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Flexible organic crystalline materials exhibiting both mechanical and optical properties have received significant attention due to their potential applications in flexible optical devices. Despite numerous examples reported in recent years, the use of organic salts or biologically related molecules for constructing such materials remains relatively scarce. We investigate the elastic bending ability of both guaninium chloride dihydrate single crystals and a novel material formed by this guanine salt doped with acridine orange in its acidic form. Even though the presence of the dye does not induce significant changes in the host crystalline structure, our findings reveal an unexpected increase in the maximum elastic strain from 1.06% in the guanine-based material to 1.50% when intracrystalline acridine orange is present. Emission lifetime and absorption coefficient in the doped crystals showed their optical quality and their ability to act as light guides, even under bent geometries with optical loss coefficients of 19.5 and 12.2 dB/mm, respectively (reference values of the straight crystals). Thus, these results shed light on the intriguing colored biomaterials observed in various organisms, such as geckos, spiders, and fishes, where structural coloration alone cannot account for the observed phenomena. Our results underscore the potential of guaninium chloride dihydrate as a versatile platform for developing bioinspired materials with tailored mechanical and optical properties through judicious choice of dopants.

Bimetallic trans-[RuII(tpm)(bpy)(μNC)RuII(L)4(CN)]2+, where bpy is 2,2′-bipyridine, tpm is tris(1-pyrazolyl)methane and L = 4-methoxypyridine (MeOpy) or pyridine (py), was examined using ultrafast vis-NIR transient absorption spectroscopy. Of great relevance are the longest-lived excited states in the form of strongly coupled photoinduced mixed-valence systems, which exhibit intense photoinduced absorptions in the NIR and are freely tunable by the judicious choice of the coordination spheres of the metallic ions. Using the latter strategy, we succeeded in tailoring the excited state lifetimes of bimetallic complexes and, in turn, achieving significantly longer values relative to related monometallic complexes. Notable is the success in extending the lifetimes, when considering the higher density of vibrational states, as they are expected to facilitate nonradiative ground-state recovery.

In the present study, we report the photophysical properties of colloidal ensembles of silicon quantum dots (SiDs) and gold nanoparticles (AuNPs), particularly focusing on investigating metal-enhanced photoluminescence (PL) effects. AuNPs with different sizes, (27 ± 10) and (88 ± 12) nm, and ca. 3.4 nm-size SiD with different surface groups, either covered with an oxidized surface film bearing Si–OH surface groups or grafted with propylamine leading to Si–(CH2)2–CH2–NH2terminal functionalities, were tested to evaluate the gold enhancement of SiD PL. The NPs were characterized by high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, and gel electrophoresis, whereas the photophysical properties of the NPs, alone and in colloidal ensembles at different concentrations, were investigated by absorption and steady-state and time-resolved PL studies, including quantum yield determinations. Enhanced absorption and PL of SiDs in the presence of AuNPs was evidenced, leading in the most favorable cases to ca. 10 times increase in SiD brightness. This effect depends strongly on the SiD surface coating and its interaction with citrate-capped gold surfaces, where these interactions govern particle aggregation and relative distance distributions among SiDs and AuNPs in the ensembles. The nature of these interactions and how they affect metal-enhanced luminescence is thoroughly discussed. The present study provides significant information on the effect of SiD surface groups and surface charge on the metal-enhanced luminescence phenomenon in colloidal aqueous suspensions.

Despite the large body of work on {Ru(bpy)2} sensitizer fragments, the same attention has not been devoted to their {Ru(py)4} analogues. In this context, we explored the donor–acceptor trans-[Ru(L)4{(μ-NC)Cr(CN)5}2]4–, where L = pyridine, 4-methoxypyridine, 4-dimethylaminopyridine. We report on the synthesis and the crystal structure as well as the electrochemical, spectroscopical, and photophysical properties of these trimetallic complexes, including transient absorption measurements. We observed emission from chromium-centered d–d states upon illuminating into either MLCT or MM′CT absorptions of {Ru(L)4} or {Ru-Cr}, respectively. The underlying energy transfer is as fast as 600 fs with quantum efficiencies ranging from 10% to 100%. These results document that {Ru(py)4} sensitizer fragments are as efficient as {Ru(bpy)2} in short-range energy transfer scenarios.

This paper describes our recent work using ultrafast laser spectroscopy to examine the fundamental properties of metal particles. Two studies are presented. First, the characteristic time scale for electron-phonon coupling in Au particles with sizes between 2 and 120 nm has been examined by bleach recovery measurements. These experiments show that the coupling between the electrons and phonons is independent of particle size, to within the signal-to-noise of our experiments. We have also used transient absorption spectroscopy to examine the low-frequency "breathing" modes of the Au particles. These modes are impulsively excited by the rapid lattice heating that accompanies electron-phonon coupling. The breathing motion contributes to the transient absorption signal because the position of the plasmon band depends on the free electron density and, thus, the particle volume. The measured frequencies are inversely proportional to the radius, and almost exactly match the predictions of classical mechanics calculations for Au.