Fig. 3: Vibrational coupling to the organic excitons with variable charge transfer.
From: Decoupling excitons from high-frequency vibrations in organic molecules
a, Molecular structures of the TADF molecules studied (4CzIPN and APDC-DTPA) b, Time-resolution-corrected excited-state Raman spectra of the TADF (4CzIPN and APDC-DTPA). Asterisks indicate the solvent mode. See Extended Data Figs. 1a and 4b for a wavelength-resolved analysis of APDC-DTPA and 4CzIPN. The three-pulse IVS experiment on 4CzIPN solution is detailed in Supplementary Information section 7. c, Experimentally obtained non-radiative rates of the studied low energy-gap molecules. Orange circles represent radical emitters. The blue circle represents TADF. The grey circles represent non-fullerene acceptors36 (IO-4Cl, ITIC, o-IDTBR, Y5 and Y6). d, Vibrational coupling to the frontier molecular orbitals of APDC-DTPA (TADF) and TTM-3PCz (radical) obtained from first-principles DFT. The hole-accepting orbitals of both TADF (HOMO of APDC-DTPA) and the radical (HOMO of TTM-TPA) are localized on the central N atom with a non-bonding character, which is reflected in the lower coupling to the high-frequency phenylic ring-stretching modes. The electron-accepting level of the radical (SOMO of TTM-TPA) has a non-bonding character and suppressed high-frequency coupling with respect to its HOMO, whereas for the TADF structures, the hole-accepting level (HOMO of APDC-DTPA) makes a significant orbital contribution in the vicinity of the planar π bonds and shows reasonable high-frequency coupling.
