236 © 2025 The Author(s). Published by College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License An Article Review: Charge-Transfer of Polyenes and Carotenes Azhar Mohammed Hasan Wahhab 1* and Hamsa Munam Yaseen 2 1,2 Department of Chemistry, College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad, Baghdad, Iraq. *Corresponding Author. Received: 22 June 2023 Accepted: 23 July 2023 Published: 20 July 2025 doi.org/10.30526/38.3.3614 Abstract When an electron moves from one atom or molecule to another, a charge-transfer complex is formed. The other objects must be able to accept these electrons, and one entity must have free electrons or a tendency to donate them. This resembles an internal oxidation-reduction reaction more. This research aims to shed light on charge transfer complexes formed by polyenes and carotenes, which act as electron-donating molecules due to their alternating double and single bonds. This allows them to create such complexes when interacting with organic molecules that lack electrons. These complexes exhibited distinctive optical and physicochemical properties, enabling them to be adapted for a wide range of applications. In addition, the researchers demonstrated significant interest in the study of the ability of some of these compounds to form self-internal charge-transfer complexes, also known as intramolecular charge-transfer complexes, and their precise electronic and dynamic states. Keywords: Carotenes, Charge-Transfer complex, Physicochemical properties, Polyenes. 1. Introduction A complex made from the union of two or more molecules is known as a charge-transfer complex (CT complex) or an electron donor-acceptor complex (EDA complex). For this kind of complicated situation, the electrostatic attractiveness equipment balances the force. A photoelectric shift into an inspired photoelectric state is capable of occurring in several distinct aggregates. The visible electromagnetic frequency domain is where this change's excitation strength occurs quite frequently, giving these aggregates their distinctively passionate color. The fact that the absorption spectra of CCT complexes often differ from those of the donor and acceptor is one of their properties (1). For the spectrophotometric determination of drugs (2-9), pesticides, herbicides (10,11), dyes (12), and organic particles, including polyenes and carotenes, an elementary CT is a standard response. A polyunsaturated chemical called polyene has at least three conjugated double bonds that alternate between double (C=C) and single (C-C) bonds. This conjugation produces specific, peculiar optical characteristics. Human antibiotics made from polyenes include trichomycin, candidin, nystatin, pimaricin, methylpartricin, and amphotericin B (13). Plants can create the unsaturated hydrocarbon compound known as carotene. In contrast, animals cannot (except for a few aphids and spider mites, which acquired the carotene-producing genes from fungi). https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0004-6641-8925 mailto:azhar.Hasan2105m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8809-603X mailto:hamsa.m.y@ihcoedu.uobaghdad.edu.iq IHJPAS. 2025, 38(3) 237 Carotene has the chemical formula C40Hx. Significant pigments for photosynthesis include carotenoids. Their structures do not contain oxygen (14). 2.Materials and Methods 2.1. Charge-transfer of polyenes with chloranil A report demonstrating the potential for producing a CT from the interaction of polyenes with chloranil was published in 1971 by Iida et al. 2.2. Adsorption of some charge-transfer complexes of polyenes on the solid films It was investigated whether various electron-acceptor complexes could adsorb on solid films. All of the trans forms of Provitamin A, trans-beta-apo-8'-carotenal, astatine, and methylbixin were employed as polyenes in the current study. These polyenes were carefully layered onto the quartz surface as polycrystalline thin films. 