**1. Introduction**

Procainamide, 4-amino-N-(2-(diethylamino)ethyl)benzamide (PA, Figure 1), is used to treat abnormal heart rhythms, namely Wolff–Parkinson–White syndrome (WPWS) associated arrhythmias [1,2]. According to the Vaughan Williams classification, it is classified as a class IA agent with a sodium-channel-blocking effect [1,2].

Recently, extensive care has been given to the development of the formation of charge transfer (CT) complexes derived from an electron donor and an acceptor molecule. Due to the intriguing structures; physical and chemical properties; applications in different fields, especially optical materials [2,3]; drug–receptor interactions [4]; solar energy and surface chemistry [5]; field-effect transistors; light-emitting devices, lasers, and sensors and stimuli-responsive behavior [6]; organic semiconductor properties [7,8]; and various biological applications [9,10], the synthesis of CT complexes is of interest. CT complexes are formed with unique types of interactions, which are incorporated in the formation of π-π stacking of the aromatic complexes, hydrogen bonds, and/or electron transfer from a donor to an acceptor [5,11–13]. The reaction mechanism of electron transfer from the

**Citation:** Rahman, A.F.M.M.; Bakheit, A.H.; Rahman, S.; Mostafa, G.A.E.; Alrabiah, H. Procainamide Charge Transfer Complexes with Chloranilic Acid and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone: Experimental and Theoretical Study. *Processes* **2023**, *11*, 711. https://doi.org/10.3390/ pr11030711

Academic Editors: Iliyan Ivanov, Stanimir Manolov and Donatella Aiello

Received: 19 January 2023 Revised: 8 February 2023 Accepted: 26 February 2023 Published: 27 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

donor to the acceptor of the CT complexes was reported by Mullikan [14,15]. It should be noted that molecular acceptors can be used for the determination of drugs in dosage forms [16]. Nevertheless, the formation of the CT complexes is echo-friendly, inexpensive, simple, and easy compared to other techniques [17]. On the other hand, CT complexes are used to remove and utilize discarded drugs from the environment [18]. Here, we report the synthesis and characterization of two new CT complexes 'procainamide-chloranilic acid' (PA-ChA) and 'procainamide-2,3-dichloro-5,6-dicyano-1,4-benzoquinone' (PA-DDQ). The structures of the CT complexes were elucidated using UV, fluorescence, FTIR, and NMR spectrometry. Electronic properties and conductometry were evaluated. A spectroscopic study was carried out to determine the formation constant and stoichiometry of the CT complexes. In addition, different physicochemical properties of the CT complexes were assessed to determine their stability. Furthermore, electronic structures were examined by DFT calculations to determine the frontier molecular orbitals and the relocation of the electron density.

**Figure 1.** Chemical structures of procainamide and its complexes.
