Charge transfer and first hyperpolarizability: cage-like radicals C59X and lithium encapsulated Li@C59X (X=B, N)

Abstract

Very recently, two new cage-like radicals (C59B and C59N) formed by a boron or nitrogen atom substituting one carbon atom of C60 were synthesized and characterized. In order to explore the structure-property relationships of combination the cage-like radical and alkali metal, the endohedral Li@C59B and Li@C59N are designed by lithium (Li) atom encapsulated into the cage-like radicals C59B and C59N. Further, the structures, natural bond orbital (NBO) charges, and nonlinear optical (NLO) responses of C59B, C59N, Li@C59B, and Li@C59N were investigated by quantum chemical method. Three density functional methods (BHandHLYP, CAM-B3LYP, and M05-2X) were employed to estimate their first hyperpolarizabilities (β tot) and obtained the same trend in the β tot value. The β tot values by BHandHLYP functional of the pure cage-like radicals C59B (1.30 × 10(3) au) and C59N (1.70 × 10(3) au) are close to each other. Interestingly, when one Li atom encapsulated into the electron-rich radical C59N, the β tot value of the Li@C59N increases to 2.46 × 10(3) au. However, when one Li atom encapsulated into the electron-deficient radical C59B, the β tot value of the Li@C59B sharply decreases to 1.54 × 10(2) au. The natural bond orbital analysis indicates that the encapsulated Li atom leads to an obvious charge transfer and valence electrons distribution plays a significant role in the β tot value. Further, frontier molecular orbital explains that the interesting charge transfer between the encapsulated Li atom and cage-like radicals (C59B and C59N) leads to differences in the β tot value. It is our expectation that this work will provide useful information for the design of high-performance NLO materials.

New insight into the photophysics and reactivity of trigonal and tetrahedral arylboron compounds

“…The unusual behavior of the excited states of organoboron compounds has provided new avenues of exploration for improving the photonic properties of hybrid materials. [1][2][3][4][5][6][7][8][9][10][11] In particular, these compounds combine the properties of extended organic π-systems with the unique features of semi-metals, leading to novel materials with many desirable chemical and physical properties (larger extinction coefficients, Lewis acid-base reactivity, stronger emission intensities, etc.). 4,[12][13][14][15][16][17][18][19][20] The presence of the empty p z orbital on the trigonal boron atom and its effective π-electron extension with attached aryl groups has been used to advantage by several research groups to provide new candidates for modern optoelectronic materials.…”

“…[5][6][7]12 The replacement of selected carbon atoms with main-group heteroatoms such as boron has proven useful in circumventing some shortcomings of purely organic systems. 1,2,8,[21][22][23][24] Such strategies can provide a powerful alternative to carbon-based photochemistry and photophysics by allowing access to novel electronically excited states. For example, the Lewis acidic character of boron atoms has led to interesting chemical, spectroscopic and optoelectronic properties, such as the intense luminescence found in certain semiconductor materials.…”

Structural, Electronic, and Nonlinear Optical Properties of C66H4 and C70Cl6 Encapsulating Li and F Atoms

“…In application, fullerenes are famous for their good nonlinear optical properties due to the three-dimensional (3D) delocalized π-electron conjugated system. In recent years, it has been discovered that the presence of metal atoms can further improve the nonlinear optical properties of fullerenes. , As we introduced Li atoms to C 66 H 4 and C 70 Cl 6 , the first hyperpolarizability (β) was calculated to reveal the influence of Li atoms on the nonlinear optical properties of C 66 H 4 and C 70 Cl 6 . The hyperpolarizability β is defined as: where β ijk is tensorial components of the first hyperpolarizability.…”

“…In recent years, it has been discovered that the presence of metal atoms can further improve the nonlinear optical properties of fullerenes. 37,38 As we introduced Li atoms to C 66 H 4 and C 70 Cl 6 , the first hyperpolarizability (β) was calculated to reveal the influence of Li atoms on the nonlinear optical properties of C 66 H 4 and C 70 Cl 6 . The hyperpolarizability β is defined as: for the electron transfer from the metal atom to the external carbon cage and the symmetry reduction after metal atom encapsulation.…”

Metal–metal bonding in biscycloheptatrienyl dimetal compounds of the second‐row transition metals

“…Analysis of the frontier bonding molecular orbitals indicated a formal Os-Os quintuple bond (r 1 2p 1 2d) in singlet (h 5 AC 5 H 5 ) 2 Os 2 and a formal Re-Re sextuple bond (2r 1 2p 1 2d) in singlet (h 5 AC 5 H 5 ) 2 Re 2 , thereby giving the metals in both molecules the favored 18-electron metal configurations. However, subsequent studies showed that isomeric perpendicular M 2 (m-C 5 H 5 ) 2 structures (M 5 Re, [34] Os [35] ) with bridging C 5 H 5 rings have considerably lower energies, so that these metal-metal multiply bonded species are not likely to be realized experimentally.…”