With a new photolabile protecting group – exclusively cleavable by two-photon-excitation – complex light scenarios for three-dimensional uncaging are possible.

Efficient sunlight harvesting and re-directioning onto small areas has great potential for more widespread use of precious high-performance photovoltaics but so far intrinsic solar concentrator loss mechanisms outweighed the benefits. Here we present an antenna concept allowing high light absorption without high reabsorption or escape-cone losses. An excess of randomly oriented pigments collects light from any direction and funnels the energy to individual acceptors all having identical orientations and emitting ~90% of photons into angles suitable for total internal reflection waveguiding to desired energy converters (funneling diffuse-light re-directioning, FunDiLight). This is achieved using distinct molecules that align efficiently within stretched polymers together with others staying randomly orientated. Emission quantum efficiencies can be >80% and single-foil reabsorption <0.5%. Efficient donor-pool energy funneling, dipole re-orientation, and ~1.5–2 nm nearest donor–acceptor transfer occurs within hundreds to ~20 ps. Single-molecule 3D-polarization experiments confirm nearly parallel emitters. Stacked pigment selection may allow coverage of the entire solar spectrum.

The binding of glucagon-like peptide-1 (GLP-1) to a planar phospholipid bilayer is measured using single-molecule total internal reflection fluorescence microscopy. From several reports in the literature, GLP-1 has been shown to be a random coil in free solution, adopting a folded, α-helix conformation when intercalated into membrane environments. Single-molecule fluorescence measurements of GLP-1 binding to supported lipid bilayers show evidence of two populations of membrane-associated molecules having different residence times, suggesting weakly adsorbed peptides and strongly bound peptides in the lipid bilayer. The path to and from a strongly bound (folded, intercalated) state would likely include an adsorbed state as an intermediate, so that the resulting kinetics would correspond to a consecutive first-order reversible three-state model. In this work, the relationships between measured single-molecule residence times and the microscopic rates in a three-state kinetic model are derived and used to interpret the binding of GLP-1 to a supported lipid bilayer. The system of differential equations associated with the proposed consecutive-three state kinetics scheme is solved, and the solution is applied to interpret histograms of single-molecule, GLP-1 residence times in terms of the microscopic rates in the sequential two-step model. These microscopic rates are used to estimate the free energy barrier to adsorption, the fraction of peptides adsorbing to the membrane surface that successfully intercalate in the bilayer, the lifetime of inserted peptides in the membrane, and the free energy change of insertion into the lipid bilayer from the adsorbed state. The transition from a random coil in solution to a folded state in a membrane has been recognized as a common motif for insertion of membrane active peptides. Therefore, the relationships developed here could have wide application to the kinetic analysis of peptide-membrane interactions.

We present a direct comparison of two-photon spectra of various carotenoid-tetrapyrrole dyads and phthalocyanines (Pc) as well as chlorophylls (Chl) in the spectral range between 950 and 1360 nm, corresponding to one-photon spectra between 475 and 680 nm. For carotenoids (Car) with 8, 9, or 10 conjugated double bonds, the two-photon absorption cross section of states below the optical allowed carotenoid S is at least about 3-10 times higher than that of Pc or chlorophyll a and b at 550/1100 nm. A quantitative comparison of spectra from Pc with and without carotenoids of eight and nine conjugated double bonds confirms energy transfer from optically forbidden carotenoid states to Pc in these dyads. When considering that less than 100% efficient energy transfer reduces the two-photon contribution of the carotenoids in the spectra, the actual Car two-photon cross sections relative to Chl/Pc are even higher than a factor of 3-10. In addition, strong spectroscopic two-photon signatures at energies below the optical allowed carotenoid S state support the presence of additional optical forbidden carotenoid states such as S*, S, or, alternatively, contributions from higher vibronic or hot S states dominating two-photon spectra or energy transfer from the carotenoids. The onset of these states is shifted about 1500-3500 cm to lower energies in comparison to the S states. Our data provides evidence that two-photon excitation of the carotenoid S*, S, or hot S states results in energy transfer to tetrapyrroles or chlorophylls similar to that observed with the Car S two-photon excitation.

We developed three bathochromic, green‐light activatable, photolabile protecting groups based on a nitrodibenzofuran (NDBF) core with D‐π‐A push–pull structures. Variation of donor substituents (D) at the favored ring position enabled us to observe their impact on the photolysis quantum yields. Comparing our new azetidinyl‐NDBF (Az‐NDBF) photolabile protecting group with our earlier published DMA‐NDBF, we obtained insight into its excitation‐specific photochemistry. While the “two‐photon‐only” cage DMA‐NDBF was inert against one‐photon excitation (1PE) in the visible spectral range, we were able to efficiently release glutamic acid from azetidinyl‐NDBF with irradiation at 420 and 530 nm. Thus, a minimal change (a cyclization adding only one carbon atom) resulted in a drastically changed photochemical behavior, which enables photolysis in the green part of the spectrum.