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

Abstract

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.

Effects of Encapsulating Tube and Encapsulated Molecular Chain Length on the Second-Order Nonlinear Optical Responses of Carbon Nanotubes Filled with Head-To-Tail Polar Molecules

“…The effects of tube diameter and arrangement pattern of filled molecules on the second-order NLO properties of complexes formed by head-to-tail dipolar molecules in nanotubes were studied in detail. ,,, Some assumptions (such as the extrapolation procedure and the bottom-up modelling strategy) about the effect of chain length on the second-order NLO properties of the complexes have been proposed. The evolution of the second-order NLO properties of the aligned head-to-tail molecules with chain length is investigated by using quantum chemical calculations in the present work.…”

One-dimensional nanospace confinement effects on the chemical properties of organic molecules in carbon nanotubes: Quantum chemical calculation analyses

“…That is, B97D calculations are cost-effective, and at the same time they have exhibited good performance in reproducing the interaction energies obtained from accurate CCSD(T) calculations. Accordingly our previous studies employed B97D calculations to successfully reveal key interactions determining the structures of π-conjugated guest molecules inside armchair (m,m) tubes [18][19][20][21][22][23]. For (m,m) tube models, finite-length (m,m) tubes terminated by H atoms were used, whose lengths are 22 or 40 Å.…”

“…Along the fundamental concept, we have investigated the structural and electronic properties of π-conjugated molecules inside nanotubes. This account will review our DFT findings in our relevant publications [18][19][20][21][22][23].…”

“…Because of the presence of π conjugated molecules within these structures, nanotubes can attain new and unique electronic properties that originate from the π electrons of the entrapped molecules [6][7][8][9][10][11][12][13][14][15][16]. The electronic properties are determined by the structure of the molecule itself, as well as its arrangement within the nanotube determined by the intermolecular interactions between adjacent guest molecules [18][19][20][21][22][23].…”

“…In these directions, our group has been interested in thiophene oligomers or p,p′-dimethyaminonitorostilbene (DANS) molecules (Fig. 1) [18][19][20][21][22][23], that can be encapsulated into carbon nanotubes, because they exhibit unique optical properties [10][11][12][13][14][15][16][17].…”