Ruthenium(II) Polypyridyl Complexes Coordinated Directly to the

Aug 22, 2017 - A series of new Bodipy dyes incorporating the π-extended isoquino[5,6-c]pyrrole have been synthesized and characterized. The dyes disp...
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Ruthenium(II) Polypyridyl Complexes Coordinated Directly to the Pyrrole Backbone of π‑Extended Boron Dipyrromethene (Bodipy) Dyes: Synthesis, Characterization, and Spectroscopic and Electrochemical Properties Shawn Swavey,* Sreedhar V. Kumar, and Jeremy Erb Department of Chemistry, University of Dayton, 300 College Park, Dayton, Ohio 45469-2357, United States S Supporting Information *

ABSTRACT: A series of new Bodipy dyes incorporating the π-extended isoquino[5,6-c]pyrrole have been synthesized and characterized. The dyes display intense Bodipy (π−π*) transitions and emissions with high quantum efficiencies. Spectroscopic, electrochemical, and theoretical calculations are used to give insight into the frontier orbitals. Coordination of {Ru(bpy)2Cl}+ subunits to the peripheral isoquinol nitrogen atoms of the Bodipy dyes leads to three new bis-Ru(II)-polypyridyl-Bodipy complexes with the Ru(II) centers in direct contact with the dipyrrin core. Spectroscopic studies of the complexes reveal the traditional metal to ligand charge transfer (MLCT) transitions associated with Ru(dπ) to bpy(π*) transitions. However, a more intense transition above 600 nm is also observed. This transition is independent of the meso-substituents of the dipyrrin and is shifted to lower energy by as much as 25 nm compared to that of the Bodipy dyes without the Ru(II) subunits. Spectroscopic, electrochemical, and spectroelectrochemical studies suggest that the Bodipy π-orbitals are destabilized by coordination of the Ru(II) moieties. All three Ru2−Bodipy complexes show the ability to generate singlet oxygen when irradiated within the photodynamic therapy window (600−850 nm) as evidenced by singlet oxygen trapping experiments.

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phototherapeutics.13,14 As stated, the majority of this research is focused on limiting the electronic interaction between the Bodipy dye and the Ru(II) polypyridyl complexes despite being covalently connected. There is, of course, a considerable advantage in generating compounds capable of intense dual emission; even so, the literature is sparse when it comes to examples of combining Bodipy dyes with Ru(II) polypyridyl complexes. We have been unable to find evidence of examples in which Ru(II) polypyridyl complexes are coordinated directly to the Bodipy core. Understandably, if the goal is to maintain limited electronic communication, coordinating the complexes directly to each other would not be ideal. On the other hand, it does pose an interesting exercise to evaluate the effect of combining two complexes with rich electrochemical and spectroscopic properties in such a way that favors electronic communication. To that end this laboratory has adapted our previously reported solid state dipyrrin reactions utilizing π-extended pyrroles15,16 to incorporate within the pyrrole unit nitrogen coordination sites. In this report, we describe the synthesis and characterization of new Bodipy dyes formed from isoquinopyrrole and a variety of aldehydes. These particular Bodipy dyes are equipped

INTRODUCTION For several years a growing interest in developing strategies to combine ruthenium(II) polypyridyl complexes with 4,4′difluoro-4-bora-3a,4a-diaza-s-indacene (Bodipy) dyes has emerged.1−8 To maintain the integrity of the properties displayed by the individual components, recent work in this area has focused on tethering ruthenium(II) complexes to the meso-positions of the Bodipy dyes. By extending the distance between the Bodipy core and the Ru(II) polypyridyl complexes, while maintaining a covalent connection, the hope has been to limit the electronic communication between the emitting centers and thus generate dual emission. This, however, has been difficult to achieve, and an exhaustive literature search has revealed only one example in which this has been successfully accomplished.4 In this example the Bodipy dye is connected through a meso-phenyl group to phenanthroline which is subsequently coordinated to {Ru(bpy)2}2+. Through this elegant synthetic route, the authors achieved a complex capable of maintaining the luminescent properties of both the Bodipy dye and the Ru(II) polypyridyl complex. The impetus for much of this work is due, in part, to the rich optical properties of the individual components, including intense absorption in the visible region of the spectrum and high quantum efficiencies. Applications range from electro-optics,9−11 light-harvesting for solar cells,10,12 and © XXXX American Chemical Society

Received: June 27, 2017

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DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Route to New Bodipy Dyes

to allow for coordination of two {Ru(bpy)2Cl}+ complexes directly to the Bodipy pyrrole units. To our knowledge this represents the first series of bis-ruthenium(II) Bodipy dyes of this kind.

Table 1. Spectroscopic and Electrochemical Data for Bodipy Dyes 1−3

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RESULTS AND DISCUSSION Bodipy Dyes: Synthesis, Characterization, and Theoretical Calculations. We have recently described a two-step synthetic strategy toward new Bodipy dyes incorporating naphthyl and fluoranthro pyrroles.15,16 Herein, we have expanded this methodology to include isoquino[5,6-c]pyrrole and a variety of aldehydes, Scheme 1. The choice of isoquino[5,6-c]pyrrole allows for two coordination sites positioned on the dipyrrin core. The aldehydes represented present both electron donating and electron withdrawing substituents allowing for investigation of the effect of these meso-substituents on the photophysical and electrochemical properties of the dyes. In this procedure, the desired aldehyde and isoquinopyrrole were dissolved in a minimum of solvent (choice of solvent depends only on the solubility of the reagents), typically 1−2 mL. Once the reagents were dissolved, the solvent was removed under reduced pressure, and the resulting solid homogeneous mixture was heated in a water bath to 90 °C, at which point the brownish mixture turns a bright purple. Heating was allowed to continue for ca. 20 min, and the purple paste was chromatographed on silica to remove any unreacted or polymerized material. The crude dipyrromethene was combined with excess triethyl amine and boron trifluoroetherate in DCM under nitrogen and allowed to stir at room temperature overnight. Workup of the reaction mixture followed by chromatography and recrystallization from DCM/hexanes gave the desired Bodipy dyes in roughly 15% yield. 1H NMR and high resolution mass spectrometry (SI Sections S1 and S2, respectively) confirmed the proposed structures. In general, Bodipy dyes display intense absorption bands in the visible region of the electromagnetic spectrum, a consequence of coordination to the BF2 group resulting in alignment of the π-orbitals of the dipyrromethene.17,18 In addition, these dyes typically generate sharp emission lines with near unit quantum efficiencies when excited at their absorption maxima. The spectrosopic properties of Bodipy compounds 1− 3 display intense absorption and emission spectra in the visible region of the spectrum (Figures S1−S3), with maximum absorption bands ranging from 585 to 587 nm, Table 1. This bathochromic shift, compared to the spectra of traditional Bodipy dyes, is a consequence of the extended π-system granted by the isoquinol pyrrole units. It has been noted that

