ARTICLE pubs.acs.org/JPCC
Photophysical Dynamics of a Ruthenium Polypyridine Dye Controlled by Solvent pH Maximilian Br€autigam,†,^ Maria W€achtler,†,^ Sven Rau,‡,§ J€urgen Popp,†,^ and Benjamin Dietzek*,†,^ †
Institute for Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller University Jena, Helmholtzweg 4, 07743 Jena, Germany ^ Institute of Photonic Technology (IPHT) Jena e.V., Albert-Einstein-Straße 9, 07745 Jena, Germany § Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-N€urnberg, Egerlandstraße 1, 91058 Erlangen, Germany
bS Supporting Information ABSTRACT: The photophysics of the novel ruthenium dye [Ru(tmBiBzIm)(dppz)(tbbpy)]2+ (tmBiBzIm = 5,50 ,6,60 -tetramethyl-2,2 0 -bibenzimidazole, dppz = dipyrido[3,2-a:2 0 ,3,3 0 -c] phenazine, tbbpy = 4,40 -di-tert-butyl-2,20 -bipyridine) is investigated, which might be suitable as a model compound for intracellular DNA and pH sensors. The combination of three different bidentate ligands allows for controlling the photophysics by two distinct mechanisms: (i) protonation and deprotonation of the tmBiBzIm and (ii) hydrogen bonding to the phenazine nitrogens of the dppz ligand. As will be reported, deprotonation of the tmBiBzIm ligand causes a bathochromic shift of the metal-to-ligand charge-transfer transition, although the tmBiBzIm ligand itself does not directly contribute to the light absorption. Furthermore, tmBiBzIm deprotonation shortens the overall excited-state lifetime of the complex significantly. Although the protonation stage of the tmBiBzIm directly impacts the excited-state properties of the dye, the overall photoinduced dynamics is dominated by the dppz ligand. Consequently, addition of water to the solvent affects the excited-state relaxation pathway as known from, for example, [Ru(phen)2dppz]2+ (phen = 1,10-phenanthroline) complexes.
’ INTRODUCTION In past decades, a wide variety of applications for ruthenium dyes has been established, among which are their use as DNA sensors,17 photocatalysts,812 and photosensitizers in dyesensitized solar cells (Gr€atzel cells).1318 For all these applications, it is beneficial to gain maximum controllability of the photophysical processes underlying the respective molecular function. To this end, molecular units that enable switching of the complex properties and the respective property-determining, light-induced processes are introduced. For example, DNA sensing by rutheniumdppz complexes (dppz = dipyrido[3,2a:20 ,3,30 -c]phenazine) is enabled by the so-called light switch effect, that is, in aqueous solutions, luminescence of the systems is observed only in the presence of DNA.1 In the latter case, water forms hydrogen bonds with the noncoordinating nitrogen atoms of the dppz ligand, thereby stabilizing an excited state centered on the phenazine sphere (phz) of the ligand, as compared with a luminescent phenantroline-centered (phen) metal-to-ligand charge-transfer (MLCT) state. As the phenazine-centered state decays rapidly back to the ground state, no luminescence is observed in solutions containing water. Upon intercalation of the dppz ligand into the major groove of a DNA helix, water molecules hydrogen-bonded to the phenazine nitrogen atoms are extruded, and the stabilization of the nonemissive phenazine-centered state is lost. Consequently, the luminescent r 2011 American Chemical Society
phenantroline-centered MLCT state cannot decay via the phenazinecentered state, and MLCT luminescence is observed.19 Furthermore, it has been shown that the photophysics of Rudppz complexes can also be influenced by intramolecular interactions exploiting variations of the dppz-substitution pattern. The introduction of structurally very simple modifications, that is, bromine substitution at the phenantroline or phenazine moiety, can be used to control the complex emission quantum yield and its excited-state dynamics. Upon introduction of bromine at the phen (phz) sphere of the dppz ligand, the luminescence quantum yield increases (decreases), and ground-state recovery is notably accelerated in the latter case.20 It was observed that extending the π scaffold of the dppz ligand to yield a tpphz bridging ligand (tpphz = tetrapyrido[3,2-a:20 ,30 c:300 ,200 -h:2000 -3000 -j]phenazine) does not affect the basic photophysics of the underlying dppz subunit.10,2123 Furthermore, ligand structures derived from the dppz motif have been introduced for increased pH sensitivity.2429 The study at hand aims at unraveling the ultrafast photoinduced processes in the novel ruthenium dye [Ru(tmBiBzIm)(dppz) (tbbpy)]2+ (tmBiBzIm = 5,50 ,6,60 -tetramethyl-2,20 -bibenzimidazole, Received: September 21, 2011 Revised: November 23, 2011 Published: December 16, 2011 1274
dx.doi.org/10.1021/jp209103m | J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C
ARTICLE
Figure 1. Structural formula of the investigated tris-heteroleptic Ru dye in its deprotonated form (Ru) (black). The structure of the protonated species (RuH2) is indicated in gray.
