Two stable boron dipyrromethene (BODIPY)-based antiaromatic macrocycles, Mc-Fur and Mc-Th, were synthesized through a one-pot Knoevenagel condensation reaction between a BODIPY precursor and furan-2,5-dicarboxaldehyde or thiophene-2,5-dicarboxaldehyde, respectively. 1H NMR spectroscopic characterization of the two macrocycles supported their highly antiaromatic character. The oxidation properties of the two macrocycles were studied through electron spin resonance spectroscopy and UV/Vis absorption spectrophotometry, which suggested the formation of a stable monoradical cation species on first oxidation followed by an aromatic dicationic species on subsequent oxidation. Both molecules have a nearly planar π-conjugated backbone and show a strong tendency to aggregate in solution due to efficient stacking of the antiaromatic macrocycles. Transient absorption and two-photon absorption (TPA) measurements in solution and aggregated states of the macrocycles revealed that aggregation resulted in large enhancement of TPA cross sections and increased excited-state lifetimes, in accordance with the decrease in the antiaromatic character in the aggregated state.
Bibliographical noteFunding Information:
The work in Singapore was financially supported by an A*STAR JCO grant (1431AFG100) and the MOE Tier 3 Programme (MOE2014-T3-1-004). The work at Yonsei University was supported by the National Research Foundation of Korea (NRF) through a grant funded by the South Korean government (MEST; no. 2016R1E1A1A01943379).
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All Science Journal Classification (ASJC) codes
- Organic Chemistry