Bodipy

λabs (nm)

ε (M−1 cm−1)

λem (nm)

ϕfla

LUMO (eV)

HOMO (eV)

1 2 3

585 587 585

75 30020 131 000 138 000

594 594 592

0.50 0.45 0.81

−3.66 −3.76 −3.76

−5.86 −5.68 −5.62

a

Fluorescence quantum yields were obtained using Rhodamine 6G as a reference (ϕ = 0.94 in ethanol).21

the electronic transitions associated with Bodipy dyes result from excitation of the HOMO electrons localized on the dipyrrin core. It is therefore not surprising that, in the case of Bodipy dyes 1−3, the excitation wavelength appears to be independent of the meso-substituent, Table 1. Likewise, the emission spectra indicate modest Stokes shifts ranging from 201 to 347 cm−1 for 1−3 which is typical of Bodipy dyes. One aspect that appears to be influenced by the type of mesosubstituent is evident from the fluorescent quantum yields, Table 1. It is not clear at this time why the quantum yields seem to vary so widely, and we hesitate to draw any conclusions from a relatively small sample of dyes. Further studies are underway to determine if the observed differences are an anomaly or a function of the aromatic substituents. Cyclic voltammetry experiments were performed to probe the HOMO and LUMO energies of 1−3. The voltammograms were run in dry DCM using a nonaqueous Ag/Ag+ (10 mM AgNO3) reference electrode and ferrocene as an internal standard. Figure 1 (top CV) illustrates the electrochemical properties of dye 1; dyes 2 and 3 are illustrated in Figures S4 and S5, respectively. For the Bodipy dyes 2 and 3, a reversible redox couple in the cathodic region with E1/2 = −1.04 V (Figures S4 and S5, respectively) is observed while for 1 the reversible redox couple is slightly more cathodic with E1/2 = −1.14 V. Similarly, dyes 2 and 3 show weak irreversible oxidation waves with Ep = 0.88 and 0.82 V, respectively, with dye 1 displaying a more intense irreversible oxidation wave with Ep = 1.06 V. The reduction waves correspond to LUMO energies of −3.76 eV for dyes 2 and 3 and −3.66 eV for dye 1.19 The HOMO energies correspond to −5.86, −5.68, and −5.62 eV for dyes 1, 2, and 3, respectively, Table 1. Theoretical calculations are often employed to understand the structure and photophysical properties of BODIPY compounds.22−29 In particular, frontier molecular orbital energies and shapes are often calculated using density functional theory (DFT) or time-dependent density functional theory (TD-DFT) to further the design process, since calculations are generally faster than experimental testing and B

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Figure 1. Cyclic voltammograms of 1, top, and Ru2-1, bottom, in deoxygenated DCM containing TBAPF6 as supporting electrolyte, and ferrocene as an internal standard. Glassy carbon working electrode, platinum wire auxiliary, and reference electrode nonaqueous Ag/Ag+.

Figure 2. Nodal patterns for the frontier molecular orbitals of dyes 1 and 2.

analysis.30−34 Time-dependent density functional theory (TDDFT) is also heavily used as a predictive tool since it performs with a favorable speed versus accuracy ratio, despite the inadequacies of the vertical approximation such as overestimation of the HOMO−LUMO energy gap and underestimation of the absorbance wavelength.35,36 In fact, these tools are the most widely employed computational tools to model ground state and excited state properties of small molecules.37 Range-separated hybrid functionals such as CAMB3LYP perform well in TD-DFT calculations to predict trends in BODIPY properties.38 We performed a series of calculations on dyes 1−3. Geometry optimizations at the B3LYP/6-31g(d) level with a polarizable continuum model (PCM) to model bulk solvent effects in chloroform were calculated using the DFT method. All three structures provided similar geometries with the arylmeso-group orthogonal to the relatively flat Bodipy core. The frontier molecular orbitals reveal similarities with other Bodipy compounds from the literature, such as the characteristic population of the meso-carbon with orbital density upon the HOMO to LUMO transition. Bodipy dye 1 shows an additional interesting feature since the arm is significantly populated in the HOMO and almost devoid of orbital density in the LUMO. This may explain the difference in the oxidation potential for dye 1 compared to 2 and 3 (which differ only slightly, Section S4). It is reasonable to assume that the peak potential at 1.06 V for dye 1 represents overlapping oxidation of the 3-methoxy-4-hydroxyphenyl side arm and the Bodipy πorbitals. Diagrams of their nodal patterns are depicted in Figure 2. PCM-TD-DFT calculations at the B3LYP/cc-pVTZ level in chloroform predict the dominant transition for 1−3 to be the HOMO to LUMO excitation for all compounds with high oscillator strengths (1.37−1.38). Each BODIPY was predicted to have a similar λmax with little difference observed for each substitution. For example, 1 was calculated to be within 2 nm of 2 (1, 518 nm; 2, 517 nm). This trend agrees with the observed experimental results, which differ by only 2 nm, Table 1. It is clear from both experimental and theoretical approaches that the effect of the meso-substituent plays a minimal role in the photophysical properties of the Bodipy dyes. Ru2−Bodipy Complexes: Synthesis, Electrochemistry, and Spectroscopy. As indicated, the incorporation of

isoquino-pyrrole into the Bodipy dyes gives two coordination sites directly on the dipyrrin core. This was accomplished by reacting the Bodipy dyes with an excess of cis-Ru(bpy)2Cl2 in refluxing ethanol under nitrogen, Scheme 2. The hexafluorophosphate salt of the complexes was obtained by addition of the reaction mixture to an aqueous solution of potassium hexafluorophosphate followed by filtration and washing with DI water. The air-dried precipitate was chromatographed on neutral alumina and recrystallized from a DCM/hexanes mixture to give the products in yields ranging from 50% to 70%. The products were analyzed by 1H NMR, high resolution mass spectrometry, and elemental analysis, Section S3. Cyclic voltammetry of the Ru2−Bodipy complexes lends insight into the effect of the peripheral Ru(II) centers on the Bodipy orbital energies. Figure 1 illustrates these effects on Ru2-1 (bottom CV, Figure 1) compared to its Bodipy analogue 1. The Ru2-1 complex, Figure 1, bottom, displays a redox couple with E1/2 = −1.03 V (ΔE = 70 mV) associated with the Bodipy LUMO. A broad irreversible oxidation process with Ep = 0.95 V, ascribed to the oxidation of the 3-methoxy-4hydroxyphenyl side arm, followed by a more intense oxidation with Ep = 1.09 V representing the oxidation of the Bodipy HOMO. These potentials correspond to HOMO/LUMO energies of −5.89 and −3.77 eV (Table 2), respectively, compared to −5.86 and −3.66 eV (Table 1) for its Bodipy analogue. This reflects, for Ru2-1, stabilization of the Bodipy π*-orbitals with an apparent stabilization of the Bodipy-π orbitals upon the coordination of two {Ru(bpy)2Cl}+ groups. In addition, a single redox couple with E1/2 = 0.50 V (ΔE = 70 mV) corresponds to the Ru(III/II) couple, indicating that the two Ru(II) centers act independently of each other. Cyclic voltammograms of the Ru2-2 and Ru2-3 complexes are illustrated in Figures S9 and S10, respectively, with the relevant data given in Table 2. It is worth noting that in the cyclic voltammograms of the complexes reduction of Ru(III) back to Ru(II) is extremely sharp, indicating a very fast electron transfer process. This however only occurs when the scan range is extended to include oxidation of the Bodipy π-orbitals which suggests that upon oxidation of the Bodipy core the complex is physisorbed onto the electrode. When the scan range is truncated to only look at the Ru(III/II) couple the redox process gives the typical reversible behavior, Figures S11−S13. C

DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 2. Route to New Ru2−Bodipy Complexes

Table 2. Spectroscopic and Electrochemical Data for Ru2−Bodipy Complexes complex Ru2-1

Ru2-2

Ru2-3

a

λmax (nm) 295 375 514 610 295 365 507 602 295 368 508 602

ε (M−1 cm−1)

redox potential

93 900 24 135 22 840 53 400 150 400 40 960 32 400 51 900 123 000 32 500 26 300 42 937

redox assignment

orbital energya

E1/2 = −1.03 V E1/2 = 0.50 V Epa = 1.09 V

0/−

Bodipy Ru(III/II) Bodipy+/0

−3.77 eV −5.30 eV −5.89 eV

E1/2 = −1.03 V E1/2 = 0.48 V Epa = 1.15 V

Bodipy0/− Ru(III/II) Bodipy+/0

−3.77 eV −5.28 eV −5.95 eV

E1/2 = −1.05 V E1/2 = 0.50 V Epa = 1.12 V

Bodipy0/− Ru(III/II) Bodipy+/0

−3.75 eV −5.30 eV −5.92 eV

From cyclic voltammetry data.19

redox chemistry.1−6 This is due to coordination of the Ru(II) center to strong field polypyridyl ligands. In the case of our Ru2−Bodipy complexes, however, one of the coordination sites is taken up by a weak field, π-donor chloride ligand, resulting in a destabilization of the Ru(II) t2g orbitals and oxidation of the Ru(II) centers prior to oxidation of the Bodipy core. One literature example of a Ru(II)−Bodipy dyad in which the Bodipy is linked to a {Ru(tpy)(bpy)Cl}+ subunit through a phenyl bridge displays the Ru(III/II) redox couple between the Bodipy0/− and Bodipy+/0 redox couples; however, no electronic communication between the two entities was observed.39 The electronic spectra, performed at room temperature in dry DCM, of the three Ru2−Bodipy complexes are illustrated in Figures S6−S8 and the data compiled in Table 2. The three spectra are similar to intense bipyridyl(π−π*) transitions at 295 nm accompanied by broad lower energy Ru(dπ) to bipyridyl(π*) metal to ligand charge transfer (MLCT) transitions appearing at ca. 370 and 510 nm. In addition, an intense transition at 610, 602, and 602 nm for Ru21, Ru2-2, and Ru2-3, respectively, is observed with molar absorptivities ranging from 43 000 to 53 000 M−1 cm−1. These lower energy transitions represent a significant bathochromic shift when compared to spectra from their Bodipy analogues. It has been noted for several ruthenium polypyridyl−Bodipy dyads that their spectra represent a linear combination of the spectra of the individual components due to weak electronic interactions between the ruthenium polypyridyl and Bodipy units of the dyads.6,7,39 For this reason, a comparison of Bodipy-1, Ru2-1, and the Ru2-dipyrrin,40 as well as Bodipy-2, Ru2-2, and Ru2-dipyrrin,41 are illustrated in Figures 3 and 4, respectively.

From the electrochemical data, we are able to construct a Jablonski diagram for the Ru2−Bodipy complexes and their Bodipy analogues, Scheme 3. From this diagram, it appears that Scheme 3. Jablonski Diagram of the Orbital Energies for the Bodipy Dyes and the Ru2−Bodipy Complexes Obtained from the Cyclic Voltammetry Experiments19

the Bodipy π- and π*-orbitals for dye 1 show the greatest effect from the electron donating meso-substituent; however, this is not reflected in the electronic spectra of the dyes whose λmax differ by only a couple of nanometers. Upon coordination of two {Ru(bpy)2Cl}+ groups to the Bodipy dyes, relatively small changes in the π*-orbitals of the Bodipy core are observed; however, there is significant stabilization of the Bodipy πorbitals. In many of the Ru−Bodipy dyads which have been studied the Ru(III/II) redox couple falls outside of the Bodipy D

DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. UV−vis spectra of 1, Ru2-1, and Ru2-dipyrrin in DCM at room temperature (RT).

Figure 4. UV−vis spectra of 2, Ru2-2, and Ru2-dipyrrin in DCM at RT.

It is clear from Figures 3 and 4 that, in the case of the Ru2− Bodipy complexes, the spectra do not represent a linear combination of the individual subunits. This suggests that the ruthenium polypyridyl and Bodipy subunits are indeed in electronic communication. From the spectroscopic data it is

apparent that upon coordination of the {Ru(bpy)2Cl}+ moieties to the Bodipy core a bathochromic shift of the lowest energy transition of 15−25 nm is observed, Tables 1 and 2. It is reasonable to assume that the red-shifted lowest energy transition observed in the spectra of the Ru2−Bodipy E

DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 5. UV−vis spectra of Ru2-1 in DCM before (red) and after (blue) bulk electrolysis of the solution at 0.65 V vs Ag/Ag+. Working electrode = platinum mesh flag, auxiliary electrode = platinum wire.

