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Zhang Z, Wu YS, Tang KC, et al. 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. J Am Chem Soc. 2015;137(26):8509-20doi: 10.1021/jacs.5b03491.
Zhang, Z., Wu, Y. S., Tang, K. C., Chen, C. L., Ho, J. W., Su, J., Tian, H., & Chou, P. T. (2015). 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. Journal of the American Chemical Society, 137(26), 8509-20. https://doi.org/10.1021/jacs.5b03491
Zhang, Zhiyun, et al. "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." Journal of the American Chemical Society vol. 137,26 (2015): 8509-20. doi: https://doi.org/10.1021/jacs.5b03491
Zhang Z, Wu YS, Tang KC, Chen CL, Ho JW, Su J, Tian H, Chou PT. 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. J Am Chem Soc. 2015 Jul 08;137(26):8509-20. doi: 10.1021/jacs.5b03491. Epub 2015 Jun 29. PMID: 26075574.
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J Am Chem Soc. 2015 Jul 08;137(26):8509-20. doi: 10.1021/jacs.5b03491. Epub 2015 Jun 29.

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.

Journal of the American Chemical Society

Zhiyun Zhang, Yu-Sin Wu, Kuo-Chun Tang, Chi-Lin Chen, Jr-Wei Ho, Jianhua Su, He Tian, Pi-Tai Chou

Affiliations

  1. ‡Department of Chemistry, National Taiwan University, Taipei, 10617 Taiwan, R.O.C.

PMID: 26075574 DOI: 10.1021/jacs.5b03491

Abstract

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.

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