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Triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate
Journal of Luminescence 215 (2019) 116691
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate Glyus L. Sharipov, Adis A. Tukhbatullin
T
⁎
High-energy Chemistry and Catalysis Laboratory, Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, 141 Prospekt Oktyabrya, 450075, Ufa, Russia
A R T I C LE I N FO
A B S T R A C T
Keywords: Triboluminescence Ruthenium(II) complex Inert gases OH luminescence
The triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex is detected during the mechanical grinding. The intense lines of N2 in the UV region and a band at 619 nm appeared due to luminescence of [Ru(bpy)3]2+ ion and coincided with the photoluminescence spectrum of the crystals are observed in the emission spectrum in air. The luminescence of N2 is due to electrification of the crystals during the destruction and subsequent discharges in the gas phase. We showed that the luminescence of [Ru(bpy)3]2+ does not occur due to absorption of UV luminescence of N2, because there is only luminescence of the crystal in O2 environment, whereas the luminescence of N2 is completely suppressed. The intense lines coincided with those of Ne and Ar atoms in the electric discharge are observed in the triboluminescence spectra of ruthenium(II) complex in neon and argon environments. In this case, there is an increase in intensity of N2 lines and of a band of [Ru (bpy)3]2+ due to more intense discharges than during the tribodestruction without inert gases. *OH radical is also detected in the triboluminescence spectrum due to mechanochemical decomposition of water molecules in the [Ru(bpy)3]Cl2·6H2O crystalline hydrate.
1. Introduction Coordination compounds of transition platinum group metals possess high activity in catalytic reactions [1–3] and unique luminescent properties [4,5]. Bipyridine complexes, for example, are chemically stable, exhibit intense luminescence, and can be used as a main component in organic luminescent diodes [6–9]. The triboluminescence (TL) or luminescence during the destruction of crystals [11] of a Pt(II) complex was detected [10]. It should also be noted that photoluminescent (PL), electroluminescent, and chemiluminescent properties of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate due to metal-to-ligand charge-transfer (MLCT) are widely described in the literature [8,12–15]. The sonochemiluminescence of this ruthenium(II) complex was recently detected during the single and multibubble sonolysis of aqueous solutions [16,17]. The expansion of spectral luminescent studies of such metal complexes with various excitation ways of luminescence will allow us to detail our knowledge about basic mechanisms of formation and deactivation of their electronically excited states. Triboluminescence, for example, is a promising method to reveal the luminescent properties of crystalline metal complexes under mechanical action on them. A TL spectrum of crystals in air can contain gas phase luminescence (lines of N2) and the luminescence of a crystal ⁎
itself [11,18–20]. When the composition of a gas environment surrounding the crystals is changed, a TL spectrum contains lines of gases and their light-emitting decomposition products together with those of nitrogen [21–24], which coincide with the emission spectra in electrical discharges in most cases. In this work, the TL of a ruthenium(II) complex was studied for the first time with the monitoring of spectral components previously detected in the TL of other solid-state substances. 2. Experimental section Commercially available tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex (Aldrich) was used to study TL and PL. The experimental equipment, excitation, and registration methods of TL spectra are described in detail in Refs. [21,25]. The luminescence was recorded in air, molecular oxygen, and inert gases (Ne and Ar). The gases were supplied to the crystal layer with a tube in the working cell at a rate of up to 15 mL/s. To generate a gaseous atmosphere, the working cell was tightly sealed. The TL or PL spectra and the lifetimes of the excited state were acquired on a Fluorolog-3 (Horiba Jobin Yvon) spectrofluorometer equipped with a Hamamatsu R928P photomultiplier tube. When PL and the lifetime were studied, the crystals were placed into a solid sample holder (model 1933) that was excited
Corresponding author. E-mail address: [email protected] (A.A. Tukhbatullin).
