Magnetic Properties, Spin-Vibration Couplings, and Temperature Effects in Phenalenyl and Triangulene.

We introduce a computational methodology for evaluating and analyzing spin-vibration couplings in molecular systems, enabling insights into the interplay between electronic spins and molecular vibrations. By mapping ab initio electronic structure calculations onto molecular spin Hamiltonians, our approach captures those vibrational interactions potentially driving spin relaxation process. Spin-vibration couplings, derived from Holstein and Peierls terms, highlight the pivotal role of vibrational mode symmetry in spin decoherence and efficient energy dissipation.

-Acenoacene molecules: tuning of the singlet and triplet excitation energies by modifying their radical character.

The energy difference between singlet and triplet excitons, or Δ, is a key parameter for novel light-emission mechanisms (, TADF or thermally activated delayed fluorescence) or other photoactivated processes. We have studied a set of conjugated molecules (-acenoacenes and their heteroatom-doped analogues) to observe the evolution of their excited-state properties upon increasing the system size with and without substitution with a pair of N atoms. Since these molecules exhibit a (ground-state) diradicaloid character, together with marked correlation effects influencing the excited-states formed, we have applied a variety of theoretical methods (FT-DFT, TD-DFT, SF-TD-DFT, CIS, CIS(D), SCS-CC2, SA-CASSCF, and SC-NEVPT2) to bracket the accuracy of the results while concomitantly providing insights into electronic structure.