tbbpy = 4,40 -di-tert-butyl-2,20 -bipyridine, referred to as RuH2 in its doubly protonated and as Ru in its deprotonated state; see Figure 1). The studied complex bears three distinct bidentate ligands coordinated to the Ru2+ ion. The use of different ligand architectures, in particular, the combination of a dppz and a tmBiBzIm ligand into a single coordination sphere, allows for tuning of the photoinduced properties of the complex by different molecular mechanisms. Thus, the complex investigated might present a step toward a system for joint pH sensing and DNA detection. In contrast to other work, which utilized a modified dppz ligand itself to sense pH changes,26 RuH2 includes the tmBiBzIm ligand as a pH-responsive unit into the complex architecture bearing the well-known dppz ligand. As will be detailed, the pH-responsive tmBiBzIm ligand changes the photophysical properties of the complex reversibly upon protonation (RuH2) and deprotonation (Ru) without contributing to the electronic excitation in the visible range itself. Although the effect of tmBiBzIm protonation and deprotonation on the absorption spectra of ruthenium tmBiBzIm complexes has been investigated before,30 no photophysical study exists on ruthenium complexes simultaneously bearing a tmBiBzIm and a dppz ligand. As will be shown, the effects of the deprotonation at the tmBiBzIm ancillary ligand are of quantitative nature (i.e., acceleration of excited-state electron transfer processes and excited-state decay). The work describes the protonation/ deprotonation-dependent excited state topology and photoinduced dynamics in RuH2 and Ru by combining resonance Raman scattering with femtosecond time-resolved absorption spectroscopy. Particular emphasis will be put on the solvent dependence of the photoinduced dynamics, that is, especially on the effect of water addition to acetonitrile, because it has been shown that the solvent’s water content is a critical parameter for the photoinduced dynamics in Rudppz complexes. To this end, the obtained results are discussed in the context of the well studied photophysics of [Ru(tbbpy)2(dppz)]2+.
’ EXPERIMENTAL SECTION Sample Preparation. The synthesis and characterization of RuH2 is reported elsewhere.31 For spectroscopic measurements, the samples were dissolved in aerated acetonitrile (ACN). To deprotonate the complex, LiH was added to the ACN solution in excess. After leaving the suspension to rest overnight, the clear
Figure 2. Absorption spectra of RuH2 in various solvents and of the deprotonated form Ru. The inset shows the derivative of the absorption spectrum of RuH2 in dichloromethane within the range of the MLCT absorption.
supernatant solution was investigated. For solvent-dependent, time-resolved measurements, the complexes were additionally dissolved in a mixture of ACN and 5 vol % water. Experimental Setup. Resonance Raman spectra at ambient temperatures were recorded using a 90-scattering arrangement. The excitation light was delivered either by an argon ion laser (Spectra-Physics 2018, λ = 458, 502, and 515 nm) or a krypton ion laser (model Coherent Innova 301C, λ = 413, 476, 488, 530, and 568 nm). The wavelengths used are in resonance with the electronic transition associated with the metal-to-ligand chargetransfer (MLCT) absorption (see Figure 2). A rotating cell was employed to prevent sample degradation.32 The scattered light was collected and focused with an objective onto the entrance slit of an Acton SpectraPro 2758i spectrometer. The spectrally dispersed light was detected using a liquid-nitrogen-cooled CCD camera (Princeton Instruments). The concentration of the sample was optimized for a maximum signal-to-noise ratio and was set in the 104 M range, since higher concentrations lead to an increased opacity and dilutions below 104 M show less intense bands. The setup for transient absorption spectroscopy has been described previously.23 The pump pulses (temporal length below 150 fs) to excite the protonated complex RuH2 (deprotonanted Ru) complex were centered at 477 (544) nm and were delivered by a TOPAS-C. A supercontinuum served as a broad-band probe. The pump-pulse energy was 1.4 μJ, and typical probe intensities fall into the range of a hundred nanojoules. Probe and reference intensities were detected on a double-stripe diode array and converted into differential absorption (DA) signals using a commercially available detection system (Pascher Instruments AB). For a kinetic analysis, the DA signals recorded as a function of the delay time and the probe wavelength were chirp-corrected and subsequently subjected to a global fit routine using a sum of exponential functions for data analysis.33 The wavelengthdependent, pre-exponential factors correspond to the so-called decay-associated spectra (DAS) connected with the kinetic components. To avoid prominent contributions from coherent artifacts,34,35 the pulse-overlap region was excluded in the data fitting procedure. 1275
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C
ARTICLE
Sample integrity was ensured by recording absorption spectra prior and post each resonance Raman and transient absorption measurement. No sample degradation was observed.