https://doi.org/10.1016/j.jlumin.2019.116691 Received 24 June 2019; Received in revised form 7 August 2019; Accepted 9 August 2019 Available online 09 August 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
unchanged, but they sharply increase, so that this is an additional confirmation of excitation of nitrogen molecules adsorbed on the surface of the crystals, but not in the atmosphere [18–20]. Apparently, the intensity of ruthenium(II) band masked by those of inert gases also increases. Similar effect of inert gases on the intensity of TL was earlier observed for inorganic lanthanide salts [13,20,21]. Such an effect of inert gases on the intensity of TL is due to a change in electrophysical properties of the atmosphere surrounding the crystals (an increase in electrification and discharge phenomena during the tribodestruction). At the same time, some polyatomic gases or solidstate additives quench the TL [21,23–27]. Molecular oxygen, for example, quenches the emission of N2 during the TL of terbium(III) compounds, whereas the luminescence of Tb3+ ions remains unchanged [21]. This is a confirmation of the fact that there is no photoluminescent excitation mechanism of Tb3+. Similarly, there is only a band of [Ru(bpy)3]2+ ions in the TL spectrum during the tribodestruction of ruthenium(II) complex in O2 environment, and the luminescence of N2 is completely suppressed (Fig. 3a). At the same time, the luminescence intensity of [Ru(bpy)3]2+ almost remains unchanged. This indicates that the luminescence of ruthenium(II) complex is excited not due to absorption of UV luminescence of N2. Considering these facts, the TL of ruthenium(II) complex arises either due to bombardment of the surface of the crystals with charged particles or during electron-hole recombination in the crystal layer. At the same time, it should be noted that [Ru(bpy)3]Cl2 crystals are asymmetric [12,13]. As a result, it is possible to exclude the mechanism of TL proposed for centrosymmetric crystals [28–32]. It is due to local dissymmetry in a solid body along the packing planes in crystals during tribodestruction and, accordingly, separation of opposite charges. In addition, the intensity of TL of [Ru(bpy)3]Cl2 remains unchanged during the mechanical action in contrast to centrosymmetric crystals, whose TL decreases or terminates during grinding/destruction of the crystals under tribological processes [28,30,32]. Additional comparative studies are needed for further detailed identification of the mechanisms of excitation of [Ru (bpy)3]2+; for example, with different excitation of emission of [Ru(bpy)3]Cl2 crystals and environmental changes. This will be the aim of the following study. We only note that there was bombardment of the crystal surfaces with electrons arising during discharges [21]. Indeed, excited products *OH and *O formed by decomposition of water molecules of a crystalline hydrate and molecular oxygen were observed in the TL spectra of lanthanide salts in Ar and O2 environments. No lines of *O were identified in the spectra during TL of ruthenium(II) complex in oxygen atmosphere probably because of low intensity. An electronically excited *OH radical, however, was registered under argon at low pressure (up to 130 kPa) in the UV spectral region (Fig. 3b) during the tribodestruction of the [Ru(bpy)3]Cl2 complex. The ruthenium(II) complex exists as a crystalline hydrate under standard ambient pressure and temperature, and it contains six H2O molecules. The decomposition of crystallization water is possible during the mechanical action to form the excited product due to electronic impacts: H2O → *OH + H.
Fig. 1. (Solid line) TL and (dash line) PL spectra of the ground [Ru(bpy)3]Cl2 crystals in air at 298 K. Fluorolog-3, λexс = 450 nm, Δλ = 8 nm for TL and 2 nm for PL. The inset shows the decay curve (620 nm) under pulsed excitation by NanoLED-455 laser diode (λexc = 453 nm).
