Multistate and Multicolor Photochromism through Selective

Nov 23, 2015 - Upon irradiation under UV light, 1oo converts only to 1oc without the observation of 1co and dually ring-closed species 1cc. In contras...
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Multistate and Multicolor Photochromism through Selective Cycloreversion in Asymmetric Platinum(II) Complexes with Two Different Dithienylethene−Acetylides Bin Li, Hui-Min Wen, Jin-Yun Wang, Lin-Xi Shi, and Zhong-Ning Chen* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China S Supporting Information *

ABSTRACT: Four asymmetric bis(dithienylethene−acetylide) platinum(II) complexes trans-Pt(PEt3)2(L1o)(L5o) (1oo), trans-Pt(PEt 3 ) 2 (L2o)(L5o) (2oo), trans-Pt(PEt3)2(L3o)(L5o) (3oo), and trans-Pt(PEt3)2(L4o)(L5o) (4oo) with two different dithienylethene−acetylides (L1o− L5o) were designed to modulate stepwise, multistate, and multicolor photochromism by modifying ring-closure absorption wavelengths. Upon irradiation under UV light, 1oo converts only to 1oc without the observation of 1co and dually ring-closed species 1cc. In contrast, both mixed ring-open/ closed species oc and co as well as dually ring-closed species cc are observed upon UV light irradiation of 2oo−4oo, implying that a substantial stepwise photochromic process occurs following 2oo−4oo → 2oc−4oc/2co−4co → 2cc−4cc. The conversion percentage of dually ring-closed species at the photostationary state (PSS) is progressively increased following 1cc (0%) → 2cc (40%) → 3cc (86%) → 4cc (>95%), coinciding with the progressive red-shift of ring-closure absorption bands in free L1c (441 nm) → L2c (510 nm) → L3c (556 nm) → L4c (591 nm). Particularly, compound 2 affords four states (2oo, 2co, 2oc, and 2cc) with different colors (colorless, purple, blue, and dark blue, respectively) through a selective photochemical cycloreversion process upon irradiation with appropriate wavelengths of light. Although stepwise photocyclization reactions 3oo → 3co/3oc → 3cc and 4oo → 4co/4oc → 4cc are observed, multicolor photochromism of 3oo and 4oo could not be achieved because ring-closure absorption bands between L3c/L4c and L5c are significantly overlapped. The stepwise photochemical processes are well demonstrated by NMR, UV−vis, and infrared (IR) spectroscopy and time-dependent density functional theory (TD-DFT) computational studies.

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INTRODUCTION Photochromic compounds that can undergo a reversible structural and color change between two isomers upon irradiation with appropriate wavelengths of light have attracted much attention due to their potential applications in opoelectronics, material science, and biological fields.1,2 Dithienylethene (DTE) derivatives with heterocyclic aryl groups have been extensively investigated because of their excellent performance such as fast response, durable fatigue resistance, and thermally irreversible properties.3−5 Recent research effort has been devoted to incorporate two or several photochromic units into one molecule to achieve multiple colors and states upon irradiation with appropriate light, thus affording potential applications in optoelectronic devices such as multifrequency optical memories and data storage.6 Although many systems that integrate one DTE moiety to a transition metal have been reported,7−26 multiDTE based metal complexes incorporating several DTE moieties are still limited.6,27−39 Because of facile intramolecular energy transfer from a ring-open DTE moiety to a ring-closed one that prohibits further photocyclization for ring-open DTE units,40 it is highly challenging to access all the possible © XXXX American Chemical Society

switchable isomers. Particularly, the conversion to the fully ring-closed isomer is always unattainable. When two identical dithienylethene−acetylide (DTE− acetylide) ligands are incorporated to a gold(I),36 platinum(II),35,37 or ruthenium(II/III)32,38,39 center to afford metal bis(DTE−acetylide) complexes, a stepwise ring-closing/opening process has been observed upon irradiation with appropriate wavelengths of light following oo⇋co⇋cc through reversible photochemical reactions. It is demonstrated that stepwise photochromism in these metal-coordinated systems could be modulated by modifying DTE−acetylide ligands.39 It is found that with the gradual red-shift of ring-closure absorption maxima in DTE−acetylide ligands, stepwise photochromism is increasingly facilitated in metal coordinated systems with dual DTE−acetylides. On the other hand, when two different DTE−acetylides are combined to a metal center to give an asymmetric coordination system, four different states including oo, co, oc, and cc are likely attained upon irradiation with appropriate wavelengths of light through a stepwise and Received: September 22, 2015

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DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Synthetic Routes to Asymmetric Platinum(II) Complexes 1oo−4oo

Figure 1. UV−vis absorption spectral changes of 1oo (a), 2oo (b), 3oo (c), and 4oo (d) in CH2Cl2 solutions (2 × 10−5 M) at ambient temperature upon irradiation at 365 nm to the PSS.

moiety as well as introducing a substituent such as phenyl or pyridyl on the 5-position of thienyl rings. As a result, free ligands show a progressive red-shift of the ring-closure absorption maxima following L1c (441 nm) → L2c (510 nm) → L3c (556 nm) → L4c (591 nm) → L5c (602 nm) (Figure S1). As depicted in Scheme 1, platinum(II) complexes 1oo−4oo (trans-Pt(PEt3)2(L1o)(L5o) (1oo), trans-Pt(PEt3)2(L2o)(L5o) (2oo), trans-Pt(PEt3) 2 (L3o)(L5o) (3oo), and trans-Pt(PEt3)2(L4o)(L5o) (4oo)) were prepared by a two-step reaction procedure. trans-Pt(PEt3)2Cl2 reacts first with 1 equiv of L5o in the presence of Bu4NF and CuI to give complex trans-Pt(PEt3)2(L5o)Cl, followed by the reaction with 1 equiv of L1o−L4o through fluoride-induced desilylation and

selective ring-closing/opening process. In this paper, we are devoted to achieve multicolor and multistate photochromism, taking advantage of four trans-platinum(II) complexes (Scheme 1) that incorporate two different photochromic DTE− acetylides through bis(Pt−acetylide) bonds. It is demonstrated that distinct multicolor and multistate changes are exhibited upon irradiation with appropriate wavelengths of light, in which stepwise photocyclization and selective cycloreversion are successfully achieved for two different DTE switches.

