Excited-State Planarization Couples Charge-Transfer Character and Spin-Orbit Coupling to Enable High Efficiency Solvatochromism in an Anti-Kasha Donor-Acceptor Phosphor
Abstract
A single, synthetically controllable structural coordinate capable of simultaneously enhancing charge-transfer (CT) character and spin-orbit coupling (SOC) is highly sought after in purely organic chromophore design, yet has not been demonstrated. We show that excited-state planarization (ESP) in an anthracene-anthraquinone donor-acceptor emitter is exactly such a coordinate, governing one electronic variable, the CT weight of the emissive singlet, that simultaneously sets SOC into an acceptor-localized triplet channel in a near-linear, quantified relationship (R2 = 0.997), and we propose this as a general, transferable design principle for donor-acceptor chromophores. The resulting CT character exhibits a Solvatochromic response that exceeds current literature values for a neutral, purely organic, small-molecule donor-acceptor chromophore, with a slope of 25,384 cm-1 per unit Δf and R2 = 0.928 across a nine-solvent panel, which is the best yet reported. Finally, the compound exhibits genuine room-temperature phosphorescence (RTP) despite an anomalously small experimental singlet-triplet gap (0.08 eV), with emission confirmed, computationally and experimentally, to originate from the second triplet state rather than the lowest, a definitive instance of anti-Kasha phosphorescence; we provide a plausible, computationally supported mechanism for this behavior, in which reverse intersystem crossing (RISC) suppression is the most plausible explanation.
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BibTeX
@misc{singh2026excitedstate,
title = {{Excited-State Planarization Couples Charge-Transfer Character and Spin-Orbit Coupling to Enable High Efficiency Solvatochromism in an Anti-Kasha Donor-Acceptor Phosphor}},
author = {Ajeet K. Singh and Nancy Punia and Ayushi Tiwari and Swapnil Ganguly and Inamur Rahaman Laskar},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010011/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010011/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Excited-State Planarization Couples Charge-Transfer Character and Spin-Orbit Coupling to Enable High Efficiency Solvatochromism in an Anti-Kasha Donor-Acceptor Phosphor
AU - Ajeet K. Singh
AU - Nancy Punia
AU - Ayushi Tiwari
AU - Swapnil Ganguly
AU - Inamur Rahaman Laskar
PY - 2026
DA - 2026/10/06
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010011/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010011/v1
AB - A single, synthetically controllable structural coordinate capable of simultaneously enhancing charge-transfer (CT) character and spin-orbit coupling (SOC) is highly sought after in purely organic chromophore design, yet has not been demonstrated. We show that excited-state planarization (ESP) in an anthracene-anthraquinone donor-acceptor emitter is exactly such a coordinate, governing one electronic variable, the CT weight of the emissive singlet, that simultaneously sets SOC into an acceptor-localized triplet channel in a near-linear, quantified relationship (R2 = 0.997), and we propose this as a general, transferable design principle for donor-acceptor chromophores. The resulting CT character exhibits a Solvatochromic response that exceeds current literature values for a neutral, purely organic, small-molecule donor-acceptor chromophore, with a slope of 25,384 cm-1 per unit Δf and R2 = 0.928 across a nine-solvent panel, which is the best yet reported. Finally, the compound exhibits genuine room-temperature phosphorescence (RTP) despite an anomalously small experimental singlet-triplet gap (0.08 eV), with emission confirmed, computationally and experimentally, to originate from the second triplet state rather than the lowest, a definitive instance of anti-Kasha phosphorescence; we provide a plausible, computationally supported mechanism for this behavior, in which reverse intersystem crossing (RISC) suppression is the most plausible explanation.
ER -