2.3. Semi conduction effects of some polyenes charge-transfer complexes and their applications The semiconducting characteristics of certain polyene-iodine (CT) compounds and their uses in solid-state batteries were the subject of a study by Sen et al., published in 1993. 3. Results In charge-transfer complexes of polyenes with chloranil, the absorption spectrum, which provided the maximum absorption wavelength, the equilibrium constant, the molar absorptivity coefficient, as well as thermodynamic parameters, showed the difference in concentration between chloranil, as the acceptor, and polyenes, as the donor. According to the most recent research on the polyene CT complex, natural polyenes may be affected by the electron transfer relationship in vivo (15). Some solid films of some charge-transfer complexes of polyenes were subjected to I2, Br2, HNO3, and ICl fumes. After the solid film was exposed to the vapors, the absorption spectra were captured at 28 °C. For [trans- carotene, -Apo-8'-carotenal, Astacene, and Methylbixin], the observed peak with λmax was at approximately 11550 cm -1 , 12000 cm -1 ,13150 cm -1 , and 13200 cm -1 , respectively, in the case of I2. Unquestionably, the solution's observable charge-transfer absorption peak typically occurs at a shorter wavelength than it does in the solid state (16). The outcomes of semi conduction effects of some polyenes charge-transfer complexes and their applications showed that while the energy required to activate the charge-transfer complex reduces, conductivity increases by orders of magnitude. Because of this, batteries with the configuration Mg/ (polyene-iodine CT complex)/graphite were created, taking advantage of these complexes as cathodic electrodes (17). 4. Discussion There is a possibility of producing Intramolecular CT complexes of polyenes. This issue was addressed in numerous papers. To analyze two sequels of donor-acceptor polyenes with increasing length, Blanchard-Desce et al. (1995) provided electro-optical absorption data. The empirical results show that the redshift of the intramolecular charge-transfer complex absorption peak is guided by the lengthening of the polyene chain connecting the donor and acceptor terminal groups, which also increases the excited and transition state dipoles. At the same time, the ground state's dipole is mostly unaltered. Due to this, reported photoinduced dipole moment changes (up to 33 D) were obtained with a corresponding increase in molecule elongation (up to 27°), leading to highly excited state polarization (18). Wagner et IHJPAS. 2025, 38(3) 238 al. (2013) published a study that effectively combines theoretical concepts and experimental findings to understand the ICT complex state of peridinin, as shown in Figure (1). The study shows that bond-order reversal caused by the interaction of the more highly polar excited singlet states with the more polar solvent is what creates the developed state. Time- resolved pump-probe spectroscopy experiments on these distinct states, as a function of the solvent nature, are introduced to start the investigation (19). Figure 1. The molecular structure of peridinin (19). To fully comprehend the electronic structure and dynamics of the intramolecular CT state, an article was published in 2014. In this article, different donor-acceptor substituted compounds from the diphenyl polyene series and ethenyl indoles are discussed in terms of excited-state intramolecular CT, photoisomerization, and fluorescence probe features. The research demonstrated that the ground state of linear polyenes is covalent, non-polar, and particularly unaffected by solvent polarity or substituents. The following low-lying states often represent the photodynamic retinal polyenes singlet excited state: 1(n-π*), 1 Ag* (π-π*a dipole forbidden transition), and 1 Bu* (π-π*, a allowed transition). The following factors have impacted these electronic states: (i) the medium, such as polar, non-polar, or solvents for hydrogen bonds. (ii) the geometrical structure of the polyene chain. (iii) a functional group that is located at the polyene chain's end. The protein-bound, photoactive