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RESULTS AND DISCUSSION Five ethynyl-DTE ligands L1o−L5o with different ring-closure absorption maxima were designed and synthesized.37,38 The ring-closure absorption position of these DTEs is modulated by the position of thienyl rings attached to the cyclopentene B

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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Scheme 2. Stepwise and Selective Photochromic Processes and Color Conversions of Complex 2 in CH2Cl2 Solution and PMMA Film (25%)

CuI-catalyzed Pt−acetylide σ-coordination, giving complexes 1oo−4oo as asymmetric metal coordinated systems. UV−vis Spectral Studies. Complexes 1oo−4oo exhibit intense absorption bands at ca. 260−360 nm due to intraligand (IL) transitions within two DTE−acetylides together with absorption shoulder bands tailing to 450 nm, arising mainly from 5d(Pt) → π*(CC-DTE/PEt3) metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) transitions from one ring-open CC-DTE to the other one, as revealed by time-dependent density functional theory (TDDFT) studies (Tables S1−S15). Upon irradiation of 1oo in CH2Cl2 under UV light at 365 nm, while four intense absorptions at 263, 296, 326, and 346 nm gradually decreased, two new bands centered at 378 and 627 nm (Figure 1a) occurred and enhanced progressively before the solution reached photostationary state (PPS), ascribable to the ring-closing process L5o → L5c to produce mixed ring-open/closed species 1oc. The ring-closing absorption band due to L1o → L1c to afford the other mixed ringopen/closed species 1co, however, was unobserved. At the photostationary state (PSS), the species in solution is totally 1oc without detection of 1co or 1cc by NMR studies (vide infra). The UV−vis absorption spectral changes of 2oo in CH2Cl2 are presented in Figure 1b. When a CH2Cl2 solution of 2oo was irradiated under UV light at 365 nm, a new broad band appeared progressively at 450−750 nm, arising most likely from the photocyclization of DTE moieties. At the beginning stage of UV light irradiation, two distinct broad bands with maxima at ca. 530 and 625 nm (Figure S3) were observed due to

respective photocyclization of L2o and L5o to give 2co and 2oc, respectively. Upon further irradiation at 365 nm, the maximum at 530 nm was gradually attenuated due to 2co → 2cc transformation. Upon sufficient irradiation at 365 nm, the solution reached the PSS composed of 2oc and 2cc, in which the maximum of the low-energy band was observed at 619 nm. Conversely, when the solution at the PSS was kept to irradiate at 672 nm (Figure S4), the band at 619 nm attenuated and finally disappeared whereas an absorption with maximum at 530 nm was observed, indicating that 2cc converted to 2co due to the cycloreversion of L5c to L5o with the blue-black turning into purple (Scheme 2). If the solution at the PSS was irradiated at 447 nm (Figure S5), the absorption maximum at 619 nm was a little red-shifted to 625 nm due to the 2cc → 2oc conversion through the cycloreversion of L2c with the blueblack turning into blue. Consequently, 2cc could be converted to 2co or 2oc through selective cycloreversion at L5c or L2c upon irradiation at 672 or 447 nm so as to display distinct color change from blue-black into purple (2co) or blue (2oc), respectively. In fact, both L5c and L2c exhibited cycloreversion reactions upon irradiation at >460 nm, resulting in stepwise 2cc → 2co/2oc → 2oo conversions with color conversions of blueblack → purple/blue → colorless. Photochromic conversions and photoinduced color changes of complex 2 are depicted in Scheme 2. The CH2Cl2 solution of 2oo was colorless before photoirradiation. On the one hand, upon UV light irradiation of 2oo at 365 nm, it turned first into blue and then blue-black when the solution reached the photostationary state (PSS). On the other hand, when the solution at the PSS was irradiated at 672 nm, the blue-black C

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. 31P NMR spectral changes of 1oo (a), 2oo (b), 3oo (c), and 4oo (d) in CDCl3 (5 × 10−3 M) under UV light irradiation at 365 nm to the PSS.

band is attributable to stepwise photocyclization 4oo → 4co/ 4oc → 4cc. The absence of two separate absorption bands for mixed ring-open/closed species 4co and 4oc at the beginning stage of UV light irradiation is due to the close absorption energy between ring-closed L4c and L5c. As a result, it is impossible to find a suitable wavelength of light for selective cycloreversion of 4cc at L4c or L5c to attain 4oc or 4co, respectively. NMR Spectral Studies. Upon irradiation of 1oo at 365 nm, while the P signal at 11.20 ppm was gradually reduced, a new signal occurred at 11.58 ppm (Figure 2a) due to the formation of mixed ring-open/closed 1oc through the ring-closing process L5o → L5c. Upon keeping irradiation at 365 nm for quite a long time, other new signals in 31P NMR spectra were not observed, implying that the photocyclization of 1oo → 1co as well as the further 1oc → 1cc ring-closing process did not occur. At the PSS, one P signal at 11.58 ppm was only observed, suggesting the presence of >95% of 1oc. Conversion maximum and percentages at the PSS for complexes 1−4 are summarized in Table 1. The 31P NMR signal of 2oo in CDCl3 occurred at 11.24 ppm. When a CDCl3 solution of 2oo was irradiated at 365 nm, with the gradual attenuation of P signal at 11.24 ppm (Figure 2b), two new signals were observed at 11.55 and 11.60 ppm due to the photocyclization of L2o or L5o to give mixed ringopen/closed species 2co and 2oc, respectively. Further irradiation of the solution resulted in the observation of another new signal at 11.90 ppm due to dually ring-closed species 2cc. With a progressive enhancement of the signal of 2cc at 11.90 ppm, the signal of 2co at 11.55 ppm decreased and finally vanished at the PSS, implying a complete conversion of 2co to 2cc. The P signals of mixed ring-open/closed species 2co and 2oc increasing first and then decreasing is undoubtedly indicative of a stepwise ring-closing process following 2oo →