complexes is due to either a destabilization of the Bodipy πorbitals, stabilization of the Bodipy π*-orbitals, or some combination of both. From the electrochemical data and Jablonski diagram, Scheme 3, it is apparent that limited stabilization of the Bodipy π-orbitals would not explain this bathochromic shift. Destabilization of the Bodipy π-orbitals does not appear to be an explanation of the bathochromic shift since the electrochemical data (Scheme 3) indicate a stabilization of these orbitals. To this point we have not considered the Ru(II) dπ-orbitals when discussing the frontier orbitals. If we assume the Ru(II) dπ-orbitals represent the HOMO, then the lowest energy transition would be a Ru(dπ) to Bodipy(π*) MLCT transition. However, on the basis of the electrochemical data alone this MLCT transition would see a much greater bathochromic shift than what is observed in the electronic spectra. We are left with the possibility that the oxidation potentials observed for the Bodipy π-orbitals (for the Ru2−Bodipy complexes) are not a true representation of their orbital energy, and in fact, these orbitals are more likely destabilized upon coordination of the {Ru(bpy)2Cl}+ moieties. This is not unreasonable since measuring the oxidation potentials of the Bodipy π-orbitals requires first oxidation of the Ru(II) centers to Ru(III) leading to an overall +4 charge on the complexes. This would result in a significant electrostatic effect at the electrode surface resulting in an anodic shift of subsequent oxidation waves. With the proposed spectral assignments, it is reasonable to expect limited emission due to internal quenching. Even in the case of reported ruthenium polypyridyl Bodipy dyads, where electronic communication between the ruthenium and Bodipy cores is minimized, both the phosphorescence of the Ru(II) center and the fluorescence of the Bodipy were quenched.1,2 As expected, we were unable to detect emission upon excitation at the lowest energy absorption band, for the Ru2−Bodipy

complexes, in DCM at 298 K and in a 1:1 DCM/toluene glass at 77 K. The observation that the Ru2−Bodipy complexes are nonemissive at room temperature and in a frozen glass supports a quenching mechanism by either energy transfer or intersystem crossing. To further probe the transition assignments, spectroelectrochemical experiments were performed on the Ru2−Bodipy complexes. To accomplish this, solutions of the Ru2−Bodipy complexes, containing TBAPF6 as supporting electrolyte, were bulk electrolyzed at a potential capable of oxidizing the Ru(II) centers to Ru(III) (0.65 V vs Ag/Ag+) while the electronic absorption spectrum was monitored. Figure 5 illustrates the spectrum of Ru2-1 prior to oxidation (red) and after oxidation of the Ru(II) centers to Ru(III) centers (blue). Upon oxidation of the Ru(II) centers to Ru(III), the transitions at 375 and 514 nm are no longer present in the spectrum, in agreement with their assignment as MLCT transitions. The intensity of the peripheral bipyridine CT transition at 295 nm is reduced, and a shoulder at 314 nm appears. Most noticeable, however, is that the initial intense broad absorption at 610 nm becomes sharper and more intense, undergoing a hypsochromic shift of 25 nm, to 585 nm. The resulting spectrum from the oxidation of the Ru(II) centers to Ru(III) is identical to the spectrum observed for the Bodipy dye 1, minus the bipyridine CT transition, Figure S1. The hypsochromic shift observed for the oxidized complexes is likely a consequence of fewer dπ electrons, leading to weaker π-backbonding and hence a weaker RuIII(dπ)− N(isoquinol) bond,42,43 weakening the effects of the Ru(dπ) orbitals on the Bodipy π-orbitals. The result is the return of the Bodipy (π−π*) ILCT transition as seen for the Bodipy dye in the absence of the Ru(II) moieties. The Ru2-2 and Ru2-3 complexes behave in a similar fashion as illustrated in Figures S14 and S15, respectively. It is important to note that 100% of the original F

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Figure 6. Time-dependent generation of singlet oxygen upon irradiation at l > 550 nm. (A) [DPBF] = 25 μM, [Ru2-1] = 0.75 μM. (B) [DPBF] = 41 μM, [Ru2-2] = 1.2 μM. (C) [DPBF] = 36 μM, [Ru2-3] = 1.4 μM.

onto the Bodipy core. The results of the electrochemical and spectroscopic analysis are summarized in the Jablonski diagram, Scheme 3. From this diagram it is apparent that the {Ru(bpy)2Cl}+ groups have little effect on the Bodipy π*orbitals; however, stabilization of the Bodipy π-orbitals appears evident. This is in contrast to the bathochromic shift observed in the electronic spectra of the Ru2−Bodipy complexes when compared to their Bodipy analogues. Spectroelectrochemical experiments indicate that when the Ru(II) centers are oxidized to Ru(III) the Bodipy orbitals relax to their original energies observed prior to coordination of the Ru(II) moieties. The fact that the original Ru2−Bodipy spectrum is regenerated after oxidation of the Ru(II) centers indicates that they maintain coordination throughout the electrolysis process. A plausible explanation of the bathochromic shift observed is that indeed the Bodipy π-orbitals have been destabilized by coordination of the Ru(II)-polypyridyl complexes. In addition, these new complexes show the ability to generate singlet oxygen within the PDT window.

spectra are recovered upon bulk electrolysis of the solutions at a potential cathodic to the Ru(III/II) couple (0.30 V vs Ag/Ag+), indicating that the complexes are intact throughout the entire experiment. Another notable and puzzling observation was that oxidized solutions of the complexes showed the ability to regenerate their original spectra in the absence of an applied potential. At first, we thought this was a light driven process, but oxidized solutions placed in the dark for approximately 24 h also recovered their original spectra; however, the original spectra were recovered much faster under ambient light. The reason for this observation is unclear at this point, but further studies are underway to investigate this phenomenon. These results, however, strongly suggest that the oxidation state of the peripheral Ru-centers plays a complex role in the position of the lowest energy CT transition. As previously suggested the interest in Ru(II)−Bodipy complexes is wide-ranging due to their potential applications. Of particular interest to this research lab is the use of these complexes in photodynamic therapy (PDT). As such, the ability to produce singlet oxygen within the photodynamic therapy window is paramount. To this end, a preliminary study of the ability of the Ru2−Bodipy complexes to generate singlet oxygen was performed. Acetonitrile solutions of the complexes and the singlet oxygen trap44,45 1,3-diphenylisobenzofuran (DPBF) were irradiated with a 300 W mercury arc lamp equipped with a 550 nm band-pass filter. The kinetics of the production of singlet oxygen was monitored spectrophotometrically as the absorption of DPBF (λmax = 411 nm) decreases upon reaction with the singlet oxygen generated, Figure 6. For all three complexes, a significant decrease in the DPBF absorption is observed at concentration ratios of DPBF to Ru2-complex of ca. 30:1. It is noteworthy that by using the 550 nm band-pass filter the lowest energy transition is the source of singlet oxygen generation; in addition, this transition is within the PDT window. Further studies are underway to evaluate the ability of these complexes to function as PDT photosensitizers.

