Controlling optoelectronic properties through protonation with π-extended triphenodioxazine diimides

We present a combined approach integrating chemical synthesis, computational methods and advanced ultrafast spectroscopy to explore the properties of triphenodioxazine diimides (TPDODI). The TPDODI derivative shows significant redshifted absorption (lmax = 556 nm) and emission (lmax = 569 nm) compared to other non-diimide TPDO derivatives. Protonation of the TPDODI leads to further redshifts in absorption (lmax = 638 nm and 715 nm for mono- and diprotonated states, respectively), with the diprotonated form absorbing up to 800 nm. However, protonation also triggers competitive nonradiative decay processes, confirmed by transient absorption spectroscopy and linked to the Energy Gap Law via high-frequency molecular vibrations detected by two-dimensional electronic spectroscopy. Computational analysis supports these findings, particularly in highlighting the enhanced electron affinity of the monoprotonated species (LUMO = -3.61 eV vs. -4.98 eV for the neutral and monoprotonated forms, respectively). These results underscore the versatility of TPDODI for optoelectronic applications, providing key insights into the finetuning of n-type semiconductors, catalysts, and other advanced materials.