الفهرس 
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Abstract
In this study we report the synthesis and characterization of some heteroleptic Cr(III) complexes of the form [Cr(Phen)2L](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’-di-tert-butyl-2,2’-bipyridine (4,4’-dtbpy); 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), 4,7-dimethyl-1,10-Phenanthroline (4,7-DMP). Heteroleptic complexes were prepared in two stages via the intermediate [Cr(Phen)2(CF3SO3)2](CF3SO3) and five examples have been crystallographically characterized. Steady-state absorption and luminescence emission characteristics of these complexes were measured in 1M 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 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_00, was found to vary within the narrow range 163.1 to 165.0 kJ mol-1, across the series. Transient absorption spectra in degassed, air-equilibrated, and oxygen saturated 1M HCl aqueous solution 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 ×107 M-1 s-1. The observation of singlet oxygen luminescence, which was photosensitized by the aforementioned complexes, was conducted in a deuterium oxide (D2O) environment. The luminescence intensity at a wavelength of 1270 nm was utilized to determine the singlet oxygen quantum yields (Φ_Δ) for these complexes. The determined quantum yields ranged from 0.23 to 0.44. Additionally, the fraction of the excited 2E state that was quenched by oxygen (P_D^(O_2 )) fell within the range of 0.22 to 0.68, while the efficiency of singlet oxygen production (f_∆^D) ranged from 0.44 to 0.90.
The process through which the excited 2E state is quenched by oxygen can be elucidated by employing a spin statistical model. This model allows for the estimation of the relative contributions of charge transfer (CT) and non-charge transfer (nCT) deactivation pathways. The parameter p_CT, which represents this balance, was determined to range from 0.35 to 0.68 for the series of Cr(III) complexes under investigation.