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EXPERIMENTAL SECTION

Materials. All chemicals were reagent grade and used without further purification. Isoquino[5,6-c]pyrrole46 and cis-dichloro(bis-2,2′bipyridine) ruthenium(II)47 were synthesized as previously described. Chromatography was performed on a Teledyne CombiflashRf+ equipped with UV detection. High resolution mass spectral analysis was performed at the Mass Spectrometry and Proteomics Facility at the Ohio State University. Elemental analysis was performed at Atlantic Microlabs Inc., Norcross, Georgia. 1H NMR spectra were recorded on a Bruker 300 MHz NMR spectrophotomer at 298 K. Electronic absorption spectra were recorded at room temperature using an HP8453 photodiode array spectrophotometer with 2 nm resolution. All spectra were recorded at 298 K. Room temperature luminescence spectra in a 1 cm quartz spectrophotometer fluorescence cell (Starna) in DCM were run on a Cary Eclipse fluorescence spectrophotometer. Cyclic voltammograms were recorded under a nitrogen atmosphere using a one-compartment, three-electrode cell, CH-Instruments, equipped with a platinum wire auxiliary electrode. The working electrode was a 2.0 mm diameter glassy carbon disk from CH-Instruments, which was polished first using 0.30 μm followed by 0.05 μm alumina polish (Buehler) and then sonicated for 10 s prior to use. Potentials were referenced to a Ag/Ag+ (10 mM AgNO3) nonaqueous electrode with ferrocene as an internal standard, CHInstruments. The supporting electrolyte was 0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6), and the measurements were made in dry DCM. Spectroelectrochemical measurements conducted using a locally constructed H-cell, which uses a quartz cuvette as the working compartment. The working and auxiliary compartments were separated by a fine porous glass frit. The working electrode was a high surface area platinum mesh, and the auxiliary electrode was a platinum wire. The reference electrode was a Ag/Ag+ nonaqueous electrode.

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CONCLUSIONS A series of new bis-ruthenium(II) Bodipy complexes and their Bodipy analogues have been synthesized and characterized. The Bodipy dyes display the typical intense absorption transitions along with intense emission with high quantum yields. Incorporation of the π-extended pyrroles leads to a bathochromic shift in the absorption and emission spectra when compared to spectra of traditional Bodipy dyes. In addition, the π-extended pyrroles contain nitrogen coordination sites allowing for coordination of {Ru(bpy)2Cl}+ groups directly G

DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

(d, J = 9.6 Hz, 1H), 5.18 (s, 2H). HR-ES-MS: m/z = 561.20571 [M + H]+ (calcd for C36H24N4F2B 561.20566). Ru2−Bodipy-1. Bodipy-1 (0.020 g, 0.030 mmol) and excess cisdichloro(bis-2,2′-bipyridine) ruthenium(II) (0.043 g, 0.090 mmol) were dissolved in reagent grade ethanol (ca. 15 mL), deoxygenated for 5 min, and refluxed for 3 h under nitrogen, protected from light. The reaction mixture was cooled to room temperature and added dropwise to 100 mL of a saturated aqueous potassium hexafluorophosphate solution. The resulting precipitate was vacuum filtered and air-dried overnight. The product was chromatographed on neutral alumina using a 9:1 DCM/methanol mobile phase, collecting the blue band, followed by recrystallization from a DCM/hexanes solution. Yield 19 mg, 69%. 1H NMR (300 MHz, CD2Cl2) δ: 10.06 (d, J = 5.8 Hz, 1H), 8.71 (s, 1H), 8.49 (d, J = 5.1 Hz, 1H), 8.39 (dd, J = 8.6, 3.2 Hz, 1H), 8.35−8.26 (m, 2H), 8.20−8.12 (m, 2H), 8.09 (d, J = 5.6 Hz, 1H), 8.04−7.95 (m, 1H), 7.93 (t, J = 4.5 Hz, 1H), 7.83 (t, J = 2.0 Hz, 1H), 7.83 (t, J = 2.3 Hz, 1H), 7.83−7.76 (m, 1H), 7.73 (dt, J = 7.6, 3.7 Hz, 2H), 7.69−7.59 (m, 1H), 7.59−7.39 (m, 1H), 7.24−7.15 (m, 2H), 7.09 (dt, J = 6.4, 3.7 Hz, 2H), 6.99 (s, 1H), 6.81 (s, 1H), 6.59 (t, J = 7.1 Hz, 1H), 6.57−6.37 (m, 2H), 5.62−5.47 (m, 1H), 5.02−4.91 (m, 1H), 3.78 (s, 3H), 3.75 (s, 3H). HR-ES-MS: m/z = 774.61518 [M]2+ (calcd for [C78H59N12O4Cl2BF2Ru2]2+ 774.61249). Anal. Calcd for C78H59N12O4Cl2P2F14BRu2·3H2O: C, 49.46; H, 3.46; N, 8.89. Found: C, 49.30; H, 3.37; N, 8.58. Ru2−Bodipy-2. Bodipy-2 (0.010 g, 0.017 mmol) and cis-dichloro(bis-2,2′-bipyridine) ruthenium(II) (0.025 g, 0.052 mmol) were dissolved in reagent grade ethanol (ca. 15 mL), deoxygenated for 5 min, and refluxed for 3 h under nitrogen, protected from light. The reaction was cooled to room temperature and added dropwise to 100 mL of a saturated aqueous potassium hexafluorophosphate solution. The resulting precipitate was vacuum filtered and air-dried overnight. The product was chromatographed on neutral alumina using a 9:1 DCM/methanol mobile phase, collecting the blue band, followed by recrystallization from a DCM/hexanes solution. Yield 12 mg, 79%. 1H NMR (300 MHz, CD2Cl2) δ: 10.05 (d, J = 5.2 Hz, 1H), 9.98 (d, J = 4.4 Hz, 1H), 9.90 (s, 1H), 8.74 (s, 1H), 8.39 (d, J = 4.8 Hz, 8H), 8.35−8.25 (m, 10H), 8.15 (dt, J = 19.6, 8.6 Hz, 5H), 8.00 (dd, J = 12.5, 5.3 Hz, 2H), 7.95−7.63 (m, 6H), 7.50 (ddt, J = 20.1, 16.4, 7.2 Hz, 5H), 7.21 (t, J = 4.1 Hz, 2H), 7.17 (d, J = 4.1 Hz, 3H), 7.09 (dd, J = 13.4, 7.0 Hz, 3H), 6.89 (t, J = 8.2 Hz, 1H), 6.47−6.19 (m, 1H), 5.55 (d, J = 4.3 Hz, 1H), 4.96 (s, 2H). HR-ES-MS: m/z = 747.0999 [M]2+ (calcd for [C76H53N12Cl2BF4Ru2]2+ 747.1015). Anal. Calcd for C76H53N12Cl2P2F16BRu2·0.5C6H14: C, 51.93; H, 3.31; N, 9.20. Found: C, 51.90; H, 3.44; N, 9.09. Ru2−Bodipy-3. Bodipy-3 (0.014 g, 0.025 mmol) and cis-dichloro(bis-2,2′-bipyridine) ruthenium(II) (0.036 g, 0.075 mmol) were dissolved in reagent grade ethanol (ca. 15 mL), deoxygenated for 5 min, and refluxed for 3 h under nitrogen, protected from light. The reaction was cooled to room temperature and added dropwise to 100 mL of a saturated aqueous potassium hexafluorophosphate solution. The resulting precipitate was vacuum filtered and air-dried overnight. The product was chromatographed on neutral alumina using a 9:1 DCM/methanol mobile phase, collecting the blue band, followed by recrystallization from a DCM/hexanes solution. Yield 14 mg, 64%. 1H NMR (300 MHz, CD2Cl2): δ 10.09 (s, 1H), 10.04 (d, J = 6.7 Hz, 2H), 9.96 (d, J = 6.7 Hz, 2H), 8.92 (s, 2H), 8.40−8.24 (m, 7H), 8.23−8.05 (m, 6H), 8.04−7.87 (m, 10H), 7.76 (d, J = 5.2 Hz, 6H), 7.70 (d, J = 8.2 Hz, 4H), 7.50 (d, J = 5.6 Hz, 3H), 7.33−7.00 (m, 4H), 6.28 (dd, J = 23.4, 9.8 Hz, 3H), 5.31 (d, J = 6.9 Hz, 3H), 4.97 (d, J = 7.9 Hz, 2H). HR-ES-MS: m/z = 729.1093 [M] 2+ (calcd for [C76 H55N 12 Cl2BF2Ru2]2+ 729.1104). Anal. Calcd for C76H55N12Cl2P2F14BRu2: C, 52.22; H, 3.17; N, 9.62. Found: C, 52.03; H, 3.51; N, 9.24.