’ RESULTS AND DISCUSSION This section, which presents the spectroscopic data and a photophysical discussion of the results, contains two aspects: The first part focuses on the impact of protonation/deprotonation on the steady-state absorption spectra and the consequences for the energetic ordering of low-lying excited states. The second part aims at a description of the picosecond photoinduced dynamics as a function of the solvent and the protonation state of the complex. Thereby, a detailed picture of the photoinduced processes in RuH2 is obtained, which forms the basis for the potential use of the complex for simultaneous DNA detection and pH sensing. Focus on Energetics. The ground state absorption of RuH2 in ACN exhibits a large bathochromic shift upon deprotonation with LiH forming Ru (see Figure 2). The resultant color change from brown to violet can be observed by eye. UV/vis measurements performed to quantify the spectral shift of the absorption band in the visible range of the spectrum reveal that the MLCT absorption36 is displaced from 440 to 518 nm. This falls into the range of deprotonation-induced spectral shifts previously reported for other RuBiBzIm complexes.30 From this finding, we conclude that deprotonation of the tmBiBzIm ligand mainly influences the energetic position of the electronic ground state by up-shifting the HOMO (Ru d orbital) energy. This results in the bathochromic shift of the MLCT band. As can be seen in Figure 2, further absorption bands are present in the blue part of the absorption spectra: The bands below 400 nm, whose maxima do not shift upon deprotonation, are assigned to ligand-centered ππ* transitions.36 The absence of band shifts below 400 nm suggests that the respective bands are due to ππ* transitions associated with the dppz and the tbbpy ligands. However, the band shapes are altered. These changes can be accounted by the changes in the electronic structure of the tmBiBzIm ligand upon deprotonation, which influences ππ* transitions on the tmBiBzIm. Finally, it should be noticed that the rather broad MLCT band exhibits some structural details, which become more pronounced in its derivative spectrum (inset of Figure 2). As will be detailed further when discussing the results of resonance Raman spectroscopy, the individual structural features might be assigned to different MLCT transitions from the ruthenium d orbitals to π* orbitals of individual ligands. In particular, it will be shown that MLCT from the Ru2+ ion to both the tbbpy and the dppz ligand contribute to the broad visible absorption band, but no direct contribution of the tmBiBzIm ligand is present. On the other hand, contributions of vibronic progressions to the observed fine structure of the absorption spectrum cannot be excluded. The presence of vibronic progression is not uncommon for rutheniumMLCT transitions. The energetic distances of the shoulders in the absorption spectrum are 1770 and 1230 cm1, which are in agreement with previously reported values for vibronic progression.3739 Hence, it is plausible that both different MLCT transitions and vibronic progression overlap and contribute to the observed fine structure of the absorption spectrum. To decipher the contributions of the various ligand fragments to the MLCT band and to investigate the excited-state dynamics
Figure 3. Resonance Raman spectra of RuH2 in acetonitrile (A), acetonitrile/5 vol % water mixture (B), and after treatment with an excess amount of LiH in ACN to yield Ru (C). The resonance Raman spectra in panels AC were recorded with 476 nm excitation. (D) Resonance Raman spectrum of Ru in acetonitrile solution with LiH upon excitation at 530 nm. The resonance Raman spectrum of the reference compound [Ru(tbbpy)2(dppz)]2+ at 476 nm (E) was used to assign the vibrational modes associated with tbbpy (+) or dppz () ligands. Solvent bands are marked with an asterisk.
