Tuning Solid-State Emission with Molecular Torsion in Dibenzosuberenylidene-Derived Organic Dyes

Pace, Domenic; Crocker, Reece D.; Kendrick, William J.; Zhang, Bolong; Wong, Wallace W. H.; Bhadbhade, Mohan; Schmidt, Timothy W.; Nguyên, Thành Vinh

doi:10.26434/chemrxiv-2023-s9l13

Cited by 1 publication

(1 citation statement)

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“…1), which consists of an anilinium and a dibenzotropylium cationic moieties. [46][47][48][49] The bench-stable protonated and doubly charged HDMAPAN-(BF4)2 has a bench-stable conjugate base (DMAPAN-BF4, Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Remote Electrostatic Repulsion Trigged by Excited State Antiaromaticity Relief as Origin of Photoacidity in an Organic Dye

Gomes

Pace

Zubiria‐Ulacia

et al. 2023

Preprint

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Photoacids are molecules which become (more) acidic under photoirradiation, and they find valuable applications in organic synthesis and biological chemistry. We herein report a new photoacid, HDMAPAN-(BF4)2, which functions by a different photoacidity mechanism than existing ones. HDMAPAN-(BF4)2, consisting of one dibenzotropylium and one anilinium moiety connected together by a biaryl C-C bond, shows an exceptionally low computed Delta_pKa(hv) (-12.3), which is within the range of superphotoacids. Surprisingly, despite the electronic S0 to S1 transition being located in the dibenzotropylium unit, the photoexcitation affects the acidity of the proton on the anilinium unit. Our computational investigations using TD-DFT reveal that the photoacid is functioning by a new mechanism, in which the excited state antiaromatic character of the dibenzotropylium unit in the S1 state unleashes a local reorganization of the charge distribution, alleviating the destabilizing antiaromatic character. Upon excitation, the positive charge within the dibenzotropylium system is localized on the carbons closest to the anilinium ring, creating an increased electrostatic repulsion against the acidic proton. Placing spacers between the dibenzotropylium and the anilinium moieties gradually reduced the computed Delta_pKa, supporting the electrostatic repulsion between the two ring systems as the main source to the strong photoacidity in HDMAPAN-(BF4)2. Finally, using DFT calculations with point charges, we show that a fractional positive charge indeed destabilizes the anilinium system when it is in close proximity.

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Section: Introductionmentioning

confidence: 99%