Design, Synthesis and Photophysical Studies of Luminescent Rhodium(III) Complexes in Near‐Infrared Region
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Abstract A series of near‐infrared (NIR)‐emitting cyclometalated rhodium(III) complexes have been designed, synthesized and characterized. The NIR luminescence has been realized by rational design of strong σ‐donor cyclometalating (C^N) ligand with extended π‐conjugation structure for decreasing the energy level of intraligand (IL) state. In addition, the investigation of substituents on the benzo[ g ]quinoxaline moiety as the carbon‐donor demonstrated that the luminescence can be further shifted to the red by the introduction of electron‐donating thienyl groups. The luminescence maxima of these complexes are ranging from 763 nm to 792 nm with the luminescence quantum yield (Φ lum ) of 0.41 %–0.66 % in dichloromethane solution. This work demonstrates the first example of NIR‐phosphorescent rhodium(III) complexes and provides an alternative for diversifying the development of NIR materials.Keywords:
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The phosphorescent state of the 1,2,4,5-tetracyanobenzene-naphthalene charge-transfer complex in rigid solution and in single crystal of 1:1 composition was studied in detail through measurements of the phosphorescence, phosphorescence excitation, E.S.R., and microwave-induced delayed phosphorescence spectra. From the analysis of these spectra it is concluded that there are two types of the complexes with different charge-transfer characters both in rigid solution and in crystal. The crystal was found to have three types of phosphorescent sites: Site 1, naphthalene as a shallow trap; Site 2, the complex, the phosphorescent state of which has the character of a locally (within naphthalene) excited triplet state perturbed by the charge-transfer interaction; Site 3, the complex, the phosphorescent state of which is mainly of charge-transfer triplet. Phosphorescence spectra from the individual sites were separately observed with the aid of the microwave-induced delayed phosphorescence technique. The temperature dependence of the phosphorescence spectrum in the crystalline state was explained by considering the energy transfer among these sites. In addition to the three types of phosphorescence, delayed charge-transfer fluorescence due to triplet-triplet annihilation was observed.
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Abstract Developing pure organic materials with ultralong lifetimes is attractive but challenging. Here we report a concise chemical approach to regulate the electronic configuration for phosphorescence enhancement. After the introduction of d–pπ bonds into a phenothiazine model system, a phosphorescence lifetime enhancement of up to 19 times was observed for DOPPMO, compared to the reference PPMO. A record phosphorescence lifetime of up to 876 ms was obtained in phosphorescent phenothiazine. Theoretical calculations and single‐crystal analysis reveal that the d–pπ bond not only reduces the (n, π*) proportion of the T 1 state, but also endows the rigid molecular environment with multiple intermolecular interactions, thus enabling long‐lived phosphorescence. This finding makes a valuable contribution to the prolongation of phosphorescence lifetimes and the extension of the scope of phosphorescent materials.
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The quinoxaline derivatives are beneficial compounds because of their various medicinal and industrial applications. They are well-known for application in organic light emitting devices, polymers and pharmaceutical agents. The quinoxaline-containing polymers are applicable in optical devices due to their thermal stability and low band gap. There are many reported procedures for the synthesis of bis- and polyquinoxalines and quinoxaline-containing macrocycles. The quinoxaline-based compounds as fascinating structures are important subjects of interest in either basic or applied sciences. This review summarizes the latest progresses related to the quinoxalines, quinoxaline-containing macrocycles, and bis- and poly quinoxalines, including the synthesis, functionalization and modification methods and applications of these compounds.
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Abstract Developing pure organic materials with ultralong lifetimes is attractive but challenging. Here we report a concise chemical approach to regulate the electronic configuration for phosphorescence enhancement. After the introduction of d–pπ bonds into a phenothiazine model system, a phosphorescence lifetime enhancement of up to 19 times was observed for DOPPMO, compared to the reference PPMO. A record phosphorescence lifetime of up to 876 ms was obtained in phosphorescent phenothiazine. Theoretical calculations and single‐crystal analysis reveal that the d–pπ bond not only reduces the (n, π*) proportion of the T 1 state, but also endows the rigid molecular environment with multiple intermolecular interactions, thus enabling long‐lived phosphorescence. This finding makes a valuable contribution to the prolongation of phosphorescence lifetimes and the extension of the scope of phosphorescent materials.
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An equation that relates the ratio of fluorescence to phosphorescence quantum yields as function of temperature to basic photophysical parameters is considered. The quantum yields were obtained from three compounds on three different solid matrices. Fluorescence quantum yields did not change much with temperature, while phosphorescence quantum yields changed more substantially with temperature. For some of the systems considered, it was possible to show that, as the temperature was lowered, the quantum yield ratio was only a function of the phosphorescence lifetime of the phosphor. However, with other systems, the quantum yield ratio was dependent on both the rate constant of intersystem crossing from the singlet state to the triplet state and the phosphorescence lifetime. The equation discussed is important in defining the fundamental parameters that cause the luminescence quantum yield ratio to change as temperature is lowered.
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The review article attempts to give recent advances on quinoxaline and its derivatives. Some pathways to the synthesis of quinoxaline, quinoxaline-2-one and quinoxaline-2,3-dione were reported using simple reactive quinoxaline synthon. In addition, the reactions, biological and technological applications of derivatives of quinoxaline and related compounds were reported.
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