Photoresponsive polymers are commonly used for applications such as controlled drug delivery, patterned thin films of hydrogels and polymer brushes, photodegradable materials, and liquid crystal actuators.1 Photoresponsive polymers are unique as they can change shape when exposed to a certain wavelength, intensity, or polarization of light while not requiring an electrical circuit or tethered power supply. However, the majority of photoresponsive polymers are based on the azobenzene moiety and the conversion of light into mechanical work is often inefficient. This work summarizes the relaxation behavior of a novel photopolymer film derived from stilbene and its unsensitized analog. Experiments are conducted quantifying the relaxation behavior of the films. The relaxation behavior of the photopolymer is analyzed by comparing fractional order and integer order Maxwell models. All results are statistically validated using Bayesian uncertainty methods to obtain posterior densities for the model parameters. It is shown that the fractional order Maxwell model is superior based on errors that are an order of magnitude lower than the integer order Maxwell model.
It is well known that the rate and efficiency of photon upconversion via triplet–triplet annihilation (TTA-UC) are strongly dependent on the energetics of the sensitizer and acceptor molecules. In rigid scaffoldings, where the dyes are fixed in position, the structure and orientation of the molecules also presumably play an important role. We investigate how the variation in the position of the phosphonate surface binding group on 9,10-diphenylanthracene influences TTA-UC in self-assembled bilayers on ZrO2. Interestingly, meta- or para-substitution of the anthracene dye with phosphonate groups had minimal influence on their energetics, surface loadings, or sensitizer to acceptor triplet energy transfer efficiency. However, the TTA-UC efficiency is three times lower with the meta-substituted dye, which is attributed to its threefold decrease in its triplet excited state lifetime relative to the para-substituted dye.
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