at −2.64 V can be assigned to

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

The Supporting Information is available free of charge at

Article

pyridine-based reduction. The irreversible oxidation waves at

(50%); light-yellow solid. H NMR (600 MHz, CDCl

, 25 °C, TMS,

ppm): 8.57 (d, J = 9 Hz, 2H, Ar−H), 7.78 (d, J = 9 Hz, 2H, Ar−H),

1.50 V may be attributed to the oxidation of the metal

.74 (s, 2H, Ar−H), 6.52 (s, 2H, thiophene−H), 1.99 (s, 6H, CH ).

centers. Similarly, one new irreversible reduction at a less

negative potential (−1.01 vs SCE) was also observed for 2

upon photocyclization.

−

IR (KBr pellet, cm ): 2923 (s), 2853 (m), 1654 (w), 1592 (m), 1456

(

s), 993 (m), 790 (m). Anal. Calcd for C H Br Cl S : C, 48.27; H,

.36. Found: C, 48.22; H, 2.64.

,7-Di(pyridin-4-yl)-9,10-bis(5-chloro-2-methylthien-3-yl)-phe-

nanthrene (L). S4 (0.90 g, 1.5 mmol), pyridine-4-boronic acid (0.46

g, 3.75 mmol), K CO (1.24 g, 9 mmol), and Pd(PPh ) (104 mg,

.09 mmol) were added to a degassed mixture of water/EtOH/

toluene (v/v/v = 15/15/10 mL). Then the mixture was reﬂuxed for

24 h under a nitrogen atmosphere. The solvent was removed under

vacuum, and the residue was puriﬁed by column chromatography

24 14 2 2 2

The CV studies show that in both 1 and 2 the thiophene-

based reduction potentials are much less negative than those

observed for the free ligand. The coordination of the ligand to

the metal usually stabilizes the π* level in the ligand and lowers

the energy of the π* orbital. The greater overlap of the

thiophene-based reductions in 1 compared to that in free

ligand implies a smaller electronic energy gap on coordination

to the Re Cl cluster center, and the greater separation in 2

3 4

(silica gel, ethyl acetate) to yield 0.60 g of a white powder (yield

7%). H NMR (600 MHz, CDCl , 25 °C, TMS, ppm): 8.91 (d, J =

shows a larger electronic energy gap upon coordination to the

Re (OBu) cluster center.

.4 Hz, 2H, Ar−H), 8.70 (d, J = 4.8 Hz, 4H, Py−H ), 8.00 (d, J = 8.4

Hz, 2H, Ar−H), 7.90, 7.86 (ss, 2H, Ar−H), 7.56 (m, 4H, Py−H ),

.60, 6.56 (ss, 2H, thiophene−H), 2.09, 2.04 (ss, 6H, CH ). IR (KBr

CONCLUSIONS

−1

■

pellet, cm ): 2925 (w), 1594 (s), 1477 (m), 1384 (w), 807 (s). Anal.

Two photoresponsive rectangular molecules with Re Cl and

Calcd for C34

9.02; H, 3.64; N, 5.10.

Complex [Re (CO) (C H Cl N S )(μ -Cl) ] (1). Re (CO) (13

H22Cl N S : C, 68.80; H, 3.74; N, 4.72. Found: C,

2 2 2

Re OBu clusters based on a new photochromic ligand were

prepared in this article, and the electrochemical properties of

the new compounds were studied. The complexes underwent

reversible photochromic reactions in solution and intercon-

verted by irradiation with UV and visible light. The CV studies

showed that in 1 and 2 the coordination of the ligand to metal

centers resulted in the thiophene-based reduction potentials

being less negative than those observed for free ligand, and the

photophysical and electrochemical properties were modulated

accordingly by irradiation with UV or visible light.

34 22

mg, 0.02 mmol), L (6 mg, 0.01 mmol), chloranilic acid (2 mg, 0.01

mmol), and toluene/acetone (8:1, 7 mL) were sealed in a Teﬂon ﬂask

20 mL) in a steel bomb. The bomb was heated to 140 °C and kept at

this temperature for 70 h and then cooled to 25 °C. Yellow-brown

crystals of 1 were isolated by ﬁltration, washed with acetone, and then

air-dried in a dark environment. Yield 12 mg (50%). H NMR (600

(

MHz, DMSO-d , 25 °C, TMS, ppm): 9.27 (d, J = 9 Hz, 4H, Ar−H),

.87 (d, J = 6 Hz, 8H, Py−H ), 8.27 (d, J = 6.6 Hz, 4H, Ar−H), 7.93

(m, 8H, Py−H ), 7.86 (s, 4H, Ar−H), 6.98, 6.81 (ss, 4H, thiophene−

−

H), 2.08, 2.02 (dd, J = 3 Hz, 12H, CH ). IR (KBr pellet, cm ): 2043

(

vs), 2026 (vs), 1907 (vs), 1614 (s), 1477 (w), 1384 (w), 802 (m).

EXPERIMENTAL SECTION

General. H NMR spectra were obtained using a Bruker Avance

00 (400 MHz) or Agilent 600 (600 MHz) spectrometer. Chemical

■

Anal. Calcd for C H Cl N O Re S : C, 39.87; H, 1.84; N, 2.32.

