Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis Juwon Oh, Young Mo Sung, Hirotaka Mori, Seongchul Park, Kjell Jorner, Henrik Ottosson, Manho Lim, Atsuhiro Osuka, Dongho Kim  Chem  Volume 3, Issue 5, Pages 870-880 (November 2017) DOI: 10.1016/j.chempr.2017.09.005 Copyright © 2017 Elsevier Inc. Terms and Conditions

Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Structural Change by the Reversal of Aromaticity and Molecular Structures of Congeners (A) Schematic illustration for the reversal of aromaticity and accompanied structural change. (B) Molecular structures of aromatic and antiaromatic congeners 1–4. Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 FTIR and TRIR Spectra of 1 and 2 (A and B) FTIR spectra of (A) 1 and (B) 2 in the solid state (see also Figure S15). (C and D) TRIR spectra of (C) 1 and (D) 2 in CH2Cl2 upon photoexcitation at 550 nm. Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Optimized Molecular Structures of 1 and 2 in the S0, SQ, and T1 States (A and B) Overlapped S0-, SQ-, and T1-state structures of (A) 1 and (B) 2 (the meso-C6F5 groups and hydrogen atoms are omitted for clarity). (C and D) Mean-plane deviations and dihedral-angle standard deviations of (C) 1 and (D) 2 in the S0, SQ, and T1 states. Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Calculated IR Spectra of 1 and 2 and Comparison with Experimental IR Spectra (A and B) Calculated S0-state (top), SQ-state (middle), and T1-state (bottom) IR spectra of (A) 1 and (B) 2. (C and D) Simulated (top) and experimental (bottom) TRIR spectra of (C) 1 and (D) 2 in CH2Cl2. Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 5 Calculated SQ-State IR Spectra with Variation in Molecular Distortion (A and B) Mean-plane deviation and harmonic oscillator model of aromaticity (HOMA) plot for (A) 1wo and (B) 2wo without meso-C6F5 groups, depending on the z axis distortion. (C and D) Calculated SQ-state IR spectra of (C) A–E and (D) F–J. (E and F) Change in IR activities of (E) A–E and (F) F–J. For 1wo, the symmetric in-plane stretching modes around 1,404 and 1,610 cm−1 changed to asymmetric out-of-plane modes (B1g → B2u and B3g → B2u, respectively), and asymmetric stretching motions around 1,272 (B2u), 1,300 (B2u), 1,358 (B1u), 1,438 (B3u), and 1,468 (B2u) cm−1 became IR active in the out-of-plane direction for the further distorted structures (A → E). For 2wo, the IR activities of the asymmetric out-of-plane stretching motions decreased around 1,273 (B1u), 1,325 (B3u), 1,499 (B2u), and 1,586 (B1u) cm−1 and changed to symmetric in-plane motions around 1,472 (B1u → B1g) and 1,528 (B2u → B1g) cm−1 upon structural change (F → J). (Although this procedure is not fully rigorous because the harmonic approximation is not valid away from the minimum structure, the results still give qualitative information.) Chem 2017 3, 870-880DOI: (10.1016/j.chempr.2017.09.005) Copyright © 2017 Elsevier Inc. Terms and Conditions