solution turned into purple (2co). When the blue-black solution at the PSS was irradiated at 447 nm, it turned to blue (2oc). Further irradiation of purple (2co) or blue (2oc) solution at >460 nm resulted finally in the formation of colorless 2oo (Figure S6). As a result, upon irradiation of the solution at the PSS with appropriate wavelengths of light, four states (2cc, 2co, 2oc and 2oo) and four colors (blue-black, purple, dark blue and colorless) were attained through selective cycloreversion processes 2cc → 2co (irradiation at 672 nm), 2cc → 2oc (irradiation at 447 nm) and 2co/2oc → 2oo (irradiation at >460 nm), respectively. Upon UV light irradiation of a CH2Cl2 solution of 3oo at 365 nm, the intense absorption bands at 259, 271, 297, and 355 nm gradually weakened. Meanwhile, ring-closure absorption maximum occurred first at 596 nm (Figure 1c) and then showed a gradual red-shift to 613 nm at the PSS with the colorless solution becoming blue. The distinct red-shift of ringclosure absorption demonstrated unambiguously that stepwise photocyclization occurred following 3oo → 3co/3oc → 3cc. Unlike 2oo, at the beginning stage of UV light irradiation, two distinct broad bands due to 3co and 3oc were not observed because ring-closing absorption bands of L3o → L3c and L5o → L5c are highly overlapped. As a result, upon UV light irradiation of 3oo, an obvious red-shift of ring-closing maximum from 596 to 613 nm demonstrates that dually ringclosed species 3cc is produced through mixed ring-open/closed species 3oc and 3co. Nevertheless, it is difficult to find a suitable wavelength of light for selective cycloreversion of L3c or L5c because both ring-closing absorption bands show a large spectral overlapping (Figure S7). When the solution of 4oo was irradiated at 365 nm, ringclosing absorption maximum occurred first at 620 nm and then gradually red-shifted to 636 nm at the PSS (Figure 1d). Similarly, such a distinct red-shift of ring-closing absorption D

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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electronic donation of P donors to the Pt center upon photocyclization. The photochromic cyclization/cycloreversion processes (2oo⇄2co/2oc⇄2cc) were also examined by 1H NMR spectral studies in CDCl3 (Figure 4). Upon irradiation with

Table 1. Conversion Maximum and Conversion Percentages at PSS for 1−4 conversion maximuma,b 1oo 2oo 3oo 4oo

>95% (→1oc, 100 min) 18% (→2co, 23 min), 60% (→ 2oc, 70 min) 28% (→3co, 50 min), 41% (→ 3oc, 65 min) 53% (→4co/4oc, 35 min)

contents at PSSc 1oc (>95%), 100 min 2oc (60%), 2cc (40%), 120 min 3co (5%), 3oc (9%), 3cc (86%), 240 min 4cc (>95%), 160 min

a

Conversion percentages measured by NMR spectroscopy in CDCl3 solutions (5 × 10−3 M). bIrradiation time for reaching the corresponding state under UV light at 365 nm. cPercentages of various species at the PSS and the time to PSS upon irradiation of 1oo−4oo at 365 nm.

2co/2oc → 2cc. At the PSS, the observation of only the signal of 2oc at 11.60 and that of 2cc at 11.90 ppm indicated that the solution was a mixture of 2oc and 2cc. From the 31P NMR spectral changes, the contents of four isomeric species against irradiation time are shown in Figure 3. It is revealed unambiguously that 2oo was first converted to 2co/2oc and then to 2cc upon keeping irradiation at 365 nm. The percentages of 2oc and 2cc at the PSS were estimated as 60% and 40%, respectively. Conversely, when the solution at the PSS was subsequently irradiated at 672 nm (Figure S9), with the gradual decay and final disappearance of the P signal of 2cc at 11.90 ppm and that of 2oc at 11.60 ppm, those at 11.55 ppm due to 2co and 11.24 ppm due to 2oo were generated and progressively enhanced, suggesting that 2cc and 2oc converted to 2co and 2oo through selective photochemical cycloreversion at L5c, respectively. Similarly, when the solution at the PSS was irradiated at 447 nm (Figure S10), with the gradual decrease and final disappearance of the P signals of 2cc at 11.90 ppm, that of 2oc at 11.60 ppm is progressively increased, indicating that 2cc transformed to 2oc following selective cycloreversion at L2c. It appears that the P signals are gradually shifted to downfield from 2oo to 2co/2oc then to 2cc because of the enhanced

Figure 4. 1H NMR spectral changes of 2oo in CDCl3 (5 × 10−3 M) upon irradiation at 365 nm to the PSS.

appropriate wavelengths of light, chemical shifts of thienyl protons exhibit characteristic responses to the corresponding photochemical conversion 2oo⇄2co/2oc⇄2cc. In the 1H NMR spectrum of 2oo, the thienyl protons occurred at 6.51 (Haoo), 6.77 (Hcoo), 6.79 (Hboo), and 7.51 (Hdoo) ppm, respectively. Upon irradiation of 2oo under UV light at 365 nm, while signals Hcoo and Hdoo gradually decreased and finally disappeared, new ring-closed signals occurred at 6.03 ppm for Hcoc/cc and 6.89 ppm for Hdoc/cc which intensified progressively before the PSS due to the formation of 2oc and 2cc. On the other hand, with the gradual attenuation of signals Haoo at 6.51 ppm and Hboo at 6.79 ppm upon 2oo irradiated at 365 nm, ring-closed signals were observed at 5.28 ppm for Haco/cc, 6.00

Figure 3. Relative contents changes of 1oo (a), 2oo (b), 3oo (c), and 4oo (d) in CDCl3 (5 × 10−3 M) under UV light irradiation at 365 nm to the PSS. E

