TY - JOUR

T1 - The involvement of triplet states in the isomerization of retinaloids

AU - Filiba, Ofer

AU - Borin, Veniamin A.

AU - Schapiro, Igor

N1 - Funding Information: I. S. acknowledges support by the DFG through SFB 1078, project C6. I. S. thanks the Israel Science Foundation (Research Center grant no. 3131/20). Publisher Copyright: © 2022 The Royal Society of Chemistry.

PY - 2022/10/17

Y1 - 2022/10/17

N2 - Rhodopsins form a family of photoreceptor proteins which utilize the retinal chromophore for light energy conversion. Upon light absorption the retinal chromophore undergoes a photoisomerization. This reaction involves a non-radiative relaxation through a conical intersection between the singlet excited state and the ground state. In this work we studied the possible involvement of triplet states in the photoisomerization of retinaloids using the extended multistate (XMS) version of CASPT2. To this end, truncated models of three retinaloids were considered: protonated Schiff base, deprotonated Schiff base and the aldehyde form. The optimized geometries of the reactant, the product and the conical intersection were connected by a linear interpolation of internal coordinates to describe the isomerization. The energetic position of the low-lying singlet and triplet states as well as their spin-orbit coupling matrix elements (SOCME) were calculated along the isomerization profile. The SOCME values peaked in vicinity of the conical intersection for all the retinaloids. Furthermore, the magnitude of SOCME is invariant to the number of double bonds in the model. The SOCME for the protonated Schiff base is negligible (1.5 cm−1) which renders the involvement of the triplet state as improbable. However, the largest SOCME value of 30 cm−1 was found for the aldehyde form, followed by 15 cm−1 for the deprotonated Schiff base.

AB - Rhodopsins form a family of photoreceptor proteins which utilize the retinal chromophore for light energy conversion. Upon light absorption the retinal chromophore undergoes a photoisomerization. This reaction involves a non-radiative relaxation through a conical intersection between the singlet excited state and the ground state. In this work we studied the possible involvement of triplet states in the photoisomerization of retinaloids using the extended multistate (XMS) version of CASPT2. To this end, truncated models of three retinaloids were considered: protonated Schiff base, deprotonated Schiff base and the aldehyde form. The optimized geometries of the reactant, the product and the conical intersection were connected by a linear interpolation of internal coordinates to describe the isomerization. The energetic position of the low-lying singlet and triplet states as well as their spin-orbit coupling matrix elements (SOCME) were calculated along the isomerization profile. The SOCME values peaked in vicinity of the conical intersection for all the retinaloids. Furthermore, the magnitude of SOCME is invariant to the number of double bonds in the model. The SOCME for the protonated Schiff base is negligible (1.5 cm−1) which renders the involvement of the triplet state as improbable. However, the largest SOCME value of 30 cm−1 was found for the aldehyde form, followed by 15 cm−1 for the deprotonated Schiff base.

UR - http://www.scopus.com/inward/record.url?scp=85141840255&partnerID=8YFLogxK

U2 - https://doi.org/10.1039/d2cp03791b

DO - https://doi.org/10.1039/d2cp03791b

M3 - Article

C2 - 36278932

SN - 1463-9076

VL - 114

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

IS - 1

ER -