TY  - JOUR
A1  - Hong, Yongseok
A1  - Kim, Woojae
A1  - Kim, Taeyeon
A1  - Kaufmann, Christina
A1  - Kim, Hyungjun
A1  - Würthner, Frank
A1  - Kim, Dongho
T1  - Real-time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda-dimer by Ultrafast Time-Domain Raman Spectroscopy
JF  - Angewandte Chemie International Edition
N2  - In π-conjugated organic photovoltaic materials, an excimer state has been generally regarded as a trap state which hinders efficient excitation energy transport. But despite wide investigations of the excimer for overcoming the undesirable energy loss, the understanding of the relationship between the structure of the excimer in stacked organic compounds and its properties remains elusive. Here, we present the landscape of structural dynamics from the excimer formation to its relaxation in a co-facially stacked archetypical perylene bisimide folda-dimer using ultrafast time-domain Raman spectroscopy. We directly captured vibrational snapshots illustrating the ultrafast structural evolution triggering the excimer formation along the interchromophore coordinate on the complex excited-state potential surfaces and following evolution into a relaxed excimer state. Not only does this work showcase the ultrafast structural dynamics necessary for the excimer formation and control of excimer characteristics but also provides important criteria for designing the π-conjugated organic molecules.
KW  - excimer
KW  - vibrational coherence
KW  - time-resolved impulsive stimulated raman spectroscopy
KW  - structural dynamics
KW  - perylene bisimide
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318788
VL  - 61
IS  - 13
ER  - 
TY  - JOUR
A1  - Sung, Jooyoung
A1  - Kim, Pyosang
A1  - Fimmel, Benjamin
A1  - Würthner, Frank
A1  - Kim, Dongho
T1  - Direct observation of ultrafast coherent exciton dynamics in helical π-stacks of self-assembled perylene bisimides
JF  - Nature Communications
N2  - Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with pi-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π-π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.
KW  - systems
KW  - molecules
KW  - J-aggregate behavior
KW  - absorption
KW  - spectroscopy
KW  - photoluminescence
KW  - diffusion
KW  - fluorescence
KW  - excimer formation
KW  - organic semiconductors
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148157
VL  - 6
IS  - 8646
ER  -