Detour to success: photoswitching indirect excitation.

Photoswitchable molecules that undergo nanoscopic changes upon photoisomerisation can be harnessed to control macroscopic properties such as colour, solubility, shape, and motion of the systems they are incorporated into. These molecules find applications in various fields of chemistry, physics, biology, and materials science. Until recently, research efforts have focused on the design of efficient photoswitches responsive to low-energy (red or near-infrared) irradiation, which however may compromise other molecular properties such as thermal stability and robustness.

Triplet Upconversion under Ambient Conditions Enables Digital Light Processing 3D Printing.

The rapid photochemical conversion of materials from liquid to solid (i.e., curing) has enabled the fabrication of modern plastics used in microelectronics, dentistry, and medicine.

Triplet sensitization enables bidirectional isomerization of diazocine with 130 nm redshift in excitation wavelengths.

Diazocines are bridged azobenzenes with phenyl rings connected by a CH-CH group. Despite this rather small structural difference, diazocine exhibits improved properties over azobenzene as a photoswitch and most importantly, its configuration is more stable than the isomer. Herein, we reveal yet another unique feature of this emerging class of photoswitches.

Microfluidic oxygen tolerability screening of nanocarriers for triplet fusion photon upconversion.

The full potential of triplet fusion photon upconversion (TF-UC) of providing high-energy photons locally with low-energy excitation is limited in biomedicine and life sciences by its oxygen sensitivity. This hampers the applicability of TF-UC systems in sensors, imaging, optogenetics and drug release. Despite the advances in improving the oxygen tolerability of TF-UC systems, the evaluation of oxygen tolerability is based on comparing the performance at completely deoxygenated (0% oxygen) and ambient (20-21%) conditions, leaving the physiological oxygen levels (0.

Azobenzene Photoswitching with Near-Infrared Light Mediated by Molecular Oxygen.

Efficient photoisomerization between the cis and the trans states of azobenzenes using low-energy light is desirable for a range of applications in, e.g., photobiology yet challenging to accomplish directly with modified azobenzenes.

Expanding excitation wavelengths for azobenzene photoswitching into the near-infrared range endothermic triplet energy transfer.

Developing azobenzene photoswitches capable of selective and efficient photoisomerization by long-wavelength excitation is an enduring challenge. Herein, rapid isomerization from the - to -state of two -functionalized bistable azobenzenes with near-unity photoconversion efficiency was driven by triplet energy transfer upon red and near-infrared (up to 770 nm) excitation of porphyrin photosensitizers in catalytic micromolar concentrations. We show that the process of triplet-sensitized isomerization is efficient even when the sensitizer triplet energy is substantially lower (>200 meV) than that of the azobenzene used.

Endothermic and Exothermic Energy Transfer Made Equally Efficient for Triplet-Triplet Annihilation Upconversion.

Expanding the anti-Stokes shift for triplet-triplet annihilation upconversion (TTA-UC) systems with high quantum yields without compromising power density thresholds () remains a critical challenge in photonics. Our studies reveal that such expansion is possible by using a highly endothermic TTA-UC pair with an enthalpy difference of +80 meV even in a polymer matrix 1000 times more viscous than toluene. Carrying out efficient endothermic triplet-triplet energy transfer (TET) requires suppression of the reverse annihilator-to-sensitizer TET, which was achieved by using sensitizers with high molar extinction coefficients and long triplet state lifetimes as well as optimized annihilator concentrations.

Efficient photon upconversion at remarkably low annihilator concentrations in a liquid polymer matrix: when less is more.

A green-to-blue triplet-triplet annihilation upconversion of 24.5% quantum yield was achieved at a remarkably low 600 μM annihilator concentration in a viscous polymer matrix. This was made possible by utilizing a ZnTPP-based photosensitizer with exceptionally long 11 ms phosphorescence lifetime.