ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Investigation on Y-shaped tri-fluoromethyl substituted quinoxalines: synthesis, optical and morphological studies

Ayilam Viswanathan Rajalakshmi and Nallasamy Palanisami

Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore, India

E-mail: palanisami.n@gmail.com

Received: 1 February 2020  Accepted: 23 June 2020

Abstract:

Abstract

Y-shaped tri-fluoromethyl substituted quinoxaline derivatives 2,3-bis(4-methoxyphenyl)-6-(trifluoromethyl)quinoxaline (1) and 2,3-bis((E)-4-methoxystryryl)-6-(trifluoromethyl)quinoxaline (2) have been synthesized and characterized using various analytical and spectroscopic techniques (¹H,¹³C, ¹⁹F NMR, FT-IR and HR-Mass). Optical properties such as absorption, emission, quantum yield, effect of solvent polarities and Aggregation Induced Emission (AIE) have been illustrated. The compound 1 exhibited negative solvatochromism and compound 2 positive solvatochromism which are in correlation with π* values by Kamlet and Taft. Compounds 1 and 2 showed large Stoke’s shifts attributed to more polar excited state of the compounds as compared to that of polar ground state, due to the presence of electron withdrawing trifluoromethyl group. Both the compounds displayed fluorescence in solid state and AIE state due to the restricted intramolecular rotation. The compounds 1 and 2 exhibited low quantum yields because of ICT (Intramolecular charge transfer) attributed to the presence of electron-donating methoxy phenyl unit and an electron-withdrawing quinoxaline unit. AIE exhibited by both the compounds in THF/water mixture were due to the formation of nano-aggregates, it is further characterised by DLS and determined the particle size to be 196.8 nm for compound 1 and 197.3 nm for compound 2. Compound 1 appeared as ice flakes and compound 2 as a cluster consisting of various micro crystals like projections in the images determined by scanning electron microscope (SEM).

Graphic abstract

Keywords: Quinoxaline; Fluorescence; Quantum yield; AIE

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01266-3

Chemical Papers 74 (12) 4507–4516 (2020)