## 4 Conclusions  
The formation of quinine CT complexes with DDQ and TCNQ has been studied. The characterization of Q-CT complexes was investigated in solution using spectrophotometry. [PERSON]'s method was used to calculate the molar ratio and the results was agreed with the Benesi-Hildebrand method (1:1 ratio). The characterization of the formed complexes was carried out by studying the spectroscopic parameters e.g., oscillator strength, transition dipole moment, ionization potential, the energy of CT complex, resonance energy, dissociation energy... etc were estimated. The results confirmed the formation of the formed Q-CT complexes with high stability. On the other hand, the synthesized Q-CT complexes were investigated and confirmed using FTIR, NMR and conductometry.  
Quantum chemical calculations (optimization and MEP maps) were presented at the theory level of DFT/B3 LYP to give a deeper insight into H-bond interactions, hybridization, and CT charging distributions. The results obtained using theoretical calculation methods allowed us to determine several molecular properties of the studied CT complex components. A comparison was presented between the experimental results and those calculated by the different theoretical methods from both donor and acceptor. The two sets of results were shown to be similar both structurally and electronically.  
In summary, due to the simplicity of the preparation and various application of CT complexes, our method will be opened a new door to develop such study of researcher over the world.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12030978/s1](https://www.mdpi.com/article/10.3390/app12030978/s1)]([https://www.mdpi.com/article/10.3390/app12030978/s1](https://www.mdpi.com/article/10.3390/app12030978/s1)), Figure S1. FTIR spectrum of quinine; Figure S2. FTIR spectrum of DDQ; Figure S3. FTIR spectrum of TCNQ; Figure S4. The 1H NMR spectrum of quinine in acetone-d6; Table S1. Mulliken charge of DDQ, TCNQ, Q-DDQ and Q-TCNQ; Table S2. Observed IR frequencies, calculated IR frequencies, and probable vibrational assignments of quinine with scaling value 0.96; Table S3. Observed IR frequencies, calculated IR frequencies, calculated IR frequencies, and probable vibrational assignments of qui-nine-DDQ CT complex with scaling value 0.96; Table S4. Observed IR frequencies, calculated IR frequencies, and probable vibrational assignments of qui-nine-TCNQ CT-complex with scaling value 0.96; Table S5. Fukui indices analysis of Quinine; Table S6. Fukui indices analysis of DDQ; Table S7. Fukui indices analysis of TCNQ.  
Visualization and formal analysis A.M.H. and R.A.-S.; Methodology and writing--review and editing, H.I.A., Computational study T.A.Y.; Synthesis and characterization S.T.G.; Methodology, validation and writing-original draft., G.A.E.M. and H.A.; All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Deanship of Scientific Research at King Saud University for funding the work through Research Group Project No. RG-1438-045.  
Not applicable.  
All data resulted from this study was presented in the manuscript and supplementary material.  
The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding the work through Research Group Project No. RG-1438-045.  
The authors declare that no conflict of interest associated with this study.