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

Amna Bibi; Shabbir Muhammad; Shafiq UrRehman; Shamsa Bibi; Shahid Bashir; Khurshid Ayub; Muhammad Adnan; Muhammad Khalid

doi:10.1021/acsomega.1c03218

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

ACS Omega. 2021 Sep 13;6(38):24602-24613. doi: 10.1021/acsomega.1c03218. eCollection 2021 Sep 28.

Authors

Amna Bibi¹, Shabbir Muhammad², Shafiq UrRehman¹, Shamsa Bibi¹, Shahid Bashir³, Khurshid Ayub⁴, Muhammad Adnan⁵, Muhammad Khalid⁶

Affiliations

¹ Department of Chemistry, University of Agriculture Faisalabad, Faisalabad 38000, Pakistan.
² Department of Physics, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia.
³ Centre for Ionic University of Malaya, Department of Physics, University of Malaya, Kuala Lumpur 50603, Malaysia.
⁴ Department of Chemistry, COMSATS University, Abbottabad Campus, Islamabad 22060, Pakistan.
⁵ Graduate School, Department of Chemistry, Chosun University, Gwangju 501-759, Republic of Korea.
⁶ Department of Chemistry, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan 64200, Pakistan.

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 (α_iso) 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.