with a xenon lamp at 450 W or NanoLED pulsed solid-state laser diode. All experiments were performed at room temperature (298 K). 3. Results and discussion The intense lines of molecular nitrogen (Fig. 1) corresponding to (C3Пu–B3Пg) transitions are detected during the grinding the [Ru (bpy)3]Cl2 crystals in air environment in the UV region of a TL spectrum. The lines of *N2 in the TL spectra appear due to discharges arising in the cracks or between the surfaces of microcrystals oppositely charged during their destruction, which was shown for various solid substances [11,18–20]. The lines of N2 in the TL spectrum of the ruthenium(II) complex, therefore, indicate that there are discharges in this case. At the same time, there is a band at 619 nm in the red region of the spectrum during TL despite low quantum yield of photoluminescence for [Ru(bpy)3]Cl2 (~0.04 in aqueous solution at 298 K [12,13]). The TL spectrum of ruthenium(II) complex coincides in this region with the PL spectrum of the ground [Ru(bpy)3]Cl2 crystals (Fig. 1). The lifetime of the excited ion state *[Ru(bpy)3]2+ during PL is 0.28 μs (Fig. 1). The coincidence of TL spectra with a PL one indicates that their emitters are identical despite different mechanisms of occurrence. This emitter is an electronically excited ion *[Ru(bpy)3]2+. It appears due to transition of an electron from π-orbitals of the triplet ligand to a d shell of a metal [12]. [Ru(bpy)3]2+ may be excited via several ways according to possible mechanisms of occurrence of TL [11,18–20]. Ruthenium(II), for example, is excited due to absorption of emission of N2 with subsequent reradiation (photoluminescent mechanism) in the presence of N2 emission in the UV region of TL spectrum. In addition, the luminescence of ruthenium(II) complex is possible as a result of electrification of crystals during the tribodestruction due to direct excitation during bombardment by discharge electrons or during electronhole recombination of charges separated by the action of electric field in crystals (electroluminescence) [11,18,21–23]. One of the effective ways to identify a mechanism of reradiation is the study of TL in the atmosphere of gases, which activate or quench the luminescence [21,23–25]. As a result, the TL of ruthenium(II) complex was studied with a change in the atmosphere surrounding the crystals. Fig. 2 shows the TL spectra obtained in the atmosphere of neon and argon. It is clear that there are intense lines of Ne (550–800 nm) and Ar (680–840 nm) in the IR region of the spectrum. A band of [Ru(bpy)3]2+ is invisible among those of inert gases because of relatively weak luminescence. In this case, the N2 lines in the TL spectra not only remain
4. Conclusions In summary, the lines of molecular nitrogen at 300–430 nm and the emission of [Ru(bpy)3]2+ ion at 619 nm were recorded in triboluminescence spectrum during the destruction of ruthenium(II) complex. The spectrum of a solid-state TL (*[Ru(bpy)3]2+ emitter) coincides with the PL spectrum of crystals and corresponds to MLCT transition. Only band of [Ru(bpy)3]2+ ion was observed in the TL spectrum during tribodestruction of the ruthenium(II) complex in the O2 atmosphere, whereas no lines of N2 were recorded, confirming the absence of photoluminescent mechanism. There was a noticeable increase in TL intensity of [Ru(bpy)3]Cl2 crystals in neon and argon, and the lines of Ne and Ar atoms were also recorded in the TL spectrum. An effect of inert gases on TL intensity of ruthenium(II) complex is due to a change in 2
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
Fig. 2. TL spectra of [Ru(bpy)3]Cl2 in: (a) neon and (b) argon atmosphere. T = 298 K, Fluorolog-3, Δλ = 3 nm.
Fig. 3. TL spectra of [Ru(bpy)3]Cl2: (a) in O2 atmosphere and (b) at 300–440 nm during injection of Ar under pressure up to 130 kPa. All spectra were recorded under 298 K on Fluorolog-3. Δλ: (a) 8 and (b) 3 nm.
action and subsequent electrical discharges.
electrophysical properties of the atmosphere surrounding the crystals. The luminescence of OH radical (309 nm) was detected in the triboluminescence spectrum of [Ru(bpy)3]Cl2·6H2O crystals during tribodestruction in argon environment. The excited product *OH appears due to mechanochemical decomposition reaction of crystallization water: H2O → *OH + H. This reaction is initiated by electronic shocks during electrification of ruthenium(II) complex crystals under mechanical
Acknowledgements This work was supported by the Russian Science Foundation (grant no. 19-73-00017). The spectrofluorometric and spectrophotometric studies were performed using the equipment in of the “Agidel” 3
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
Collective Usage Centre at the Institute of Petrochemistry and Catalysis (Ufa Federal Research Centre, Russian Academy of Sciences).
