Subphthalocyanines and Subnaphthalocyanines:  Nonlinear Quasi-Planar Octupolar Systems with Permanent Polarity

Abstract

The second-harmonic generation (SHG) response of unsubstituted subnaphthalocyanines (SubNcs) has been measured for the first time by electric field-induced second-harmonic generation (EFISH) (1.064 and 1.90 µm) and hyper-Rayleigh scattering (HRS) (1.064 µm) experiments. The quadratic hyperpolarizability derived from the experiments is significant (β HRS (0) ) 34.7 × 10 -30 esu) and similar to that also measured under the same conditions for the related unsubstituted subphthalocyanine (SubPc) molecule (β HRS (0) ) 38.3 × 10 -30 esu). To meaningfully discuss the nonlinear optical (NLO) data, semiempirical INDO/S calculations of the permanent dipole moments of the ground and excited states (Q band) have been performed. Moreover, the dipolar transition moments connecting the ground and degenerate excited states and the two excited states have been also determined. The calculations suggest that for those low-energy excited states responsible for the Q optical absorption band, the two molecules (SubPc and SubNc) behave very approximately as planar π-conjugated octupoles with D 3h symmetry but having a permanent dipole moment along the perpendicular halogen-boron axis. The charge distribution along this axis is not appreciably influenced by the optical excitation, that is, light-induced charge motion only occurs inside the macrocycle without significant contribution of the apical Cl atom. The β HRS and γ EFISH data have been quantitatively analyzed with a three-level model, taking into account that only electronic terms contribute to the EFISH hyperpolarizability. As a consequence of this analysis, a sound rationale to describe the NLO behavior of these Pc-related compounds (SubPcs and SubNcs) has now emerged.

Optically Tunable Nonlinearities in Polymers Based on Photoisomerizable Metal-Based Coordination Complexes

“…Many synthesis strategies have been developed to build molecular structures in various non-centrosymmetric geometries, allowing multipolar field-chromophore interactions that lead to a wide variety of macroscopic polarization responses. [23][24][25][26][27][28][29][30][31][32][33] In this context, the flexibility brought by coordination chemistry enables the design of chromophores built around the same ion core (here Zn II ) and ligands but with different symmetries (C 2v , D 3 , and D 2d ). [34] In order to rationalize the diversity of possibilities, a simplified scheme was proposed at an early stage.…”

Density Functional Theory Study on Subtriazaporphyrin Derivatives: Dipolar/Octupolar Contribution to the Second-Order Nonlinear Optical Activity

“…12,13 More recently, multipolar, especially octupolar molecules have been developed as alternative NLO chromophores since these molecules do not possess a permanent dipole moment and therefore can easily form noncentrosymmetric bulk materials as required to obtain a large macroscopic 2 nd -NLO response. [19][20][21][22][23][24][25][26][27][28][29][30][31] In 2010, the structure, electronic distribution, molecular orbitals, infrared (IR) spectra, and electronic absorption spectra of a full series of low-symmetrical fluoroboron-subtriazaporphyrin (FB-SubTAP) derivatives were systematically investigated based on density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculation. Due to their distinct structural, optical, and electronic properties, the SubPc derivatives have attracted much research interests.…”

“…Due to their distinct structural, optical, and electronic properties, the SubPc derivatives have attracted much research interests. 20,[28][29][30][31] For example, Torres et al studied the NLO response of SubPcs with electron-donating or -accepting substituents at the peripheral positions. 27a In addition, as a typical octupolar molecule with 14-π electron aromatic structure, the 2 nd -NLO activities of SubPc and its analogues have been experimentally and theoretically investigated.…”

Comparative electronic structures and UV–vis spectra of tribenzosubporphyrin, tribenzomonoazasubporphyrin, tribenzodiazasubporphyrin, and subphthalocyanine: Insight from DFT and TDDFT calculations

“…Subphthalocyanines have nonplanar, bowl-like structures along with a 14 -electron aromatic core with a trigonal-pyramidal boron atom as the central atom. They exhibit strong UV-vis absorption, intense fluorescence, and remarkable nonlinear optical properties and hence can be potentially applied as chromophores in molecular electronics [14][15][16][17][18], nonlinear optics materials [5,[10][11][12][13][19][20][21][22], photodynamic therapy [23,24], and light-harvesting [25][26][27][28][29]. In 2006, the analogues of subphthalocyanines in which all meso-nitrogen atoms were substituted with the sp 2 -hybrid carbons, the tribenzosubporphyrines [30], were synthesized and characterized as their boron complexes.…”