Found: C, 39.62; H, 2.01; N, 2.46.

Complex [Re (CO) (C H Cl N S )(μ -OBu ) ]( BuOH) (2).

Re (CO)10 (13 mg, 0.02 mmol), L (6 mg, 0.01 mmol), and 1-

butanol (8 mL) were used in the preparation of 2, following the above

procedure for the preparation of 1. Yield 18 mg (70%), yellow

crystals. H NMR (600 MHz, CD Cl , 25 °C, TMS, ppm): 8.43 (brs,

8H, Py−H ), 7.75−7.52 (m, 8H, Ar−H), 7.23 (brs, 8H, Py−H ),

40 22

2 2

34 22

shifts are reported relative to residual solvent signals: CDCl : H δ

.27; DMSO-d₆: ¹H δ 2.47; CD Cl : H δ 5.33. The apparent

2 2

multiplicity is reported as “s” = singlet, “d” = doublet, “dd” = two

doublets, “m” = multiplet, “brs” = broad singlet, or “ss” = two singlets.

Element analyses were performed on a PerkinElmer model 240C

−

analyzer. Infrared (IR) spectra were obtained in the 400−4000 cm

.22−7.07 (m, 4H, Ar−H), 6.73−6.61 (m, 4H, thiophene−H), 4.43

range using a Bio-Rad FTS-40 infrared spectrometer. Photo-

luminescence spectra were measured on a FLS920 ﬂuorescence

spectrophotometer. Emission spectra were collected at 1 nm

resolution with an excitation and emission slit width of 3 nm. UV−

visible absorbance was measured using a Shimadzu UV mini-1240

spectrophotometer. Cyclic voltammetry and diﬀerential pulse

voltammetry measurements were performed using a CHI660D (CH

Instruments) electrochemical workstation. Electrolyte solutions (0.1

(

brs, 8H, OCH CH CH CH ), 2.28−1.93 (m, 12H, CH ), 2.08 (brs,

H, OCH CH CH CH ), 1.51 (brs, 8H, OCH CH CH CH ), 1.14

2 2 2 3 2 2 2 3

−

(brs, 8H, OCH CH CH CH ). IR (KBr pellet, cm ): 2020 (vs),

2 2 2 3

006 (vs), 1889 (vs), 1613 (s), 1384 (w), 806 (m). Anal. Calcd for

C H N O S Re Cl : C, 46.11; H, 3.72; N, 2.07. Found: C, 45.75; H,

3.45; N, 2.10.

52 50

M Bu NPF ) were prepared with dry DMF and degassed with N

ASSOCIATED CONTENT

■

before use. A platinum-wire counter electrode, a saturated calomel

electrode (SCE) as the reference electrode, and a glassy carbon (GC)

working electrode were used. All chemicals were of reagent-grade

purity or better and used as received. 2,7-Dibromophenanthraquinone

sı Supporting Information

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01845.

(

S1), 4,4′-dibromobiphenyl-2,2′-dicarboxylic acid (S2), 4,4′-

dibromo-2,2′-bis(5-chloro-2-methylthiophene-3-carbonyl)-biphenyl

1_H_N_M_R_s_p_e_c_t_r_a_o_f_l_i_g_a_n_d_L_a_n_d_c_o_m_p_l_e_x₂_;_I_R_s_p_e_c_t_r_a

of L and complexes 1 and 2; photographs of the color

change of 2; switching cycles; and a diﬀerential pulse

voltammogram (PDF)

(

S3), and 2,7-dibromo-9,10-bis(5-chloro-2-methylthien-3-yl)-phe-

nanthrene (S4) were prepared according to literature methods.

,4′-Dibromo-2,2′-bis(5-chloro-2-methylthiophene-3-carbonyl)-

biphenyl (S3). R = 0.40 (petroleum ether/CH Cl 2:1); yield 3.2 g

(

51%); light-yellow solid. H NMR (400 MHz, CDCl , 25 °C, TMS,

ppm): 7.67 (dd, J = 2 Hz, J = 8 Hz, 2H, Ar−H), 7.49 (d, J = 2 Hz,

Accession Codes

H, Ar−H), 7.26 (dd, J = 2 Hz, J = 8 Hz, 2H, Ar−H), 6.70 (s, 2H,

CCDC 2011070−2011072 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by

emailing data_request@ccdc.cam.ac.uk, or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

−

thiophene−H), 2.51 (s, 6H, CH ). IR (KBr pellet, cm ): 3081 (w),

(

919 (w), 1654 (vs), 1583 (w), 1514 (s), 1454 (s), 1349 (s), 1263

m), 1230 (vs), 1181 (s), 995 (s), 820 (s). Anal. Calcd for

C H Br Cl O S : C, 45.81; H, 2.24. Found: C, 45.57; H, 2.70.

