Design, Synthesis, and Density Functional Theory Studies of Indole Hydrazones as Colorimetric "Naked Eye" Sensors for F Ions

Rima D Alharthy; Nadeem Ahmed; Saman Mubarak; Muhammad Yaqub; Muhammad Khalid; Iqra Shafiq; Muhammad Adnan Asghar; Ataualpa Albert Carmo Braga; Zahid Shafiq

doi:10.1021/acsomega.3c00821

Design, Synthesis, and Density Functional Theory Studies of Indole Hydrazones as Colorimetric "Naked Eye" Sensors for F Ions

ACS Omega. 2023 Apr 7;8(15):14131-14143. doi: 10.1021/acsomega.3c00821. eCollection 2023 Apr 18.

Authors

Affiliations

¹ Department of Chemistry, Science & Arts College, Rabigh Branch, King Abdulaziz University, Rabigh 21911, Saudi Arabia.
² Institute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800, Pakistan.
³ Institute of Chemistry, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan 64200, Pakistan.
⁴ Centre for Theoretical and Computational Research, Khwaja Fareed University of Engineering & Information Technology, Rahim Yar Khan 64200, Pakistan.
⁵ Department of Chemistry, Division of Science and Technology, University of Education, Lahore 89002, Pakistan.
⁶ Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, São Paulo 05508-000, Brazil.

Abstract

A new series of sensors SM-1 to SM-3 was designed and synthesized using indole carboxaldehydes (2a-2c) and 2,4-dinitrophenyl hydrazine. Accompanied by the synthesis, density functional theory investigation was also accomplished at the M06-2X/6-311G+(d,p) functional. A reduction in band gap (ΔE = 4.702-4.230 eV) along with a bathochromic shift (λ_max = 433.223-471.584 nm) was seen in deprotonated chromophores than their neutral sensors. Further, significant charge transference from indole toward dinitrophenyl hydrazine was also examined. Global reactivity parameters also expressed the greater stability of sensors than that of their deprotonated form. SM-3 displayed high selectivity toward F ions as compared to SM-1 and SM-2, which respond to both F^- and CN^- ions. The electronic absorption spectrum was recorded in CH₃CN. The sensor SM-3 showed high selectivity toward F^- ions with a low detection limit (8.69 × 10^-8), and the binding constant for SM-3 was determined as 7.7 × 10⁵. The sensor displayed naked eye views as the color of solution changed from mustard to purple with a red shift of 96 nm. The mechanism suggests deprotonation from the NH group, which was confirmed by ¹H NMR. The sensor is found to be useful for detection of F^- ions in the real sample and for analytical application (test strip).