Harnessing Fluorescence versus Phosphorescence Ratio via Ancillary

Article pubs.acs.org/JPCC

Harnessing Fluorescence versus Phosphorescence Ratio via Ancillary Ligand Fine-Tuned MLCT Contribution Ilya Kondrasenko,† Kun-you Chung,‡ Yi-Ting Chen,‡ Juha Koivistoinen,§ Elena V. Grachova,∥ Antti J. Karttunen,*,⊥ Pi-Tai Chou,*,‡ and Igor O. Koshevoy*,† †

University of Eastern Finland, Department of Chemistry, Joensuu 80101, Finland National Taiwan University, Department of Chemistry, Taipei 10617, Taiwan § University of Jyväkylä, Department of Chemistry, P.O. Box 35, FI-40014 Jyväskylä, Finland ∥ St.-Petersburg State University, Institute of Chemistry, St.-Petersburg 198504, Russia ⊥ Aalto University,Department of Chemistry, FI-00076 Aalto, Finland ‡

S Supporting Information *

ABSTRACT: A series of gold(I) alkynyl-diphosphine complexes (XC 6 H 4 C 2 Au)PPh 2 spacerPPh 2 (AuC2 C 6 H 4 X); spacer = C2(C6H4)nC2 (A1, n = 2, X = CF3; A2, n = 2, X = OMe; A3, n = 3, X = CF3; A4, n = 3, X = OMe), (C6H4)n (B5, n = 3, X = OMe; B6, n = 4, X = OMe) were prepared, and their photophysical properties were investigated. The luminescence behavior of the titled compounds is dominated by the diphosphine spacer, which serves as an emitting ππ* chromophore. The complexes exhibit dual emission, comprising low and high energy bands of triplet (phosphorescence) and singlet (fluorescence) origins, respectively. The electron-donating characteristics of ancillary groups X significantly affect the LLCT/MLCT contribution of both alkynyl ligand and the metal center into the lowest lying excited state. In turn, it substantially influences the rate of intersystem crossing kisc S1 → Tm (m ≥ 1) that allows for tuning the ratio fluorescence vs phosphorescence without alteration of the chromophore core. Quantum chemical analysis of the excited states at the CC2/TZVP level of theory supports the experimental observations. Crystalline complexes A2 and B5, which exhibit dominating phosphorescence emission, for the first time for the unsupported gold luminophores were probed as molecular oxygen sensors (max KSV1 = 63 atm−1).

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which can be slower than 1011−1012 s−1. This is in sharp contrast to the late transition metal complexes having dπ contribution in the lowest lying state (e.g., metal to ligand charge transfer, MLCT), in which the rate constant of S1 (ππ*) → Tn (ππ*, n ≥ 1) intersystem crossing, kisc, is commonly >1012 s−1. When the ISC rate constant kisc becomes comparable to that of S1 → S0 radiative decay (i.e., of the order 109−1010 s−1), dual emission comprising fluorescence and phosphorescence can be observed at room temperature both in solution and the solid state.14−20 The compounds demonstrating wellseparated singlet and triplet emissions of commensurable intensities remain scarce. Nevertheless, this class of luminophores holds a potential to serve as means for the development of novel detection techniques17,21−25 and photonic devices.26,27 However, in the case of slow ISC, the dπ orbitals, which are capable of participating in the metal to ligand dπ → π* charge transfer (MLCT), contribute to a higher excited state Sn (n ≥

INTRODUCTION Combining the transition metal ions with organic chromophores has proven to be an effective strategy for the diversification of their photophysical and optoelectronic properties.1 A variety of hybrid metal−organic and organometallic compounds with intriguing optical characteristics found applications in the fields of organic light emitting devices,2,3 imaging,4−6 sensing,3,7−9 solar energy conversion,10 and photocatalysis.11,12 The presence of a heavy element can efficiently induce spin− orbit coupling and considerably accelerate the process of intersystem crossing (ISC), which leads to the population of the lowest triplet state T1 with high efficiency. The T1 → S0 radiative decay gives rise to long-lived phosphorescence that substantially expands the functionality of luminescent materials and the areas of their practical utilization.13 The late transition metal complexes, for which the lowest lying transition has mainly an intraligand ππ* character, possess several unique features. In particular, the limited contribution of the metal dπ orbitals into the excited state results in relatively slow rates of S1 (ππ*) → Tn (ππ*, n ≥ 1) intersystem crossing, © XXXX American Chemical Society

Received: March 24, 2016 Revised: May 19, 2016

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DOI: 10.1021/acs.jpcc.6b03064 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C 2). The corresponding ISC Sn → Tm (m, n ≥ 2) is dramatically accelerated to the rates ≫1011 s−1 that makes it competitive with the internal conversion Sn → S1 and/or vibrational relaxation. As a result, the ratio for the fluorescence vs phosphorescence is excitation-wavelength dependent, which is unconventional from the viewpoint of classical spectroscopy in the condensed phase. In other words, increasing the ISC efficiency and thus harvesting of less fluorescence and more phosphorescence via using higher energy excitation, is so far a rare but important phenomenon that does not follow the traditional Kasha’s rule.18 As it was shown, slow rate of S1 → Tn ISC can be systematically probed by varying the distance r between the center of ligand chromophore and the heavy metal core with small MLCT contribution (e.g., AuI ion). As the spin orbit coupling is roughly proportional to Z4/r3 (Z is the atomic number),28 hence the ratiometric fluorescence/phosphorescence intensity could be fine-tuned via distance dependent external heavy atom effect.19,29 Since the variation of geometry parameters (i.e., r value) and/or the nature of the heavy element could be a synthetically challenging task, we explored a possibility to influence the emission parameters of the metal−chromophore systems through the modulation of electronic characteristics of the peripheral constituents, which are expected to influence the energy of dπ orbitals. Herein, via rational altering the ancillary ligands in the gold-diphosphine compounds, we report on the harnessing of the fluorescence versus phosphorescence by tuning the MLCT contribution to the dominant ππ* transition, paving a new dimension to the late transition metal complexes.