The measurements were made in 0.1 M Bu4NPF6 dry DCM solutions. The electrolysis potential was controlled by a CH-Instruments 630A electrochemical analyzer. Acetonitrile solutions of 1,3-diphenylisobenzofuran (DPBF, singlet oxygen quencher) and the complexes at roughly a 30:1 ratio in quartz cuvettes were irradiated in the presence of oxygen using a 300 W mercury-arc lamp equipped with a long bandpass filter cutting off wavelengths below 550 nm. The progress of singlet oxygen production, monitored using the HP8453 photodiode array spectrometer, was determined by observing the decrease in the maximum absorption band at 411 nm associated with the singlet oxygen trap DPBF as a function of irradiation time. Computational Methods. Geometry optimizations were performed using Gaussian 0948 by employing density functional theory with the Becke3−Lee−Yang−Parr hybrid functional B3LYP functional and the Pople valence double-ζ 6-31g* basis set with a polarizable continuum model (PCM) to model bulk solvent effects. Use of B3LYP as a functional and 6-31g* as a basis set has been used recently for calculating the geometry of Bodipy compounds.49 Default settings were chosen for convergence criteria for the geometry optimization. These optimizations were then subjected to frequency calculations at the same level of theory, and structures were checked for imaginary frequencies using Gauss view 5.0.9 in order to ensure that the calculated geometry represented a true energy minimum. Orbital figures were generated from our DFT experiments. TD-DFT calculations were subsequently performed at the PCM-TD-CAMB3LYP/cc-pVTZ level of theory using Gaussian 09. The correlation consistent polarized valence triple-ζ basis set was recommended for use with CAM-B3LYP.38 All calculations were performed using the services of the Ohio Supercomputer Center. Bodipy Synthesis. The Bodipy dyes were synthesized by combining 0.100 g (0.595 mmol) of isoquino[5,6-c]pyrrole and a 1.5 excess (0.892 mmol) of the desired aldehyde (i.e., 3-methoxy-4hydroxy benzaldehyde, 4-fluorobenzaldehyde, and benzaldehyde) in a minimum amount (1 mL) of DCM/methanol (4:1) followed by removal of the solvent under reduced pressure. The resultant homogeneous solid was heated in a water bath at 90 °C for 20 min. The purple paste was purified by column chromatography on silica gel collecting a bright red/orange band at 2% methanol in DCM. After removal of the solvent, the reactant was dissolved in 3 mL of dry DCM and deoxygenated for 10 min. To this solution, triethylamine (100 μL) was added and stirred for 5 min at room temperature, at which time boron trifluoroetherate was added, and the reaction mixture was allowed to stir overnight under nitrogen at room temperature. The reaction mixture was washed with distilled water and extracted into dichloromethane, and the solvent was removed. The reaction mixture was purified by column chromatography with 2% methanol in DCM and recrystallized from a DCM/hexanes mixture to give a dark blue powder. Bodipy-1. Yield 40 mg, 21%. 1H NMR (300 MHz, CDCl3): δ 9.20−9.07 (m, 2H), 8.83 (s, 1H), 8.67 (d, J = 5.7 Hz, 1H), 8.58−8.47 (m, 1H), 8.04 (t, J = 6.6 Hz, 1H), 7.94 (d, J = 5.8 Hz, 1H), 7.67−7.59 (m, 1H), 7.55 (d, J = 8.9 Hz, 1H), 7.36−7.24 (m, 1H), 7.19−7.12 (m, 1H), 7.10 (s, 1H), 6.92 (t, J = 4.9 Hz, 1H), 6.80 (d, J = 8.1 Hz, 1H), 6.74−6.65 (m, 1H), 6.60 (t, J = 7.6 Hz, 1H), 6.53 (d, J = 9.3 Hz, 1H), 5.08 (s, 2H), 3.94 (s, 3H), 3.85 (s, 3H). HR-ES-MS: m/z = 652.220 [M + H]+ (calcd for C38H28N4O4BF2 652.209). Bodipy-2. Yield 24 mg, 14%. 1H NMR (300 MHz, CDCl3): δ 9.43 (s, 1H), 9.21−9.08 (m, 3H), 8.92−8.76 (m, 2H), 8.66 (dd, J = 11.2, 6.5 Hz, 1H), 8.53 (d, J = 6.8 Hz, 1H), 8.39 (d, J = 8.7 Hz, 1H), 8.12 (s, 1H), 7.99 (d, J = 7.4 Hz, 1H), 7.83 (d, J = 7.4 Hz, 1H), 7.67 (d, J = 7.4 Hz, 1H), 7.59−7.46 (m, 1H), 7.67 (d, J = 7.4 Hz, 1H), 7.59−7.46 (m, 1H), 7.31 (s, 1H), 7.08−6.89 (m, 2H), 6.57−6.26 (m, 2H), 5.13 (s, 2H). HR-ES-MS: m/z = 597.18719 [M + H]+ (calcd for C36H22N4F4B 597.18743). Bodipy-3. Yield 22 mg, 13%. 1H NMR (300 MHz, CDCl3): δ 9.09 (d, J = 9.2 Hz, 1H), 8.88−8.73 (m, 2H), 8.66 (dd, J = 10.8, 5.7 Hz, 1H), 8.53−8.44 (m, 2H), 8.10 (d, J = 8.7 Hz, 1H), 8.04 (d, J = 4.9 Hz, 1H), 8.00 (d, J = 6.2 Hz, 1H), 7.91 (t, J = 7.3 Hz, 1H), 7.82 (dt, J = 15.1, 7.1 Hz, 2H), 7.75−7.63 (m, 1H), 7.50 (dd, J = 18.3, 7.9 Hz, 2H), 7.31 (d, J = 5.0 Hz, 4H), 7.21 (s, 1H), 6.41 (d, J = 9.1 Hz, 1H), 6.31

