Third- and high-order nonlinear optical properties of an intramolecular charge-transfer compound

Abstract

An oligo(phenylenevinylene) bridged intramolecular charge-transfer (ICT) compound, (TCNQ) 2 OPV 3 , has been synthesized and its third-and fifth-order nonlinear optical refraction indexes have been determined by measurement with the 4f system with a phase-object, under near-infrared excitation.Organic p-conjugated molecules have been extensively studied and applied in diverse elds ranging from eld-effect transistors (FETs), by taking advantage of the "click-type" near-quantitative [2 + 2] cycloadditions with appropriately activated alkynes, followed by retro-electrocyclizations. These naturally stable, nonplanar chromophores are ideal platforms for efficient intramolecular charge-transfer (ICT) processes and are regarded as promising nonlinear optical materials. [19][20][21][22][32][33][34][35][36] In this work, we have designed and synthesized an oligo-(phenylenevinylene) (OPV) bridged ICT compound, (TCNQ) 2 -OPV 3 , and studied its third-and h-order optical nonlinearities by a nonlinear optical imaging technique with the phase-object (NIT-PO) at the entry of a 4f coherent imaging system. 37 The method is based on a 4f system with top-hat beams and its theoretical model is simple Fourier optics, which leads to many advantages such as simple optical alignment, very high sensitivity and insensitivity to statistical uc-tuations of the laser beam.38 The improved technique of greater signal sensibility can be used to measure the nonlinear absorption and refraction at the same time. Another vital advantage of the technique is that it can extract information about both the magnitude and the sign of the nonlinear coefcients simultaneously with only one-laser-shot 39 without the necessarity of scanning of the sample as that of the Z-scan method.40 Although the method was initially developed to measure the nonlinear refraction index of the materials, it can simultaneously measure the nonlinear refraction index and nonlinear absorption coefficient of materials conveniently from the analysis of three experiment images.41 Moreover, the results of different sensitivity of nonlinear absorption and refraction are given by choosing different phase shi of the phase object. 42As an efficient method, the technique of measurement has successfully utilized to study the kinetics of photo-induced effects by shot-by-shot measurements. 43The ICT compound (TCNQ) 2 OPV 3 has been synthesized following the [2 + 2] cycloaddition and the subsequent retroelectrocyclization of TCNQ with the OPV bridged alkynes which have been activated by electronic donating groups (Fig. 1a and Scheme S1 in the ESI †). The compound displays two charge-transfer (CT) bands at 470 nm and 677 nm, respectively, in CH 2 Cl 2 in the UV-vis absorbance spectra, resulting from the two different D-A transitions of the compound (Fig. 1c and S1 in the ESI †). A distinct solvatochromic effect of (TCNQ) 2 OPV 3 has been observed in varied solvents, which was a characteristic behavior of the dipolar ICT molecules. [19][20][21][22]44 The major CT band at 677 nm (1.83 eV...

Nonlinear Optical Properties and Applications of Fluorenone Molecular Materials

“…[16] Organic NLO materials, on the other hand, have been demonstrated to feature various advantages, including very high molecular hyperpolarizabilities, a large diversity of structures and ease of processing. [17][18][19][20][21][22] The fact that molecular structures of organic NLO dyes can be designed and synthesized with a large flexibility, together with the exploitation of multiple synergetic supramolecular interactions allows the construction of hierarchical self-assembled architectures on the micro-and nanoscale. [4,[23][24][25][26][27] This results in subwavelength scale materials with well-defined structures and highly anisotropic optical properties, that could serve as building blocks for integrated photonic circuits.…”

Aggregation‐induced emission materials for nonlinear optics

“…The push–pull structures or D‐π‐A systems are prevalent in AIE molecules owing to their standout properties, [ 133,134 ] e.g., strong and tunable intramolecular charge transfer, [ ,135 ] highly ordered crystal packings or assemblies. [ 136 ] Besides, being sensitive to polarity, the introduction of push–pull structures is an effective strategy to improve the molecular hyperpolarizability efficiently and induce the NLO hyperpolarizability.…”

Tuning Intramolecular Charge Transfer through Adjusting Hydrogen Bonding by Anions

“…[1] These intramolecular processes could lead to the transient alternation of the electronic properties such as energies of electronic state, electron density distribution and dipole moments, which could tune the emission color by both covalent modifications of the fluorescence chromophores and its non-covalent interactions with the surrounding micro-environment. [2] Therefore, molecules capable of ICT have practical and potential applications in sensing, [3,2a-c,4] nonlinear optics, [5] catalysis, [6] semiconducting, [7] thermochromism, [8] organic light-emitting materials. [9] The optical and electronic properties of perylene bisimide (PBI) dyes have been tuned by substitution, [1g,10] controlling the local π-π stacking arrangements, [11] and supramolecular assembly with electron donating/accepting molecules.…”