and Ph2C2(C6H4)2C2PPh2 (53 mg, 0.093 mmol). Precipitated by slow addition of excess of hexanes to a CH2Cl2-toluene solution (4 cm3, 1:1 v/v mixture) of A2. Nearly colorless microcrystalline material (81 mg, 72%). Single crystals suitable for X-ray diffraction analysis were obtained by a gas phase diffusion of pentane into a dichloromethane−toluene solution (1:1 v/v mixture) of 2 at room temperature. 1H NMR (CDCl3; 298 K, δ): 7.88 (dd, JPH 14.1, JHH 7.7 Hz, 8H, ortho-H Ph), AB system centered at 7.67 (JHH 8.4 Hz, 8H, C6H4C2P), 7.55− 7.48 (m, 12H, meta+para-H Ph), 7.47 (d, JHH 8.8 Hz, 4H, metaHC6H 4OMe), 6.81 (d, JHH 8.8 Hz, 4H, ortho-H C6H4OMe), 3.80 (s, 6H, OMe). 31P{1H} NMR (CDCl3; 298 K, δ): 16.9 (s). Anal. Calcd. for C58H42Au2O2P2: C, 56.78; H, 3.45. Found: C, 57.36; H 3.72. (AuC2C6H4CF3)2(Ph2C2(C6H4)3C2PPh2) (A3). Prepared analogously to A1 using (AuC2C6H4CF3)n (54 mg, 0.148 mmol) and Ph2C2(C6H4)3C2PPh2 (50 mg, 0.077 mmol). Precipitated by slow addition of excess of hexanes to a CH2Cl2−toluene solution (4 cm3, 1:1 v/v mixture) of A3. Nearly colorless microcrystalline material (94 mg, 92%). 31P{1H} NMR (CDCl3; 298 K, δ): (s). 1H NMR (CDCl3; 298 K, δ): 7.89 (dd, JPH 14.2 Hz, JHH 7.9 Hz, 8H, ortho-H Ph), 7.73 (s, 4H, C6H4C6H4C6H4), 7.70 (s, 8H, C6H4C2P), 7.60 (d, JHH 8.3 Hz, 4H, C6H4CF3), 7.54 (dm, JHH 7.6 Hz, 8H, metaH Ph), 7.53 (d, JHH 8.3 Hz, 4H, C6H4CF3). 7.51 (m, 4H, para-H Ph). 31P{1H} (CDCl3, 298 K; δ) 16.5 (s). Anal. Calcd. for C64H40Au2F6P2: C, 55.75; H, 2.92. Found: C, 55.86; H 3.12. (AuC2C6H4OMe)2(Ph2C2(C6H4)3C2PPh2) (A4). Prepared analogously to A1 using (AuC2C6H4OMe)n (62 mg, 0.189 mmol) and Ph2C2(C6H4)3C2PPh2 (63 mg, 0.098 mmol). Precipitated by slow addition of excess of hexanes to a CH2Cl2CHCl3 solution (2.5 cm3, 2:0.5 v/v mixture) of A4. Colorless flaky material (86 mg, 70%). 1H NMR (CDCl3, 298 K; δ) 7.89 (dd, JPH 14.2 Hz, JHH 7.6 Hz, 8H, ortho-H Ph), 7.72 (s, 4H, C6H4 C6H4C6H4), 7.69 (s, 8H, C6H4C2P), 7.53 (m, 4H, paraH Ph), 7.51 (dm, JHH 7.6 Hz, 8H, meta-H Ph), 7.47 (d, JHH 8.9 Hz, 4H, meta-H C6H4OMe), 6.81 (d, JHH 8.9 Hz, 4H, orthoH C6H4OMe), 3.80 (s, 6H, OMe). 31P{1H} (CDCl3, 298 K; δ) 16.9 (s). Anal. Calcd. for C64H46Au2O2P2: C, 59.00; H, 3.56. Found: C, 58.76; H 3.55. (AuC2C6H4OMe)2(Ph2(C6H4)3PPh2) (B5). Prepared analogously to A1 using (AuC2C6H4OMe)n (78 mg, 0.238 mmol) and Ph2 (C6H4)3PPh2 (73 mg, 0.122 mmol). Precipitated by slow addition of excess of diethyl ether to a CH2Cl2−toluene solution (5 cm3, 1:1 v/v mixture) of B5. Nearly colorless microcrystalline material (131 mg, 88%). 1H NMR (CDCl3; 298 K, δ): 7.71 (s, 4H, C6H4C6H4C6H4), 7.75−7.58 (m, 16H), 7.56−7.48 (m, 12H), 7.47 (d, JHH 8.8 Hz, 4H, meta-H C6H4OMe), 6.81 (d, JHH 8.8 Hz, 4H, ortho-H C6H4OMe), 3.80 (s, 6H, OMe). 31P{1H} NMR (CDCl3; 298 K, δ): 42.4 (s). Anal. Calcd. for C60H46Au2O2P2: C, 57.43; H, 3.70. Found: C, 57.21; H 3.71. (AuC2C6H4OMe)2(Ph2(C6H4)4PPh2) (B6). Prepared analogously to A1 using (AuC2C6H4OMe)n (52 mg, 0.159 mmol) and Ph2C2(C6H4)4C2PPh2 (58 mg, 0.086 mmol). Precipitated by slow addition of excess of hexanes to a CH2Cl2CHCl3 solution (2.5 cm3, 2:0.5 v/v mixture) of B6. Colorless microcrystalline material (97 mg, 92%). 1H NMR (CDCl3; 298 K, δ): AB system centered at 7.74 (JHH 8.6 Hz, 8H,  C6H4P), 7.70−7.58 (m, 16H), 7.56−7.49 (m, 12H), 7.48 (d, JHH 8.8 Hz, 4H, meta-H C6H4OMe), 6.81 (d, JHH 8.8 Hz, 4H, ortho-H C6H4OMe), 3.80 (s, 6H, OMe). 31P{1H} NMR

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EXPERIMENTAL SECTION General Comments. The diphosphines PPh2C2(C6H4)nC2PPh2 (n = 2 (L1), 3 (L2))30,31 and PPh2(C6H4)nPPh2 (n = 3 (L3))32 were synthesized according to published procedures. PPh2(C6H4)nPPh2 (n = 4 (L4)) was prepared analogously to L3 from 4,4‴-dibromoquaterphenyl. Complexes {Au(1-C2-4-X-C6H4)}n (X = CF3, OMe) were prepared similarly to (AuC2Ph)n33 using commercially available alkynes 1-HC2-4-X-C6H4. Other reagents were used as received. The solution 1H, 31P{1H} and 1H1H COSY NMR spectra were recorded on a Bruker 400 MHz Avance spectrometer. Microanalyses were carried out at the analytical laboratory of the University of Eastern Finland. (AuC2C6H4CF3)2(Ph2C2(C6H4)2C2PPh2) (A1). (AuC2C6H4CF3)n (90 mg, 246 mmol) was suspended in CH2Cl2 (10 cm3) and Ph2C2(C6H4)2C2PPh2 (70 mg, 0.123 mmol) was added. The suspension turned into slightly opaque solution within minutes. The reaction mixture was stirred for 30 min in the absence of light, treated with activated charcoal, passed through a layer of Al2O3 (neutral, 0.5 × 3 cm2) and evaporated. Amorphous solid was dissolved in CHCl3 (2 cm3) and an excess of hexanes was slowly added to cause precipitation of A1. The resulting colorless microcrystalline material was washed with pentane, diethyl ether and vacuumdried (144 mg, 90%). 1H NMR (CDCl3; 298 K, δ): 7.88 (dd, JPH 14.2 Hz, JHH 7.9 Hz, 8H, ortho-H Ph), AB system centered at 7.68 (JHH 8.4 Hz, 8H, C6H4C2P), 7.60 (d, JHH 8.1 Hz, 4H, C6H4CF3), 7.57−7.49 (m, 16H). 31P{1H} NMR (CDCl3; 298 K, δ): 16.6 (s). Anal. Calcd. for C58H36Au2F6P2: C, 53.47; H, 2.79. Found: C, 53.31; H 2.88. (AuC2C6H4OMe)2(Ph2C2(C6H4)2C2PPh2) (A2). Prepared analogously to A1 using (AuC2C6H4OMe)n (60 mg, 0.183 mmol) B


