Fractional dependence of the free energy of activation on the driving force of charge transfer in the quenching of the excited states of substituted phenanthroline homoleptic ruthenium(<scp>ii</scp>) complexes in aqueous medium

Akl, Hossam N.; Salah, Dina; Abdel‐Samad, Hesham S.; Aziz, Ayman A. Abdel; Abdel-Shafi, Ayman A.

doi:10.1039/d3ra01280h

Cited by 2 publications

(5 citation statements)

References 93 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast to our previous studies with ionic sensitizers, such as Ru(II) complexes, 42 , 44 , 56 where the rate constant of back dissociation of the encounter complexes k –d was taken as 3 × k d × M, (where M is the unit mole per liter) or 2 × k d × M in the case of Ir(III) and Re(I) complexes, the agreement between the calculated and experimental data presented in Table 3 is obtained when considering the rate constant of back dissociation of the encounter complexes, k –d = k d × M, which is similar to that used in the case of aromatic hydrocarbons in nonaqueous media. 22 − 25 , 105 − 107 Figure 11 shows the dependence of log( k D ) on p CT .…”

Section: Resultscontrasting

confidence: 85%

“…In contrast to our previous studies with ionic sensitizers, such as Ru(II) complexes, ,, where the rate constant of back dissociation of the encounter complexes k –d was taken as 3 × k d × M, (where M is the unit mole per liter) or 2 × k d × M in the case of Ir(III) and Re(I) complexes, the agreement between the calculated and experimental data presented in Table is obtained when considering the rate constant of back dissociation of the encounter complexes, k –d = k d × M, which is similar to that used in the case of aromatic hydrocarbons in nonaqueous media. − ,− Figure shows the dependence of log( k D ) on p CT . The nonlinear increase of log( k D ) with p CT is best described by the rearrangement of eq ( k D = Σ k Δ E P /(1 – p CT )) with Σ k Δ E P = 1.65 × 10 7 s –1 , which is much lower than observed for Ru(II) complexes for which Σ k Δ E P = 2.4 × 10 9 s –1 .…”

Section: Resultssupporting

confidence: 72%

“…It is worth noting that the oxygen quenching rate constant for these Cr(III) complexes is at least 2 orders of magnitude slower than that for the corresponding Ru(II) complexes. For comparison, the oxygen quenching rate constant photosensitized by [Ru(Phen) 3 ] 2+ is 4.6 × 10 9 M –1 s –1, whereas the value drops to 4.4 × 10 7 M –1 s –1 for [Cr(Phen) 3 ] 3+ . On the other hand, the singlet oxygen quantum yield is approximately the same for both sensitizers.…”

Section: Resultsmentioning

confidence: 99%

“… 18 , 19 , 40 , 41 The majority of these studies have been concerned on the study of singlet oxygen generation photosensitized by ruthenium(II) polypyridyl complexes in aqueous and nonaqueous media. 41 − 56 Photosensitization of singlet oxygen by metal complexes other than Ru(II) has also been reported 57 − 69 using, for example, complexes of Pd(II) and Pt(II), 57 − 61 , 65 − 68 Os(II) with terpyridyl ligands, 64 Au(I), 62 Ir(III), 63 , 65 , 66 and Re(I). 69 …”

Section: Introductionmentioning

confidence: 95%

“…Studies on singlet oxygen photosensitization by coordination compounds are very limited in comparison with those reported for aromatic compounds. ,,, The majority of these studies have been concerned on the study of singlet oxygen generation photosensitized by ruthenium(II) polypyridyl complexes in aqueous and nonaqueous media. − Photosensitization of singlet oxygen by metal complexes other than Ru(II) has also been reported − using, for example, complexes of Pd(II) and Pt(II), − ,− Os(II) with terpyridyl ligands, Au(I), Ir(III), ,, and Re(I) …”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Mechanism of Oxygen Quenching of the Excited States of Heteroleptic Chromium(III) Phenanthroline Derivatives

Alazaly,

Clarkson,

Ward

et al. 2023

Inorg. Chem.

Self Cite

View full text Add to dashboard Cite

In this study, we report the synthesis and characterization of some heteroleptic Cr(III) complexes of the form [Cr(Phen) 2 L](OTf) 3 , where Phen = 1,10-phenanthroline and L is either 2,2′-bipyridine (bpy) or its derivatives, such as 4,4′dimethyl-2,2′-bipyridine (4,4′-DMB), 4,4′-dimethoxy-2,2′-bipyridine (4,4′-DMOB), 4,4′-ditert-butyl-2,2′-bipyridine (4,4′-d t bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-DMB), 4,4′-dimethoxycarbonyl-2,2′-bipyridine (4,4′-dmcbpy) or 1,10-phenanthroline derivatives, such as 5-methyl-1,10-phenanthroline (5-Me-Phen) and 4,7-dimethyl-1,10-phenanthroline (4,7-DMP). Heteroleptic complexes were prepared in two stages via the intermediate [Cr(Phen) 2 (CF 3 SO 3 ) 2 ](CF 3 SO 3 ) and five examples have been crystallographically characterized. Steady-state absorption and luminescence emission characteristics of these complexes were measured in 1 M HCl solutions. The luminescence quantum yield of these complexes was found to be the lowest for [Cr(Phen) 2 (4,4′-dmcbpy)](OTf) 3 and the highest for [Cr(Phen) 2 (4,4′-DMB)](OTf) 3 with values of 0.31 × 10 −2 and 1.48 × 10 −2 , respectively. The calculated excited state energy, E 0−0 , was found to vary within the narrow range of 163.1−165.0 kJ mol −1 across the series. Transient absorption spectra in degassed, air-equilibrated, and oxygen-saturated 1 M HCl aqueous solutions were also measured at different time decays and demonstrated no significant differences, indicating the absence of any ion-separated species in the excited state. Excited-state decay traces at the wavelength of maximum absorption were used to calculate oxygen quenching rate constants, k q , which were found to be in the range 3.26−5.27 × 10 7 M −1 s −1 . Singlet oxygen luminescence photosensitized by these complexes was observed in D 2 O, and its luminescence intensity at 1270 nm was used for the determination of singlet oxygen quantum yields for these complexes, which were in the range of 0.20−0.44, while the fraction of the excited 2 E state quenched by oxygen was in the range of 0.22−0.68, and the efficiency of singlet oxygen production was in the range of 0.44−0.90. The mechanism by which the excited 2 E state is quenched by oxygen is explained by a spin statistical model that predicts the balance between charge transfer and noncharge transfer deactivation pathways, which was represented by the parameter p CT that was found to vary from 0.35 to 0.68 for this series of Cr(III) complexes.

show abstract