We propose to fundamentally transform the photoexcitation process in photomechanical polymers using efficient triplet energy sensitization. This enables mechanical motion remotely from visible light thus opening up new opportunities to design laser controlled machines that can operate free from electromagnetic interference and untethered to power supplies.  To realize such materials, high efficiency photostriction is necessary to compete with conventional smart materials (e.g., piezoelectric, magnetostrictive, shape memory alloys) which will be enabled by new molecular sensitized photopolymers and quantum dot nanocomposites. This new approach overcomes a serious photomechanical limitation which has relied on direct excitation of azobenzene polymers using ultra-violet (UV) light to elicit photostrain. These high photon energies are necessary to overcome the trans-cis energy barrier along the singlet potential energy surface of azobenzene but also produces excessive heat and UV damage. Strategically integrated molecular or quantum dot (QD) sensitizers will create photoexcited triplet states that produce the same photoisomerization at a fraction of the input photonic energy. The use of longer wavelengths will provide deeper penetration of light thus enabling bulk photostriction and tunable penetration of light for wavelength selective control over photostriction in three dimensions unlike any other known multifunctional material.

We have preliminary data demonstrating this using a new molecular sensitized stilbene polymer that has produced 16× better performance in comparison to an equivalent, non-sensitized, azobenzene polyimide polymer. Whereas these favorable optical properties can enable three dimensional photomechanics, the fundamental mechanisms governing triplet energy transfer (TET) are poorly understood and have yet to be optimized. Additionally, semiconducting quantum dots are excited into a mixed singlet-triplet states, circumventing the energy losses observed in molecules due to intersystem crossing. Integration of photochemically active quantum dots into a photomechanical polymer will be the first of its kind that enables broadband light absorption and enhanced photomechanical efficiency.