(Invited) Construction of Organic and Inorganic Hybrid Nanomaterials Utilizing Acene Derivatives for Efficient Singlet Fission

Abstract

Singlet fission (SF) is highly expected to improve the solar energy conversion properties by generating two excitons from one photon absorption. Among various organic compounds, acene derivatives such as tetracene and pentacene are promising for occurrence of efficient SF. For example, pentacenes meet the energy-level matching condition between a singlet and two triplet states: [E(S1) ≥ 2E(T1)]. However, the molar absorption coefficients of pentacenes in the ca. 400–500 nm region are extremely limited, whereas quantum dots, such as CdSe/ZnS (QD), possess high fluorescence quantum yields and particle-size-dependent fluorescence wavelengths. Thus, a combination of QD (D) and pentacene (A) provides a system of both an enhanced light-harvesting efficiency throughout the solar spectrum and an efficient conversion of the harvested light into the triplet states by SF. Based on these points, m-phenylenebridged bis(triisopropylsilylethynyl) (TIPS)-pentacene dimer-functionalized QD was synthesized to examine the sequential photoinduced process from energy transfer to SF. In femtosecond transient absorption measurements, initial energy transfer from QD to pentacene (quantum yield: 87%) and subsequent SF were efficiently observed. The quantum yield of triplet states of pentacene units (Φ T) based on the excitation of QD attained ~160%.[1] Additionally, the related molecular systems will be briefly discussed in this presentation.[2,3] References [1] Sakai, H.; Inaya, R.; Tkachenko, N. V.; Hasobe, T. Chem. Eur. J. 2018, 24, 17062-17071. [2] Sakai, H.; Inaya, R.; Nagashima, H.; Nakamura, S.; Kobori, Y.; Tkachenko, N. V.; Hasobe, T. J. Phys. Chem. Lett. 2018, 9, 3354-3360. [3] Nakamura, S.; Sakai, H.; Nagashima, H.; Kobori, Y.; Tkachenko, N. V.; Hasobe, T. ACS Energy Lett. 2019, 4, 26-31.