A set of thioxanthone derivatives bearing strongly electrondonating dialkylamino groups have been synthesized efficiently via the Buchwald−Hartwig, Sonogashira, and Heck reactions. Compounds possessing both one and two donors have been prepared. Their optical properties proved to be intriguing. The presence of the amino group alone increased the fluorescence quantum yield 100 times. Dyes possessing arylethylene and arylethynyl linkages absorbed UV radiation and violet light while emitting (weakly) red light, as a consequence of different geometries at ground and excited states. Our design led to an increase in two-photon absorption cross sections at the wavelength of interest (800 nm) to the highest values ever recorded for thioxanthones, while maintaining excellent solubility due to the fact that all new photoinitiators are highly viscous oils at room temperature. Some of the prepared D−π−A−π−D systems also proved to be initiators in two-photon polymerization.

We demonstrate that controlled assembly of eukaryotic photosystem I with its associated light harvesting antenna complex (PSI-LHCI) on plasmonically active silver nanowires (AgNWs) substantially improves the optical functionality of such a novel biohybrid nanostructure. By comparing fluorescence intensities measured for PSI-LHCI complex randomly oriented on AgNWs and the results obtained for the PSI-LHCI/cytochrome c (cyt c) bioconjugate with AgNWs we conclude that the specific binding of photosynthetic complexes with defined uniform orientation yields selective excitation of a pool of chlorophyll (Chl) molecules that are otherwise almost non-absorbing. This is remarkable, as this study shows for the first time that plasmonic excitations in metallic nanostructures can not only be used to enhance native absorption of photosynthetic pigments, but also - by employing cyt c as the conjugation cofactor - to activate the specific Chl pools as the absorbing sites only when the uniform and well-defined orientation of PSI-LHCI with respect to plasmonic nanostructures is achieved. As absorption of PSI alone is comparatively low, our approach lends itself as an innovative approach to outperform the reported-to-date biohybrid devices with respect to solar energy conversion.

We report on the synthesis of long silver nanowires using the hydrothermal method, with H2O2 as the reducing agent. Our approach yields nanowires with an average diameter and length of about 100 nm and 160 µm, respectively, reaching the maximum length of 800 µm. Scanning electron microscopy (SEM) measurements revealed the presence of a thick, inhomogeneous poly(vinylpyrrolidone) (PVP) layer covering the nanowires, which with time becomes much more uniform, leading to well-defined extinction peaks in the ultraviolet-visible (UV-Vis) spectra. This change in morphology is evidenced also by the fluorescence enhancement behavior probed using protein complexes. Wide-field and confocal fluorescence microscopy measurements demonstrate strong, 10-fold enhancement of the protein emission intensity, accompanied by a reduction of the fluorescence decay time. In addition, for the aged, one-month-old nanowires, the uniformity of the intensity profile along them was substantially improved as compared with the as-synthesized ones. The results point towards the importance of the morphology of plasmonically active silver nanowires when considering their application in enhancing optical properties or achieving energy propagation over submillimeter distances.