Chapter 15
Transient Circular Dichroism Approach
to Chirality Detection in Dark
Photo-Excited States
Yasuyuki Araki
Abstract A transient circular dichroism (CD)-based approach, called time-resolved
circular dichroism (TRCD) spectroscopy, serves as an alternative to circularly polarized luminescence (CPL) spectroscopy for the investigation of excited-state chirality. The experimental apparatus for TRCD measurements was designed and is
presented here. The Jones calculus approach to assessing experimental observables
is also reported. Finally, to demonstrate the feasibility of TRCD, the CD spectrum of
the photo-excited state of [6]carbohelicene is obtained.
15.1 Introduction
We may recognize circularly polarized luminescence (CPL) and circular dichroism
(CD) as well-known fingerprints of the chirality possessed by chiral molecules [1–
3]; thus, the spectroscopy of CD and CPL are considered useful, unique, and
irreplaceable tools to obtain the chiral molecular picture in many problems in
chemical and biological fields [4–6].
At the same time, studies of electronically excited states are usually performed by
fluorescence and absorption spectroscopy. Moreover, transient fluorescence and
absorption measurements often reveal the dynamic behavior of the electronically
excited states, and such experiments give us direct insight into the excited states,
e.g., the lifetime of the electronically excited state. Such characteristics of the
electronically excited states obtained by fluorescence lifetime and transient absorption studies are useful for the material development of light-emitting materials at
high quantum yield; therefore, we presume that transient CPL and CD experiments
could clarify the dynamics of the excited “chiral” states, and such knowledge
contributes to the further development of efficient CPL-emitting materials. In a strict
sense, transient CPL and CD do not provide the same information. CPL only
Y. Araki (*)
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai,
Japan
e-mail: y.araki@tohoku.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
T. Mori (ed.), Circularly Polarized Luminescence of Isolated Small Organic
Molecules, https://doi.org/10.1007/978-981-15-2309-0_15
327
Transient Circular Dichroism Approach
to Chirality Detection in Dark
Photo-Excited States
Yasuyuki Araki
Abstract A transient circular dichroism (CD)-based approach, called time-resolved
circular dichroism (TRCD) spectroscopy, serves as an alternative to circularly polarized luminescence (CPL) spectroscopy for the investigation of excited-state chirality. The experimental apparatus for TRCD measurements was designed and is
presented here. The Jones calculus approach to assessing experimental observables
is also reported. Finally, to demonstrate the feasibility of TRCD, the CD spectrum of
the photo-excited state of [6]carbohelicene is obtained.
15.1 Introduction
We may recognize circularly polarized luminescence (CPL) and circular dichroism
(CD) as well-known fingerprints of the chirality possessed by chiral molecules [1–
3]; thus, the spectroscopy of CD and CPL are considered useful, unique, and
irreplaceable tools to obtain the chiral molecular picture in many problems in
chemical and biological fields [4–6].
At the same time, studies of electronically excited states are usually performed by
fluorescence and absorption spectroscopy. Moreover, transient fluorescence and
absorption measurements often reveal the dynamic behavior of the electronically
excited states, and such experiments give us direct insight into the excited states,
e.g., the lifetime of the electronically excited state. Such characteristics of the
electronically excited states obtained by fluorescence lifetime and transient absorption studies are useful for the material development of light-emitting materials at
high quantum yield; therefore, we presume that transient CPL and CD experiments
could clarify the dynamics of the excited “chiral” states, and such knowledge
contributes to the further development of efficient CPL-emitting materials. In a strict
sense, transient CPL and CD do not provide the same information. CPL only
Y. Araki (*)
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai,
Japan
e-mail: y.araki@tohoku.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
T. Mori (ed.), Circularly Polarized Luminescence of Isolated Small Organic
Molecules, https://doi.org/10.1007/978-981-15-2309-0_15
327