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Pentiptycene‐Derived Light‐Driven Molecular Brakes: Substituent Effects of the Brake Component
Author(s) -
Sun WeiTing,
Huang YauTing,
Huang GuanJhih,
Lu HsiuFeng,
Chao Ito,
Huang ShouLing,
Huang ShingJong,
Lin YingChih,
Ho JinnHsuan,
Yang JyeShane
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000764
Subject(s) - substituent , photoisomerization , chemistry , steric effects , rotation (mathematics) , crystallography , stereochemistry , isomerization , organic chemistry , geometry , mathematics , catalysis
Five pentiptycene‐derived stilbene systems ( 1 R ; R =H, OM, NO, Pr, and Bu) have been prepared and investigated as light‐driven molecular brakes that have different‐sized brake components ( 1 H < 1 OM < 1 NO < 1 Pr < 1 Bu ). At room temperature (298 K), rotation of the pentiptycene rotor is fast ( k rot =10 8 –10 9 s −1 ) with little interaction with the brake component in the trans form (( E )‐ 1 R ), which corresponds to the brake‐off state. When the brake is turned on by photoisomerization to the cis form (( Z )‐ 1 R ), the pentiptycene rotation can be arrested on the NMR spectroscopic timescale at temperatures that depend on the brake component. In the cases of ( Z )‐ 1 NO , ( Z )‐ 1 Pr , and ( Z )‐ 1 Bu , the rotation is nearly blocked ( k rot =2–6 s −1 ) at 298 K. It is also demonstrated that the rotation is slower in [D 6 ]DMSO than in CD 2 Cl 2 . A linear relationship between the free energies of the rotational barrier and the steric parameter A values is present only for ( Z )‐ 1 H , ( Z )‐ 1 OM , and ( Z )‐ 1 NO , and it levels off on going from ( Z )‐ 1 NO to ( Z )‐ 1 Pr and ( Z )‐ 1 Bu . DFT calculations provide insights into the substituent effects in the rotational ground and transition states. The molar reversibility of the E–Z photoswitching is up to 46 %, and both the E and Z isomers are stable under the irradiation conditions.