TY - JOUR

T1 - ortho-substituted 2-phenyldihydroazulene photoswitches

T2 - Enhancing the lifetime of the photoisomer by ortho-aryl interactions

AU - Ranzenigo, Anna

AU - Cordero, Franca M.

AU - Cacciarini, Martina

AU - Nielsen, Mogens Brøndsted

N1 - Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2021

Y1 - 2021

N2 - Photochromic molecules are systems that undergo a photoisomerization to high-energy isomers and are attractive for the storage of solar energy in a closed-energy cycle, for example, in molecular solar thermal energy storage systems. One challenge is to control the discharge time of the high-energy isomer. Here, we show that different substituents in the ortho position of a phenyl ring at C-2 of dihydroazulene (DHA-Ph) significantly increase the half-life of the metastable vinylheptafulvene (VHF-Ph) photoisomer; thus, the energy-releasing VHF-to-DHA back-reaction rises from minutes to days in comparison to the corresponding para-and meta-substituted systems. Systems with two photochromic DHA-Ph units connected by a diacetylene bridge either at the para, meta and ortho positions and corresponding to a linear or to a cross-conjugated pathway between the two photochromes are also presented. Here, the ortho substitution was found to compromise the switching properties. Thus, irradiation of ortho-bridged DHA-DHA resulted in degradation, probably due to the proximity of the different functional groups that can give rise to side-reactions.

AB - Photochromic molecules are systems that undergo a photoisomerization to high-energy isomers and are attractive for the storage of solar energy in a closed-energy cycle, for example, in molecular solar thermal energy storage systems. One challenge is to control the discharge time of the high-energy isomer. Here, we show that different substituents in the ortho position of a phenyl ring at C-2 of dihydroazulene (DHA-Ph) significantly increase the half-life of the metastable vinylheptafulvene (VHF-Ph) photoisomer; thus, the energy-releasing VHF-to-DHA back-reaction rises from minutes to days in comparison to the corresponding para-and meta-substituted systems. Systems with two photochromic DHA-Ph units connected by a diacetylene bridge either at the para, meta and ortho positions and corresponding to a linear or to a cross-conjugated pathway between the two photochromes are also presented. Here, the ortho substitution was found to compromise the switching properties. Thus, irradiation of ortho-bridged DHA-DHA resulted in degradation, probably due to the proximity of the different functional groups that can give rise to side-reactions.

KW - Cross-conjugation

KW - Electrocyclic reactions

KW - Linear conjugation

KW - Photochromism

KW - Positional isomerism

U2 - 10.3390/molecules26216462

DO - 10.3390/molecules26216462

M3 - Journal article

C2 - 34770871

AN - SCOPUS:85118399162

VL - 26

JO - Molecules

JF - Molecules

SN - 1420-3049

IS - 21

M1 - 6462

ER -