2 2

,7-Dibromo-9,10-bis(5-chloro-2-methylthien-3-yl)-phenan-

threne (S4). R = 0.50 (petroleum ether/CH Cl 2:1); yield 1.5 g

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Normal University, Jinan 250014, P. R. China; orcid.org/

Article

(

8) Rajendran, T.; Manimaran, B.; Lee, F.-Y.; Lee, G.-H.; Peng, S.-

AUTHOR INFORMATION

■

M.; Wang, C. M.; Lu, K.-L. First Light-Emitting Neutral Molecular

Rectangles. Inorg. Chem. 2000, 39, 2016−2017.

(

Corresponding Author

Jian-Ping Ma − College of Chemistry, Chemical Engineering and

Materials Science, Collaborative Innovation Center of

Functionalized Probes for Chemical Imaging, Key Laboratory of

Molecular and Nano Probes, Ministry of Education, Shandong

9) Rajendran, T.; Manimaran, B.; Liao, R.-T.; Lin, R.-J.;

Thanasekaran, P.; Lee, G.-H.; Peng, S.-M.; Liu, Y.-H.; Chang, I. J.;

Rajagopal, S.; Lu, K.-L. Synthesis and Photophysical Properties of

Neutral Luminescent Rhenium-Based Molecular Rectangles. Inorg.

Chem. 2003, 42, 6388−6394.

10) Benkstein, K. D.; Hupp, J. T.; Stern, C. L. Synthesis and

000-0002-5300-3307 ; Email: xxgk123@163.com

Characterization of Molecular Rectangles Based upon Rhenium

Authors

Thiolate Dimers. Inorg. Chem. 1998, 37, 5404−5405.

(11) Nagarajaprakash, R.; Kumar, C. A.; Mobin, S. M.; Manimaran,

Guo-Xia Jin − College of Chemistry, Chemical Engineering and

Materials Science, Collaborative Innovation Center of

Functionalized Probes for Chemical Imaging, Key Laboratory of

Molecular and Nano Probes, Ministry of Education, Shandong

Normal University, Jinan 250014, P. R. China; orcid.org/

B. Multicomponent Self-Assembly of Thiolato- and Selenato-Bridged

Ester-Functionalized Rhenium(I)-Based Trigonal Metallaprisms: Syn-

thesis and Structural Characterization. Organometallics 2015, 34,

(

24−730.

12) Manimaran, B.; Rajendran, T.; Lu, Y.-L.; Lee, G.-H.; Peng, S.-

000-0001-5554-6412

M.; Lu, K.-L. Novel one-pot synthesis of luminescent neutral

rhenium-based molecular rectangles. J. Chem. Soc., Dalton Trans.

2001, 515−517.

Teng Wang − College of Chemistry, Chemical Engineering and

Materials Science, Collaborative Innovation Center of

Functionalized Probes for Chemical Imaging, Key Laboratory of

Molecular and Nano Probes, Ministry of Education, Shandong

Normal University, Jinan 250014, P. R. China

Yanyan Sun − QiLu Pharmaceutical (HaiNan) Company Ltd.,

Haikou, Hainan 570314, People’s Republic of China

Yu-Long Li − College of Chemistry and Environmental

Engineering, Sichuan University of Science & Engineering,

Zigong 643000, People ’s Republic of China; orcid.org/

(13) Benkstein, K. D.; Hupp, J. T.; Stern, C. L. Luminescent

mesoporous molecular materials based on neutral tetrametallic

rectangles. Angew. Chem., Int. Ed. 2000, 39, 2891 −2893.

(14) Benkstein, K. D.; Hupp, J. T.; Stern, C. L. Molecular Rectangles

Based on Rhenium(I)Coordination Chemistry. J. Am. Chem. Soc.

998, 120, 12982−12983.

15) Dinolfo, P. H.; Williams, M. E.; Stern, C. L.; Hupp, J. T.

Rhenium-Based Molecular Rectangles as Frameworks for Ligand-

Centered Mixed Valency and Optical Electron Transfer. J. Am. Chem.

Soc. 2004, 126, 12989−13001.

000-0002-5579-3269

16) Dinolfo, P. H.; Hupp, J. T. Tetra-Rhenium Molecular

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c01845

Rectangles as Organizational Motifs for the Investigation of Ligand-

Centered Mixed Valency: Three Examples of Full Delocalization. J.

Am. Chem. Soc. 2004, 126, 16814−16819.

Notes

(17) Liao, R.-T.; Yang, W.-C.; Thanasekaran, P.; Tsai, C.-C.;

The authors declare no competing ﬁnancial interest.

Sathiyendiran, M.; Liu, Y.-H.; Rajendran, T.; Lin, H.-M.; Tsengb, T.-

W.; Lu, K.-L. Rhenium-based molecular rectangular boxes with large

inner cavity and high shape selectivity towards benzene molecule.

Chem. Commun. 2008, 3175−3177.

ACKNOWLEDGMENTS

■

We are grateful for ﬁnancial support from NSFC (grant no.

1771120).

(18) Rajakannu, P.; Hussain, F.; Shankar, B.; Sathiyendiran, M.

Unprecedented single-crystal-to-single-crystal topochemical confor-

mational change and photoreduction of ethylene units in π -stacked

metallomacrocycle. Inorg. Chem. Commun. 2012 , 26 , 46 −50.

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