- Excited-State Conformational/Electronic Responses of Saddle-Shaped N, N ′-Disubstituted-Dihydrodibenzo[ a, c ]phenazines: Wide-Tuning Emission from Red to Deep Blue and White Light Combination
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A tailored strategy is utilized to modify 5,10-dimethylphenazine (DMP) to donor-acceptor type N,N′-disubstituted-dihydrodibenzo[a,c]phenazines. The representative compounds DMAC (N,N′-dimethyl), DPAC (N,N′-diphenyl), and FlPAC (N-phenyl-N′-fluorenyl) reveal significant nonplanar distortions (i.e., a saddle shape) and remarkably large Stokes-shifted emission independent of the solvent polarity. For DPAC and FlPAC with higher steric hindrance on the N,N′-substituents, normal Stokes-shifted emission also appears, for which the peak wavelength reveals solvent-polarity dependence. These unique photophysical behaviors are rationalized by electronic configuration coupled conformation changes en route to the geometry planarization in the excited state. This proposed mechanism is different from the symmetry rule imposed to explain the anomalously long-wavelength emission for DMP and is firmly supported by polarity-, viscosity-, and temperature-dependent steady-state and nanosecond time-resolved spectroscopy. Together with femtosecond early dynamics and computational simulation of the reaction energy surfaces, the results lead us to establish a sequential, three-step kinetics. Upon electronic excitation of N,N′-disubstituted-dihydrodibenzo[a,c]phenazines, intramolecular charge-transfer takes place, followed by the combination of polarization stabilization and skeletal motion toward the planarization, i.e., elongation of the π-delocalization over the benzo[a,c]phenazines moiety. Along the planarization, DPAC and FlPAC encounter steric hindrance raised by the N,N′-disubstitutes, resulting in a local minimum state, i.e., the intermediate. The combination of initial charge-transfer state, intermediate, and the final planarization state renders the full spectrum of interest and significance in their anomalous photophysics. Depending on rigidity, the N,N′-disubstituted-dihydrodibenzo[a,c]phenazines exhibit multiple emissions, which can be widely tuned from red to deep blue and even to white light generation upon optimization of the surrounding media.
- Zhang, Zhiyun,Wu, Yu-Sin,Tang, Kuo-Chun,Chen, Chi-Lin,Ho, Jr-Wei,Su, Jianhua,Tian, He,Chou, Pi-Tai
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- Charge Transfer and Addition Products between Alkylated Phenazine Donors and Ethanetetracarbonitrile (TCNE): Crystal and Molecular Structure of the Dye 2,2'-(2,3,5,10-Tetrahydro-5,10-dimethylphenazine-2,3-ylidene)bis(propanedinitrile) (TMPP)
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Mixing solution of 5,10-dimethyl-5,10-dihydrophenazine (M2P) and TCNE yields different solid reaction products with nearly 1:1 donor:acceptor stoichiometry.Without excluding air the reaction leads to an oxygen-containing intermediate of stoichiometry C19H15N5O (1).The dark green to black crystals are twinned having cell dimensions a = 14.34 Angstroem, b = 30.10 Angstroem, c = 4.17 Angstroem, β = 90.1 deg and crystallizing in the monoclinic space group P21/n.Violet needles of the 1:1 salt, M2P+TCNE- (2), are obtained only by excluding moisture and oxygen.They crystallize in always twinned specimens in a tetragonal space group, the unit cell along the needle axis being 7.46(3) Angstroem.Lustrous (brass-like) crystals of TMPP (3) (formula C20H12N6), Mr = 336.358, dc = 1.35 Mg*m-3) are obtained under air and in most solvents.They crystallize in the monoclinic space group C2/c with a = 9.674(3) Angstroem, b = 19.411(8) Angstroem, c =9.603(3) Angstroem, V = 1657.4(9) Angstroem3, β = 113.20(2) deg, and Z = 4.The structure determination yielded in the final refinement an Rw index of 0.076. 3 is a condensation product of M2P and TCNE under loss of 1 mol of H2.Two rings of the former M2P molecule are planar.The ring with two "condenced" >C=(CN)2 groups is twisted.The >C=(CN)2 groups are also twisted with respect to each other and out of the "molecular" plane because of sterical hindrance.The molecules form regular stacks along the z axis with interplanar distances of 4.75(2) Angstroem.The linearly polarized strong optical reflection which causes the metallic luster is polarized perpendicular to the molecular planes, indicating appreciable intermolecular CT interactions.Corresponding products are obtained with the donors 5,10-dihydro-5,10-dimethylphenazine (E2P) and 5-methylphenazinium hexafluorophosphate (MP+PF6-), thus representing a new class of thermally and chemically highly stable dyes with strong electron-donating and -withdrawing centers on one molecule.
- Dietz, K.,Keller, H. J.,Noethe, D.,Wehe, D.
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- Preparation and Properties of Electron Donor Acceptor Complexes of the Compounds having Capto-dative Substituents
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In order to examine the "capto-dative" substitution-effect on the electrical conductivity, five compounds which have capto-dative substituents were prepared.Electron withdrawing (capto) group was nitro- or cyano-substituted phenyl and electron donating (dative) one was 5-methyl-5,10-dihydrophenazinyl moiety.The character of intramolecular electron donor acceptor complex of the five compounds were demonstrated by their uv spectra.Electron donor acceptor complexes of them with tetracyanoquinodimethane were prepared and their electrical resistivities were measured.
- Sugimoto, Akira,Kotani, Takeshi,Tsujimoto, Junko,Yoneda, Shigeo
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p. 435 - 438
(2007/10/02)
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- MECHANISM OF BROMINATION OF SOME AROMATIC AMIDES BY N-BROMOSUCCINIMIDE
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It was established that in polar organic solvents N-bromosuccinimide acts as a one-electron oxidizing agent for tertiary aromatic amines and N,N-substituted dihydrophenazines.Depending on the structure of the amines and the nature of the medium, the maximum current concentration of the radical-cations in these reactions amounts to 90percent of the initial amine.It was shown that the intermediate radical-cations of the substituted amines can then be transformed into the bromination products by reaction with the bromide ion formed during dissociation of the bromosuccinimide radical- anion.The mechanism of the investigated reactions in the light and in the dark is discussed.
- Koshechko, V. G.,Inozemtsev, A. N.
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p. 315 - 318
(2007/10/02)
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