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The Journal of Physical Chemistry C (CDCl3; 298 K, δ): 42.4 (s). Anal. Calcd. for C66H50Au2O2P2: C, 59.56; H, 3.79. Found: C, 59.65; H 3.79. X-ray Structure Determination. The crystal of A2 was immersed in cryo-oil, mounted in a Nylon loop, and measured at a temperature of 150 K. The diffraction data were collected on a Bruker Kappa Apex diffractometer using Mo Kα radiation (λ = 0.71073 Å). The APEX234 program package was used for cell refinements and data reductions. The structures were solved by direct methods using the SHELXS-201435 program with the WinGX36 graphical user interface. A semiempirical absorption correction (SADABS)37 was applied to all data. Structural refinements were carried out using SHELXL-2014.35 The dichloromethane crystallization solvent molecule was partially lost and therefore was refined with 0.5 occupancy. A series of geometric and displacement constraints and restraints were applied to this moiety. Additionally, some of the lost solvent could not been resolved unambiguously. The contribution of the missing solvent to the calculated structure factors was taken into account by using a SQUEEZE routine of PLATON.38 The missing solvent was not taken into account in the unit cell content. All hydrogen atoms were positioned geometrically and constrained to ride on their parent atoms, with CH = 0.95−0.99 Å, Uiso = 1.2−1.5 Ueq (parent atom). The crystallographic details are summarized in Table S1 of the Supporting Information (SI). Photophysical Measurements. The steady-state absorption and emission spectrum were recorded in CH2Cl2 with a Hitachi (U-3310) spectrophotometer and an Edinburgh (FS920) fluorometer. Coumarin 480 and Rodamine 6G (quantum yields of 0.87 in methanol and 0.95 in ethanol, respectively) were used as reference dyes to determine the emission quantum yields in CH2Cl2. In order to determine the phosphorescence quantum yield, the samples were degassed by three freeze−pump−thaw cycles. Picosecond lifetime measurements were performed using an Edinburgh OB 900-L timecorrelated single photon counting (TCSPC) system with a system response time of 25 ps. A femtosecond Ti-Sapphire oscillator (80 MHz, Tsunami, Spectra-Physics) served as the light source after the third harmonic generation of the fundamental laser. Computational Details. The quantum chemical calculations were carried out using the Second-Order Approximate Coupled-Cluster method (CC2), which is an approximation of the Coupled Cluster Singles and Doubles (CCSD) method.39 All atoms were described by a triple-valence-zeta quality basis set with polarization functions (def2-TZVP for Au, def-TZVP for other elements).40 Scalar relativistic effects were taken into account by employing a 60-electron relativistic effective core potential for gold.41 The resolution-of-the-identity technique was used to speed up the calculations.42,43 The geometries of both ground and excited states were fully optimized.44−46 The S0 → S1 excitations were determined at the optimized ground state S0 geometries, while the S1 → S0 and T1 → S0 emissions were determined at the optimized S1 and T1 geometries, respectively. CC2 has been shown to produce excitation energies that compare well with experimental values.47 Furthermore, CC2 is not affected by the so-called spurious charge-transfer states that often result in problems for Timedependent Density Functional Theory (TD-DFT).48 For the molecules studied here, CC2 showed superior performance in comparison to TD-DFT-PBE0. For example, for the complex A2, TD-DFT predicts S0 → S1 wavelength of 442 nm, while

CC2 predicts 314 nm, and the experimental value is 306 nm. For the S1 → S0 emission, the wavelengths are 545 (TD-DFT), 367 (CC2), and 350 nm (experiment). Finally, for the T1 → S0 emission, the wavelengths are 768 (TD-DFT), 550 (CC2), and 525 nm (experiment). The studied complexes can rotate freely around the P(spacer)P axis and we utilized C2h point group symmetry to facilitate comparisons with the experiments and to speed up calculations. The procedure for carrying out the atoms-in-molecules (Bader) analysis of the S0 and S1 electron densities is outlined in the SI. All electronic structure calculations were carried out with the TURBOMOLE program package (version 7.0).49

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RESULTS AND DISCUSSION Synthesis and Characterization. The target dinuclear compounds (XC6H4C2Au)PPh2spacerPPh2(AuC2C6H4X) were prepared following a well-established synthetic route,33,50−52 which involves reactions of (AuC2R)n polymers with corresponding diphosphine ligands PPh2-spacer-PPh2 in 2:1 molar ratio (see Experimental Section). The complexes form two series (A1−A4) and (B5, B6) based on the type of diphosphine spacers, comprising alkynyl-phenylene PPh2C2(C6H4)nC2PPh2 (A1, n = 2, X = CF3; A2, n = 2, X = OMe; A3, n = 3, X = CF3; A4, n = 3, X = OMe) or phenylene backbones PPh2(C6H4)nPPh2 (X = OMe, n = 3 (B5), 4 (B6)), Scheme 1. The similar species H1−H4 bearing phenylacetylene ligands PhCC were described in our earlier publications.19,52 Scheme 1. Structures of complexes A1−A4, B5, B6, and H1− H4

All compounds were isolated as nearly colorless microcrystalline powders in good yields (70−92%). Complex A2 was characterized crystallographically (Figure 1). The solid state structure of A2 reveals the expected bidentate binding mode of the ligand to the gold centers and a typical linear coordination geometry of the metal ions.50,53−55 Two molecules of A2 were found to form a dimer via aurophilic contacts (Au···Au distance is 3.0652(4) Å), that is quite common for this type of phosphine-supported Au(I) species.52,54,56,57 All titled complexes were investigated by 1H, 31P{1H} NMR spectroscopy and elemental analyses. The 31P{1H} NMR spectra of these compounds show singlet resonances with characteristic chemical shift 16.5−16.9 and 42.4 ppm for A and B series, respectively. The observed δ parameters for A1−A4 complexes are virtually identical to the characteristics of close congeners (PhC2Au)2PPh2C2(C6H4)nC2PPh219 and demonstrate only slight variation upon changing the X substituent of the C


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The Journal of Physical Chemistry C

pounds. To attain this goal, we attempted to modify the model complexes (PhC2Au)PPh2C2(C6H4)nC2PPh2(AuC2Ph) (n = 2 (1H), 3 (2H)), which exhibit low and high energy bands of different ratio and intensity depending on the number of phenylene groups.19 Introduction of the substituents X with contrasting electronic characteristics into the alkynyl moieties XC6H4C2 does not show a pronounced influence on the energy of a low lying absorption S0 → S1 for the pairs of diphosphine-related complexes A1, A2 and A3, A4 (Table 1 and Figure 2). Quantum chemical analysis of the excited states at the CC2/ TZVP level of theory (see the Experimental Section for computational details) reveals that this low energy transition for CF3-functionalized species A1 and A3 can be ascribed to a phosphine-localized intraligand π → π* excitation (Figures 3 and S1, Table 2). In particular, for the complex A3, the contribution of the RAu fragment to the S0 → S1 excitation is only 7%. However, changing the X = CF3 to a MeO group significantly increases the participation of boththe alkynyl fragment and the gold centerinto the S0 → S1 electronic transitions. These CCR IL/LLCT and MLCT contributions are particularly visible for the complex A2 (Figure 3), and dramatically decrease upon elongation of the diphosphine spacer from A2 (n = 2) to A4 (n = 3), in which the contribution of the RAu fragment to the S0 → S1 excitation drops from 44% (A2) to 15% (A3), Table 2 and Figure S1. The latter can be assigned to the increase of π-conjugation and stabilization (destabilization) of the LUMO (HOMO) levels of the diphosphine spacer, diminishing the involvement of metal dπ and alkynyl orbitals into the HOMO.19,52 In contrast to the absorption spectra, the X groups have a drastic effect on the luminescence properties of compounds A1−A4 (Figure 2). The emission spectrum of the CF3containing complex A1 exhibits strong high energy HE band (λem = 352 nm, the F band) along with weak lower energy LE band (λem = 527 nm, the P band) of 30-fold smaller intensity (Φf/Φp is 0.12/0.004). The observed lifetimes for the F band (τobs = 46 ps) and drastic quenching of the P band by molecular oxygen allow for the assignment of HE and LE emissions to fluorescence and phosphorescence, respectively, which is in line with analogous analysis done earlier for the congener H1 compound.19,52 Interestingly, complex A2 bearing electrondonating group X = MeO demonstrates an opposite behavior from the viewpoint of fluorescence vs phosphorescence ratio. The spectrum of A2 also displays two bands, which have essentially the same energy as those observed for A1 (Table 1). However, the red-shifted P band (λem = 525 nm) now has 6-

Figure 1. Molecular view of the complex A2. Selected interatomic distances (Å) are C(1)Au(1) 2.018(5), C(38)Au(2) 2.007(5), P(1)Au(1) 2.2732(13), P(2)Au(2) 2.2670(12), Au(1)Au(2′) 3.0652(4). Symmetry transformations to generate equivalent atoms (′): 1/2−x, 3/2−y, 1−z.