Figure 4. Integrated resonance Raman intensities of the bands at 1535 and 1567 cm1, characteristic for the tbbpy and the dppz ligand, respectively, of RuH2 and Ru.
at the FranckCondon point, resonance, Raman scattering experiments are performed. Resonance Raman measurements highlight vibrational modes, which display a large nuclear displacement in the excited-state geometry as compared with the ground-state geometry. Along these modes, a rapid sub-20 fs wave packet motion occurs, and the corresponding vibrational signals in the Raman spectra are enhanced.40,41 Thereby, it is possible to distinguish between individual ligands that contribute to a given MLCT absorption band in a heteroleptic complex. 1276
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C
ARTICLE
Figure 5. Differential absorption spectra at selected delay times of (A) RuH2 in acetonitrile and (C) deprotonated Ru in acetonitrile upon addition of LiH (due to pump scatter induced by the LiH suspension the spectral region of the pump pulse is omitted). All spectra of Ru were smoothed using the SavitzkyGolay method (see Supporting Information Figure S2 for spectra without smoothing). (B, D) Respective transient absorption kinetics, which were spectrally averaged in a range of (10 nm around the indicated central wavelength.
In the experiments performed here, the excitation wavelength was varied between 413 and 568 nm, probing the range of the MLCT absorption. As can be seen in Figure 3, the resonance Raman spectra of RuH2 and Ru measured at 476 nm show exclusively bands that are also detectable for the reference compound [Ru(tbbpy)2(dppz)]2+.20 Therefore, as already indicated above, it is concluded that the tmBiBzIm ligand does not contribute to the charge-transfer transition in the dye, independent of the protonation state. This conclusion holds true for Ru and RuH2 dissolved in ACN and the ACN/H2O mixture and is consistent with resonance Raman studies on the related system [Ru(tbbpy)2(tmBiBzIm)]2+.42,43 Notably, the resonance Raman spectrum at 476 nm recorded for the deprotonated Ru shows significant spectral differences when compared with the protonated RuH2: tbbpy bands in Ru appear to be stronger than those associated with vibrations located on the dppz ligand, which are especially visible for the band at 1535 cm1. However, it has to be kept in mind that deprotonation already impacts the UV/vis absorption of the complex by bathochromically shifting the MLCT absorption from 440 to 518 nm, corresponding to a bandshift of 3422 cm1. To record resonance Raman scattering in resonance with the red-shifted MLCT band, the excitation wavelength is altered to 530 nm. The resultant resonance Raman spectrum of Ru closely resembles the spectra recorded for RuH2 at 476 nm (see Figure 3). Thus, the spectrum of the deprotonated species recorded at 476 nm excitation (Figure 3) is comparable to the spectrum of protonated
RuH2 with 413 nm excitation wavelength (see Supporting Information Figure S1). This indicates that deprotonation does not alter the nature of the electronic transitions fundamentally though shifting the MLCT absorption maximum of the complex by raising the HOMO. In particular, it is important to note that only the dppz and the tbbpy ligands contribute to the low-energy MLCT transition of the deprotonated species Ru as observed in RuH2. Further information on the contributions of the individual ligands to the MLCT transition can be obtained from the dispersion of the resonance Raman spectra (Figure 4). This approach is exemplified by monitoring the wavelength dependence of selected resonance Raman active vibrations, which are associated with individual ligands. In particular, the Raman bands at 1535 and 1567 cm1 were used because they present deformation vibrations characteristic for the tbbpy and dppz ligand, respectively.44 To evaluate the dispersion of the resonance Raman intensities, the raw spectra were normalized to the solvent band at 918 cm1, the molecular bands of interest were fitted with Gaussian profile, and the corresponding functions were integrated. The integral value is plotted as a function of excitation wavelength. The resultant graph shows a maximum enhancement of the dppz band (1567 cm1) at 476 nm and, thus, at longer excitation wavelengths compared to the maximum enhancement of the tbbpy mode (maximum intensity of the 1535 cm1 mode at 458 nm excitation). From this trend, it is possible to conclude that within the broad MLCT band, excitation at longer wavelengths preferentially causes a charge transfer 1277