[16]
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Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate Glyus L. Sharipov, Adis A. Tukhbatullin
T
⁎
High-energy Chemistry and Catalysis Laboratory, Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, 141 Prospekt Oktyabrya, 450075, Ufa, Russia
A R T I C LE I N FO
A B S T R A C T
Keywords: Triboluminescence Ruthenium(II) complex Inert gases OH luminescence
The triboluminescence of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex is detected during the mechanical grinding. The intense lines of N2 in the UV region and a band at 619 nm appeared due to luminescence of [Ru(bpy)3]2+ ion and coincided with the photoluminescence spectrum of the crystals are observed in the emission spectrum in air. The luminescence of N2 is due to electrification of the crystals during the destruction and subsequent discharges in the gas phase. We showed that the luminescence of [Ru(bpy)3]2+ does not occur due to absorption of UV luminescence of N2, because there is only luminescence of the crystal in O2 environment, whereas the luminescence of N2 is completely suppressed. The intense lines coincided with those of Ne and Ar atoms in the electric discharge are observed in the triboluminescence spectra of ruthenium(II) complex in neon and argon environments. In this case, there is an increase in intensity of N2 lines and of a band of [Ru (bpy)3]2+ due to more intense discharges than during the tribodestruction without inert gases. *OH radical is also detected in the triboluminescence spectrum due to mechanochemical decomposition of water molecules in the [Ru(bpy)3]Cl2·6H2O crystalline hydrate.
1. Introduction Coordination compounds of transition platinum group metals possess high activity in catalytic reactions [1–3] and unique luminescent properties [4,5]. Bipyridine complexes, for example, are chemically stable, exhibit intense luminescence, and can be used as a main component in organic luminescent diodes [6–9]. The triboluminescence (TL) or luminescence during the destruction of crystals [11] of a Pt(II) complex was detected [10]. It should also be noted that photoluminescent (PL), electroluminescent, and chemiluminescent properties of tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate due to metal-to-ligand charge-transfer (MLCT) are widely described in the literature [8,12–15]. The sonochemiluminescence of this ruthenium(II) complex was recently detected during the single and multibubble sonolysis of aqueous solutions [16,17]. The expansion of spectral luminescent studies of such metal complexes with various excitation ways of luminescence will allow us to detail our knowledge about basic mechanisms of formation and deactivation of their electronically excited states. Triboluminescence, for example, is a promising method to reveal the luminescent properties of crystalline metal complexes under mechanical action on them. A TL spectrum of crystals in air can contain gas phase luminescence (lines of N2) and the luminescence of a crystal ⁎
itself [11,18–20]. When the composition of a gas environment surrounding the crystals is changed, a TL spectrum contains lines of gases and their light-emitting decomposition products together with those of nitrogen [21–24], which coincide with the emission spectra in electrical discharges in most cases. In this work, the TL of a ruthenium(II) complex was studied for the first time with the monitoring of spectral components previously detected in the TL of other solid-state substances. 2. Experimental section Commercially available tris(2,2′-bipyridyl)ruthenium(II) dichloride hexahydrate complex (Aldrich) was used to study TL and PL. The experimental equipment, excitation, and registration methods of TL spectra are described in detail in Refs. [21,25]. The luminescence was recorded in air, molecular oxygen, and inert gases (Ne and Ar). The gases were supplied to the crystal layer with a tube in the working cell at a rate of up to 15 mL/s. To generate a gaseous atmosphere, the working cell was tightly sealed. The TL or PL spectra and the lifetimes of the excited state were acquired on a Fluorolog-3 (Horiba Jobin Yvon) spectrofluorometer equipped with a Hamamatsu R928P photomultiplier tube. When PL and the lifetime were studied, the crystals were placed into a solid sample holder (model 1933) that was excited
Corresponding author. E-mail address: [email protected] (A.A. Tukhbatullin).
