Wearable health and wellness trackers based on optical detection are promising candidates for public health uses due to their noninvasive tracking of vital health signs. However, so far, the use of rigid technologies hindered the ultimate performance and form factor of the wearable. Here, we demonstrate a new class of flexible and transparent wearables based on graphene sensitized with semiconducting quantum dots (GQD). We show several prototype wearable devices that are able to monitor vital health signs noninvasively, including heart rate, arterial oxygen saturation (SpO2), and respiratory rate. Operation with ambient light is demonstrated, offering low-power consumption. Moreover, using heterogeneous integration of a flexible ultraviolet (UV)–sensitive photodetector with a near-field communication circuit board allows wireless communication and power transfer between the photodetectors and a smartphone, offering battery-free operation. This technology paves the way toward seamlessly integrated wearables, and empowers the user through wireless probing of the UV index.
Since the initial report by Lehn et al. in 1979, ruthenium tris(bipyridine) ([Ru(bpy) 3 ] 2+ ) and its numerous derivatives were applied as photosensitizers (PSs) in a large panel of photocatalytic conditions while the bis(terpyridine) analogues were disregarded because of their low quantum yields and short excited-state lifetimes. In this study, we prepared a new terpyridine ligand, 4′-(4-bromophenyl)-4,4‴:4″,4‴′-dipyridinyl-2,2′:6′,2″-terpyridine (Bipytpy) and used it to prepare the heteroleptic complex [Ru(Tolyltpy)(Bipytpy)](PF 6 ) 2 (1; Tolyltpy = 4′tolyl-2,2′:6′,2′-terpyridine). Complex 1 exhibits enhanced photophysical properties with a higher quantum yield (7.4 × 10 -4 ) and a longer excited-state lifetime (3.8 ns) compared to those of [Ru(Tolyltpy) 2 ](PF 6 ) 2 (3 × 10 -5 and 0.74 ns, respectively). These enhanced photophysical characteristics and the potential for PS-catalyst interaction through the peripheral pyridines led us to apply the complex for visible-light-driven hydrogen evolution.The photocatalytic system based on 1 as the PS, triethanolamine as a sacrificial donor, and cobaloxime as a catalyst exhibits sustained activity over more than 10 days under blue-light irradiation (light-emitting diode centered at 450 nm). A maximum turnover number of 764 was obtained after 12 days.
In
this work photochromic properties of N-salicylideneanilines
were modified using a crystal engineering approach. Co-crystallization
allowed modification of the structural arrangement and electronic
properties of the target compounds altering its photochromic behavior
without having to change the nature of the molecule. A co-crystal
of N-salicylideneaniline and citraconic acid characterized
by a zwitterionic anil character and showing inverted photochromic
behavior when compared to the parent anil is reported here for the
first time.
In
this contribution, we aim to modify the photochromic properties
of anils using a crystal engineering approach. Previous work has shown
cocrystallization to alter the photochromic behavior of anils. Here,
a full screening of 15 anil derivatives (including 8 newly described
anils) with 21 coformers (carboxylic acids, amides, and halogenated
benzene derivatives) was performed, resulting in 89 new anil cocrystals.
This large amount of results allows drawing statistically valid insights
on the complex photochromic mechanism providing evidence of a continuous
phenomenon instead of the classic binary photochromic/nonphotochromic
one. This is supported by the discovery of “weakly photochromic
compounds” presented in this contribution. All the results
allowed confirming that an enol-imine character is a requirement and
that reducing the amount of short contacts involving the moieties
of interest is an interesting way to fine-tune properties as this
acts on both electronic and structural aspects. Following this “continuous
hypothesis”, the role of the dihedral angle has been explored
and shown to be related to the intensity of photochromism instead
of being determinant for its occurrence. In addition, in this contribution,
we present a novel way of interpreting DRS (diffuse reflectance spectroscopy)
data.
Salicylideneanilines are characterized by a tautomer equilibrium, between an enol and a keto form of different colors, at the origin of their remarkable thermochromic, solvatochromic, and photochromic properties. The enol form is usually the most stable but appropriate choice of substituents and conditions (solvent, crystal, host compound) can displace the equilibrium toward the keto form so that there is a need for fast prediction of the keto:enol abundance ratio. Here we demonstrate the reliability of a combined theoretical-experimental method, based on comparing simulated and measured UV/visible absorption spectra, to determine this keto/enol ratio. The calculations of the excitation energies, oscillator strengths, and vibronic structures of both enol and keto forms are performed for all excited states absorbing in the relevant (visible and near-UV) wavelength range at the time-dependent density functional theory level by accounting for solvent effects using the polarizable continuum model. This approach is illustrated for two salicylideneaniline derivatives, which are present, in solution, under the form of keto-enol mixtures. The results are compared to those of chemometric analysis as well as ab initio predictions of the reaction free enthalpies.
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