TY  - JOUR
A1  - Gäbert, Chris
A1  - Rosenstingl, Tobias
A1  - Linsler, Dominic
A1  - Dienwiebel, Martin
A1  - Reinicke, Stefan
T1  - Programming viscosity in silicone oils
BT  - reversible tuning of rheological properties in 9-anthracene ester-terminated polydimethylsiloxanes
JF  - ACS applied polymer materials
N2  - Programmable oils feature tunable viscosity and therefore possess potential for technical improvements and innovative solutions in many lubricated applications. Herein, we describe the first assessment of the variability of rheological properties of light-programmable 9-anthracene ester-terminated polydimethylsiloxanes (PDMS-As), including implications that arise with UV-light as an external trigger. We applied a modified rheometer setup that enables the monitoring of dynamic moduli during exposure to UV-light. The reversible dimerization of anthracene esters is used to either link PDMS chains by UV-A radiation (365 nm) or cleave chains by UV-C radiation (254 nm) or at elevated temperatures (>130 degrees C). Thermal cleavage fully restores the initial material properties, while the photochemical cleavage of dimers occurs only to a limited extent. Prolonged UV radiation causes material damage and in turn reduces the range of programmable rheological properties. The incomplete cleavage contributes to a gradual buildup of viscosity over a course of several switching cycles, which we suggest to result from chain length-dependent reaction kinetics. Material property gradients induced during radiation due to attenuation of the light beam upon its passing through the oil layer have to be considered, emphasizing the need for proper mixing protocols during the programming step. The material in focus shows integrated photorheology and is suggested to improve the performance of silicone oils in friction systems.
KW  - polysiloxane
KW  - lubricant
KW  - light-programmable viscosity
KW  - anthracene
KW  - dimerization
KW  - reversible chain extension
Y1  - 2020
U6  - https://doi.org/10.1021/acsapm.0c00794
SN  - 2637-6105
VL  - 2
IS  - 12
SP  - 5460
EP  - 5468
PB  - ACS Publications
CY  - Washington, DC
ER  - 
TY  - JOUR
A1  - Schwarze, Thomas
A1  - Kelling, Alexandra
A1  - Sperlich, Eric
A1  - Holdt, Hans-Jürgen
T1  - Influence of regioisomerism in 9-anthracenyl-substituted dithiodicyanoethene derivatives on photoinduced electron transfer controlled by intramolecular charge transfer
JF  - ChemPhotoChem
N2  - In this paper, we report on the fluorescence behaviour of three regioisomers which consist of two 9-anthracenyl fluorophores and of differently substituted dithiodicyanoethene moieties. These isomeric fluorescent probes show different quantum yields (phi(f)). In these probes, an oxidative photoinduced electron transfer (PET) from the excited 9-anthracenyl fluorophore to the dithiodicyanoethene unit quenches the fluorescence. This quenching process is accelerated by an intramolecular charge transfer (ICT) of the push-pull pi-electron system of the dithiodicyanoethene group. The acceleration of the PET depends on the strength of the ICT unit. The higher the dipole moment of the ICT unit, the stronger the observed fluorescence quenching. To the best of our knowledge, this is the first report of a regioisomeric influence on an oxidative PET by an ICT.
KW  - anthracene
KW  - charge transfer
KW  - electron transfer
KW  - fluorescence
KW  - isomerism
Y1  - 2021
U6  - https://doi.org/10.1002/cptc.202100070
SN  - 2367-0932
VL  - 5
IS  - 10
SP  - 911
EP  - 914
PB  - Wiley-VCH
CY  - Weinheim
ER  -