alkynyl ligand XC6H4C2 from electron-withdrawing  CF3 to electron-donating OMe group. The proton NMR spectra (see Experimental Section) for A1−A4 and B5, B6 match well the proposed structures. The given assignment is additionally supported by the comparison with the patterns reported for the related Au(I) compounds containing these diphosphine ligands.19,52 Together with 31P NMR data, the results of spectroscopic studies in solution point that all the complexes exist in their molecular forms, without appreciable intermolecular aggregation via Au···Au interactions. Photophysical Properties. The bridging phosphine ligands, which possess phenylene- or alkynyl-phenylene bridging π-systems, determine the emission characteristics of their Au(I) complexes (RAu)PPh2spacerPPh2(AuR), as it was previously shown in our publications.19,52,56 The length of the spacer allows for the variation of the effective distance between the organic ππ* chromophore center and the heavy atom (Au), which affects the spin−orbit coupling and, under favorable conditions, enhances S1 (ππ*) → T1 (ππ*) intersystem crossing, resulting in appearance of phosphorescence bands. In addition to the studied distance modulation, we aimed to explore the possible effect of the electronic properties of ancillary ligands R, bound to Au(I) ions, on the dual emission of the (RAu)PPh2spacerPPh2(AuR) com-

Table 1. Photophysical Properties of the Au(I) Complexes A1−A4 and B5, B6 in CH2Cl2 (298 K) A1 1Ha A2 A3 2Ha A4 3Ha B5 4Ha B6 a

X

λab/nm (10−4 ε/cm−1 M−1)

CF3 H OMe CF3 H OMe H OMe H OMe

287(6.9), 316(5.9) 320(5.7) 306(6.6) 287(6.2), 320(6.3) 340(7.2) 323(6.8) 285(5.5) 302 (13) 285(5.5), 320(5.6) 303 (11)

λem (nm) 352, 361, 350, 375, 372, 375, 360, 352, 373, 372,

372, 525 370, 395, 550 395, 510 371, 534 391,

527, 570 525, 570 547 548, 591 514, 552 532

Φfb

τf (ps)

Φpb

τp (μs)

0.12 0.077 0.004 0.35 0.4 0.084 0.16 0.021 0.53 0.17

46 65 29 177 450 39 75 69 213 125

0.004 0.034 0.024 0.002 0.02 0.059 0.08 0.12 0.062 0.0008

266 296 320 70 680 290 266 330 2060 294

Ref. 19 bThe excitation wavelength is 300 nm. D


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Figure 2. UV−vis absorption and emission spectra of A1−A4 in degassed CH2Cl2. The emission was acquired via excitation at the peak wavelength of the lowest lying absorption band.

Figure 3. Electron density difference plots for the lowest energy singlet excitation (S0 → S1), singlet emission (S1 → S0), and triplet emission (T1 → S0) of the complexes A1 and A2 (isovalue 0.002 au). During the electronic transition, the electron density increases in the blue areas and decreases in the red areas. Hydrogen atoms omitted for clarity.

Table 2. Computational Photophysical Results for the Complexes A1−B6 (CC2/TZVP Level of Theory)a λ (S0 → S1) (nm) theor. A1 A2 A3 A4 B5 B6

307 314 325 326 312 327

(2.9) (2.1) (3.4) (3.4) (2.4) (3.2)

λ (S1 → S0) (nm)

λ (T1 → S0) (nm)

contribution to S0 → S1 (%)

exp.b

theor.

exp.b

theor.

exp.b

RAuc

diphosphinec

316 306 320 323 302 303

357 367 378 378 359 380

352 350 375 375 352 372

550 550 565 565 537 560

527 525 547 548 514 532

20 44 7 15 31 10

80 56 93 85 69 90

a

Wavelenghts in nm, oscillator strengths given in parentheses. bExperimental excitation and emission wavelengths correspond to solution-state data monitored at peak value. cContribution of the RAu fragment/diphosphine fragment to the S0 → S1 excitation (%). The contribution % has been determined from atoms-in-molecules (Bader) analysis of the S0 and S1 electron densities (see SI for details).

fold larger intensity than the F band (Φf/Φp is 0.004/0.024), see Figure 2A. Thus, in the series of the complexes containing the same diphosphine chromophore (A1, H1 and A2), the Φf/ Φp ratio is determined by the electronic characteristics of the ancillary ligand, namely by the substituent X of the alkyne, and severely drops upon increase of its electron-donating ability: CF3 (Φf/Φp = 30) > H (2.26) > OMe (0.17).

This trend can be qualitatively rationalized in terms of changing the energy level of Au(I) dπ orbitals, which are responsible for the MLCT contribution into the excited state. According to the absorption measurements and the computational studies, HOMO/LUMO are mainly composed of π/π* orbitals of the diphosphine conjugated spacer, the levels of which are nearly independent of the variation of ancillary alkynes. Conversely, the electron donating X group is expected E


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The Journal of Physical Chemistry C to increase the electron density on the metal ion and therefore destabilize Au(I) dπ orbitals, raising their energies and bringing them closer to the π level of conjugated organic chromophore. Consequently, a smaller energy separation between the metal and ligand orbitals should lead to a larger mixing of ππ* and MLCT excited states, resulting in the appearance of a prominent or even dominating phosphorescence emission detected for A2. Preserving almost the same emission wavelengths in A1 and A2 indicates that the S1−T1 energy gap remains intact upon modification of the alkynyl ligand. As a result, a constant ΔES1−T1 value calculated to be ∼27 kcal/mol for A1 and A2 (as a difference in peak wavelengths between F and P bands) is in the range found for other aromatic species, and proves the prevailing ππ* nature in the lowest lying excited states. The ascendant character of fluorescence in the emission profile of A1 and a relatively high quantum efficiency points to a slow intersystem crossing rate S1 → Tm (m ≥ 1), which cannot compete with much faster S1 → S0 radiative decay for this complex. The ISC rate constant is given as follows: k isc ∝

Figure 4. UV−vis absorption and emission spectra of B5 and B6 in degassed CH2Cl2. The emission was acquired via excitation at the peak wavelength of the lowest lying absorption band.

In accordance with the tendency found for A1−A4 compounds, B5 exhibits a smaller relative intensity of F band vs P band (Φf/Φp = 0.175) in comparison to its phenylacetylene congener 3H (Φf/Φp = 2.0).19 However, MeOfunctionalization of 4H does not induce emergence of appreciable phosphorescence in B6, but causes a substantial decrease of fluorescence quantum yield from 0.53 to 0.17, pointing to the activation of nonradiative decay pathways instead of MLCT contribution to the excited states. The title compounds show different photophysical behavior in the solid state. Complexes A1−A4 display weak room temperature emissions (Figure S3), which appear as poorly resolved HE broad bands for all of them except A2. The latter compound demonstrates only the LE band virtually at the same wavelength as it was found in the solution (vide supra), which, together with large Stokes shift, indicates the relaxation form the triplet excited state. Cooling the powder samples A1−A4 to 77 K does not change substantially their emission profiles, but dramatically increases phosphorescence intensity for A2. By analogy with solution luminescence of these species, weak HE bands of A1, A3, and A4 may be assigned to the intraligand transitions 1ππ* transitions. Low intensity at both 298 and 77 K suggests effective quenching of fluorescence as a result of solid state aggregation that is often observed for singlet luminophores.60 Nearly identical emission energies are observed for A2 in both solution and solid. Since A2 in solution exists in molecular form, while it forms dimer in the crystalline state, the similar emission spectral feature points to a negligible effect of aurophilic interactions on the corresponding photophysics. Instead, the transition is dominated by the moiety of diphosphine bridges. Similarly to A1, A3, and A4, complexes B5 and B6 as solids exhibit weak fluorescence at 298 K, which is almost independent of temperature. However, in addition to HE bands of singlet origins, both compounds display intense phosphorescence emissions at 77 K (Figure 5). It was shown previously that fluorescence vs phosphorescence intensity could depend on the excitation wavelength both in solution and in the solid film.18,19,61 To further extend this concept, we probed complexes A4 and B5 to vary the intensity ratio of the singlet and triplet bands. As depicted in Figure S4, the LE emissions can be significantly enhanced upon increasing the excitation energy. The observed phenomenon corresponds to the population of the T1 state via Si → Tj (i, j >