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Spatial plots of LUMO and LUMO+1 of 4oo, 4oc, 4co, and 4cc involved in photochemical cyclization and cycloreversion.

ppm for Hbco, and 6.01 ppm for Hbcc. The new signal at 6.00 ppm for Hbco disappeared upon further irradiation at 365 nm, suggesting that 2oo converted first to 2co and then to 2cc. At the PSS, the integral area ratio of the signals at 5.28 (Hacc) and 6.51 (Haoc) ppm is ca. 2:3 (Figure 4), suggesting 40% of 2cc and 60% of 2oc as estimated by 31P NMR spectral studies. Upon irradiation of 3oo at 365 nm, the P signal at 11.26 ppm decreased gradually and finally vanished. Two new P signals occurred first at 11.59 and 11.63 ppm and progressively increased due to the formation of mixed ring-open/closed species 3co and 3oc (Figure 2c), respectively. Further irradiation of the solution at 365 nm resulted in the two new P signals at 11.59 ppm (3co) and 11.63 ppm (3oc) gradually decreasing and almost vanishing at the PSS, whereas another new peak was observed at 11.93 ppm due to the formation of dually ring-closed product 3cc through the conversion of 3co/ 3oc→ 3cc. At the PSS, the P signal integral ratio suggested the presence of 5% of 3co, 9% of 3oc, and 86% of 3cc (Figure 2c). When the solution at the PSS was subsequently irradiated at 672 nm (Figure S11), with the gradual decay and final disappearance of the P signal for 3cc at 11.93 ppm, the signal at 11.59 ppm due to 3co was progressively enhanced, suggesting that 3cc was converted to 3co due to cycloreversion of L5c to L5o. However, the other mixed ring-open/closed species 3oc is unattained from 3cc through selective photoinduced cycloreversion because ring-closing absorption bands of L3c and L5c show significant overlapping. Stepwise photochromic reactions of 4oo were unambiguously supported by 31P NMR spectral studies (Figure 2d). Upon irradiation of 4oo at 365 nm, with the gradual decrease and final vanishing of the P signal at 11.24 ppm (4oo), a new P signal progressively occurred at 11.62 ppm due to the

formation of 4co and 4oc. The P signal of 4co is severely overlapped with that of 4oc because of their comparable electronic effect of L4c and L5c. Upon further irradiation at 365 nm, the P signal at 11.62 ppm (4co/4oc) gradually decreased and finally vanished, whereas another new peak occurred at 11.95 ppm (4cc) due to the conversion of 4co and 4oc to 4cc. At the PSS, one P signal at 11.95 ppm was observed, suggesting the presence of >95% of 4cc (Figure 2d). Infrared Spectra Studies. The infrared (IR) band of complexes 1oo−4oo due to CC stretching mode occurred at 2092 cm−1 in CH2Cl2 solution. Upon irradiation of 1oo−4oo at 365 nm (Figure S15−S18), an obvious red-shift (20−30 cm−1) to lower wavenumber was always observed, ascribed to the increase of π-system upon photocyclization at the DTE units so that π electron of the acetylides is largely delocalized to the whole coordination system, thus attenuating the CC bonding. Particularly, the ν(CC) frequency exhibited a progressive decrease with the stepwise ring-closure reactions 3oo (2092 cm−1) → 3co/3oc (2073 cm−1) → 3cc (2070 cm−1) and 4oo (2092 cm−1) → 4co/4oc (2073 cm−1) → 4cc (2069 cm−1). Computational Studies. Molecular orbital compositions involved in UV−vis absorption and transition assignments in the ground state are provided in Tables S1−S15. The plots of LUMO and LUMO+1 of 4oo, 4oc, 4co, and 4cc associated with photocyclization and cycloreversion are shown in Figure 5, and those of other species are provided in Figure S20. For 1oo−4oo, the HOMO is populated on two ring-open DTE−acetylides and 5d orbitals of platinum (ca. 25% population) whereas the LUMO is focused on one of the two ring-open ligands. The low-energy UV absorption bands result from electron promotion from HOMO to LUMO+n (n F

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

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(70.14%)/(27.26%). Only one ring-closing absorption band centered at 653 nm is theoretically predicted because the transition energy of π → π* states of both L4c and L5c is quite close to each other.

= 0, 1, 2, or 3), which is characteristic of the IL (intraligand) state of DTE−acetylide mixed with significant MLCT from Pt to DTE−acetylide and LLCT transitions from one DTE− acetylide to the other one. Actually, only LUMO+n involved in the UV absorption transitions would participate in photochemical ring-closure of 1oo−4oo. For 1oo, the LUMO and LUMO+1 are responsible for ringclosure of L1o and L5o to produce 1co and 1oc, respectively. Nevertheless, the calculated ring-closing absorption of 1co at 446 nm due to the ring-closure of L1o is very weak (oscillator strength of only 0.0715), implying that only a very small portion of 1co can be generated upon irradiation of 1oo under UV light. Furthermore, this ring-closing absorption is also close to the calculated low-energy absorption of 1oo at 408 nm, implying that 1co can be readily converted to 1oo through cycloreversion. Thus, the fact that 1co is experimentally inaccessible is reasonably predicted by theoretical studies. The low-energy absorption of 2co−4co is typical of IL transition localized on respective ring-closed L2c−L4c due to electron promotion from HOMO to LUMO with intense oscillator strength larger than 0.75. In contrast, the ring-closure absorption bands of 1oc−4oc at ca. 625−635 nm are mainly attributed to HOMO → LUMO transition at L5c. For mixed ring-open/closed species, the unoccupied frontier orbitals involved in the UV absorption bands are responsible for further photocyclization of the ring-open DTE moiety whereas those involved in the ring-closing absorption bands in the visible region are always related to the cycloreversion of the ring-closed DTE moiety.40,41 For 1oc−4oc, the further ringclosure at L1o−L4o is associated with the LUMO+1 whereas the cycloreversion at L5c is closely related to the LUMO. However, for 1co−4co, the LUMO+1 as the primarily unoccupied frontier orbital involved in the UV absorption process is responsible for further ring-closure at L5o whereas the LUMO is involved in cycloreversion at L1c−L4c. For 2cc, the HOMO/HOMO−1 is concentrated at L5c (82.30%)/L2c (81.65%) with a little population at L2c (12.29%)/L5c (14.07%). The LUMO and LUMO+1 are focused on L5c (95.39%) and L2c (90.61%), respectively. The calculated low-energy absorption bands centered at 620 and 503 nm due to HOMO → LUMO and HOMO−1 → LUMO+1 are typical of the IL π → π* character of L5c and L2c, respectively, mixed with a little LLCT state from L2c/L5c to L5c/L2c. The occurrence of two separate ring-closing absorption bands for 2cc arising from L2c and L5c suggests that it is viable to attain mixed ring-open/closed species 2oc or 2co through selective cycloreversion at L2c or L5c upon irradiation at 447 or 672 nm, respectively. The HOMO/HOMO−1 of 3cc is distributed to both L3c (44.56%/50.23%) and L5c (49.22%/47.02%) whereas the LUMO and LUMO+1 are only populated at L5c (90.41%) and L3c (88.27%), respectively. The calculated ring-closure absorption maxima at 630 (L5c) and 563 (L3c) nm are featured with IL π → π* transitions of L5c and L3c, respectively, together with a significant LLCT state between L3c and L5c. A large overlapping between the ring-closing bands of L5c and L3c makes it difficult to achieve experimentally mixed ring-open/closed species 3oc or 3co through selective cycloreversion at L3c or L5c. The HOMO/HOMO−1 of 4cc is mainly resident at both L4c (57.57%)/(37.95%) and L5c (36.05%)/(60.08%). In contrast to that of 2cc and 3cc, the LUMO/LUMO+1 of 4cc is also populated on both L4c (26.26%)/(69.85%) and L5c

