Chemically Modified Quinoidal Oligothiophenes for Enhanced Linear and Third-Order Nonlinear Optical Properties

Abstract

In the present investigation, quantum chemical calculations have been performed in a systematic way to explore the optoelectronic, charge transfer, and nonlinear optical (NLO) properties of different bis­(dicyanomethylene) end-functionalized quinoidal oligothiophenes. The effect of different conformations (linking modes of thiophene rings) on conformational, optoelectronic, and NLO properties are studied from the best-performed dimer to octamer. The optical and NLO properties of all the selected systems (1–7) are calculated by means of density functional theory (DFT) methods. Among all the designed compounds, the largest linear isotropic (αiso) polarizability value of 603.1 × 10–24 esu is shown by compound 7 which is ∼12, ∼16, ∼9, ∼11, ∼10, and ∼4 times larger as compared to compounds 1–6, respectively. A relative investigation is performed considering the expansion in third-order NLO polarizability as a function of size and conformational modes. Among all the investigated systems, system 7 shows the highest value of static second hyperpolarizability ⟨γ⟩ with an amplitude of 7607 × 10–36 esu at the M06/6-311G** level of theory, which is ∼521, ∼505, ∼38, ∼884, ∼185, and ∼15 times more than that of compounds 1–6, respectively. The extensively larger ⟨γ⟩ amplitude of compound 7 with higher oscillator strength and lower transition energy indicates that NLO properties are remarkably dependent upon linking modes of thiophene rings and its chain length. Furthermore, to trace the origin of higher nonlinearities, TD-DFT calculations are also performed at the same TD-M06/6-311G** level of theory. Additionally, a comprehensive understanding of the effect of structure/property relationship on the NLO polarizabilities of these investigated quinoidal oligothiophenes is obtained through the inspection of Frontier molecular orbitals, the density of states (TDOS and PDOS), and molecular electrostatic potential diagrams including the transition density matrix. Hence, the current examination will not just feature the NLO capability of entitled compounds yet additionally incite the interest of experimentalists to adequately modify the structure of these oligothiophenes for efficient optical and NLO applications.

Single-Crystal Investigation, Hirshfeld Surface Analysis, and DFT Study of Third-Order NLO Properties of Unsymmetrical Acyl Thiourea Derivatives

“…The origin of hyperpolarizabilities with full parameter dependence has been studied in our previous studies . For more detailed studies about the abovementioned two-level and three-level approximations, we encourage the reader to look into the works of Bredes et al and Nakano et al, along with others. , For the purpose of brevity, we can currently consider transition energy as a crucial factor owing to its cubic terms, which are involved in the denominator of the two-level and three-level approximations . The UV–visible spectra indicate that MBTB shows lower transition energy as compared to BTCC , which might have contributed more to enhancing its NLO response property as compared to BTCC .…”

“…56,57 For the purpose of brevity, we can currently consider transition energy as a crucial factor owing to its cubic terms, which are involved in the denominator of the two-level and three-level approximations. 58 The UV−visible spectra indicate that MBTB shows lower transition energy as compared to BTCC, which might have contributed more to enhancing its NLO response property as compared to BTCC.…”

DFT study of alkali and alkaline earth metal-doped benzocryptand with remarkable NLO properties

“…It gives information about intermolecular charge transfer (ICT) and their hidden potentials. 54 TDM analysis was computed using B3LYP/6-31G+(d, p) level of theory and its colorful 3-D illustration was attained using Multiwfn software. The TDM graphs of the cage BC and all other doped complexes are shown in Fig.…”

Theoretical investigation of electronic structures, second-order NLO responses of cyclometalated Ir(iii) and Rh(iii) counterpart complexes: effect of metal centers

“…[1][2][3][4] Nowadays, the applications of NLO materials have been extended to field-effect transistors, photovoltaics, organic light-emitting diodes (OLEDs) and holographic imaging. [5][6][7][8][9] Most related works have focused on organic NLO materials in contrast to inorganic materials because of their many attractive advantages, such as large electro-optical coefficients, easy fabrication, quick response time, tailorability and chemical stability. 10,11 Driven by the demand for NLO materials, continuous strides are made towards the development of novel organic NLO materials with a good response.…”