Researches on "Excited-State Conformational / Electronic Responses of Saddle Shaped N, N-Disubstituted-Dihydrodibenzo [a, c] phenazines" by Tian He, Ph.D., Professor Jianhua Sun and Professor Zhou Weitai from National Taiwan University, Wide Tuning Emission from Red to Deep Blue and White Light Combination "is published in the journal J. Am. Chem. Soc. 2015, 137, 8509-8520, DOI: 10.1021 / jacs, July 8 .5b03491).
In-depth understanding of the organic light-emitting state excited process is a very challenging task. Conjugated molecules, when excited by light, typically exhibit very distinct photophysical properties such as greater Stokes shift, multiple luminescence, and environmental responsiveness if their excited states have electron configurations and / or structures that greatly differ from the ground state Glow and so on. Recently, Prof. Dr. Zhi-Yun Su and Prof. Dr. Huang Wei directed against dihydrobenzophenazine by the research group of Prof. Jian-Hua Su and observed the single-molecule broad-spectrum luminescence through the rigid regulation of solvents (W. Huang, et al., Chem. Commun , 2015, 51, 4462-4464). As a result, they proposed a new mechanism called "vibration induced emission". However, a new concept requires careful and sufficient experimental data to demonstrate. Therefore, in further expanding the molecular system and Molecular structure at the same time, they and internationally renowned ultra-fast spectral scientist Professor Zhou Bi Tai cooperation, Dr. Zhang Zhiyun went to Taiwan University and spectroscopy scholars go through three years of in-depth exploration, and now get the preliminary results peer recognition, the full report of JACS A series of donor-acceptor "saddle-shaped" phenazine compounds exhibit very large Stokes shift emissions and this anomaly is unaffected by solvent polarity.
In the excited state, the "saddle-shaped" molecular conformation will tend to be planarized, accompanied by changes in the distribution of electron clouds, which leads to its unique photophysical behavior. The mechanism is validated by the steady-state and ultra-fast time-resolved spectroscopy related to polarity, viscosity and temperature. The three-step kinetic process has been initially established by the computational simulation of the ultrafast spectrum and the potential energy surface of femtoseconds: N, N - Disubstituted - dihydrodibenz [a, c] phenazine compounds by the light-induced excitation, the first intramolecular charge transfer occurs, followed by the polar stability and the molecular skeleton of the plane of the process, expanding the dibenzo [a, c] phenazine structure? - Delocal plane. In the process of planarization, the steric barrier caused by N, N-diaryl is overcome, resulting in a local minimum energy state, ie, an intermediate state. Thus, anomalous spectral phenomena of interest have been generated by the combination of three initial states of charge transfer, intermediate state and final planarization. In addition, N, N-disubstituted-dihydrodibenz [a, c] phenoxazines exhibit multicolored luminescence through the rigid control of the external environment, and can be controlled from red to blue in a large wavelength range, White light can be obtained under the conditions. This provides a new idea for the design of novel monomolecular wide-spectrum luminescent materials in the future. Expanded luminescent materials designed and synthesized based on the new mechanism of "vibration induced emission" are under further study.
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