Two-photon absorption reveals low-energy excited states of a 2,5,8-triamino-heptazine chromophore

Charles W. Stark; Johanna Arak; Aleksander Trummal; Merle Uudsemaa; Meelis-Mait Sildoja; Juri Pahapill; Aleks Rebane

doi:10.1117/12.3022312

20 June 2024 Two-photon absorption reveals low-energy excited states of a 2,5,8-triamino-heptazine chromophore

Charles W. Stark, Johanna Arak, Aleksander Trummal, Merle Uudsemaa, Meelis-Mait Sildoja, Juri Pahapill, Aleks Rebane

Proceedings Volume 13004, Nonlinear Optics and its Applications 2024; 130040T (2024) https://doi.org/10.1117/12.3022312
Event: SPIE Photonics Europe, 2024, Strasbourg, France

Conference Poster

Abstract

Triamino-heptazines (TAH's) comprise the fundamental building blocks of graphitic carbon nitride, an alluring material with promising applications in optoelectronics. However, the core D_3h molecular symmetry enforces a forbidden lowest-energy excited singlet state, making it a challenge to characterize via conventional spectroscopy. Here, we measure oneand two-photon absorption spectra of an acidic form of triamino-heptazine, 3H-TAH, and use reversible acid/base titration to further probe the symmetry of the low-energy transitions in aqueous solution, which suggests the molecular base structure is dimelem. Two-photon absorption reveals two distinct low-energy transitions in acidic conditions, both of which are one-photon forbidden. The lowest energy state additionally becomes one-photon allowed in basic conditions. Spectroscopic changes can be described according to chromophore symmetry switching, with C_3h, D_3h, or C_s point group symmetry in respective acidic, neutral, or basic environments.

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

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Charles W. Stark, Johanna Arak, Aleksander Trummal, Merle Uudsemaa, Meelis-Mait Sildoja, Juri Pahapill, and Aleks Rebane "Two-photon absorption reveals low-energy excited states of a 2,5,8-triamino-heptazine chromophore", Proc. SPIE 13004, Nonlinear Optics and its Applications 2024, 130040T (20 June 2024); https://doi.org/10.1117/12.3022312

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