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. 2020 Sep 4:8:776.
doi: 10.3389/fchem.2020.00776. eCollection 2020.

Stability, Aromaticity, and Photophysical Behaviors of Macrocyclic Molecules: A Theoretical Analysis

Wei Wei  1 , Wenhui Ren  2 , Wei Jian  1 , Baohui Xia  3 , Hongxing Zhang  1 , Fu-Quan Bai  1 , Wei Li  2
Affiliations

Stability, Aromaticity, and Photophysical Behaviors of Macrocyclic Molecules: A Theoretical Analysis

Wei Wei et al. Front Chem. .

Abstract

The macrocyclic molecules with terthiophene (TTH) isomers unit exhibit intriguing properties in terms of aromaticity, stability, and absorption. In this work, we theoretically designed a series of macrocyclic molecules featured with TTH and dithienothiophene (DTT) π-conjugated building units, which are used to permute pyrrole unit in porphyrin skeleton. Density functional theory and time-dependent DFT methods are used to evaluate the performance of the designed molecules. Our simulations show that molecules 1-3 exhibit excellent optoelectronic performance. Specifically, the molecule with the DTT unit is more stable than the one with TTH unit in terms of aromaticity and aromatic stabilization energy. This is because DTT unit enhances the coplanarity of the molecular material, facilitating electronic communication. Calculation of vertical electronic excitations suggests the absorption feature of these molecules is mainly contributed by the electronic excitations of higher occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO)+1 and HOMO-1 → LUMO. Judging from the key parameters determining the overall performance, 3 stands out because of its good planarity, large HOMO-LUMO gap, and strong aromaticity among all molecules. Interestingly, molecule 1 has the current density flow distributes around the outer section of TTH unit; in contrast, molecule 3 with DTT unit has the current density flow located at the inner section of DTT, which is beneficial for stability and aromaticity. Second-order perturbation energies are calculated to rationalize this observation. We expect that these research results can provide valuable insights into the rational design of novel molecular materials for a variety of applications.

Keywords: DFT/TD-DTF; aromaticity; macrocyclic molecules; molecular modification; porphyrin.

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Figures

Scheme 1
Scheme 1
Sketch structures of molecules 1–3.
Figure 1
Figure 1
Optimized molecular structures of 1–3 in their ground states.
Scheme 2
Scheme 2
The isodesmic reactions of 1–3.
Figure 2
Figure 2
Molecular orbital distributions and diagrams of the frontier molecular orbitals (from HOMO-3 to LUMO+3) for 1–3.
Figure 3
Figure 3
Computed AICD plots of 1–3 with an isosurface value of 0.03. Aromatic species exhibit clockwise diatropic circulations.
See this image and copyright information in PMC

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