A Description of Vibrational Modes in Hexaphyrins: Understanding the Aromaticity Reversal in the Lowest Triplet State

Aromaticity reversal in the lowest triplet state, or Baird's rule, has been postulated for the past few decades. Despite numerous theoretical works on aromaticity reversal, experimental study is still at a rudimentary stage. Herein, we investigate the aromaticity reversal in the lowest excited...

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Bibliographic Details
Published in:Angewandte Chemie 2016-09, Vol.128 (39), p.12109-12113
Main Authors: Sung, Young Mo, Oh, Juwon, Naoda, Koji, Lee, Taegon, Kim, Woojae, Lim, Manho, Osuka, Atsuhiro, Kim, Dongho
Format: Article
Language:English
Subjects:
Absorption
Aromaticity
Aromatizität
Atomic energy levels
Baird-Regel
Bleaching
Chemistry
Excitation spectra
Femtosecond
Hexaphyrine
Infrared radiation
Infrared spectroscopy
Rhodium
Spectra
Spectrum analysis
Stretching
Triplet state
Vibration mode
Zeitauflösende IR-Spektroskopie
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Summary:Aromaticity reversal in the lowest triplet state, or Baird's rule, has been postulated for the past few decades. Despite numerous theoretical works on aromaticity reversal, experimental study is still at a rudimentary stage. Herein, we investigate the aromaticity reversal in the lowest excited triplet state using a comparable set of [26]‐ and [28]hexaphyrins by femtosecond time‐resolved infrared (IR) spectroscopy. Compared to the relatively simple IR spectra of [26]bis(rhodium) hexaphyrin (R26H), those of [28]bis(rhodium) hexaphyrin (R28H) show complex IR spectra the region for the stretching modes of conjugated rings. Whereas time‐resolved IR spectra of R26H in the excited triplet state are dominated by excited state IR absorption peaks, while those of R28H largely show ground state IR bleaching peaks, reflecting the aromaticity reversal in the lowest triplet state. These contrasting IR spectral features serve as new experimental aromaticity indices for Baird's rule. Good Vibrations: Schwingungsspektroskopie und quantenmechanische Rechnungen wurden genutzt, um die gegensätzlichen IR‐spektroskopischen Signaturen im niedrigsten Triplett‐ und im Grundzustand zu untersuchen. Dabei wurden neue experimentelle Belege für eine Umkehr der Aromatizität in [26]‐ und [28]Hexaphyrinen gewonnen.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.201603631