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C from the ruthenium to the dppz ligand, whereas at shorter excitation wavelengths, the tbbpy ligand dominantly contributes to the MLCT transition.20 This finding holds true for both Ru and RuH2, as can be seen in Figure 4. Focus on Dynamics. Having considered the dynamics at the FranckCondon point and its dependence on the protonation pattern, we shall now focus on the photoinduced transient picosecond dynamics in Ru and RuH2 (see Figure 5). The overall features of the differential absorption spectra of the dye resemble the characteristic spectral shapes of related Ru complexes;20 that is, the ground-state bleach (GSB) is accompanied by a strong excited-state absorption (ESA) band in the 600650 nm range. As can be seen, the maximum of the shortdelay-time differential absorption shifts upon deprotonation by 573 cm1 from 622 to 645 nm (Figure 5 A, C). This finding most likely results from the bathochromically shifted GSB (see Figure 2). However, the deprotonation also has a significant effect on the energetic position of the excited states of Ru. In RuH2, the excited-state decays slowly and has not fully decayed within the temporal window of 1.6 ns accessible in the experiment. However, upon deprotonation, the excited state decays in less than 1 ns. Furthermore, the rise of the prominent differential absorption band in the red part of the spectrum appears accelerated in Ru, for which a comparison of the various differential absorption kinetics indicates a band shift on some10-ps time scale. This can be seen from the ESA rise times recorded at different probe wavelengths. To evaluate the differential absorption data quantitatively, a global fitting routine has been applied, yielding characteristic time constants and decay-associated spectra, overall describing the photoinduced dynamics.33 The results of this approach are summarized in Figure 6. For RuH2 in neat ACN (Figure 6 A), three picosecond kinetic components (τ1 = 4.1 ps, τ2 = 347 ps, and τ3 ≈ 8 ns) are apparent, describing the photoinduced reaction. The long-time data is roughly approximated by the 8 ns component, as the exact time scale for complete ground-state recovery cannot be determined accurately within the experimentally accessible range of delay times. Also for RuH2 in a mixture of ACN and 5 vol% water, three picosecond components (τ1 = 4.4 ps, τ2 = 110 ps, and τ3 ≈ 2 ns) resulted from fitting the experimental data. The fastest component (τ1), which builds up the characteristic red ESA band, is assigned to the formation of a vibrationally relaxed 3MLCT state centered on the phenanthroline moiety of the dppz ligand.4347 Intersystem crossing from the initially photoexcited 1MLCT to the triplet manifold takes place rapidly with an efficiency close to unity in ruthenium polypyridine complexes48,49 and is not resolved within the experiments presented here. The DAS associated with τ2 = 347 ps (Figure 6A) reveals a differential absorption increase below 550 nm and ESA decay at longer wavelengths. This dispersion shape reflects an interconversion between two distinct spectrally separated states. Such a characteristically shaped component is common for Rudppztype complexes and is associated with the decay of the 3 MLCTdppzphen state and the simultaneous buildup of a 3 MLCTdppzphz state, in which the excess electron density resides on the phz part of the dppz ligand.20 The latter state is known to become stabilized upon formation of waterphz hydrogen bonds.19 Hence, the energy difference between the 3 MLCTdppzphen and the 3MLCTdppzphz state becomes larger upon addition of water to the acetonitrile solution,
ARTICLE
Figure 6. Decay-associated spectra reflecting the photoinduced dynamics: (A) RuH2 in ACN, (B) RuH2 the water/5 vol % water mixture, and (C) Ru in a suspension of LiH in ACN.
which explains the acceleration of the intraligand electron transfer from τ2 = 347 ps in pure ACN to 110 ps in the ACN/ 5 vol % H2O mixture. Notably, a comparable acceleration of the intraligand charge transfer was not observed in a related complex, which bears a tpphz (tetrapyrido[3,2-a:20 ,30 -c:300 ,200 -h:2000 ,3000 -j]phenazine) ligand instead of a dppz ligand.23 This might be due to the fact that in the latter system, the lone pairs of the phenazine nitrogens 1278
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C
ARTICLE
Figure 7. Schematic summary of photoinduced processes in Ru. The structure of Ru is drawn schematically, and the localization of the excess-electron density is marked in each individual state by color coding. Nonradiative processes are indicated by dotted arrows; optical transitions are represented by solid lines. Experimental data on the photophysics of Ru in dichloromethane is summarized in the Supporting Information, Figures S3S6. Intersystem crossing connecting the initially photoexcited 1MLCT to the delocalized 3MLCT cannot be temporally resolved in the experiments presented here.
