Roles of Carbon Nanotube Confinement in Enhancing Second-Order Nonlinear Optical Properties of Triiodobenzene Aggregates

• Published in: Journal of physical chemistry. C 2022-01, Vol.126 (1), p.365-377
• Main Authors: Yumura, Takashi, Fukuura, Shuta, Miki, Ryohei
• Format: Article
• Language: English
• Subjects: C: Spectroscopy and Dynamics of Nano, Hybrid, and Low-Dimensional Materials
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c08718

Dispersion-corrected density functional theory (DFT) calculations were employed to investigate stable structures of triiodobenzenes (BzI3) inside an armchair (m,m) carbon nanotube (m = 7–9), denoted by n × BzI3@(m,m), where n is the number of guests (n = 1–4). Three BzI3 isomers were considered: 1,3,5-, 1,2,4-, and 1,2,3-BzI3. DFT calculations found that nanotube confinement has an impact on n × BzI3@(m,m) structures, featuring guest orientation, positioning, and alignment. Then, we estimated a threshold value of the diameter of a tube containing BzI3 monomer in a certain orientation without repulsive host–guest interactions (D threshold). To represent the degree of nanotube confinement in 1 × BzI3@(m,m), we obtained ΔD small values by subtracting the smallest limit of D threshold of the guest from the host–tube diameter (D). Negative ΔD small values indicate strong confinement, and positive values less (much larger) than 1.0 Å indicate medium (weak) confinement. The strong and medium confinement in n × BzI3@(m,m) form a linear alignment of guests in parallel orientation with the smallest D threshold value. Reflecting from the different degrees of nanotube confinement, various types of intermolecular interactions operate. DFT calculations found that I–I intermolecular interactions are key in enhancing the second-order nonlinear optical properties of n × BzI3@(m,m). As a result, n × 1,2,4-BzI3@(8,8) with medium nanotube confinement has the most significant hyperpolarizability.