Chapter 6
Advanced Function Control
of Photochemical Reactions Using
Mesoscopic Structures
Keisuke Imaeda and Kohei Imura
Abstract Strong light fields induced on mesoscopic structures have the potential
to pave the way to develop novel excitation schemes that cannot be realized using
conventional light fields. In this chapter, we use various scanning near-field optical
microscopy techniques to obtain near-field spatial and spectral characterizations of
metal mesoscopic structures. We also describe the enhancement of molecular optical
responses by mesoscopic structures.
Keywords Mesoscopic structure · Plasmon resonance · Scanning near-field optical
microscope
6.1 Introduction
Recent advances in chemical synthesis and theoretical calculations have enabled us
to prepare advanced functional molecules for a variety of applications. However, our
understanding of the optical responses of these molecules has been mostly limited by
the dipolar approximation [1, 2]. The spatial structure of the optical field is neglected
in this approximation, resulting in selection rules involving a dipolar operator and
the wave functions of initial and final states. For instance, the optical transition from
an initial to a final state is forbidden when both states have the same symmetry. This
restriction can be overcome when the spatial scale of the optical field is comparable
to or smaller than the subwavelength scale because the optical field of excitation light
cannot be decoupled to obtain the selection rule. That is, the selection rule is modified
under a localized field excitation [3–7]. Thus, forbidden transitions become optically
accessible, leading to advanced functions of molecular systems. For this reason,
localized optical fields have the potential to overcome conventional photophysical
and photochemical restrictions that often originate from selection rules under plane
wave irradiation.
K. Imaeda · K. Imura (B)
Department of Chemistry and Biochemistry, School of Advanced Science and Engineering,
Waseda University, Shinjuku, Tokyo 169-8555, Japan
e-mail: imura@waseda.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_6
93
Advanced Function Control
of Photochemical Reactions Using
Mesoscopic Structures
Keisuke Imaeda and Kohei Imura
Abstract Strong light fields induced on mesoscopic structures have the potential
to pave the way to develop novel excitation schemes that cannot be realized using
conventional light fields. In this chapter, we use various scanning near-field optical
microscopy techniques to obtain near-field spatial and spectral characterizations of
metal mesoscopic structures. We also describe the enhancement of molecular optical
responses by mesoscopic structures.
Keywords Mesoscopic structure · Plasmon resonance · Scanning near-field optical
microscope
6.1 Introduction
Recent advances in chemical synthesis and theoretical calculations have enabled us
to prepare advanced functional molecules for a variety of applications. However, our
understanding of the optical responses of these molecules has been mostly limited by
the dipolar approximation [1, 2]. The spatial structure of the optical field is neglected
in this approximation, resulting in selection rules involving a dipolar operator and
the wave functions of initial and final states. For instance, the optical transition from
an initial to a final state is forbidden when both states have the same symmetry. This
restriction can be overcome when the spatial scale of the optical field is comparable
to or smaller than the subwavelength scale because the optical field of excitation light
cannot be decoupled to obtain the selection rule. That is, the selection rule is modified
under a localized field excitation [3–7]. Thus, forbidden transitions become optically
accessible, leading to advanced functions of molecular systems. For this reason,
localized optical fields have the potential to overcome conventional photophysical
and photochemical restrictions that often originate from selection rules under plane
wave irradiation.
K. Imaeda · K. Imura (B)
Department of Chemistry and Biochemistry, School of Advanced Science and Engineering,
Waseda University, Shinjuku, Tokyo 169-8555, Japan
e-mail: imura@waseda.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_6
93