retina was observed to absorb light at wavelengths between 380 and 780 nm. The all-trans-retinal ethanoic solution exhibits maximum absorbance at 380 nm. Retinal absorbs most effectively in ethanol when covalently linked to n-butyl amine at 440 nm (20). Femtosecond time-resolved optical spectroscopy was also used to study carotenoids and polyenes that participate in intramolecular CT. This study demonstrated that as the polarity of the solvent employed increases, the lifespan of the low-lying S1 excited state diminishes. As the number of double bonds in the conjugate system rises, this influence becomes stronger. The state characteristics of three substituted polyenes (CT) were studied: Crocetin dialdehyde, the first, is a polyene having two terminals that are replaced with carbonyl groups that form a conjugate bond with the -electrons. IHJPAS. 2025, 38(3) 239 Figure 2. Femtosecond time-resolved transient absorption spectra of different carbonyl-containing polyenes and carotenoids taken at different time delays after excitation at 406 nm in different solvents at room temperature (21). The second is (8,8'-Diapocarotenedioic acid), which has one hydroxyl group and one terminal conjugated carbonyl. The third one has two terminals, symmetrically positioned hydroxyls (2, 6, 11, 15- tetramethyl-hexadeca-2, 4, 6, 8, 10, 12, 14-heptaene-1,16-diol), using the molecular orbital theory, the results are interpreted. Only the first polyene exhibits the solvent impact on the wavelength at which it absorbs the most light. From hexane to acetonitrile to methanol, the Crocetin dialdehyde absorption spectra displayed a bathochromic impact (21, 22). 5. Conclusion This article discusses CT complexes of polyenes and carotenes with various substituted functional groups, their physical and chemical characteristics, which are discovered using multiple techniques, including UV-VIS Spectrophotometry, FTIR, electro-absorption modulation, a femtosecond spectrometer system based on an amplified Ti: Sapphire laser, and their applications. Acknowledgement The authors thank the College of Education for Pure Sciences (Ibn Al-Haitham) at the University of Baghdad for their support in completing this work. Conflict of Interest The authors declare that they have no conflicts of interest. The first polyene (Crocetin dialdehyde) The second polyene (is (8,8'- Diapocarotenedioic acid) The third polyene (2,6,11,15-tetramethyl-hexadeca- 2,4,6,8,10,12,14-heptaene-1,16- diol). IHJPAS. 2025, 38(3) 240 Funding No financial support was found. Ethical Clearance The study has been approved by the Committee of the University of Baghdad/ College of Education for Pure Science (Ibn Al-Haitham). References 1. Tang Y, Tang BZ, editors. Handbook of aggregation-induced emission. Vol. 1: Tutorial lectures and mechanism studies. Hoboken (NJ): Wiley; 2022. p. 274. 2. Yaseen HM, Mahmood RM, Sadeq RS. Spectrophotometric determination of olanzapine by charge-transfer complex formation in its pure form and pharmaceutical formulations. Int J Pharm Res. 2020; 12(1):700-709. https://doi.org/10.31838/ijpr/2020.12.01.139. 3. Alassaf NA, Zankanah FH. Sensitive spectrophotometric determination of doxycycline in pure and dosage forms using p-Bromanil. Int J Pharm Res. 2019; 11(2):90-97. https://doi.org/10.31838/ijpr/2019.11.02.016. 4. Abd-alaah HJ, Hamody AS. Design of experiments model for optimization of spectrophotometric determination of phenylephrine hydrochloride in pure and pharmaceutical formulations using p- bromanil. J Pharm Sci Res. 2019; 11(2):501-507. 5. Zankanah FH, Dikran SB. Modified simplex-spectrophotometric determination of clonazepam via charge-transfer complexation. Ibn Al-Haitham J Pure Appl Sci. 2017; 30(2):112-124. 6. Hadi H. Spectrophotometric determination of clonazepam in pure and dosage forms using charge transfer reaction. Iraq J Pharm Sci. 2015; 24(1):25-32. https://doi.org/10.31351/vol24iss1pp25-32. 