https://doi.org/10.1016/j.jlumin.2019.116691 Received 24 June 2019; Received in revised form 7 August 2019; Accepted 9 August 2019 Available online 09 August 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
unchanged, but they sharply increase, so that this is an additional confirmation of excitation of nitrogen molecules adsorbed on the surface of the crystals, but not in the atmosphere [18–20]. Apparently, the intensity of ruthenium(II) band masked by those of inert gases also increases. Similar effect of inert gases on the intensity of TL was earlier observed for inorganic lanthanide salts [13,20,21]. Such an effect of inert gases on the intensity of TL is due to a change in electrophysical properties of the atmosphere surrounding the crystals (an increase in electrification and discharge phenomena during the tribodestruction). At the same time, some polyatomic gases or solidstate additives quench the TL [21,23–27]. Molecular oxygen, for example, quenches the emission of N2 during the TL of terbium(III) compounds, whereas the luminescence of Tb3+ ions remains unchanged [21]. This is a confirmation of the fact that there is no photoluminescent excitation mechanism of Tb3+. Similarly, there is only a band of [Ru(bpy)3]2+ ions in the TL spectrum during the tribodestruction of ruthenium(II) complex in O2 environment, and the luminescence of N2 is completely suppressed (Fig. 3a). At the same time, the luminescence intensity of [Ru(bpy)3]2+ almost remains unchanged. This indicates that the luminescence of ruthenium(II) complex is excited not due to absorption of UV luminescence of N2. Considering these facts, the TL of ruthenium(II) complex arises either due to bombardment of the surface of the crystals with charged particles or during electron-hole recombination in the crystal layer. At the same time, it should be noted that [Ru(bpy)3]Cl2 crystals are asymmetric [12,13]. As a result, it is possible to exclude the mechanism of TL proposed for centrosymmetric crystals [28–32]. It is due to local dissymmetry in a solid body along the packing planes in crystals during tribodestruction and, accordingly, separation of opposite charges. In addition, the intensity of TL of [Ru(bpy)3]Cl2 remains unchanged during the mechanical action in contrast to centrosymmetric crystals, whose TL decreases or terminates during grinding/destruction of the crystals under tribological processes [28,30,32]. Additional comparative studies are needed for further detailed identification of the mechanisms of excitation of [Ru (bpy)3]2+; for example, with different excitation of emission of [Ru(bpy)3]Cl2 crystals and environmental changes. This will be the aim of the following study. We only note that there was bombardment of the crystal surfaces with electrons arising during discharges [21]. Indeed, excited products *OH and *O formed by decomposition of water molecules of a crystalline hydrate and molecular oxygen were observed in the TL spectra of lanthanide salts in Ar and O2 environments. No lines of *O were identified in the spectra during TL of ruthenium(II) complex in oxygen atmosphere probably because of low intensity. An electronically excited *OH radical, however, was registered under argon at low pressure (up to 130 kPa) in the UV spectral region (Fig. 3b) during the tribodestruction of the [Ru(bpy)3]Cl2 complex. The ruthenium(II) complex exists as a crystalline hydrate under standard ambient pressure and temperature, and it contains six H2O molecules. The decomposition of crystallization water is possible during the mechanical action to form the excited product due to electronic impacts: H2O → *OH + H.
Fig. 1. (Solid line) TL and (dash line) PL spectra of the ground [Ru(bpy)3]Cl2 crystals in air at 298 K. Fluorolog-3, λexс = 450 nm, Δλ = 8 nm for TL and 2 nm for PL. The inset shows the decay curve (620 nm) under pulsed excitation by NanoLED-455 laser diode (λexc = 453 nm).
