Controlling the S1 Energy Profile by Tuning Excited-State Aromaticity

TY - JOUR

T1 - Controlling the S1 Energy Profile by Tuning Excited-State Aromaticity

AU - Kotani, Ryota

AU - Liu, Li

AU - Kumar, Pardeep

AU - Kuramochi, Hikaro

AU - Tahara, Tahei

AU - Liu, Pengpeng

AU - Osuka, Atsuhiro

AU - Karadakov, Peter Borislavov

AU - Saito, Shohei

N1 - © 2020 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2020/9/2

Y1 - 2020/9/2

N2 - The shape of the lowest singlet excited state (S1) energy profile is of primary importance in photochemistry and related materials science areas. Here we demonstrate a new approach for controlling the shape of the S1 energy profile which relies on tuning the level of excited-state aromaticity (ESA). In a series of fluorescent π-expanded oxepins, the energy decrease accompanying the bent-to-planar conformational change in S1 becomes less pronounced with lower ESA levels. Stabilization energies following from ESA were quantitatively estimated to be 10–20 kcal/mol using photophysical data. Very fast planarization dynamics in S1 was revealed by time-resolved fluorescence spectroscopy. The time constants were estimated to be shorter than 1 ps, regardless of molecular size and level of ESA, indicating barrierless S1 planarization within the oxepin series.

AB - The shape of the lowest singlet excited state (S1) energy profile is of primary importance in photochemistry and related materials science areas. Here we demonstrate a new approach for controlling the shape of the S1 energy profile which relies on tuning the level of excited-state aromaticity (ESA). In a series of fluorescent π-expanded oxepins, the energy decrease accompanying the bent-to-planar conformational change in S1 becomes less pronounced with lower ESA levels. Stabilization energies following from ESA were quantitatively estimated to be 10–20 kcal/mol using photophysical data. Very fast planarization dynamics in S1 was revealed by time-resolved fluorescence spectroscopy. The time constants were estimated to be shorter than 1 ps, regardless of molecular size and level of ESA, indicating barrierless S1 planarization within the oxepin series.

U2 - 10.1021/jacs.0c05611

DO - 10.1021/jacs.0c05611

M3 - Article

SN - 0002-7863

VL - 142

SP - 14985

EP - 14992

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 35

ER -