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제123회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Spectroscopic Demonstration of length-dependent ultrafast depolarization dynamics of a Frenkel exciton in a sterically π-stacked Perylene Bisimide aggregate

2019년 1월 30일 17시 51분 22초
PHYS.P-96 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
4월 19일 (금요일) 11:00~12:30
Physical Chemistry
저자 및
Seongsoo Kang, Dongho Kim1,*
Yonsei University, Korea
1Department of Chemistry, Yonsei University, Korea
Although it is commonly known that π-stacked PBI aggregates of H-type exhibit a red-shifted and broad fluorescence by excimer formation with longer fluorescence lifetimes than monitored for the monomers, unveiling the nascent dynamics of a delocalized Frenkel exciton in molecular π-stacked systems as soon as photoexcitation is still far from being understood. According to our previous time-resolved emission spectroscopic observation of H-type PBI aggregates, it turned out that an initially delocalized Frenkel exciton is localized by ultrafast excimer formation. Furthermore, the migration dynamics of exciton that was not observed in small aggregates having less than four PBI subunits to form one self-assembly was confirmed in only larger aggregates consist of infinite PBI subunits. In terms of rotationally π-stacked displacement of PBI aggregates, the dynamics of a delocalized Frenkel exciton is related to coherent rearrangements of transition dipoles by the interaction between PBI subunits in ultrafast time scale. In this context, we prepared three PBI dyes forming aggregates of three different lengths of the co-facially stacked dimer, tetramer, and extended oligomer in proper conditions. The comparison of depolarization processes according to different sizes of aggregate was performed using polarization-dependent fs-transient absorption anisotropy (TAA) spectroscopic measurements with home-made NOPA pulses of the time duration (50 fs). Since in the ultrafast time window the decay profiles of anisotropy values are not affected by vibrational relaxation and rotational diffusion processes, length-dependent exciton dynamics can reveal fundamental exciton dynamics.