Efficient quantitative modeling of Herzberg-Teller vibronic two-photon absorption spectra of organic fluorophores: enhancement of parity-forbidden transitions

Aleksander Trummal; Merle Uudsemaa; Charles W. Stark; Meelis-Mait Sildoja; Jüri Pahapill; Aleksander Rebane

doi:10.1117/12.3021621

20 June 2024 Efficient quantitative modeling of Herzberg-Teller vibronic two-photon absorption spectra of organic fluorophores: enhancement of parity-forbidden transitions

Aleksander Trummal, Merle Uudsemaa, Charles W. Stark, Meelis-Mait Sildoja, Jüri Pahapill, Aleksander Rebane

Author Affiliations +

Proceedings Volume 13004, Nonlinear Optics and its Applications 2024; 130040R (2024) https://doi.org/10.1117/12.3021621
Event: SPIE Photonics Europe, 2024, Strasbourg, France

Conference Poster

Abstract

Two-photon absorption (2PA) transitions play a key role in numerous photonic applications, where many prominent features in the 2PA spectra of organic fluorophores are due to transitions between electronic-vibrational (vibronic) states. While quantum-chemical calculations excel at modelling purely electronic 2PA transitions, success in predicting vibronic properties remains limited. This is in part due to high computational costs of evaluating 2PA tensor derivatives required for Herzberg-Teller (HT) vibronic interactions, especially if carried out across full vibrational coordinate space of the chromophores. Here, we present a novel highly efficient and cost-effective approach to modelling of HT vibronic two-photon absorption spectra of organic fluorophores by using the latest version of FCclasses3 code combined with judicious pre-selection of symmetry-adapted vibrational subspace. We apply this method to a C_2h inversion-symmetric diketopyrrolopyrrole chromophore, where the 2PA spectrum is dominated by HT terms because Franck-Condon contributions vanish due to LaPorte rule. Our results are in excellent agreement with recently reported experimental 2PA spectra confirming two-photon HT coupling is indeed dominated by, B_u-symmetry modes, and is also consistent with the experimentally observed polarization ratio. However, nominally-forbidden features near the electronic-origin appear significantly larger than HT coupling permits, indicating the presence of additional phenomena.

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

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Aleksander Trummal, Merle Uudsemaa, Charles W. Stark, Meelis-Mait Sildoja, Jüri Pahapill, and Aleksander Rebane "Efficient quantitative modeling of Herzberg-Teller vibronic two-photon absorption spectra of organic fluorophores: enhancement of parity-forbidden transitions", Proc. SPIE 13004, Nonlinear Optics and its Applications 2024, 130040R (20 June 2024); https://doi.org/10.1117/12.3021621

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