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CONCLUSIONS L1o−L5o with a progressive red-shift of the ring-closure absorption maxima were utilized to modulate stepwise photochromism in asymmetric platinum(II) complexes 1oo− 4oo. Upon UV light irradiation of dually ring-open species oo at 365 nm, distinct stepwise photocyclization takes place following oo → oc/co → cc. It is found that with the progressive red-shift of ring-closure absorption of dithienylethene−acetylides in the order of L1o → L2o → L3o → L4o, dual photocyclization is increasingly facilitated in asymmetric trans-platinum(II) complexes following 1oo → 2oo → 3oo → 4oo. In particular, 2oo exhibits interesting four-state and fourcolor photochromism, in which each state/color is attainable through selective cycloreversion of 2cc upon irradiation with appropriate wavelengths of lights. It is demonstrated that the multicolor photochromism is attainable by elaborate design of asymmetric metal-coordinated systems with different DTE moieties. It appears that when ring-closing absorption bands of two different DTE moieties are sufficiently separated, it is possible to achieve all of the four states and four colors upon irradiation with different wavelengths of lights through stepwise photocyclization and selective cycloreversion.

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EXPERIMENTAL SECTION

General Procedures and Materials. All the synthetic procedures were carried out by using Schlenk techniques and vacuum-line systems under a dry argon atmosphere. Solvents were distilled under an argon atmosphere in the presence of calcium hydride. trans-Pt(PEt3)2Cl2 and L1o−L5o were prepared by literature procedures.37−39 trans-Pt(PEt3)2(L5o)Cl. To a diisopropylamine−toluene (30 mL, v/v = 2:1) solution of trans-[Pt(PEt3)2Cl2] (150 mg, 0.3 mmol) were added tetrabutylammonium fluoride (0.1 mL, 1 M in THF) and CuI (5 mg). A diisopropylamine−toluene (10 mL) solution of L5o (162 mg, 0.3 mmol) was added slowly to the above solution within 2 h in the dark. Then, the mixture was heated under reflux, and the reaction was monitored by TLC. After filtration, the solvent was removed under reduced pressure. The product was purified by silica gel column chromatography using dichloromethane−petroleum ether (v/v = 1:2) as eluent. Yield: 46% (130 mg). 1H NMR (400 MHz, CDCl3, ppm): δ 8.54 (d, J = 4.76 Hz, 1H), 7.70 (td, J1 = 7.84 Hz, J2 = 1.6 Hz, 1H), 7.62 (d, J = 7.96 Hz, 1H), 7.51 (s, 1H), 7.18−7.15 (m, 1H), 6.76 (s, 1H), 2.06−2.00 (m, 12H), 1.97 (s, 3H), 1.87 (s, 3H), 1.22−1.14 (m, 18H). 31 P NMR (CDCl3, ppm): δ 15.03 (JPt−P = 2918 Hz). ESI-MS: m/z (%) 935.8 (100) [M + 1]+. Anal. Calcd for C34H42ClF6NP2PtS2·1/ 2CH2Cl2: C, 42.28; H, 4.43; N, 1.43. Found: C, 42.32; H, 4.37; N, 1.32. IR (KBr): 2109 cm−1 (CC). Synthesis of 1oo. To a dichloromethane (30 mL) solution of trans-Pt(PEt3)2(L5o)Cl (186 mg, 0.2 mmol) and L1o (118 mg, 0.24 mmol) were added tetrabutylammonium fluoride (0.1 mL, 1 M in THF) and CuI (5 mg). The reaction mixture was stirred in the dark at ambient temperature for 1 d, and the reaction was monitored by TLC. The solution was concentrated under reduced pressure, and the product was purified by silica gel column chromatography using dichloromethane−petroleum ether (v/v = 2/3) as eluent. Yield: 56% (148 mg). 1H NMR (400 MHz, CDCl3, ppm): δ 8.55 (d, J = 4.80 Hz, 1H), 7.70 (td, J1 = 7.64 Hz, J2 = 1.56 Hz, 1H), 7.62 (d, J = 8.00 Hz, 1H), 7.52 (s, 1H), 7.18−7.15 (m, 1H), 6.78 (s, 1H), 6.49 (s, 1H), 2.46 (s, 3H), 2.44 (s, 3H), 2.17−2.06 (m, 12H), 1.98 (s, 3H), 1.86 (s, 3H), 1.76 (s, 3H), 1.72 (s, 3H), 1.20−1.12 (m, 18H). 31P NMR (161.97 MHz, CDCl3, ppm): δ 11.20 (JPt−P = 2359 Hz). 13C NMR (CDCl3, ppm): 151.7, 149.6, 147.8, 146.9, 144.2, 143.9, 142.6, 141.2, 139.0, G

DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

maximum force, root-mean-square (rms) force, maximum displacement, and rms displacement were set by default. Then, 100 singlet excited states of these investigated complexes in dichloromethane were calculated by the time-dependent DFT (TD-DFT)45 method based on the optimized geometrical structures. The solvent effects were taken into account by the polarizable continuum model method (PCM).46 The self-consistent field (SCF) convergence criteria of rms density matrix and maximum density matrix were set at 10−8 and 10−6 au, respectively, in all these electronic structure calculations. The iterations of excited states continued until the changes on energies of states were no more than 10−7 au between the iterations, and then, convergences were reached in all of these excited states. In these calculations, the Lanl2dz effective core potential47 was used to describe the inner electrons of Pt, S, and P atoms, while its associated double-ζ basis set of Hay and Wadt was employed for the remaining outer electrons. Other nonmetal atoms of F, N, C, and H were described by the allelectron basis set of 6-31G(p,d).48 To precisely describe the molecular properties, one additional f-type polarization function was employed for the Pt (αf = 0.18) atom.49 Visualization of the optimized structures and frontier molecular orbitals were performed by GaussView. The Ros and Schuit method (C-squared population analysis method, SCPA)50 was supported to analyze the partition orbital composition by using Multiwfn 3.3 program.51

136.7, 134.1, 129.1, 126.9, 126.7, 126.0, 124.2, 123.9, 123.7, 122.2, 121.1, 118.5, 100.3 (s, CC), 16.4 (t, J(C, P) = 17.2 Hz, CH2−P), 15.5 (s, CH3), 15.3 (s, CH3), 15.2 (s, CH3), 15.0 (s, CH3), 14.8 (s, CH3), 14.4 (s, CH3), 8.3 (s, CH3, −Et). ESI-MS: m/z (%) 1319 (100) [M]+. Anal. Calcd for C53H55F12NP2PtS4: C, 48.25; H, 4.20; N, 1.06. Found: C, 48.52; H, 4.09; N, 0.98. IR (CH2Cl2): 2092 cm−1 (CC). Synthesis of 2oo. This compound was prepared by the same synthetic procedure as that of 1oo except for the use of L2o (115 mg, 0.24 mmol) in place of L1o. Yield: 60% (157). 1H NMR (400 MHz, CDCl3, ppm): δ 8.55 (d, J = 4.32 Hz, 1H), 7.70 (td, J1 = 7.72 Hz, J2 = 1.56 Hz, 1H), 7.63 (d, J = 7.96 Hz, 1H), 7.51 (s, 1H), 7.18−7.15 (m, 1H), 6.79 (s, 1H), 6.77 (s, 1H), 6.51 (s, 1H), 2.44 (s, 3H), 2.15−2.08 (m, 12H), 1.98 (s, 3H), 1.86 (s, 3H), 1.85 (s, 3H), 1.69 (s, 3H), 1.23− 1.15 (m, 18H). 31P NMR (161.97 MHz, CDCl3, ppm): δ 11.24 (JPt−P = 2887 Hz). 13C NMR (CDCl3, ppm): 149.8, 149.5, 144.6, 144.4, 144.2, 143.7, 141.2, 141.0, 139.0, 136.8, 134.1, 129.3, 127.1, 126.0, 124.6, 124.2, 124.0, 122.2, 120.7, 118.6, 100.7 (s, CC), 16.5 (t, J(C, P) = 17.7 Hz, CH2−P), 15.4 (s, CH3), 15.3 (s, CH3), 14.8 (s, CH3), 14.4 (s, CH3), 14.2 (s, CH3), 8.3 (s, CH3, −Et). ESI-MS: m/z (%) 1305(100) [M + 1]+. Anal. Calcd for C52H53F12NP2PtS4·3H2O·C6H12: C, 47.85; H, 4.09; N, 1.07. Found: C, 47.98; H, 4.29; N, 1.02. IR (KBr): 2092 cm−1 (CC). Synthesis of 3oo. This compound was prepared by the same synthetic procedure as that of 1oo except the use of L3o (115 mg, 0.24 mmol) in place of L1o. Yield: 58% (152 mg). 1H NMR (400 MHz, CDCl3, ppm): δ 8.54 (d, J = 4.72 Hz, 1H), 7.68 (td, J1 = 7.72 Hz, J2 = 1.54 Hz, 1H), 7.62 (d, J = 7.96 Hz, 1H), 7.50 (s, 1H), 7.19−7.14 (m, 1H), 6.77 (s, 2H), 6.69 (s, 1H), 2.40 (s, 3H), 2.14−2.10 (m, 12H), 1.98 (s, 3H), 1.86 (s, 6H), 1.80 (s, 3H), 1.23−1.16 (m, 18H). 31P NMR (161.97 MHz, CDCl3, ppm): δ 11.26 (JPt−P = 2339 Hz). 13C NMR (CDCl3, ppm): 150.4, 149.5, 147.4, 144.5, 144.2, 142.5, 139.7, 139.0, 137.5, 136.9, 134.4, 131.3, 130.9, 128.8, 126.8, 126.7, 126.0, 124.8, 124.4, 124.0, 122.2, 118.5, 100.8 (s, CC), 16.5 (t, J(C, P) = 17.5 Hz, CH2−P), 15.1 (s, CH3), 14.8 (s, CH3), 14.4 (s, CH3), 14.3 (s, CH3), 14.2 (s, CH3), 8.3 (s, CH3, −Et). ESI-MS: m/z (%) 1304 [M]+. Anal. Calcd for C52H53F12NP2PtS4: C, 47.85; H, 4.09; N, 1.07. Found: C, 47.68; H, 4.21; N, 1.18. IR (CH2Cl2): 2092 cm−1 (CC). Synthesis of 4oo. This compound was prepared by the same synthetic procedure as that of 1oo except the use of L4o (130 mg, 0.24 mmol) in place of L1o. Yield: 69% (188 mg). 1H NMR (400 MHz, CDCl3, ppm): δ 8.57 (d, J = 4.12 Hz, 1H), 7.69 (t, J1 = 7.76 Hz, 1H), 7.65 (d, J = 7.92 Hz, 1H), 7.56 (d, J = 7.56 Hz, 2H), 7.55 (s, 1H), 7.40 (t, J = 7.58 Hz, 2H), 7.32 (t, J = 7.40 Hz, 1H), 7.27 (s, 1H), 7.21−7.18 (m, 1H), 6.80 (s, 2H), 2.16−2.10 (m, 12H), 2.00 (s, 3H), 1.99 (s, 3H), 1.88 (s, 6H), 1.25−1.17 (m, 18H). 31P NMR (161.97 MHz, CDCl3, ppm): δ 11.24 (JPt−P = 2336 Hz). 13C NMR (CDCl3, ppm): 151.6, 149.5, 144.4, 142.3, 142.0, 141.3, 139.1, 136.9, 133.4, 129.0, 127.8, 127.6, 127.5, 126.8, 126.7, 126.0, 125.9, 125.6, 124.3, 124.2, 124.0, 122.2, 118.6, 100.7 (s, CC), 16.5 (t, J(C, P) = 17.7 Hz, CH2− P), 14.9 (s, CH3), 14.6 (s, CH3), 14.5 (s, CH3), 14.1 (s, CH3), 8.3 (s, CH3, −Et). ESI-MS: m/z (%) 1367 (100) [M]+. Anal. Calcd for C57H55F12NP2PtS4: C, 50.07; H, 4.05; N, 1.02. Found: C, 49.86; H, 4.03; N, 1.18. IR (CH2Cl2): 2092 cm−1 (CC). Physical Measurements. 1H, 13C, and 31P NMR spectra were performed on a Bruker Avance III (400 MHz) spectrometer with SiMe4 as the internal reference and H3PO4 as the external reference. UV−vis absorption spectra were measured on a PerkinElmer Lambda 35 UV−vis spectrophotometer. Infrared spectra (IR) were recorded on a Magna 750 FT-IR spectrophotometer. Elemental analyses (C, H, and N) were carried out on a PerkinElmer model 240 C elemental analyzer. Electrospray ionization mass spectrometry (ESI-MS) was recorded on a Finnigan DECAX-30000 LCQ mass spectrometer. UV light was produced using a ZF5 UV lamp (365 nm), and visible light irradiation was carried out by using a LZG220 V 1KW tungsten lamp with cutoff filters. Theoretical Methodology. All the calculations were implemented in the Gaussian 03 program package.42 The density functional theory (DFT)43 with the gradient-corrected correlation functional PBE1PBE44 was first used to optimize the geometrical structures in the ground states. In the optimization processes, the convergent values of