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DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry 1

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(13) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L. Y.; Burgess, K. BODIPY dyes in photodynamic therapy. Chem. Soc. Rev. 2013, 42, 77−88. (14) Gill, M. R.; Thomas, J. A. Ruthenium(II) polypyridyl complexes and DNA-form structural probes to cellular imagind and therapeutics. Chem. Soc. Rev. 2012, 41, 3179−3192. (15) Swavey, S.; Coladipietro, M.; Burbayea, A.; Krause, J. A. Twostep synthetic route toward asymmetric and symmetric boron dipyrromethenes: synthesis, optical properties, and electrochemistry. Eur. J. Org. Chem. 2016, 2016, 4429−4435. (16) Swavey, S.; Quinn, J.; Coladipietro, M.; Cox, K. G.; Brennaman, M. K. Tuning the photophysical properties of BODIPY dyes through extended aromatic pyrroles. RSC Adv. 2017, 7, 173−179. (17) Loudet, A.; Burgess, K. BODIPY dyes and their derivatives: syntheses and spectroscopic properties. Chem. Rev. 2007, 107, 4891− 4932. (18) Lu, H.; Mack, J.; Nyokong, T.; Kobayashi, N.; Shen, Z. Optically active BODIPYs. Coord. Chem. Rev. 2016, 318, 1−15. (19) LUMO (eV) = −(Ered + 4.8); HOMO (eV) = −(Eox + 4.8). (20) The unexpectedly lower molar extinction coefficient for Bodipy dye 1 was observed with repeated measurements. The reason is not known and is most probably caused by the substituents on the mesophenyl of the Bodipy dye. Further studies are underway to gain insight of the substituent effect. (21) Sunahara, H.; Urano, Y.; Kojima, H.; Nagano, T. Design and Synthesis of a Library of BODIPY-Based Environmental Polarity Sensors Utilizing Photoinduced Electron-Transfer-Controlled Fluorescence ON/OFF Switching. J. Am. Chem. Soc. 2007, 129, 5597− 5604. (22) Le Guennic, B.; Scalmani, G.; Frisch, M. J.; Laurent, A. D.; Jacquemin, D. Investigating the Optical Properties of BOIMPY Dyes Using Ab Initio Tools. Phys. Chem. Chem. Phys. 2017, 19, 10554− 10561. (23) Jacquemin, D.; Moore, B.; Planchat, A.; Adamo, C.; Autschbach, J. Performance of an Optimally Tuned Range-Separated Hybrid Functional for 0−0 Electronic Excitation Energies. J. Chem. Theory Comput. 2014, 10, 1677−1685. (24) Adamo, C.; Jacquemin, D. The Calculations of Excited-State Properties with Time-Dependent Density Functional Theory. Chem. Soc. Rev. 2013, 42, 845−856. (25) Jacquemin, D.; Planchat, A.; Adamo, C.; Mennucci, B. TD-DFT Assessment of Functionals for Optical 0−0 Transitions in Solvated Dyes. J. Chem. Theory Comput. 2012, 8, 2359−2372. (26) Le Guennic, B.; Jacquemin, D. Taking Up the Cyanine Challenge with Quantum Tools. Acc. Chem. Res. 2015, 48, 530−537. (27) Chibani, S.; Laurent, A. D.; Le Guennic, B.; Jacquemin, D. Improving the Accuracy of Excited-State Simulations of BODIPY and Aza-BODIPY Dyes with a Joint SOS-CIS(D) and TD-DFT Approach. J. Chem. Theory Comput. 2014, 10, 4574−4582. (28) Runge, E.; Gross, E. K. Density-Functional Theory for TimeDependent Systems. Phys. Rev. Lett. 1984, 52, 997. (29) Casida, M. E. Time-Dependent Density-Functional Theory for Molecules and Molecular Solids. J. Mol. Struct.: THEOCHEM 2009, 914, 3−18. (30) Zhou, J.; Gai, L.; Mack, J.; Zhou, Z.; Qiu, H.; Chan, K. S.; Shen, Z. Synthesis and Photophysical Properties of Orthogonal Rhodium (III)−carbon Bonded Porphyrin−aza-BODIPY Conjugates. J. Mater. Chem. C 2016, 4, 8422−8428. (31) Wakamiya, A.; Murakami, T.; Yamaguchi, S. Benzene-Fused BODIPY and Fully-Fused BODIPY Dimer: Impacts of the RingFusing at the B Bond in the BODIPY Skeleton. Chem. Sci. 2013, 4, 1002−1007. (32) Shimizu, S.; Iino, T.; Araki, Y.; Kobayashi, N. Pyrrolopyrrole Aza-BODIPY Analogues: A Facile Synthesis and Intense Fluorescence. Chem. Commun. 2013, 49, 1621. (33) Lu, H.; Mack, J.; Yang, Y.; Shen, Z. Structural Modification Strategies for the Rational Design of Red/NIR Region BODIPYs. Chem. Soc. Rev. 2014, 43, 4778−4823.

H NMR and mass spectra; UV−vis and emission spectra of Bodipys 1−3; UV−vis spectra of Ru2-2 and Ru2-3; computational data of 1−3; cyclic voltammograms of 2, 3, Ru2-2, and Ru2-3; and spectroelectrochemical results for Ru2-2 and Ru2-3 (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Shawn Swavey: 0000-0002-3307-9523 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The Ohio Supercomputer Center is gratefully acknowledged for providing generous computational resources. REFERENCES

