Diradical and multiradical carbon nanomaterials

double exciton state

Conjugated singlet ground state diradicals have received remarkable attention owing to their potential electronic applications in organic field effect transistors (OFETs), organic photodetectors (OPDs) and near-infrared (NIR) dyes among others. Significant efforts have been devoted to stabilize the active open-shell molecules, and a large number of stable diradicals with an open-shell singlet ground state have been synthetized with dierent conjugated cores and varying diradical character.

There has been a tremendous effort also on the rationalization of the properties from a theoretical point of view, including their linear and non-linear optical properties and their application in singlet fission processes.

A distinctive character of these systems is the location of the double-exciton state, a low lying excited state dominated by the doubly excited HOMO,HOMO->LUMO,LUMO configuration, (where HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) which may influence optical and other photophysical properties.

We have shown recently, via CASPT2//CASSCF calculations and less expensive TDUDFT  and spin-flip TDDFT calculations, that for some systems displaying remarkable diradical character, the double exciton state becomes the lowest energy excited singlet state, a peculiarity which is well known for the class of polyenes. 



  1. S. Di Motta, F. Negri, D. Fazzi, C. Castiglioni, E. V. Canesi, “Biradicaloid and Polyenic Character of Quinoidal Oligothiophenes Revealed by the Presence of a Low-Lying Double-Exciton State”, J. Phys. Chem. Lett., 1 , (2010) 3334-3339.
  2. R. C. González-Cano, S. Di Motta, X. Zhu, J. T. López Navarrete, H. Tsuji, E. Nakamura, F. Negri, J. Casado Cordón, "Carbon-Bridged Phenylene-Vinylenes: On the Common Diradicaloid Origin of Their Photonic and Chemical Properties", J. Phys. Chem. C, 121 (2017), 23141–23148, DOI: 10.1021/acs.jpcc.7b08011
  3. S. Canola, J. Casado, F. Negri, "The double exciton state of conjugated chromophores with strong diradical character: insights from TDDFT calculations", Phys. Chem. Chem. Phys., 20 (2018), 24227-24238  DOI: 10.1039/c8cp04008g
  4. S. Canola, Y. Dai, F. Negri, "The low lying double-exciton state of conjugated diradicals: assessment of TDUDFT and Spin-Flip TDDFT predictions", Computation, 7, (2019),  68, DOI: 10.3390/computation7040068
  5. G. Salvitti, F. Negri, Á. J. Pérez-Jiménez, E.San-Fabián, D. Casanova, J. C. Sancho-García, "Investigating the (Poly)radicaloid Nature of Real-World Organic Compounds with DFT-Based Methods", J. Phys. Chem. A. (2020), accepted, DOI:10.1021/acs.jpca.0c01239. http://dx.doi.org/10.1021/acs.jpca.0c01239