Improving the optical properties of [5] circulene with different electron donors and acceptor substitutions (push-pull s
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ORIGINAL PAPER
Improving the optical properties of [5] circulene with different electron donors and acceptor substitutions (push-pull system) Abbas Hamidi 1 & Hamid Reza Shamlouei 1,2 & Afsaneh Maleki 1 & Bijan Mombeini Goodajdar 1 Received: 19 June 2020 / Accepted: 10 November 2020 / Published online: 23 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this research, the circulene molecule was selected, and the electron donor and acceptor groups were attached to improve its optical properties. Large negative values of enthalpies, Gibbs free energies, and exothermic energies of formation for these molecules, especially for the CN-CIR-NHLi molecule, show that their formation is highly reasonable. It was illustrated that the Eg of the circulene molecule was lowered in the electron donor and acceptor groups’ presence, while the CN-CIR-NHLi and CF3CIR-NHLi molecules have the lowest values of Eg. It was observed that the optical properties of circulene molecules were improved in electron donor and acceptor groups’ presence. Between these groups, the -CN and -CF3 as electron acceptors and NHLi substituents, as electron donor groups, yield higher enhancements on the optical properties of circulene, which is in agreement with the results obtained for Eg values. Keywords Push-pull system . [5] Circulene . Time-dependent DFT . UV-visible spectrum . Electron donor-acceptor
Introduction Photosensitizers are molecules that utilize light energy to provoke photochemical changes in other molecules [1]. Photosensitizer molecules generally absorb sunlight in the ultraviolet or visible region and transfer it to neighboring molecules to create chemical reactions, such as hydrogen generation [2, 3], photopolymerization [4, 5], photodegradation [6, 7], making dye-sensitized solar cells [8–11], preparing the triplet excited states in organic molecules [12, 13], and photodynamic therapy [14, 15]. Considering typical photosensitizers, a large framework with delocalized π electrons can be seen, which reduces the transition of energy from the ground state to an excited state. Porphyrin molecules, which are wellknown forms of photosensitizers, have excellent properties and have been employed extensively for various purposes. However, their synthesis is very expensive, and so their use has been limited. Therefore, exploring alternative materials is
* Afsaneh Maleki [email protected] 1
Department of Chemistry, Omidiyeh Branch, Islamic Azad University, Omidiyeh, Iran
2
Department of Chemistry, Lorestan University, Khorramabad, Iran
necessary. Annulene molecules are candidates for photosensitizers, as they have delocalized π structures. [n] circulenes are a class of compounds that are characterized by a central ring with [n] sides surrounded by a band of ortho-fused benzene rings. In our previous study, the optical properties of [14] annulene were studied, and the donor and acceptor groups were employed to improve its optical properties [16]. Similarly, the [26] annulene was sandwiched between
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