Chapter 16
Efficient Singlet Fission in Acene-Based
Molecular Assemblies
Taku Hasobe
Abstract In this chapter, we introduce singlet fission and related photophysical processes of acene derivatives such as pentacene and tetracene dimers and
supramolecular assemblies with gold nanoclusters. Time-resolved spectroscopic
measurements revealed the long-lived and high-yield triplet excited state through
singlet fission. Moreover, light energy conversion processes such as electron transfer
and singlet oxygen generation through singlet fission are discussed.
Keywords Singlet fission · Acene derivatives · Gold nanoclusters
16.1 Introduction
Singlet fission (SF) is a spin-allowed photophysical pathway, in which one singlet
exciton (S 1 ) is converted into two triplet excitons (2 × T 1 ) in two neighboring
molecules [1–3]. It is a promising process to improve light energy conversion properties (i.e., photovoltaics and photocatalysis) [4–6]. To proceed the SF process, the
energy-matching condition between the energy of the lowest-lying singlet excited
state E(S 1 ) and energy of two triplet excited states 2E(T 1 ) [i.e., E(S 1 ) ≥ 2 E(T 1 )]
is definitely required. SF initially enables to generate correlated triplet pairs [(TT)]
from a singlet excited state. Then, it subsequently dissociates to the two individual
triplet states [(2 × T 1 )]. As the reverse process from the correlated triplet state (TT),
triplet–triplet annihilation (TTA) also prevents generating (2 × T) because of the
competitive reaction with the dissociation process of (TT) to (2 × T 1 ).
Regarding SF molecules, polyacene derivatives satisfy the above condition. Therefore, pentacene derivatives are one of the representative SF compounds considering
E(S 1 ) = 2.1 eV and E(T 1 ) = 0.8 eV [7–12]. However, the serious problem of
pentacene is relatively low-excitation energy of excited triplet states. This means
that the oxidation and reduction properties through triplet excited states become
relatively weak. In contrast, tetracene (Tc) is a good candidate for SF considering
T. Hasobe (B)
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi,
Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan
e-mail: hasobe@chem.keio.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_16
275
Efficient Singlet Fission in Acene-Based
Molecular Assemblies
Taku Hasobe
Abstract In this chapter, we introduce singlet fission and related photophysical processes of acene derivatives such as pentacene and tetracene dimers and
supramolecular assemblies with gold nanoclusters. Time-resolved spectroscopic
measurements revealed the long-lived and high-yield triplet excited state through
singlet fission. Moreover, light energy conversion processes such as electron transfer
and singlet oxygen generation through singlet fission are discussed.
Keywords Singlet fission · Acene derivatives · Gold nanoclusters
16.1 Introduction
Singlet fission (SF) is a spin-allowed photophysical pathway, in which one singlet
exciton (S 1 ) is converted into two triplet excitons (2 × T 1 ) in two neighboring
molecules [1–3]. It is a promising process to improve light energy conversion properties (i.e., photovoltaics and photocatalysis) [4–6]. To proceed the SF process, the
energy-matching condition between the energy of the lowest-lying singlet excited
state E(S 1 ) and energy of two triplet excited states 2E(T 1 ) [i.e., E(S 1 ) ≥ 2 E(T 1 )]
is definitely required. SF initially enables to generate correlated triplet pairs [(TT)]
from a singlet excited state. Then, it subsequently dissociates to the two individual
triplet states [(2 × T 1 )]. As the reverse process from the correlated triplet state (TT),
triplet–triplet annihilation (TTA) also prevents generating (2 × T) because of the
competitive reaction with the dissociation process of (TT) to (2 × T 1 ).
Regarding SF molecules, polyacene derivatives satisfy the above condition. Therefore, pentacene derivatives are one of the representative SF compounds considering
E(S 1 ) = 2.1 eV and E(T 1 ) = 0.8 eV [7–12]. However, the serious problem of
pentacene is relatively low-excitation energy of excited triplet states. This means
that the oxidation and reduction properties through triplet excited states become
relatively weak. In contrast, tetracene (Tc) is a good candidate for SF considering
T. Hasobe (B)
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi,
Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan
e-mail: hasobe@chem.keio.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_16
275