Chapter 30
Single-Molecule Level Study and Control
of Collective Photoresponse in Molecular
Complexes and Related Systems
Martin Vacha and Shuzo Hirata
Abstract We studied nanoscale photosynergetic response of molecular complexes
and related inorganic and hybrid materials using single-molecule detection and spectroscopy. As examples, we report simultaneous electroluminescence and photoluminescence study of single CsPbBr 3 perovskite nanocrystals which revealed the origin
of blinking and of reduced quantum efficiency of electroluminescence devices. In
addition, we observed linear and quadratic Stark shift on individual nanocrystals in
different matrices. For novel I-III-IV semiconductor quantum dots, defect emission
was found to originate from multiple sites in one particle, and the phenomenon of
blinking was suppressed by multi-color excitation. In hybrid metal nanoparticleorganic dye systems, selective excitation of a localized plasmon in single gold
nanorods by the polarization of light was found to enhance Förster energy transfer
efficiency by two orders of magnitude. Localized plasmon was also found to cause
previously unknown phenomenon of enhancement of triplet Dexter transfer in photon
upconversion materials. Nanoscale study of triplet exciton diffusion in molecular
solids by visualization of upconversion emission helped to uncover heterogeneity
and the role of molecular orientation in the diffusion process.
Keywords Single-molecule spectroscopy · Electroluminescence · Perovskite
nanocrystals · Quantum dots · Plasmon enhancement · Energy transfer
30.1 Introduction
Collective photoresponse of conjugated molecular complexes is an important topic
both from the point of basic knowledge of molecular photophysics and from the point
of potential applications as photo-driven nanoscale devices. Over the past several
M. Vacha (B)
Department of Materials Science and Engineering, Tokyo Institute of Technology, Ookayama
2-12-1-S8-44, Meguro-ku, 152-8552 Tokyo, Japan
e-mail: vacha.m.aa@m.titech.ac.jp
S. Hirata
Department of Engineering Science and Engineering, The University of Electro Communications,
1-5-1 Chofugaoka, 182-8585 Chofu, Tokyo, Japan
© 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_30
515
Single-Molecule Level Study and Control
of Collective Photoresponse in Molecular
Complexes and Related Systems
Martin Vacha and Shuzo Hirata
Abstract We studied nanoscale photosynergetic response of molecular complexes
and related inorganic and hybrid materials using single-molecule detection and spectroscopy. As examples, we report simultaneous electroluminescence and photoluminescence study of single CsPbBr 3 perovskite nanocrystals which revealed the origin
of blinking and of reduced quantum efficiency of electroluminescence devices. In
addition, we observed linear and quadratic Stark shift on individual nanocrystals in
different matrices. For novel I-III-IV semiconductor quantum dots, defect emission
was found to originate from multiple sites in one particle, and the phenomenon of
blinking was suppressed by multi-color excitation. In hybrid metal nanoparticleorganic dye systems, selective excitation of a localized plasmon in single gold
nanorods by the polarization of light was found to enhance Förster energy transfer
efficiency by two orders of magnitude. Localized plasmon was also found to cause
previously unknown phenomenon of enhancement of triplet Dexter transfer in photon
upconversion materials. Nanoscale study of triplet exciton diffusion in molecular
solids by visualization of upconversion emission helped to uncover heterogeneity
and the role of molecular orientation in the diffusion process.
Keywords Single-molecule spectroscopy · Electroluminescence · Perovskite
nanocrystals · Quantum dots · Plasmon enhancement · Energy transfer
30.1 Introduction
Collective photoresponse of conjugated molecular complexes is an important topic
both from the point of basic knowledge of molecular photophysics and from the point
of potential applications as photo-driven nanoscale devices. Over the past several
M. Vacha (B)
Department of Materials Science and Engineering, Tokyo Institute of Technology, Ookayama
2-12-1-S8-44, Meguro-ku, 152-8552 Tokyo, Japan
e-mail: vacha.m.aa@m.titech.ac.jp
S. Hirata
Department of Engineering Science and Engineering, The University of Electro Communications,
1-5-1 Chofugaoka, 182-8585 Chofu, Tokyo, Japan
© 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_30
515