(1) Galletta, M.; Puntoriero, F.; Campagna, S.; Chiorboli, C.; Quesada, M.; Goeb, S.; Ziessel, R. Absorption Spectra, Photophysical Properties, and Redox Behavior of Ruthenium(II) Polypyridine Complexes Containing Accessory Dipyrromethene-BF2 Chromophores. J. Phys. Chem. A 2006, 110, 4348−4358. (2) Madhu, S.; Kumar, S.; Chatterjee, T.; Ravikanth, M. Synthesis, Xray structure, spectral and electrochemical properties of a β-meso covalently linked BODIPY-Ru(II) dipyrrin complex. New J. Chem. 2014, 38, 5551−5558. (3) Farras, P.; Benniston, A. C. Bodipy-ruthenium(II) tris-bipyridyl dyads for homogeneous photochemical oxidations. Tetrahedron Lett. 2014, 55, 7011−7014. (4) Martin, A.; byrne, A.; Dolan, C.; Forster, R. J.; Keyes, T. E. Solvent switchable dual emission from a bichromophoric rutheniumBODIPY complex. Chem. Commun. 2015, 51, 15839−15841. (5) Wang, T.; Hou, Y.; Chen, Y.; Li, K.; Cheng, X.; Zhou, Q.; Wang, X. Two novel BODIPY-Ru(II) arene dyads enabling effective photoinactivation against cancer cells. Dalton Trans. 2015, 44, 12726− 12734. (6) Wang, J.; Lu, Y.; McGoldrick, N.; Zhang, C.; Yang, W.; Zhao, J.; Draper, S. M. Dual phosphorescent dinuclear transition metal complexes, and their application as triplet photosensitizers for TTA upconversion and photodynamic therapy. J. Mater. Chem. C 2016, 4, 6131−6139. (7) Gupta, G.; Das, A.; Ghate, N. B.; Kim, T.; Ryu, J. Y.; Lee, J.; Mandal, N.; Lee, C. Y. Novel BODIPY-based Ru(II) and Ir(II) metalla-rectangles: cellular localization of compounds and their antiproliferative activities. Chem. Commun. 2016, 52, 4274−4277. (8) Wu, W.; Sun, J.; Cui, X.; Zhao, J. Observation of the room temperature phosphorescence of Bodipy in visible light-harvesting Ru(II) polyimine complexes and application as triplet photosensitizers for triplet-triplet-annihilation upconversion and photocatalytic oxidation. J. Mater. Chem. C 2013, 1, 4577−4589. (9) Benniston, A. C.; Copley, G. Lighting the way ahead with dipyrromethene (BODIPY) dyes. Phys. Chem. Chem. Phys. 2009, 11, 4124−4131. (10) Ulrich, G.; Ziessel, R.; Harriman, A. The Chemistry of Fluorescent Bodipy Dyes: Versatility Unsurpassed. Angew. Chem., Int. Ed. 2008, 47, 1184−1201. (11) Vos, J. G.; Kelly, J. M. Ruthenium polypyridyl chemistry; from basic research to applications and back again. Dalton Trans. 2006, 4869−4883. (12) Zakeeruddin, S. M.; Nazeeruddin, Md.K.; Humphry-Baker, R.; Pechy, P.; Quagliotto, P.; Barolo, C.; Viscardi, G.; Gratzel, M. Design, Synthesis, and Application of Amphiphilic Ruthenium Polypyridyl Photosensitizers in Solar Cells Based on Nanocrystalline, TiO2 Films. Langmuir 2002, 18, 952−954. I

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Inorganic Chemistry (34) Le Guennic, B.; Maury, O.; Jacquemin, D. Aza-BoronDipyrromethene Dyes: TD-DFT Benchmarks, Spectral Analysis and Design of Original near-IR Structures. Phys. Chem. Chem. Phys. 2012, 14, 157−164. (35) Boese, A. D.; Martin, J. M. Development of Density Functionals for Thermochemical Kinetics. J. Chem. Phys. 2004, 121, 3405−3416. (36) Charaf-Eddin, A.; Le Guennic, B.; Jacquemin, D. Optical Signatures of Borico Dyes: A TD-DFT Analysis. Theor. Chem. Acc. 2014, 133, 1456. (37) Laurent, A. D.; Jacquemin, D. TD-DFT Benchmarks: A Review. Int. J. Quantum Chem. 2013, 113, 2019−2039. (38) Momeni, M. R.; Brown, A. Why Do TD-DFT Excitation Energies of BODIPY/Aza-BODIPY Families Largely Deviate from Experiment? Answers from Electron Correlated and Multireference Methods. J. Chem. Theory Comput. 2015, 11, 2619−2632. (39) Odobel, F.; Zabri, H. Preparations and Characterizations of Bichromophoric systems Composed of a Ruthenium Polypyridine Complex Connected to a Difluoroborazaindacene or a Zinc Phthalocyanine Chromophore. Inorg. Chem. 2005, 44, 5600−5611. (40) Swavey, S.; Wang, M.; Lundy, N.; Allen, J. Photoreactions of DNA with a bimetallic ruthenium(II) polypyridyl complex bridged by an organic chromophore. Inorg. Chim. Acta 2017, 454 (1), 234−239. (41) Swavey, S.; Wang, M. Bimetallic ruthenium(II) bridged by a dipyrromethene chromophore: DNA binding and light driven reactions within the photodynamic therapy window. Inorg. Chem. Commun. 2015, 61, 228−230. (42) Eggleston, D. S.; Goldsby, K. A.; Hodgson, D. J.; Meyer, T. J. Structural Variations Induced by Changes in Oxidation State and Their Role in Electron Transfer. Crystal and Molecular Structures of cis-[Ru(bpy)2Cl2]·3.5H2O and cis-[Ru(bpy)2Cl2]Cl·2H2O. Inorg. Chem. 1985, 24, 4573−4580. (43) Kojima, T.; Amano, T.; Ishii, Y.; Ohba, M.; Okaue, Y.; Matsuda, Y. Synthesis and Characterization of Mononuclear and Dinuclear Ruthenium Complexes with Tris(2-pyridylmethyl)amine and Tris(5methyl-2-pyridylmethyl)amine. Inorg. Chem. 1998, 37, 4076−4085. (44) Zhou, J.; Gai, L.; Mack, J.; Zhou, Z.; Qiu, H.; Chan, K. S.; Shen, Z. Synthesis and Photophysical Properties of Orthogonal Rhodium(III)-carbon Bonded Porphyrin−aza-BODIPY Conjugates. J. Mater. Chem. C 2016, 4 (36), 8422−8428. (45) Nolan, D.; Gil, B.; Wang, L.; Zhao, J.; Draper, S. M. StructureProperty Relationships and 1O2 Photosensitization in Sterically Encumbered Diimine PtII Acetylide Complexes. Chem. - Eur. J. 2013, 19 (46), 15615−15626. (46) Lash, T. D.; Gandhi, V. Porphyrins with Exocyclic Rings 15. Synthesis of Quino- and Isoquinoporphyrins, Aza Analogues of the Naphthoporphyrins. J. Org. Chem. 2000, 65, 8020−8026. (47) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Mixed phosphine 2,2′bipyridine complexes of ruthenium. Inorg. Chem. 1978, 17, 3334− 3341. (48) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; 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.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.01; Gaussian: Wallingford CT, 2009. (49) Fabian, J. TDDFT-Calculations of Vis/NIR Absorbing Compounds. Dyes Pigm. 2010, 84, 36−53.

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DOI: 10.1021/acs.inorgchem.7b01630 Inorg. Chem. XXXX, XXX, XXX−XXX