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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.inorgchem.5b02175. Tables and figures giving additional spectroscopic and computational data. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the 973 project from MSTC (2014CB845603), the NSF of China (21390392, 21473201, U1405252, 21531008, and 21303204), and the Natural Science Foundation of Fujian Province (2012J05034 and 2013J05036).

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REFERENCES

(1) Irie, M. Chem. Rev. 2000, 100, 1685. (2) Tian, H.; Yang, S. Chem. Soc. Rev. 2004, 33, 85. (3) Myles, A. J.; Branda, N. R. Adv. Funct. Mater. 2002, 12, 167. (4) Kume, S.; Nishihara, H. Dalton Trans. 2008, 3260. (5) Irie, M.; Fukaminato, T.; Matsuda, K.; Kobatake, S. Chem. Rev. 2014, 114, 12174. (6) Fihey, A.; Perrier, A.; Browne, W. R.; Jacquemin, D. Chem. Soc. Rev. 2015, 44, 3719. (7) Ko, C.-C.; Yam, V. W.-W. J. Mater. Chem. 2010, 20, 2063. (8) (a) Akita, M. Organometallics 2011, 30, 43. (b) Motoyama, K.; Li, H.; Koike, T.; Hatakeyama, M.; Yokojima, S.; Nakamura, S.; Akita, M. Dalton Trans. 2011, 40, 10643. (9) Jukes, R. T. F.; Adamo, V.; Hartl, F.; Belser, P.; De Cola, L. Coord. Chem. Rev. 2005, 249, 1327. (10) Hasegawa, Y.; Nakagawa, T.; Kawai, T. Coord. Chem. Rev. 2010, 254, 2643. (11) Harvey, E. C.; Feringa, B. L.; Vos, J. G.; Browne, W. R.; Pryce, M. T. Coord. Chem. Rev. 2015, 282−283, 77. (12) Guerchais, V.; Ordronneau, L.; Le Bozec, H. Coord. Chem. Rev. 2010, 254, 2533. H