|⟨ΨT1|HSO|ΨS1⟩|2 (ΔES1− T1)2

where HSO is the Hamiltonian for spin−orbit coupling. As the energy gap ΔES1−T1 is not changed by the alteration of X of the alkynyl ligand, a substantial growth of kisc, that corresponds to switching the emission from the singlet state in the case of A1 to the triplet state in A2, should be driven by a larger contribution of metal dπ orbitals into the low lying transitions, i.e., the increase of MLCT character.58 In the absence of appreciable dπ participation caused by electron accepting alkyne (i.e., small internal heavy atom effect due to dπ stabilization), the Au(I) ions operate only as external heavy atoms, the influence of which falls off approximately as 1/r6, where r is the distance between the heavy element and the center of the emitting chromophore.19,59 The similar behavior is observed for the series comprising the complexes A3, H2,19 and A4 (Figure 2B and Table 1), which contain diphosphine ligand with elongated spacer  C2(C6H4)3C2. The ratio fluorescence vs phosphorescence follows the same trend as for the compounds described above and decreases as the X substituent becomes more donating to give dual emission for A4 with comparable intensities of the components: CF3 (Φf/Φp = 175) > H (20) > OMe (1.4). The experimental results are supported by the computational studies, which reveal negligible contribution of the metal orbitals into the S1 excited state for A3 and a larger participation of Au(I) ions in the S0 → S1 transition of A4 (Table 2, Figure S1). Therefore, the fine-tuning of dual luminescence can be effectively realized not only varying the molecular geometry (i.e., via spatial modulation of r parameter) that could be synthetically challenging, but also via accessible modification of the ancillary constituting blocks (changing their donor− acceptor characteristics) that allows keeping the same emissive core to attain different ratios in the emission intensity. To extend this concept of phosphorescence induction we also prepared the MeO-substituted complexes (MeOC 6 H 4 C 2 Au)Ph 2P(C 6 H 4 ) n PPh 2(AuC 2 C 6 H 4 OMe) based on the oligophenylene diphosphines, B5 (n = 3) and B6 (n = 4). The corresponding absorption and emission spectra are given in Figure 4. F


Article


Figure 5. Solid state emission spectra of B5 and B6 (λexc = 355 nm).

Figure 6. Emission spectra of the complexes A2 (a) and B5 (b) under different concentrations of O2; (c,d) the corresponding Stern−Volmer plots of A2 and B5.

phosphor [Au2{μ-(Ph2P)2NR}2I2] for the fabrication of a plastic thin film device.72 A crucial requirement for the solid state O2 phosphorescent sensors lies in sufficiently high porosity of a sample that offers good gas adsorption and well-developed internal surface to increase the probability of collisional luminescence quenching. The channels suitable for the guest molecules accommodation can be provided via (a) embedding the triplet emitting center into the suitable solid supporting material;62,73,74 (b) design of porous coordination polymers or metal−organic frameworks incorporating luminescent fragments;64,75−77 or (c) using the molecular complexes for the preparation of the crystalline materials with appreciable void space.68,78,79 According to the X-ray diffraction analysis, the potential solvent area for the crystalline complex A2 reaches 27% of the unit cell volume upon removal of all the crystallization solvent molecules. This void space considerably exceeds the corresponding values reported for the copper(I) O2-sensitive compounds,68,80 and therefore, together with triplet origin of

1) ISC in the higher excited states, which allows avoiding relatively slow S1 → Tm (m ≥ 1) ISC. Molecular Oxygen Sensing by Complexes A2 and B5. One of the successful applications of the phosphorescent complexes of transition metals encompasses photoluminescent sensing for molecular oxygen. Efficient quenching via triplet− triplet annihilation, when the triplet excited state of a luminophore undergoes a collisional exchange energy transfer with O2 (triplet ground state), results in a dramatic decrease of emission intensity and shortening of the lifetime. Several families of inorganic and organometallic compounds containing lanthanide ions and those of d-elements (Ru(II), Ir(III), Re(I), Pt(II), and Cu(I)) demonstrate a variable capability for oxygen sensing.62−68 Numerous luminescent gold(I) species have been described to date,5,57,69,70 including compounds exhibiting luminescence that is responsive to the environmental changes.8,71 Surprisingly, to the best of our knowledge, there was only one report on the O2 sensitive materials, which employs Au(I) complexesa dinuclear phosphine-iodide G


Article

The Journal of Physical Chemistry C luminescence, A2 seems to be a promising candidate in a view of a sensing application. Indeed, the dried microcrystalline A2 shows appreciable emission in the absence of oxygen (under the inert atmosphere or in vacuum, λem = 535 nm). On the contrary, upon exposure to oxygen the complex becomes very poorly emissive. The Stern−Volmer plot showing the dependence of signal intensity vs O2 concentration (Figure 6) is nonlinear and thus was treated in accordance with a two-site model,63 which takes into account possible inhomogeneity of the sample or a two-component emission. The emission fractions were fitted to be 0.9 and 0.1 with the corresponding SV constants KSV1 = 63 atm−1 and KSV1 = 0.5 atm−1, respectively. This sensitivity is comparable to that of Cu(I) isocyanide diimine complexes.79 Complex B5, which exhibits dual emission in the solid state, also demonstrates an oxygen sensing ability in a microcrystalline form. Its low energy phosphorescence band is largely quenched by O2 (Figure 6). However, the sensitivity of B5 (Ksv1 = 45 atm−1, Ksv1 = 10−4 atm−1) is visibly lower than that of A2. One possibility for the discrepancy may lie in the difference in the radiative lifetime, which, unfortunately, cannot be deduced due to the infeasibility to obtain the weak emission yield in solid. Alternatively, we simply use the phosphorescence radiative lifetime of A2 and B5 in CH2Cl2 which is deduced to be 1.3 × 10−2 s and 2.75 × 10−3 s, respectively, from Table 1. The longer radiative lifetime in A2 leads to more sensitive O2 quenching, consistent with the results shown in Figure 5. Another possibility could be due to the difference in space/ morphology. However, the failure in obtaining proper crystals of B5 makes this hypothesis pending. Moreover, fitting the SV plot with two-site approach shows large contribution of the second fraction (f 2 = 0.32), which is virtually insensitive to oxygen that greatly diminishes the sensitivity of the material. Nevertheless, the complexes A2 and B5 showing a significant contribution of triplet emission prove a promising potential for the effective employment of the gold complexes as solid state molecular oxygen sensors. A possible strategy to improve their effectiveness might involve incorporation of the phosphorescent luminophores into the supports with developed porosity that could eliminate the heterogeneity of the responsive component.

slow rates of ISC. In contrast, the electron-rich group X = MeO (A2, A4, B5, and B6) dramatically enhances the contribution of the alkynyl fragment and of the gold(I) ion into the lowest lying excited state, also confirmed by the computational analysis. An increase of the LLCT/MLCT character of electronic transition causes a substantial growth of kisc S1 → Tm (m ≥ 1) and efficiently induces the emission from the triplet state. This phenomenon allows for tuning the fluorescence vs phosphorescence ratio (Φf/Φp = 30 for A1, Φf/Φp = 2.26 for H1, Φf/Φp = 0.17 for A2) without stereochemical modification of the emitting chromophore but only through simply changing the ancillary groups, which opens up new possibilities for expanding the functionality of luminescent transition metal complexes. In addition, we demonstrated for the first time for the unsupported Au(I) compounds their potential utilization as molecular oxygen sensors, provided the species exhibit dominating phosphorescence emission and possess developed surface area.

