17573-59-0Relevant articles and documents
Cyclopropyl Group: An Excited-State Aromaticity Indicator?
Ayub, Rabia,Papadakis, Raffaello,Jorner, Kjell,Zietz, Burkhard,Ottosson, Henrik
, p. 13684 - 13695 (2017)
The cyclopropyl (cPr) group, which is a well-known probe for detecting radical character at atoms to which it is connected, is tested as an indicator for aromaticity in the first ππ* triplet and singlet excited states (T1 and S1). Baird's rule says that the π-electron counts for aromaticity and antiaromaticity in the T1 and S1 states are opposite to Hückel's rule in the ground state (S0). Our hypothesis is that the cPr group, as a result of Baird's rule, will remain closed when attached to an excited-state aromatic ring, enabling it to be used as an indicator to distinguish excited-state aromatic rings from excited-state antiaromatic and nonaromatic rings. Quantum chemical calculations and photoreactivity experiments support our hypothesis; calculated aromaticity indices reveal that openings of cPr substituents on [4n]annulenes ruin the excited-state aromaticity in energetically unfavorable processes. Yet, polycyclic compounds influenced by excited-state aromaticity (e.g., biphenylene), as well as 4nπ-electron heterocycles with two or more heteroatoms represent limitations.
How πextension or Structural Bending Alters the Properties of Boron-Doped Phenylene-Containing Oligoacenes
Kirschner, Sven,Uecker, Ise,Bolte, Michael,Lerner, Hans-Wolfram,Wagner, Matthias
, p. 2818 - 2823 (2019)
Linear annulation of two 2,3-biphenylenediyl moieties to a 1,4-dibora-2,5-cyclohexadiene core via its carbon atoms leads to the boron-doped phenylene-containing oligoacene (B-POA) DBI. The optoelectronic properties of DBI are unlike those of related boron-doped polycyclic aromatic hydrocarbons (B-PAHs), such as 6,13-dihydro-6,13-diborapentacene (DBP). Herein we disclose two new B-POAs, which provide insight into fundamental structure-property relationships. The first is a π-extended DBI congener (e-DBI), in which two 2,3-benzo[b]biphenylenediyl moieties are linearly annulated to the central B2C4 ring and behaves partly similar to DBI: it is a strong electron acceptor and has a deep red color. In contrast to the nonluminescent DBI, it shows red fluorescence (quantum yield: 12%), which changes to blue-green upon addition of excess F--ions. In the presence of 0.4 equiv of F-, nearly white emission is observed (CIE1931: (0.3320|0.4056)). If biphenylenediyl moieties are angularly attached to the B2C4 ring via their 1,2-positions, the resulting mixture of "v"- and "z"-shaped B-POA isomers (v/z-DBI) behaves distinctly different from linear DBI: the electrode potentials required for the reversible two-electron reductions of v/z-DBI are significantly more cathodic, and v/z-DBI is an orange rather than red solid and emits green light (quantum yields 65%) upon irradiation.