are sterically protected so that formation of hydrogen bonds with solventwater molecules is reduced if not inhibited. Upon addition of water, not only τ3 is shortened, but also the long time component (τ3 = 8 ns in ACN and 2 ns in ACN/H2O). A possible explanation for this apparent acceleration of τ3 in RuH2 is the stabilization of the 3MLCTdppzphz state upon formation of hydrogen bonds, causing a decreased energetic difference of the 3MLCTdppzphz state and the ground state, which accelerates the relaxation to the ground state.50 The limited experimental observation window of only 1.6 ns in relation to the estimated values of τ3, that is, 2 and 8 ns, prohibits the deduction of further quantitative results. In contrast to the photoinduced dynamics of RuH2, the deprotonated Ru shows a significantly faster ground-state recovery, which can be quantitatively described by the characteristic time constants τ1 = 1.3, τ2 = 32, and τ3 = 139 ps. Although τ1 causes the buildup of the prominent ESA band in the red part of the spectrum and is assigned to the formation of the vibrationally relaxed 3MLCTdppzphen state, DAS(τ2) shows the dispersion shape representing the 3MLCTdppzphen f 3MLCT dppzphz intraligand charge transfer. Notably, the intraligand charge transfer on the dppz ligand is accelerated upon deprotonation of the tmBiBzIm ligand, that is, the adjacent complex fragment. This points to the fact that protonation/deprotonation of the tmBiBzIm ligand not only alters the energy of the ground state but also increases the energy of both the delocalized 3 MLCT state (populated by intersystem crossing after photoexcitation of a delocalized 1MLCT state) and the 3MLCTdppz phen state (see Figure 7). These states are lifted energetically as a
result of their close vicinity to the Ru ion and, hence, to the tmBiBzIm ligand, and the effect of protonation/deprotonation on the distant 3MLCTdppzphz state is marginal. As a consequence, the energy difference between the 3MLCTdppz phen and the 3MLCTdppzphz state is increased, which causes a stronger driving force for intraligand charge transfer and shortens the characteristic time constant. Furthermore, the ground-state recovery and excited-state decay of Ru is much faster (139 ps) than in RuH2, irrespective of the solvent (>1 ns) caused by a reduced energy gap. Despite the fact that the overall photophysics of Ru is dominated by the Rudppz complex fragment, these findings illustrate that the tmBiBzIm ligand presents a versatile “molecular handle” to impact the photophysics of Ru by changes in its protonation state, while leaving the structure of the dppz ligand itself unaltered. Hence, this work indicates that the concept of combining a DNA-sensing ligand (dppz) and a pH-tunable ligand (tmBiBzIm) into a single heteroleptic complex opens the doorway to realize molecular sensors, whose photoinduced properties will be controllable by both pH changes and the presence of DNA fragments.
’ CONCLUSION The ultrafast photophysics of a Rupolypyridine complex bearing a 5,50 ,6,60 -tetramethyl-2,20 -bibenzimidazole and a dipyrido [3,2-a:20 ,3,30 -c]phenazine ligand has been investigated by resonance Raman and femtosecond time-resolved absorption spectroscopy. It is shown that the picosecond photoinduced dynamics of 1279
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C the complex in general is determined by the electronic structure of the dppz ligand. Therefore, the complex might be developed into a molecular DNA sensor as it is reported for other Rudppz complexes. In addition to the well-known response of the photophysics of Rudppz complexes to the addition of water, the tmBiBzIm ligand offers an additional degree of freedom for tuning the photophysical properties in response to environmental changes: Upon deprotonation, both the excited-state electronic structure and lifetime are altered significantly due to the stronger π-donor character of the tmBiBzIm ligand in its deprotonated form. To gain a comprehensive picture, not only the influence of deprotonation but also the effect of free protons on the dppz scaffold in the considered complex was investigated using an ACNwater mixture. Therefore, the spectroscopic results show that the complex investigated here might present a versatile lead structure for the development of complexes with tunable properties responding to independent environmental stimuli.
’ ASSOCIATED CONTENT
bS
Supporting Information. Comparison resonance Raman spectra of RuH2 and Ru at 413/476 and 476/413 nm excitation, differential absorption spectra without smoothing, data for RuH2 in dichloromethane: UV/vis absorption, emission and excitation spectra, TCSPC measurements, transient absorption data. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Phone: 0049-3641-206332. Fax: 0049-3641-206399. E-mail
[email protected]. Present Addresses ‡
Institute of Inorganic Chemistry I, University of Ulm, AlbertEinstein-Allee 11, 89081 Ulm, Germany.
’ ACKNOWLEDGMENT This research was supported financially by the Th€uringer Ministerium f€ur Bildung, Wissenschaft und Kultur (PhotoMIC, Grant No.B 514-09049). Further financial support from the Studienstiftung des deutschen Volkes (M.W., M.B.) and the Fonds der Chemischen Industrie (B.D., J.P.) is gratefully acknowledged. ’ REFERENCES (1) Friedman, A. E.; Chambron, J. C.; Sauvage, J. P.; Turro, N. J.; Barton, J. K. J. Am. Chem. Soc. 1990, 112, 4960–4962. (2) Hartshorn, R. M.; Barton, J. K. J. Am. Chem. Soc. 1992, 114, 5919–5925. (3) Jenkins, Y.; Friedman, A. E.; Turro, N. J.; Barton, J. K. Biochemistry 1992, 31, 10809–10816. (4) Haq, I.; Lincoln, P.; Suh, D.; Norden, B.; Chowdhry, B. Z.; Chaires, J. B. J. Am. Chem. Soc. 1995, 117, 4788–4796. (5) Nair, R. B.; Cullum, B. M.; Murphy, C. J. Inorg. Chem. 1997, 36, 962–965. (6) Schwalbe, M.; Karnahl, M.; Tschierlei, S.; Uhlemann, U.; Schmitt, M.; Dietzek, B.; Popp, J.; Groake, R.; Vos, J. G.; Rau, S. Dalton Trans. 2010, 39, 2768. (7) Rau, S.; Zheng, S. Curr. Top. Med. Chem. 2011in press.
