Picking a Pucker: Excited-State Charge Redistribution Navigates the BN-Reshaped Conical-Intersection Landscape in Azaborine Photochemistry
Abstract
Photoexcited benzene yields multiple isomers, whereas its BN isostere 1,2-azaborine selectively forms BN-Dewar benzene (BN-DB), despite both decaying through ringpuckered S1/S0 conical intersections (CIs). This selectivity is puzzling given that BNinduced asymmetry in 1,2-azaborine creates six distinct puckering sites and potentially multiple CIs, yet only a single photoproduct is observed. Here, we map the S1/S0 CI landscape of 1,2-azaborine using CASSCF and XMS-CASPT2 and identify eight N-, B-, and C-puckered CIs that open channels to various isomers including BN-DB and BN-benzvalene (BN-BV). BN incorporation therefore does not remove the excitedstate pathways of benzene but multiplies them. Of these CIs, only the N-puckered CIs leading to BN-DB lie below the S1 minimum, a preference we trace to S1 N→B charge redistribution. We then examine whether structural modifications that alter this redistribution can change CI accessibility, considering CH3 and F substitution and changes in B and N positions. Notably, 1,4-azaborine exhibits a qualitative shift from N→B to C→B charge redistribution. Consistently, C-and B-puckered CIs lie below the S1 minimum and may provide access to BN-BV, a versatile synthetic intermediate currently obtained through two photochemical steps. Together, these results suggest that S1 charge redistribution may be a key lever for steering azaborine photochemistry and for designing more direct routes to BN-BV.
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BibTeX
@misc{yadav2026picking,
title = {{Picking a Pucker: Excited-State Charge Redistribution Navigates the BN-Reshaped Conical-Intersection Landscape in Azaborine Photochemistry}},
author = {Annu Yadav and Mahesh Gudem},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010747/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010747/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Picking a Pucker: Excited-State Charge Redistribution Navigates the BN-Reshaped Conical-Intersection Landscape in Azaborine Photochemistry
AU - Annu Yadav
AU - Mahesh Gudem
PY - 2026
DA - 2026/10/21
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010747/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010747/v1
AB - Photoexcited benzene yields multiple isomers, whereas its BN isostere 1,2-azaborine selectively forms BN-Dewar benzene (BN-DB), despite both decaying through ringpuckered S1/S0 conical intersections (CIs). This selectivity is puzzling given that BNinduced asymmetry in 1,2-azaborine creates six distinct puckering sites and potentially multiple CIs, yet only a single photoproduct is observed. Here, we map the S1/S0 CI landscape of 1,2-azaborine using CASSCF and XMS-CASPT2 and identify eight N-, B-, and C-puckered CIs that open channels to various isomers including BN-DB and BN-benzvalene (BN-BV). BN incorporation therefore does not remove the excitedstate pathways of benzene but multiplies them. Of these CIs, only the N-puckered CIs leading to BN-DB lie below the S1 minimum, a preference we trace to S1 N→B charge redistribution. We then examine whether structural modifications that alter this redistribution can change CI accessibility, considering CH3 and F substitution and changes in B and N positions. Notably, 1,4-azaborine exhibits a qualitative shift from N→B to C→B charge redistribution. Consistently, C-and B-puckered CIs lie below the S1 minimum and may provide access to BN-BV, a versatile synthetic intermediate currently obtained through two photochemical steps. Together, these results suggest that S1 charge redistribution may be a key lever for steering azaborine photochemistry and for designing more direct routes to BN-BV.
ER -