CONCLUSIONS In summary, we describe a family of dinuclear gold(I) complexes (XC 6 H 4 C 2 Au)PPh 2 spacerPPh 2 (Au C2C6H4X) with bridging diphosphine ligands, for which we disclosed an unconventional and facile way of tuning dual emission characteristics. These compounds, possessing (phenylene)n and alkynyl(phenylene)n spacers as chromophore motifs, demonstrate photoluminescence that originates from the dominant intraphosphine ππ* transition and comprises low (phosphorescence) and high (fluorescence) energy bands. The ratio of the singlet and triplet emissions is determined by the rates of S1 → S0 radiative decay and of intersystem crossing S1 → Tm (m ≥ 1). The latter, as was shown earlier, can be modulated via variation of the effective distance reff between the perturbing Au ion and the chromophore. Alternatively, the electronic properties of ancillary groups C2C6H4X appeared to have strong influence the luminescence features of the studied compounds. The electron-withdrawing group X = CF3 (A1, A3) favors high-energy fluorescence by means of stabilization the dπ metal orbitals and therefore diminishing their participation into the low energy transitions, that results in

Notes

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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.jpcc.6b03064. (Table S1) Crystal data and structure refinement for A2; (Figures S1 and S2) electron density difference plots; (Figure S3) solid state emission spectra of A1−A4 (PDF) X-ray crystallographic data for A2 (CIF) Optimized Cartesian coordinates of the studied systems (XYZ)

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AUTHOR INFORMATION

Corresponding Authors

*Phone: +358-50-3473475. E-mail: antti.j.karttunen@aalto.fi (A.J.K.). *Phone: +886-2-3366-3894. E-mail: [email protected] (P.T.C.). *Phone: +358504422694. E-mail: igor.koshevoy@uef.fi (I.O.K.).

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the Academy of Finland (grant 268993, I.O.K.; grant 138560, A.J.K.), the Alfred Kordelin Foundation (A.J.K.), University of Eastern Finland (Spearhead project) and the Russian Foundation for Basic Research (grant 14-0300970) is gratefully acknowledged. Computational resources were provided by CSCthe Finnish IT Center for Science (A.J.K.).

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REFERENCES

(1) Castellano, F. N. Altering Molecular Photophysics by Merging Organic and Inorganic Chromophores. Acc. Chem. Res. 2015, 48, 828− 839. (2) Kalinowski, J.; Fattori, V.; Cocchi, M.; Williams, J. A. G. LightEmitting Devices Based on Organometallic Platinum Complexes as Emitters. Coord. Chem. Rev. 2011, 255, 2401−2425. (3) Wong, K. M.-C.; Chan, M. M.-Y.; Yam, V. W.-W. Supramolecular Assembly of Metal-Ligand Chromophores for Sensing and Phosphorescent OLED Applications. Adv. Mater. 2014, 26, 5558−5568.

H


Article

The Journal of Physical Chemistry C (4) Lo, K. K.-W.; Choi, A. W.-T.; Law, W. H.-T. Applications of Luminescent Inorganic and Organometallic Transition Metal Complexes as Biomolecular and Cellular Probes. Dalton Trans. 2012, 41, 6021−6047. (5) Langdon-Jones, E. E.; Pope, S. J. A. Recent Developments in Gold(I) Coordination Chemistry: Luminescence Properties and Bioimaging Opportunities. Chem. Commun. 2014, 50, 10343−10354. (6) Lo, K. K.-W. Luminescent Rhenium(I) and Iridium(III) Polypyridine Complexes as Biological Probes, Imaging Reagents, and Photocytotoxic Agents. Acc. Chem. Res. 2015, 48, 2985−2995. (7) Guerchais, V.; Fillaut, J.-L. Sensory Luminescent Iridium(III) and Platinum(II) Complexes for Cation Recognition. Coord. Chem. Rev. 2011, 255, 2448−2457. (8) He, X.; Yam, V. W.-W. Luminescent Gold(I) Complexes for Chemosensing. Coord. Chem. Rev. 2011, 255, 2111−2123. (9) McConnell, A. J.; Wood, C. S.; Neelakandan, P. P.; Nitschke, J. R. Stimuli-Responsive Metal−Ligand Assemblies. Chem. Rev. 2015, 115, 7729−7793. (10) Wong, W.-y.; Ho, C.-L. Organometallic Photovoltaics: A New and Versatile Approach for Harvesting Solar Energy Using Conjugated Polymetallaynes. Acc. Chem. Res. 2010, 43, 1246−1256. (11) Kumar, A.; Sun, S.-S.; Lees, A. J. Photophysics and Photochemistry of Organometallic Rhenium Diimine Complexes. Top. Organomet. Chem. 2010, 29, 1−35. (12) Takeda, H.; Koike, K.; Morimoto, T.; Inumaru, H.; Ishitani, O. Photochemistry and Photocatalysis of Rhenium(I) Diimine Complexes. In Inorganic Photochemistry; van Eldik, R., Stochel, G., Eds.; Elsevier: Amsterdam, 2011; pp 137−186. (13) Yam, V. W.-W. Photofunctional Organometallics  from Fundamentals to Design, Assembly and Functions. Pure Appl. Chem. 2013, 85, 1321−1329. (14) Cheng, Y.-M.; Yeh, Y.-S.; Ho, M.-L.; Chou, P.-T.; Chen, P.-S.; Chi, Y. Dual Room-Temperature Fluorescent and Phosphorescent Emission in 8-Quinolinolate Osmium(II) Carbonyl Complexes: Rationalization and Generalization of Intersystem Crossing Dynamics. Inorg. Chem. 2005, 44, 4594−4603. (15) Kozhevnikov, D. N.; Kozhevnikov, V. N.; Shafikov, M. Z.; Prokhorov, A. M.; Bruce, D. W.; Williams, J. A. G. Phosphorescence vs Fluorescence in Cyclometalated Platinum(II) and Iridium(III) Complexes of (Oligo)thienylpyridines. Inorg. Chem. 2011, 50, 3804− 3815. (16) Lu, W.; Kwok, W.-M.; Ma, C.; Chan, C. T.-L.; Zhu, M.-X.; Che, C.-M. Organic Triplet Excited States of Gold(I) Complexes with Oligo(o- or m-phenyleneethynylene) Ligands: Conjunction of SteadyState and Time-Resolved Spectroscopic Studies on Exciton Delocalization and Emission Pathways. J. Am. Chem. Soc. 2011, 133, 14120− 14135. (17) Liu, Y.; Guo, H.; Zhao, J. Ratiometric Luminescent Molecular Oxygen Sensors Based on Uni-luminophores of Ĉ N Pt(II) (acac) Complexes that Show Intense Visible-light Absorption and Balanced Fluorescence/Phosphorescence Dual Emission. Chem. Commun. 2011, 47, 11471−11473. (18) Hsu, C.-C.; Lin, C.-C.; Chou, P.-T.; Lai, C.-H.; Hsu, C.-W.; Lin, C.-H.; Chi, Y. Harvesting Highly Electronically Excited Energy to Triplet Manifolds: State-Dependent Intersystem Crossing Rate in Os(II) and Ag(I) Complexes. J. Am. Chem. Soc. 2012, 134, 7715− 7724. (19) Chang, Y.-C.; Tang, K.-C.; Pan, H.-A.; Liu, S.-H.; Koshevoy, I. O.; Karttunen, A. J.; Hung, W.-Y.; Cheng, M.-H.; Chou, P.-T. Harnessing Fluorescence versus Phosphorescence Branching Ratio in (Phenyl)n-Bridged (n = 0 ∼ 5) Bimetallic Au(I) Complexes. J. Phys. Chem. C 2013, 117, 9623−9632. (20) Geist, F.; Jackel, A.; Winter, R. F. Ligand Based Dual Fluorescence and Phosphorescence Emission from BODIPY Platinum Complexes and Its Application to Ratiometric Singlet Oxygen Detection. Inorg. Chem. 2015, 54, 10946−10957. (21) Zhang, G.; Palmer, G. M.; Dewhirst, M.; Fraser, C. L. A DualEmissive-Materials Design Concept Enables Tumour Hypoxia Imaging. Nat. Mater. 2009, 8, 747−751.

