TY - JOUR

T1 - Ultrafast excited state decay of natural UV filters

T2 - From intermolecular hydrogen bonds to a conical intersection

AU - Sherin, Peter S.

AU - Tsentalovich, Yuri P.

AU - Vauthey, Eric

AU - Benassi, Enrico

N1 - Publisher Copyright: © 2018 the Owner Societies.

PY - 2018/6/14

Y1 - 2018/6/14

N2 - Kynurenines (KNs) are natural UV filters of the human eye lens, protecting the eye tissues from solar UV radiation. Key points of their effective protection are the intramolecular charge transfer (ICT) in the excited state and the fast dissipation of absorbed light energy into heat via the intermolecular H-bonds. Herein we report that the introduction of an unsaturated double bond in the amino acid side chain, operating as an ICT-enhancing electron donor group, drastically accelerates the internal conversion (IC) due to a conical intersection (CI) between the potential energy surfaces of the excited and ground states. Our photophysical study of a deaminated KN (carboxyketoalkene, CKA), an intrinsic product of KN thermal decomposition, demonstrates an unusually fast excited state decay in a broad range of solvents of different polarity and proticity. The detailed analysis of interactions in the excited state by different computational techniques revealed that the changes in molecular structure-the twist of the carbonyl group from the plane of the aromatic ring followed by the formation of two mutually orthogonal conjugated substructures-are responsible for the CI of the excited and ground state potential energy surfaces. Intermolecular H-bonds facilitate the transition to the CI, but do not play a crucial role in the fast decay of the excited state. An extremely fast and efficient IC in CKA opens the way for the design of new types of organic UV filters and their applications in material science, cosmetics and medicine.

AB - Kynurenines (KNs) are natural UV filters of the human eye lens, protecting the eye tissues from solar UV radiation. Key points of their effective protection are the intramolecular charge transfer (ICT) in the excited state and the fast dissipation of absorbed light energy into heat via the intermolecular H-bonds. Herein we report that the introduction of an unsaturated double bond in the amino acid side chain, operating as an ICT-enhancing electron donor group, drastically accelerates the internal conversion (IC) due to a conical intersection (CI) between the potential energy surfaces of the excited and ground states. Our photophysical study of a deaminated KN (carboxyketoalkene, CKA), an intrinsic product of KN thermal decomposition, demonstrates an unusually fast excited state decay in a broad range of solvents of different polarity and proticity. The detailed analysis of interactions in the excited state by different computational techniques revealed that the changes in molecular structure-the twist of the carbonyl group from the plane of the aromatic ring followed by the formation of two mutually orthogonal conjugated substructures-are responsible for the CI of the excited and ground state potential energy surfaces. Intermolecular H-bonds facilitate the transition to the CI, but do not play a crucial role in the fast decay of the excited state. An extremely fast and efficient IC in CKA opens the way for the design of new types of organic UV filters and their applications in material science, cosmetics and medicine.

KW - GREEN FLUORESCENT PROTEIN

KW - INTERNAL-CONVERSION

KW - SOLVATION DYNAMICS

KW - HUMAN LENS

KW - SEMICLASSICAL SIMULATION

KW - MOLECULAR-MECHANISM

KW - ULTRAVIOLET FILTER

KW - KYNURENIC ACID

KW - SOLUTION-PHASE

KW - AMINO-ACIDS

UR - http://www.scopus.com/inward/record.url?scp=85048244137&partnerID=8YFLogxK

U2 - 10.1039/c8cp02183j

DO - 10.1039/c8cp02183j

M3 - Article

C2 - 29790516

AN - SCOPUS:85048244137

VL - 20

SP - 15074

EP - 15085

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 22

ER -