with a xenon lamp at 450 W or NanoLED pulsed solid-state laser diode. All experiments were performed at room temperature (298 K). 3. Results and discussion The intense lines of molecular nitrogen (Fig. 1) corresponding to (C3Пu–B3Пg) transitions are detected during the grinding the [Ru (bpy)3]Cl2 crystals in air environment in the UV region of a TL spectrum. The lines of *N2 in the TL spectra appear due to discharges arising in the cracks or between the surfaces of microcrystals oppositely charged during their destruction, which was shown for various solid substances [11,18–20]. The lines of N2 in the TL spectrum of the ruthenium(II) complex, therefore, indicate that there are discharges in this case. At the same time, there is a band at 619 nm in the red region of the spectrum during TL despite low quantum yield of photoluminescence for [Ru(bpy)3]Cl2 (~0.04 in aqueous solution at 298 K [12,13]). The TL spectrum of ruthenium(II) complex coincides in this region with the PL spectrum of the ground [Ru(bpy)3]Cl2 crystals (Fig. 1). The lifetime of the excited ion state *[Ru(bpy)3]2+ during PL is 0.28 μs (Fig. 1). The coincidence of TL spectra with a PL one indicates that their emitters are identical despite different mechanisms of occurrence. This emitter is an electronically excited ion *[Ru(bpy)3]2+. It appears due to transition of an electron from π-orbitals of the triplet ligand to a d shell of a metal [12]. [Ru(bpy)3]2+ may be excited via several ways according to possible mechanisms of occurrence of TL [11,18–20]. Ruthenium(II), for example, is excited due to absorption of emission of N2 with subsequent reradiation (photoluminescent mechanism) in the presence of N2 emission in the UV region of TL spectrum. In addition, the luminescence of ruthenium(II) complex is possible as a result of electrification of crystals during the tribodestruction due to direct excitation during bombardment by discharge electrons or during electronhole recombination of charges separated by the action of electric field in crystals (electroluminescence) [11,18,21–23]. One of the effective ways to identify a mechanism of reradiation is the study of TL in the atmosphere of gases, which activate or quench the luminescence [21,23–25]. As a result, the TL of ruthenium(II) complex was studied with a change in the atmosphere surrounding the crystals. Fig. 2 shows the TL spectra obtained in the atmosphere of neon and argon. It is clear that there are intense lines of Ne (550–800 nm) and Ar (680–840 nm) in the IR region of the spectrum. A band of [Ru(bpy)3]2+ is invisible among those of inert gases because of relatively weak luminescence. In this case, the N2 lines in the TL spectra not only remain
4. Conclusions In summary, the lines of molecular nitrogen at 300–430 nm and the emission of [Ru(bpy)3]2+ ion at 619 nm were recorded in triboluminescence spectrum during the destruction of ruthenium(II) complex. The spectrum of a solid-state TL (*[Ru(bpy)3]2+ emitter) coincides with the PL spectrum of crystals and corresponds to MLCT transition. Only band of [Ru(bpy)3]2+ ion was observed in the TL spectrum during tribodestruction of the ruthenium(II) complex in the O2 atmosphere, whereas no lines of N2 were recorded, confirming the absence of photoluminescent mechanism. There was a noticeable increase in TL intensity of [Ru(bpy)3]Cl2 crystals in neon and argon, and the lines of Ne and Ar atoms were also recorded in the TL spectrum. An effect of inert gases on TL intensity of ruthenium(II) complex is due to a change in 2
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
Fig. 2. TL spectra of [Ru(bpy)3]Cl2 in: (a) neon and (b) argon atmosphere. T = 298 K, Fluorolog-3, Δλ = 3 nm.
Fig. 3. TL spectra of [Ru(bpy)3]Cl2: (a) in O2 atmosphere and (b) at 300–440 nm during injection of Ar under pressure up to 130 kPa. All spectra were recorded under 298 K on Fluorolog-3. Δλ: (a) 8 and (b) 3 nm.
action and subsequent electrical discharges.
electrophysical properties of the atmosphere surrounding the crystals. The luminescence of OH radical (309 nm) was detected in the triboluminescence spectrum of [Ru(bpy)3]Cl2·6H2O crystals during tribodestruction in argon environment. The excited product *OH appears due to mechanochemical decomposition reaction of crystallization water: H2O → *OH + H. This reaction is initiated by electronic shocks during electrification of ruthenium(II) complex crystals under mechanical
Acknowledgements This work was supported by the Russian Science Foundation (grant no. 19-73-00017). The spectrofluorometric and spectrophotometric studies were performed using the equipment in of the “Agidel” 3
Journal of Luminescence 215 (2019) 116691
G.L. Sharipov and A.A. Tukhbatullin
Collective Usage Centre at the Institute of Petrochemistry and Catalysis (Ufa Federal Research Centre, Russian Academy of Sciences).
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