(Digital Presentation) Chiroptical Effect in Aligned Carbon Nanotube Films

Abstract

The dissymmetric interaction between circularly polarized light and solid-state materials is central to developing next-generation chiral photonic devices for applications such as spectroscopy and imaging. The strong quantum confinement in 1D single-wall carbon nanotubes (SWCNTs) features extraordinary electrical and optical properties and enables high-performance optoelectronic devices for the generation, modulation, and detection of light. The recent success of separating chirality-enriched [1], especially enantiomer-enriched, SWCNT suspensions and their macroscopic alignment assembly [2] further pushes the frontier of improving the performance and bringing new chiral functionalities of SWCNT-based optoelectronic devices. However, the chiroptical spectroscopy characterization mainly focuses on solution samples or individual SWCNTs. There has been no report of such studies in macroscopic solid-state films of SWCNTs. In this work, we investigate the circular dichroism (CD) spectroscopy of the solution and large-area films of non-racemic, chirality-mixture SWCNTs synthesized using the arc-discharge method. We prepared multiple films with various degrees of alignment using the controlled vacuum filtration method [2]. By carefully designing a cuvette that is manufactured through a stereolithography-type 3D printer (Fig. 1a) and performing a 4-configuration measurement by flipping and rotating samples (Fig. 1b), the effects from linear dichroism and birefringence can be minimized [3]. As expected, both solution and random film samples displayed zero CD; see Fig. 1c. In stark contrast, the aligned films displayed strong CD signals (~ 480 mdeg at the peak position). More surprisingly, the signs of obtained CD signals from different aligned films can be completely opposite even though their degrees of alignment, in terms of reduced linear dichroism (LDr) at the wavelength of 1035 nm, and thicknesses are nearly the same; see Fig. 1c. We will discuss possible origins of these surprising chiroptical responses in terms of slight and gradual twisted rotations of alignment directors, which can happen during spontaneous alignment in the vacuum filtration process. [1] Ichinose, Y., Eda, J., Yomogida, Y. et al. Extraction of High-Purity Single-Chirality Single-Walled Carbon Nanotubes through Precise pH Control Using Carbon Dioxide Bubbling. The Journal of Physical Chemistry C 121, 13391-13395 (2017). [2] He, X., Gao, W., Xie, L. et al. Wafer-scale monodomain films of spontaneously aligned single-walled carbon nanotubes. Nature Nanotech 11, 633–638 (2016). [3] Albano, G., Pescitelli, G. et al. Chiroptical Properties in Thin Films of π-Conjugated Systems. Chemical Reviews 120 , 10145-10243 (2020). Figure 1