jp5b01323_si_001.pdf (2.23 MB)
Spectroscopic Signature of the Aggregation-Induced Emission Phenomena Caused by Restricted Nonradiative Decay: A Theoretical Proposal
journal contribution
posted on 2015-03-05, 00:00 authored by Tian Zhang, Huili Ma, Yingli Niu, Wenqiang Li, Dong Wang, Qian Peng, Zhigang Shuai, WanZhen LiangIt
has been suggested that the exotic aggregation-induced emission
(AIE) phenomenon was caused by the restriction on the nonradiative
decay through intramolecular vibrational/rotational relaxation. There
have been other proposed mechanisms such as J-aggregation or excimer
formation, etc. Through computational studies, we propose a direct
approach to verify the AIE process, namely, using resonance Raman
spectroscopy (RRS) to explore the microscopic mechanism of AIE. Taking
examples of AIE-active 1,2-diphenyl-3,4-bis(diphenylmethylene)-1-cyclobutene
(HPDMCb) and AIE-inactive 2,3-dicyanopyrazino phenanthrene
(DCPP) for comparison, we found that for the AIEgen,
after aggregation into cluster, the intensities of low-frequency peaks
in RRS are evidently reduced relative to the high-frequency peaks,
along with a remarkable blueshift. However, the RRS of non-AIEgen
remains almost unaffected upon aggregation. Such distinctive spectroscopic
characteristics can be ascribed to the intramolecular vibrational
relaxation which is hindered for AIEgen, especially for the low-frequency
ring-twisting motions, because the RRS amplitude is proportional to
the mode vibrational relaxation energy times frequency λjωj. Thus,
RRS is a direct way to clarify the recent dispute on the AIE mechanism.
If such predictions are true, it will clearly validate the earlier
proposed restriction on the nonradiative decay through an intramolecular
vibration/rotation relaxation mechanism.