Abstract
Curved (non-planar) aromatic compounds have attracted significant research attention in the fields of basic chemistry and materials science. The contribution of the quinoidal structure in the curved π-conjugated structures has been proposed to be the key for materials functions. In this study, the curve effect on the quinoidal contribution was investigated in Kekulé-type singlet diradicals (S-DR1-4) as a sensitive probe for quinoidal structures in curved π-conjugated molecules. The quinoidal contribution in S-DR1-4 was found to increase with increasing the curvature of the curved structure, which was quantitatively analyzed using NBO analysis and the natural orbital occupation numbers computed by the CASSCF method. The curve effect on the singlet-triplet energy gap was examined by the CASPT2 method. The singlet-triplet energy gaps for the highly π-conjugated diradicals were determined for the first time using the CASPT2 method. Substantial quinoidal contribution was found in the curved structures of the delocalized singlet diradicals S-DR1-4, in contrast to its absence in the corresponding triplet states T-DR1-4.
Highlights
Curved aromatic compounds like fullerenes, buckybowls, and carbon nanotubes have attracted considerable attention from researchers in the fields of basic chemistry as well as materials science [1,2,3,4,5,6,7,8,9,10,11]
The quinoidal contribution is rationalized by the increase of diradical character in the bent structure of benzene, which is the intermediate structure for the formation of Dewar benzene [29,30,31,32]
S-DR1-4 [33,34,35,36,37] is investigated to design a sensitive probe for the quinoidal contribution (q) in curved π-conjugated molecules (Figure 1c) [35,36,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55]
Summary
Curved (non-planar) aromatic compounds like fullerenes, buckybowls, and carbon nanotubes have attracted considerable attention from researchers in the fields of basic chemistry as well as materials science [1,2,3,4,5,6,7,8,9,10,11]. According to recent reports on cycloparaphenylenes ([n]CPPs, n being the number of benzene rings in the structure) [13,14,15,16,17,18,19], which are hoop-shaped carbon molecules, the absorption bands were blue-shifted with increasing number of benzene rings [20,21,22,23,24,25] This has been explained by the quinoidal characteristic of CPPs having small ring size, such as [6]CPP (Figure 1a). The quinoidal contribution is rationalized by the increase of diradical character in the bent structure of benzene, which is the intermediate structure for the formation of Dewar benzene [29,30,31,32]. Triplet and (T) forms of DR1 were optimized to obtain C2 symmetry at the UB3LYP/6-31G(d) level of
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