7. Al-Abachi MQ, Abed SS, Alamr AMH. Charge transfer spectrophotometric determination of metronidazole in pharmaceutical formulations by normal and reverse flow injection analysis coupled with solid-phase reactor containing immobilized FePO4. Iraq J Sci. 2020; 61(7):1541- 1554. https://doi.org/10.24996/ijs.2020.61.7.1. 8. Mahmoud TY, Dikran SB, Mohammed AK. Spectrophotometric determination of sulfamethoxazole based on charge-transfer complexation with sodium nitroprusside. Ibn AL- Haitham J Pure Appl Sci. 2017; 30(3):102-113. https://doi.org/10.30526/30.3.1606. 9. Omar FK. Spectrophotometric determination of cefixime by charge transfer complex formation. Baghdad Sci J. 2013;10(3):971-976. https://doi.org/10.21123/bsj.2013.10.3.971-976. 10. Vargas-Zamarripa M, Rivera AA, Sierra U, Salas P, Serafín-Muñoz AH, Ramírez-García G. Improved charge-transfer resonance in graphene oxide/ZrO2 substrates for plasmonic-free SERS determination of methyl parathion. Chemosphere. 2023; 320:138081. https://doi.org/ 10.1016/j.chemosphere.2023.138081. 11. Adam AM, Saad HA, Atta AA, Alsawat M, Hegab MS, Refat MS, Altalhi TA, Alosaimi EH, Younes AA. Usefulness of charge-transfer interaction between urea and vacant orbital acceptors to generate novel adsorbent material for the adsorption of pesticides from irrigation water. J Mol Liq. 2022; 349:118188. https://doi.org/10.1016/j.molliq.2021.118188. 12. Chordiya K, Ali ME, Kahaly MU. Photoexcited intramolecular charge transfer in dye sensitizers: Predictive in silico screening for dye-sensitized solar cell devices. ACS omega. 2022; 7(16): 13465-12474. https://doi.org/10.1021/acsomega.1c06233. 13. Rasmussen SC. Acetylene and its polymers. Springer International Publishing, 2018; 67. 14. Niaz K. Application of natural products in SARS-CoV-2. Elsevier; 2022. 15. Iida H, Nogami T, Sawahata T, Noguchi A, Yamada K. Charge transfer complexes of polyene with chloranil. Tetrahedron Letters. 1971; 12(27):2495-2498. 16. Mallik B, Jain KM, Misra TN. Charge-transfer complexes of some linear conjugated polyenes. Biochem J. 1980;189(3):547-552. https://doi.org/10.1042/bj1890547. https://doi.org/10.31838/ijpr/2020.12.01.139 https://doi.org/10.31838/ijpr/2019.11.02.016 https://doi.org/10.31351/vol24iss1pp25-32 https://doi.org/10.24996/ijs.2020.61.7.1 https://doi.org/10.30526/30.3.1606 https://doi.org/10.21123/bsj.2013.10.3.971-976 https://doi.org/%2010.1016/j.chemosphere.2023.138081. https://doi.org/%2010.1016/j.chemosphere.2023.138081. https://doi.org/10.1016/j.molliq.2021.118188 https://doi.org/10.1021/acsomega.1c06233 https://doi.org/10.1042/bj1890547 IHJPAS. 2025, 38(3) 241 17. Sen S, Pal P, Misra TN. Semiconduction properties of some polyene-iodine charge-transfer complexes and their application in solid-state batteries. J Mater Sci. 1993; 28:1367-1371. https://doi.org/10.1007/BF01191979. 18. Blanchard-Desce M, Wortmann R, Lebus S, Lehn JM, Krämer P. Intramolecular charge transfer in elongated donor-acceptor conjugated polyenes. Chem Phys Lett. 1995; 243(5-6):526-532. https://doi.org/10.1016/0009-2614(95)00895-B. 19. Wagner NL, Greco JA, Enriquez MM, Frank HA, Birge RR. The nature of the intramolecular charge transfer state in peridinin. Biophys J. 2013; 104(6):1314-1225. https://doi.org/10.1016/j.bpj.2013.01.045. 20. Hota PK, Singh AK. Donor-acceptor conjugated linear polyenes: A study of excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties. J Fluoresc. 2018; 28:21-28. https://doi.org/10.1007/s10895-014-1430-z. 21. Enriquez MM, Fuciman M, LaFountain AM, Wagner NL, Birge RR, Frank HA. The intramolecular charge transfer state in carbonyl-containing polyenes and carotenoids. J Phys Chem. 2010; 114(38): 12416-12426. https://doi.org/10.1021/jp106113h. 22. Yukihira N, Uragami C, Horiuchi K, Kosumi D, Gardiner AT, Cogdell RJ, Hashimoto H. Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria. Commun Chem. 2022; 5(1):135. https://doi.org/10.1038/s42004-022-00749-6. http://dx.doi.org/10.1007/BF01191979 https://dx.doi.org/10.1016/0009-2614(95)00895-B https://doi.org/10.1016/j.bpj.2013.01.045 http://dx.doi.org/10.1007/s10895-014-1430-z https://doi.org/10.1021/jp106113h https://doi.org/10.1038/s42004-022-00749-6