Time-resolved Stokes shift measurements and steady-state absorption and fluorescence measurements of Coumarin 153 (C153) at different temperatures were used to explore the solvation dynamics of binary mixtures of alcohols and alkanes at various alcohol concentrations. These solvent mixtures show even at alcohol concentrations as low as 0.3% a strong Stokes shift of about 1200 cm -1 . Depending on alcohol concentration, this Stokes shift takes place on a time scale ranging from 300 ps up to several nanoseconds. These characteristic times are 2 orders of magnitude longer than the relaxation times typically found in alcohols, which is attributed to rotational reorientation of the solvent molecules. A monoexponential temporal behavior of the Stokes shift and a linear dependence of the time constants on the alkane viscosity are observed. These results and temperature dependent static fluorescence measurements strongly support a diffusion-controlled process of solvation in these mixtures.
Using static and time-resolved measurements, dynamics of non-radiative relaxation processes have been studied in self-assembled porphyrin triads of various geometry, containing the main biomimetic components, Zn-porphyrin di mers, free-base extra-ligands (porphyrin, chlorin or tetrahydroporphyrin), and electron acceptors A (quinone or pyromellitimide). The strong quenching of the dimer fluorescence is due to energy and sequential electron transfer (ET) processes to the extra-ligand (~0.9-1.7 ps), which are faster than a slower ET (34-135 ps) from the dimer to covalently linked A in toluene at 293 K. The extra-ligand Si -state decay (sS = 940-2670 ps) is governed by competing processes: a bridge (dimer) mediated long-range (rDA = 18-24 A) superexchange ET to an acceptor, and photoinduced hole transfer from the excited extra-ligand to the dimer followed by possible superexchange ET steps to low-lying charge transfer states of the triads. The subsequent ET steps dimer ! monomer ! A taking place in the triads, mimic the sequence of primary ET reactions in photosynthetic reaction centers in vivo.
Ž .Ž . The photoinduced electron transfer ET and the energy migration EM processes have been studied in liquid solutions and polymeric Ž . Ž . PMMA films for the triads consisting of the Zn-octaethylporphyrin chemical dimer the energy and electron donor, D and dipyridyl Ž . substituted tetrapyrrole extra-ligands porphyrins, chlorin, tetrahydroporphyrin as the acceptors, A. On the basis of the time correlated single photon counting technique and femtosecond pump-probe spectroscopy, it has been shown that D fluorescence quenching with time constant ranging from 1.7 to 10 ps is due to competing EM and ET processes from the dimer to A's. In addition, the fluorescence decay Ž . time shortening by ; 1.3-1.6 times in toluene at 293 K is observed for electron accepting extra-ligands in the triads. The acceptor fluorescence quenching is hard dependent on the mutual spatial arrangement of the triad subunits, but becomes stronger upon the solvent Ž . Ž . polarity increase addition of acetone to toluene solutions as well as the temperature lowering from 278 to 221 K . The possible reasons and mechanisms of the non-radiative deactivation of locally excited S -states in the triads are discussed taking into account a close lying 1 charge-separated state. The obtained experimental data are analyzed using the reduced density matrix formalism in the frame of Haken-Strobl-Reineker approach. This model includes EM and ET processes as well as the dephasing of coherence between the excited electronic states of the triad. q
Inkjet and screen printing technologies are well known in the graphic arts industry for the reproduction of texts, images, and graphics. During the last decades, these printing technologies have been attracting increasing interest for the deposition of functional materials, e.g., in the field of printed electronics and for biological applications. However, their usage is mainly limited to 2D applications, i.e., rather flat deposits ranging from nanometers to several tens of micrometers in thickness. For 3D applications, sophisticated additive manufacturing technologies are developed to manufacture structures with high shape complexities. Herein, the potential of standard inkjet and screen printing technology as tools for the development of functional 3D objects is demonstrated. 3D functional structures printed by inkjet and screen printing technology combining conductive and nonconductive materials to a multi-material structure are shown. A metal nanoparticle ink formulation is applied to inkjetprint conductive metal pillars with a high aspect ratio (in the range of 50) used as vertical interconnects. The interconnects are encapsulated with an inkjet-printed polymeric ink formulation and finally used as conductive tracks to light up a solidstate light-emitting diode (LED). Screen printing is applied to print primary batteries used as the power source for the LED.
Organic and printed electronics integration has the potential to revolutionise many technologies, including biomedical diagnostics. This work demonstrates the successful integration of multiple printed electronic functionalities into a single device capable of the measurement of hydrogen peroxide, and total cholesterol. The single-use device employed printed electrochemical sensors for hydrogen peroxide electroreduction integrated with printed electrochromic display and battery. The system was driven by a conventional electronic circuit designed to illustrate the complete integration of silicon ICs via pick and place, or using organic electronic circuits. The device was capable of measuring 8 µL samples of both hydrogen peroxide (0 to 5 mM, 2.72×10 -6 A.mM -1 ) and total cholesterol in serum from 0 to 9 mM (1.34×10 -8 A.mM -1 , r 2 =0.99, RSD <10%, n=3) which was output on a semi-quantitative linear bar display. The device could operate for 10 minutes via a printed battery and display the result for many hours or days. A mobile phone 'app' was also capable of reading the test result and transmitting this to a remote health care provider. Such a technology could allow improved management of conditions such as hypercholesterolemia.Printed electronics is being hailed as a technological revolution, equal in importance to the emergence of microelectronics over 50 years ago. The combined qualities of print-processable organic, inorganic and hybrid (semi)conductive materials which can be deposited onto flexible polymeric substrates using a range of additive, high throughput printing methodologies offer the prospect of low cost mass production capability and the potential for unprecedented levels of technological integration.
Herein, the inkjet printing of bioresorbable materials tuned to function as electrode, dielectric, and semiconductor layers is reported, thereby developing multilayered microelectronic devices such as capacitors and thin‐film transistors, potentially applicable to address specific medical needs. Polymers and natural materials, e.g., poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate), shellac, and β‐carotene, indigo inks are implemented using jettable formulations, that are either commercially procured or self‐formulated, designed explicitly to deposit fundamental layers for capacitors and transistors. Several parameters are evaluated and adjusted to precisely define a layer's thickness, topology, and geometry, matching with the properties of a fully biodegradable Ormocere substrate, explicitly developed for the specific biological applications. Furthermore, these parameters support in acquiring the intended electrical properties of layers, i.e., conductivity, insulation, semiconductivity, capacitance, and current versus voltage characteristics. The entire manufacturing process of devices is accomplished on the Ormocere substrate under ambient conditions and below 60 °C. The results exhibit that the electrical characteristics of the printed functional layers and devices show direct influence to the physical geometry of the printed features. A fully printed capacitor demonstrates capacitance of 1 nF cm−2, whereas transistors show p‐type and n‐type characteristics with current 0.18–5 μA and mobility 6 × 10−4–7 × 10−2 cm2 V−1 s−1.
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