(22) Chen, H.; Li, X.; Wu, Y.; Gao, W.; Bai, R. A Ruthenium(II) Complex with Environment-Responsive Dual Emission and its Application in the Detection of Cysteine/Homocysteine. Dalton Trans. 2012, 41, 13292−13297. (23) Lin, C.-J.; Chen, C.-Y.; Kundu, S. K.; Yang, J.-S. Unichromophoric Platinum-Acetylides That Contain Pentiptycene Scaffolds: Torsion-Induced Dual Emission and Steric Shielding of Dynamic Quenching. Inorg. Chem. 2014, 53, 737−745. (24) Hara, D.; Komatsu, H.; Son, A.; Nishimoto, S.-i.; Tanabe, K. Water-Soluble Phosphorescent Ruthenium Complex with a Fluorescent Coumarin Unit for Ratiometric Sensing of Oxygen Levels in Living Cells. Bioconjugate Chem. 2015, 26, 645−649. (25) Yoshihara, T.; Murayama, S.; Tobita, S. Ratiometric Molecular Probes Based on Dual Emission of a Blue Fluorescent Coumarin and a Red Phosphorescent Cationic Iridium(III) Complex for Intracellular Oxygen Sensing. Sensors 2015, 15, 13503−13521. (26) Reineke, S.; Seidler, N.; Yost, S. R.; Prins, F.; Tisdale, W. A.; Baldo, M. A. Highly Efficient, Dual State Emission from an Organic Semiconductor. Appl. Phys. Lett. 2013, 103, 093302. (27) Kabe, R.; Notsuka, N.; Yoshida, K.; Adachi, C. Afterglow Organic Light-Emitting Diode. Adv. Mater. 2016, 28, 655−660. (28) McGlynn, S. P.; Azumi, T.; Kinoshita, M. Molecular Spectroscopy of the Triplet State; Prentice-Hall: Englewood Cliffs, NJ, 1969; p 434. (29) Chang, Y.-C.; Tang, K.-C.; Pan, H.-A.; Koshevoy, I. O.; Karttunen, A. J.; Chou, P.-T. Harvesting Fluorescence from Efficient Tk→Sj (j, k > 1) Reverse Intersystem Crossing for ππ* Emissive Transition Metal Complexes. J. Phys. Chem. C 2013, 117, 20494− 20499. (30) Koshevoy, I. O.; Ostrova, P. V.; Karttunen, A. J.; Melnikov, A. S.; Khodorkovskiy, M. A.; Haukka, M.; Jänis, J.; Tunik, S. P.; Pakkanen, T. A. Assembly of the Heterometallic Au(I)-M(I) (M = Cu, Ag) Clusters Containing the Dialkyne-Derived Diphosphines: Synthesis, Luminescence and Theoretical Studies. Dalton Trans. 2010, 39, 9022−9031. (31) Koshevoy, I. O.; Lin, C.-L.; Karttunen, A. J.; Jänis, J.; Haukka, M.; Tunik, S. P.; Chou, P.-T.; Pakkanen, T. A. Stepwise 1D Growth of Luminescent Au(I)-Ag(I) Phosphine-Alkynyl Clusters: Synthesis, Photophysical and Theoretical Studies. Inorg. Chem. 2011, 50, 2395−2403. (32) Koshevoy, I. O.; Karttunen, A. J.; Tunik, S. P.; Haukka, M.; Selivanov, S. I.; Melnikov, A. S.; Serdobintsev, P. Y.; Khodorkovskiy, M. A.; Pakkanen, T. A. Supramolecular Luminescent Gold(I)Copper(I) Complexes: Self-assembly of the AuxCuy Clusters inside the [Au3(diphosphine)3]3+ Triangles. Inorg. Chem. 2008, 47, 9478− 9488. (33) Coates, G. E.; Parkin, C. Gold(I) Alkynyls and their Coordination Complexes. J. Chem. Soc. 1962, 3220−3226. (34) APEX2Software Suite for Crystallographic Programs; Bruker AXS, Inc.: Madison, WI, 2010. (35) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (36) Farrugia, L. J. WinGX and ORTEP for Windows: an Update. J. Appl. Crystallogr. 2012, 45, 849−854. (37) Sheldrick, G. M. SADABS-2008/1-Bruker AXS Area Detector Scaling and Absorption Correction; Bruker AXS: Madison, Wisconsin, USA, 2008. (38) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool, 1.17; Utrecht University: Utrecht, The Netherlands, 2013. (39) Christiansen, O.; Koch, H.; Jørgensen, P. The Second-Order Approximate Coupled Cluster Singles and Doubles Model CC2. Chem. Phys. Lett. 1995, 243, 409−418. (40) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (41) Andrae, D.; Häußermann, U.; Dolg, M.; Stoll, H.; Preuß, H. Energy-Adjusted Ab Initio Pseudopotentials for the Second and Third Row Transition Elements. Theor. Chem. Acc. 1990, 77, 123−141. I


Article


Containing Extended Linear Arylacetylenes. Eur. J. Inorg. Chem. 2012, 2012, 4048−4056. (62) Medina-Rodriguez, S.; Marin-Suarez, M.; Fernandez-Sanchez, J. F.; de la Torre-Vega, A.; Baranoff, E.; Fernandez-Gutierrez, A. High Performance Optical Sensing Nanocomposites for Low and Ultra-Low Oxygen Concentrations Using Phase-Shift Measurements. Analyst 2013, 138, 4607−4617. (63) Wang, X.-d.; Wolfbeis, O. S. Optical Methods for Sensing and Imaging Oxygen: Materials, Spectroscopies and Applications. Chem. Soc. Rev. 2014, 43, 3666−3761. (64) Liu, S.-Y.; Qi, X.-L.; Lin, R.-B.; Cheng, X.-N.; Liao, P.-Q.; Zhang, J.-P.; Chen, X.-M. Porous Cu(I) Triazolate Framework and Derived Hybrid Membrane with Exceptionally High Sensing Efficiency for Gaseous Oxygen. Adv. Funct. Mater. 2014, 24, 5866−5872. (65) Li, M.; Zheng, B.; Luo, D.; Sun, H.; Wang, N.; Huang, Y.; Dai, J.; Xiao, D.; Su, S.-J.; Lu, Z. Small Molecular Neutral Microcrystalline Iridium(III) Complexes as Promising Molecular Oxygen Sensors. Chem. Commun. 2015, 51, 1926−1929. (66) Nishikawa, M.; Wakita, Y.; Nishi, T.; Miura, T.; Tsubomura, T.; Long-Lived. and Oxygen-Responsive Photoluminescence in the Solid State of Copper(I) Complexes Bearing Fluorinated Diphosphine and Bipyridine Ligands. Dalton Trans. 2015, 44, 9170−9181. (67) Zhao, Q.; Zhou, X.; Cao, T.; Zhang, K. Y.; Yang, L.; Liu, S.; Liang, H.; Yang, H.; Li, F.; Huang, W. Fluorescent/Phosphorescent Dual-Emissive Conjugated Polymer Dots for Hypoxia Bioimaging. Chem. Sci. 2015, 6, 1825−1831. (68) Chakkaradhari, G.; Chen, Y.-T.; Karttunen, A. J.; Dau, M. T.; Jänis, J.; Tunik, S. P.; Chou, P.-T.; Ho, M.-L.; Igor, O. Koshevoy Luminescent Triphosphine-Cyanide d10 Metal Complexes. Inorg. Chem. 2016, 55, 2174−2184. (69) Yam, V. W.-W.; Wong, K. M.-C. Luminescent Metal Complexes of d6, d8 and d10 Transition Metal Centres. Chem. Commun. 2011, 47, 11579−11592. (70) Yam, V. W.-W.; Au, V. K.-M.; Leung, S. Y.-L. Light-Emitting Self-Assembled Materials Based on d8 and d10 Transition Metal Complexes. Chem. Rev. 2015, 115, 7589−7728. (71) Jobbágy, C.; Deák, A. Stimuli-Responsive Dynamic Gold Complexes. Eur. J. Inorg. Chem. 2014, 2014, 4434−4449. (72) Mills, A.; Lepre, A.; Theobald, B. R. C.; Slade, E.; Murrer, B. A. Use of Luminescent Gold Compounds in the Design of Thin-Film Oxygen Sensors. Anal. Chem. 1997, 69, 2842−2847. (73) Wang, Y.; Li, B.; Liu, Y.; Zhang, L.; Zuo, Q.; Shi, L.; Su, Z. Highly Sensitive Oxygen Sensors Based on Cu(I) Complex− Polystyrene Composite Nanofibrous Membranes Prepared by Electrospinning. Chem. Commun. 2009, 5868−5870. (74) Borisov, S. M.; Lehner, P.; Klimant, I. Novel Optical Trace Oxygen Sensors Based on Platinum(II) and Palladium(II) Complexes with 5,10,15,20-Meso-Tetrakis-(2,3,4,5,6-Pentafluorphenyl)-Porphyrin Covalently Immobilized on Silica-Gel Particles. Anal. Chim. Acta 2011, 690, 108−115. (75) Xie, Z.; Ma, L.; deKrafft, K. E.; Jin, A.; Lin, W. Porous Phosphorescent Coordination Polymers for Oxygen Sensing. J. Am. Chem. Soc. 2010, 132, 922−923. (76) Qi, X.-L.; Liu, S.-Y.; Lin, R.-B.; Liao, P.-Q.; Ye, J.-W.; Lai, Z.; Guan, Y.; Cheng, X.-N.; Zhang, J.-P.; Chen, X.-M. Phosphorescence Doping in a Flexible Ultramicroporous Framework for High and Tunable Oxygen Sensing Efficiency. Chem. Commun. 2013, 49, 6864− 6866. (77) Dou, Z.; Yu, J.; Cui, Y.; Yang, Y.; Wang, Z.; Yang, D.; Qian, G. Luminescent Metal−Organic Framework Films as Highly Sensitive and Fast-Response Oxygen Sensors. J. Am. Chem. Soc. 2014, 136, 5527−5530. (78) Smith, C. S.; Mann, K. R. Void Space Containing Crystalline Cu(I) Phenanthroline Complexes As Molecular Oxygen Sensors. Chem. Mater. 2009, 21, 5042−5049. (79) Smith, C. S.; Mann, K. R. Exceptionally Long-Lived Luminescence from [Cu(I) (isocyanide)2(phen)]+ Complexes in Nanoporous Crystals Enables Remarkable Oxygen Gas Sensing. J. Am. Chem. Soc. 2012, 134, 8786−8789.

