Dynamics of the triplet-pair state reveals the likely coexistence of coherent and incoherent singlet fission in crystalline hexacene.
The absorption of a photon usually creates a singlet exciton (S1) in molecular systems, but in some cases S1may split into two triplets (2×T1) in a process called singlet fission. Singlet fission is believed to proceed through the correlated triplet-pair1(TT) state. Here, we probe the1(TT) state in crystalline hexacene using time-resolved photoemission and transient absorption spectroscopies. We find a distinctive1(TT) state, which decays to 2×T1with a time constant of 270 fs. However, the decay of S1and the formation of1(TT) occur on different timescales of 180 fs and <50 fs, respectively. Theoretical analysis suggests that, in addition to an incoherent S1→1(TT) rate process responsible for the 180 fs timescale, S1may couple coherently to a vibronically excited1(TT) on ultrafast timescales (<50 fs). The coexistence of coherent and incoherent singlet fission may also reconcile different experimental observations in other acenes.
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Nicholas R
0000-0002-8562-5127
NR
Monahan
Department of Physics, Columbia University, New York, New York 10027, USA.
Dezheng
D
Sun
Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Hiroyuki
H
Tamura
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Kristopher W
KW
Williams
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
Bolei
B
Xu
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Yu
Y
Zhong
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Bharat
B
Kumar
Department of Chemistry, Columbia University, New York, New York 10027, USA.
Colin
C
Nuckolls
Honda Research Institute USA, Columbus, Ohio 43212, USA.
Avetik R
AR
Harutyunyan
Honda Research Institute USA, Columbus, Ohio 43212, USA.
Gugang
G
Chen
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
Hai-Lung
HL
Dai
Chimie des Matériaux Nouveaux, Université de Mons, B-7000 Mons, Belgium.
David
D
Beljonne
Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA.
Yi
Y
Rao
Department of Chemistry, Columbia University, New York, New York 10027, USA.
X-Y
XY
Zhu