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Article

Inorganic Chemistry (13) Liu, Y.; Lagrost, C.; Costuas, K.; Tchouar, N.; Bozec, H. L.; Rigaut, S. Chem. Commun. 2008, 6117. (14) (a) Tanaka, Y.; Inagaki, A.; Akita, M. Chem. Commun. 2007, 1169. (b) Tanaka, Y.; Ishisaka, T.; Inagaki, A.; Koike, T.; Lapinte, C.; Akita, M. Chem. - Eur. J. 2010, 16, 4762. (15) Chan, J. C.-H.; Lam, W. H.; Wong, H.-L.; Zhu, N.; Wong, W.T.; Yam, V. W.-W. J. Am. Chem. Soc. 2011, 133, 12690. (16) Morimoto, M.; Miyasaka, H.; Yamashita, M.; Irie, M. J. Am. Chem. Soc. 2009, 131, 9823. (17) Ordronneau, L.; Nitadori, H.; Ledoux, I.; Singh, A.; Williams, J. A. G.; Akita, M.; Guerchais, V.; Le Bozec, H. Inorg. Chem. 2012, 51, 5627. (18) He, B.; Wenger, O. S. Inorg. Chem. 2012, 51, 4335. (19) Zhong, Y.-W.; Vila, N.; Henderson, J. C.; Flores-Torres, S.; Abruna, H. D. Inorg. Chem. 2007, 46, 10470. (20) (a) Jukes, R. T. F.; Adamo, V.; Hartl, F.; Belser, P.; De Cola, L. Inorg. Chem. 2004, 43, 2779. (b) Fraysse, S.; Coudret, C.; Launay, J.-P. Eur. J. Inorg. Chem. 2000, 2000, 1581. (21) Neilson, B. M.; Lynch, V. M.; Bielawski, C. W. Angew. Chem., Int. Ed. 2011, 50, 10322. (22) Neilson, B. M.; Bielawski, C. W. J. Am. Chem. Soc. 2012, 134, 12693. (23) Lin, Y.; Yin, J.; Yuan, J.; Hu, M.; Li, Z.; Yu, G.-A.; Liu, S. H. Organometallics 2010, 29, 2808. (24) Indelli, M. T.; Carli, S.; Ghirotti, M.; Chiorboli, C.; Ravaglia, M.; Garavelli, M.; Scandola, F. J. Am. Chem. Soc. 2008, 130, 7286. (25) Roberts, M. N.; Nagle, J. K.; Majewski, M. B.; Finden, J. G.; Branda, N. R.; Wolf, M. O. Inorg. Chem. 2011, 50, 4956. (26) (a) Uchida, K.; Yamanoi, Y.; Yonezawa, T.; Nishihara, H. J. Am. Chem. Soc. 2011, 133, 9239. (b) Green, K. A.; Cifuentes, M. P.; Corkery, T. C.; Samoc, M.; Humphrey, M. G. Angew. Chem., Int. Ed. 2009, 48, 7867. (27) Aubert, V.; Ishow, E.; Ibersiene, F.; Boucekkine, A.; Williams, J. A. G.; Toupet, L.; Metivier, R.; Nakatani, K.; Guerchais, V.; Le Bozec, H. New J. Chem. 2009, 33, 1320. (28) (a) Zhao, H.; Al-Atar, U.; Pace, T. C. S.; Bohne, C.; Branda, N. R. J. Photochem. Photobiol., A 2008, 200, 74. (b) Tian, H.; Chen, B.; Tu, H.; Mullen, K. Adv. Mater. 2002, 14, 918. (29) (a) Yam, V. W.-W.; Lee, J. K.-W.; Ko, C.-C.; Zhu, N. J. Am. Chem. Soc. 2009, 131, 912. (b) Wong, H.-L.; Tao, C.-H.; Zhu, N.; Yam, V. W.-W. Inorg. Chem. 2011, 50, 471. (30) Tan, W.; Li, X.; Zhang, J.; Tian, H. Dyes Pigm. 2011, 89, 260. (31) Zhong, Y.-W.; Vila, N.; Henderson, J. C.; Abruna, H. D. Inorg. Chem. 2009, 48, 7080. (32) Hervault, Y.-M.; Ndiaye, C. M.; Norel, L.; Lagrost, C.; Rigaut, S. Org. Lett. 2012, 14, 4454. (33) Kim, H. J.; Jang, J. H.; Choi, H.; Lee, T.; Ko, J.; Yoon, M.; Kim, H.-J. Inorg. Chem. 2008, 47, 2411. (34) Chen, S.; Chen, L.-J.; Yang, H.-B.; Tian, H.; Zhu, W. J. Am. Chem. Soc. 2012, 134, 13596. (35) Roberts, M. N.; Carling, C.-J.; Nagle, J. K.; Branda, N. R.; Wolf, M. O. J. Am. Chem. Soc. 2009, 131, 16644. (36) Li, B.; Wu, Y.-H.; Wen, H.-M.; Shi, L.-X.; Chen, Z.-N. Inorg. Chem. 2012, 51, 1933. (37) Li, B.; Wen, H.-M.; Wang, J.-Y.; Shi, L.-X.; Chen, Z.-N. Inorg. Chem. 2013, 52, 12511. (38) Li, B.; Wang, J.-Y.; Wen, H.-M.; Shi, L.-X.; Chen, Z.-N. J. Am. Chem. Soc. 2012, 134, 16059. (39) Xu, G.-T.; Li, B.; Wang, J.-Y.; Zhang, D.-B.; Chen, Z.-N. Chem. Eur. J. 2015, 21, 3318. (40) Perrier, A.; Maurel, F.; Jacquemin, D. Acc. Chem. Res. 2012, 45, 1173. (41) Perrier, A.; Maurel, F.; Jacquemin, D. J. Phys. Chem. C 2011, 115, 9193. (42) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;

Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (43) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (44) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett. 1996, 77, 3865. (45) (a) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454. (b) Casida, M. E.; Jamorski, C.; Casida, K. C.; Salahub, D. R. J. Chem. Phys. 1998, 108, 4439. (c) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys. 1998, 109, 8218. (46) (a) Barone, V.; Cossi, M.; Tomasi, J. J. Chem. Phys. 1997, 107, 3210. (b) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem. Phys. 2002, 117, 43. (47) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270. (b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284. (c) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (48) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654. (49) Pyykkő , P.; Runeberg, N.; Mendizabal, F. Chem. - Eur. J. 1997, 3, 1451. (50) Ros, P.; Schuit, G. C. A. Theor. Chim. Acta (Berl.) 1966, 4, 1. (51) Lu, T.; Chen, F. W. J. Comput. Chem. 2012, 33, 580.

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DOI: 10.1021/acs.inorgchem.5b02175 Inorg. Chem. XXXX, XXX, XXX−XXX