The chain length and branching of the organic backbone of poly(oxyalkylene)/siloxane ureasils can be used to control the placement and orientation of a covalently-grafted perylene, leading to tunable photoluminescence.

Azobenzene photosurfactants are light-responsive amphiphiles that have garnered significant attention for diverse applications including delivery and sorting systems, phase transfer catalysis, and foam drainage. The azobenzene chromophore changes both its polarity and conformation (trans-cis isomerization) in response to UV light, while the amphiphilic structure drives self-assembly. Detailed understanding of the inherent relationship between the molecular structure, physicochemical behavior, and micellar arrangement of azobenzene photosurfactants is critical to their usefulness. Here, we investigate the key structure-function-assembly relationships in the popular cationic alkylazobenzene trimethylammonium bromide (AzoTAB) family of photosurfactants. We show that subtle changes in the surfactant structure (alkyl tail, spacer length) can lead to large variations in the critical micelle concentration, particularly in response to light, as determined by surface tensiometry and dynamic light scattering. Small-angle neutron scattering studies also reveal the formation of more diverse micellar aggregate structures (ellipsoids, cylinders, spheres) than predicted based on simple packing parameters. The results suggest that whereas the azobenzene core resides in the effective hydrophobic segment in the trans-isomer, it forms part of the effective hydrophilic segment in the cis-isomer because of the dramatic conformational and polarity changes induced by photoisomerization. The extent of this shift in the hydrophobic-hydrophilic balance is determined by the separation between the azobenzene core and the polar head group in the molecular structure. Our findings show that judicious design of the AzoTAB structure enables selective tailoring of the surfactant properties in response to light, such that they can be exploited and controlled in a reliable fashion.

The development of an efficient luminescent solar concentrator (LSC), with minimised optical losses, requires careful consideration of its principal constituting materials, a waveguide and a luminophore, in tandem. Here, a series of LSCs are fabricated utilising a poly(fluorene-altphenylene) copolymer containing on-chain perylene diimide (PDI) chromophore units as the luminophore (PBS-PFP-PDI) immobilised within a poly(oxyalkylene)/siloxane organicinorganic hybrid, known as a ureasil, as the waveguide. PBS-PFP-PDI and the ureasil both function as photoactive components, offering the possibility of energy transfer between the ureasil host and/or the PBS-PFP donor chains to the PDI acceptor, leading to reduced reabsorption losses and harvesting a broader wavelength range of the solar spectrum. A combination of studies using UV/Vis absorption, Fourier transform infrared, steady-state and time-resolved photoluminescence spectroscopies revealed that the branching of the ureasil framework influences the packing of the polymer chains, with the tri-podal ureasil structure facilitating improved dispersion of the PBS-PFP-PDI chains, while the linear di-ureasil structure promotes more intimate mixing of the PBS-PFP-PDI and the ureasil. Picosecond time-correlated single photon counting measurements reveal that strong spectral overlap, combined with efficient electronic coupling results in efficient excitation energy transfer from the ureasil to emissive trap sites localised on the PBS-PFP unit. This process inhibits subsequent energy transfer to the PDI chromophore, but leads to high solid-state photoluminescence quantum yields of >50%. The optical efficiency of the PBS-PFP-PDIureasil composites as LSCs was evaluated under AM1.5G solar simulated light delivering values of up to 5.6% using a scattering background, which could be boosted to 13.1% by increasing the percentage of PDI units per PBS-PFP chains using a model system. The results demonstrate that consideration of the combined photophysical properties of the luminophore and the waveguide are crucial to the design of next generation LSCs. 3

A single-component photorheological fluid comprised of a neutral photosurfactant in water can reversibly switch its viscosity four orders of magnitude, between high and low viscosity states, depending on the wavelength of light used.

A cationic azobenzene photosurfactant (AzoTAB) forms self-assembled structures with long-range order and optical anisotropy at high concentrations. These high-concentration mesophases are lost or disrupted with UV irradiation.

Conjugated poly(3-hexylthiophene) copolymer derivatives containing 10% appended porphyrin moieties are prepared using a supramolecular approach toward applications in organic electronics. The self-assembled polythiophene-porphyrin copolymers are synthesized by coordination of the porphyrinato central zinc ions to the imidazole-functionalized polythiophene side chains. Evidence for the self-assembly process is provided by 1 H NMR spectroscopy, single crystal X-ray diffraction, and optical absorption studies on model compounds. The polythiopheneporphyrin copolymers show an extended absorption window in the region of 420-650 nm due to the contribution of the porphyrin. Photoluminescence studies indicate concentrationdependent energy transfer from P3HT to the porphyrin. Preliminary photovoltaic studies are performed by combining the polythiophene-porphyrin copolymers with PC 61 BM in the photo active layer of bulk heterojunction organic solar cells.

Manuscript and supporting information detailing characterisation of photoresponsive viscoelastic fluids prepared from wormlike micelles composed of azobenzene surfactants. Data includes results from rheology, UV/vis absorption, transmission electron microscopy and small-angle X-ray scattering measurements.

Manuscript and supporting information detailing characterisation of photoresponsive viscoelastic fluids prepared from wormlike micelles composed of azobenzene surfactants. Data includes results from rheology, UV/vis absorption, transmission electron microscopy and small-angle X-ray scattering measurements.