ARTICLE
(8) Rau, S.; Sch€afer, B.; Gleich, D.; Anders, E.; Rudolph, M.; Friedrich, M.; G€ orls, H.; Henry, W.; Vos, J. G. Angew. Chem., Int. Ed. 2006, 45, 6215–6218. (9) Tschierlei, S.; Karnahl, M.; Presselt, M.; Dietzek, B.; Guthmuller, J.; Gonzalez, L.; Schmitt, M.; Rau, S.; Popp, J. Angew. Chem., Int. Ed. 2010, 49, 3981–3984. (10) Tschierlei, S.; Presselt, M.; Kuhnt, C.; Yartsev, A.; Pascher, T.; Sundstr€om, V.; Karnahl, M.; Schwalbe, M.; Sch€afer, B.; Rau, S.; Schmitt, M.; Dietzek, B.; Popp, J. Chem.—Eur. J. 2009, 15, 7678–7688. (11) Elvington, M.; Brown, J.; Arachchige, S. M.; Brewer, K. J. J. Am. Chem. Soc. 2007, 129, 10644–10645. (12) Lei, P.; Hedlund, M.; Lomoth, R.; Rensmo, H.; Johansson, O.; Hammarstr€ om, L. J. Am. Chem. Soc. 2008, 130, 26–27. (13) O’Regan, B.; Gr€atzel, M. Nature 1991, 353, 737–740. (14) Gr€atzel, M. Pure Appl. Chem. 2001, 73, 459–467. (15) Gr€atzel, M. Inorg. Chem. 2005, 44, 6841–6851. (16) Benk€o, G.; Kallioinen, J.; Korppi-Tommola, J. E. I.; Yartsev, A. P.; Sundstr€om, V. J. Am. Chem. Soc. 2002, 124, 489–493. (17) Benk€o, G.; Kallioinen, J.; Myllyperki€ o, P.; Trif, F.; KorppiTommola, J. E. I.; Yartsev, A. P.; Sundstr€om, V. J. Phys. Chem. B 2004, 108, 2862–2867. (18) Kallioinen, J.; Benk€ o, G.; Myllyperki€o, P.; Khriachtchev, L.; Skarman, B.; Wallenberg, R.; Tuomikoski, M.; Korppi-Tommola, J.; Sundstr€om, V.; Yartsev, A. P. J. Phys. Chem. B 2004, 108, 6365–6373. (19) Olson, E. J. C.; Hu, D.; H€ormann, A.; Jonkman, A. M.; Arkin, M. R.; Stemp, E. D. A.; Barton, J. K.; Barbara, P. F. J. Am. Chem. Soc. 1997, 119, 11458–11467. (20) Kuhnt, C.; Karnahl, M.; Tschierlei, S.; Griebenow, K.; Schmitt, M.; Sch€afer, B.; Krieck, S.; G€orls, H.; Rau, S.; Dietzek, B.; Popp, J. Phys. Chem. Chem. Phys. 2010, 12, 1357. (21) Chiorboli, C.; Rodgers, M. A. J.; Scandola, F. J. Am. Chem. Soc. 2003, 125, 483–491. (22) Campagna, S.; Serroni, S.; Bodige, S.; MacDonnell, F. M. Inorg. Chem. 1999, 38, 692–701. (23) Karnahl, M.; Kuhnt, C.; Ma, F.; Yartsev, A.; Schmitt, M.; Dietzek, B.; Rau, S.; Popp, J. ChemPhysChem 2011, 12, 2101–2109. (24) Sun, Y.; Turro, C. Inorg. Chem. 2010, 49, 5025–5032. (25) Sun, Y.; Liu, Y.; Turro, C. J. Am. Chem. Soc. 2010, 132, 5594–5595. (26) Sun, Y.; Collins, S. N.; Joyce, L. E.; Turro, C. Inorg. Chem. 2010, 49, 4257–4262. (27) Zhang, A.-G.; Zhang, Y.-Z.; Duan, Z.-M.; Wang, K.-Z.; Wei, H.-B.; Bian, Z.-Q.; Huang, C.-H. Inorg. Chem. 2011, 50, 6425–6436. (28) Chen, Y.-M.; Liu, Y.-J.; Li, Q.; Wang, K.-Z. J. Inorg. Biochem. 2009, 103, 1395–1404. (29) Han, M.