(42) Weigend, F.; Häser, M.; Patzelt, H.; Ahlrichs, R. RI-MP2: Optimized Auxiliary Basis Sets and Demonstration of Efficiency. Chem. Phys. Lett. 1998, 294, 143−152. (43) Hellweg, A.; Hättig, C.; Höfener, S.; Klopper, W. Optimized Accurate Auxiliary Basis Sets for RI-MP2 and RI-CC2 Calculations for the Atoms Rb to Rn. Theor. Chem. Acc. 2007, 117, 587−597. (44) Hättig, C.; Weigend, F. CC2 Excitation Energy Calculations on Large Molecules Using the Resolution of the Identity Approximation. J. Chem. Phys. 2000, 113, 5154−5161. (45) Hättig, C. Geometry Optimizations with the Coupled-Cluster Model CC2 Using the Resolution-of-the-Identity Approximation. J. Chem. Phys. 2003, 118, 7751−7761. (46) Köhn, A.; Hättig, C. Analytic Gradients for Excited States in the Coupled-Cluster Model CC2 Employing the Resolution-of-theIdentity Approximation. J. Chem. Phys. 2003, 119, 5021−5036. (47) Winter, N. O. C.; Graf, N. K.; Leutwyler, S.; Hättig, C. Benchmarks for 0−0 Transitions of Aromatic Organic Molecules: DFT/B3LYP, ADC(2), CC2, SOS-CC2 and SCS-CC2 Compared to High-Resolution Gas-Phase Data. Phys. Chem. Chem. Phys. 2013, 15, 6623−6630. (48) Magyar, R. J.; Tretiak, S. Dependence of Spurious ChargeTransfer Excited States on Orbital Exchange in TDDFT: Large Molecules and Clusters. J. Chem. Theory Comput. 2007, 3, 976−987. (49) Ahlrichs, R.; Bär, M.; Häser, M.; Horn, H.; Kölmel, C. Electronic Structure Calculations on Workstation Computers: the Program System Turbomole. Chem. Phys. Lett. 1989, 162, 165−169. (50) Yam, V. W.-W.; Choi, S. W.-K.; Cheung, K.-K. Synthesis and Design of Novel Tetranuclear and Dinuclear Gold(I) Phosphine Acetylide Complexes. First X-ray Crystal Structures of a Tetranuclear ([Au4(tppb)(CCPh)4]) and a Related Dinuclear ([Au2(dppb)(C CPh)2]) Complex. Organometallics 1996, 15, 1734−1739. (51) Ferrer, M.; Gutiérrez, A.; Rodríguez, L.; Rossell, O.; Lima, J. C.; Font-Bardia, M.; Solans, X. Study of the Effect of the Phosphane Bridging Chain Nature on the Structural and Photophysical Properties of a Series of Gold(I) Ethynylpyridine Complexes. Eur. J. Inorg. Chem. 2008, 2008, 2899−2909. (52) Koshevoy, I. O.; Lin, C.-L.; Hsieh, C.-C.; Karttunen, A. J.; Haukka, M.; Pakkanen, T. A.; Chou, P.-T. Synthesis, Characterization and Photophysical Properties of the PPh2-C2-(C6H4)n-C2-PPh2 Based Bimetallic Au(I) Complexes. Dalton Trans. 2012, 41, 937−945. (53) Lu, W.; Zhu, N.; Che, C.-M. Polymorphic Forms of a Gold(I) Arylacetylide Complex with Contrasting Phosphorescent Characteristics. J. Am. Chem. Soc. 2003, 125, 16081−16088. (54) Tiekink, E. R. T.; Kang, J.-G. Luminescence Properties of Phosphinegold(I) Halides and Thiolates. Coord. Chem. Rev. 2009, 253, 1627−1648. (55) Lin, Y.; Yin, J.; Yuan, J.; Hu, M.; Li, Z.; Yu, G.-A.; Liu, S. H. Synthesis, Characterization, and Properties of Binuclear Gold(I) Phosphine Alkynyl Complexes. Organometallics 2010, 29, 2808−2814. (56) Laguna, A.; Crespo, O.; Camara, J.; Koshevoy, I. O.; Ospino, I.; Smirnova, E. S.; Tunik, S. P. Emission Tuning in Dinuclear Gold Complexes with Diphosphines Containing Alkyne and/or Oligophenylene Spacers. Dalton Trans. 2012, 41, 13891−13898. (57) Schmidbaur, H.; Schier, A. Aurophilic Interactions as a Subject of Current Research: an Up-date. Chem. Soc. Rev. 2012, 41, 370−412. (58) Chou, P.-T.; Chi, Y.; Chung, M.-W.; Lin, C.-C. Harvesting Luminescence via Harnessing the Photophysical Properties of Transition Metal Complexes. Coord. Chem. Rev. 2011, 255, 2653− 2665. (59) Hsu, C.-W.; Lin, C.-C.; Chung, M.-W.; Chi, Y.; Lee, G.-H.; Chou, P.-T.; Chang, C.-H.; Chen, P.-Y. Systematic Investigation of the Metal-Structure-Photophysics Relationship of Emissive d10-Complexes of Group 11 Elements: The Prospect of Application in Organic Light Emitting Devices. J. Am. Chem. Soc. 2011, 133, 12085−12099. (60) Birks, J. B. Photophysics of Aromatic Molecules; Wiley: London, 1970; p 704. (61) Shakirova, J. R.; Grachova, E. V.; Melekhova, A. A.; Krupenya, D. V.; Gurzhiy, V. V.; Karttunen, A. J.; Koshevoy, I. O.; Melnikov, A. S.; Tunik, S. P. Luminescent AuI-CuI Triphosphine Clusters J


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