-J.; Chen, Y.-M.; Wang, K.-Z. New J. Chem. 2008, 32, 970. (30) Haga, M.-A. Inorg. Chim. Acta 1983, 75, 29–35. (31) Manuscript in preparation. (32) Kiefer, W. Appl. Spectrosc. 1973, 27, 253–257. (33) Dietzek, B.; Tschierlei, S.; Hermann, G.; Yartsev, A.; Pascher, T.; Sundstr€om, V.; Schmitt, M.; Popp, J. ChemPhysChem 2009, 10, 144–150. (34) Kovalenko, S. A.; Dobryakov, A. L.; Ruthmann, J.; Ernsting, N. P. Phys. Rev. A 1999, 59, 2369. (35) Dietzek, B.; Pascher, T.; Sundstr€om, V.; Yartsev, A. Laser Phys. Lett. 2007, 4, 38–43. (36) Karnahl, M.; Krieck, S.; G€orls, H.; Tschierlei, S.; Schmitt, M.; Popp, J.; Chartrand, D.; Hanan, G. S.; Groarke, R.; Vos, J. G.; Rau, S. Eur. J. Inorg. Chem. 2009, 2009, 4962–4971. (37) Coe, B. J.; Thompson, D. W.; Culbertson, C. T.; Schoonover, J. R.; Meyer, T. J. Inorg. Chem. 1995, 34, 3385–3395. (38) Siebert, R.; Schl€utter, F.; Winter, A.; Presselt, M.; G€orls, H.; Schubert, U. S.; Dietzek, B.; Popp, J. Cent. Eur. J. Chem. 2011, 9, 990–999. (39) Siebert, R.; Winter, A.; Schubert, U. S.; Dietzek, B.; Popp, J. Phys. Chem. Chem. Phys. 2010, 13, 1606–1617. (40) Myers, A. B. Chem. Rev. 1996, 96, 911–926. (41) Tschierlei, S.; Dietzek, B.; Karnahl, M.; Rau, S.; MacDonnell, F. M.; Schmitt, M.; Popp, J. J. Raman Spectrosc. 2008, 39, 557–559. 1280
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
The Journal of Physical Chemistry C
ARTICLE
(42) Herrmann, C.; Neugebauer, J.; Presselt, M.; Uhlemann, U.; Schmitt, M.; Rau, S.; Popp, J.; Reiher, M. J. Phys. Chem. B 2007, 111, 6078–6087. (43) Dietzek, B.; Kiefer, W.; Blumhoff, J.; B€ottcher, L.; Rau, S.; Walther, D.; Uhlemann, U.; Schmitt, M.; Popp, J. Chem.—Eur. J. 2006, 12, 5105–5115. (44) Kuhnt, C.; Tschierlei, S.; Karnahl, M.; Rau, S.; Dietzek, B.; Schmitt, M.; Popp, J. J. Raman Spectrosc. 2010, 41, 922–932. (45) Yeh, A. T.; Shank, C. V.; McCusker, J. K. Science 2000, 289, 935–938. (46) Dietzek, B.; Akimov, D.; Kiefer, W.; Rau, S.; Popp, J.; Schmitt, M. Laser Phys. Lett. 2007, 4, 121–125. (47) Henrich, J. D.; Zhang, H.; Dutta, P. K.; Kohler, B. J. Phys. Chem. B 2010, 114, 14679–14688. (48) Crosby, G. A.; Demas, J. N. J. Am. Chem. Soc. 1971, 93, 2841–2847. (49) Demas, J. N.; Taylor, D. G. Inorg. Chem. 1979, 18, 3177–3179. (50) Schulze, B.; Escudero, D.; Friebe, C.; Siebert, R.; G€ orls, H.; K€ohn, U.; Altuntas, E.; Baumgaertel, A.; Hager, M. D.; Winter, A.; Dietzek, B.; Popp, J.; Gonzalez, L.; Schubert, U. S. Chem.—Eur. J. 2011, 17, 5494–5498.
1281
dx.doi.org/10.1021/jp209103m |J. Phys. Chem. C 2012, 116, 1274–1281
