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1.
Nat Commun ; 11(1): 879, 2020 02 13.
Artigo em Inglês | MEDLINE | ID: mdl-32054851

RESUMO

Bio-hybrid light-emitting diodes (Bio-HLEDs) based on color down-converting filters with fluorescent proteins (FPs) have achieved moderate efficiencies (50 lm/W) and stabilities (300 h) due to both thermal- and photo-degradation. Here, we present a significant enhancement in efficiency (~130 lm/W) and stability (>150 days) using a zero-thermal-quenching bio-phosphor design. This is achieved shielding the FP surface with a hydrophilic polymer allowing their homogenous integration into the network of a light-guiding and hydrophobic host polymer. We rationalize how the control of the mechanical and optical features of this bio-phosphor is paramount towards highly stable and efficient Bio-HLEDs, regardless of the operation conditions. This is validated by the relationships between the stiffness of the FP-polymer phosphor and the maximum temperature reached under device operation as well as the transmittance of the filters and device efficiency.


Assuntos
Proteínas de Fluorescência Verde/genética , Luz , Organofosfatos/química , Polimetil Metacrilato/química , Semicondutores , Bioengenharia/métodos , Dicroísmo Circular , Cor , Desenho de Equipamento , Proteínas de Fluorescência Verde/química , Proteínas de Fluorescência Verde/isolamento & purificação , Mutação , Estrutura Secundária de Proteína/genética , Estrutura Terciária de Proteína/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Temperatura
2.
J Chem Phys ; 151(4): 044307, 2019 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-31370515

RESUMO

We analyze the dynamics of intramolecular singlet fission in a series of pentacene-based dimers consisting of two pentacene-like chromophores covalently bonded to a phenylene linker in ortho, meta, and para positions. The study uses a quantum dynamical approach that employs a model vibronic Hamiltonian whose parameters are obtained using multireference perturbation theory methods. The results highlight the different role of the direct and mediated mechanism in these systems, showing that the population of the multiexcitonic state, corresponding to the first step of the intramolecular singlet fission process, occurs mainly through a superexchange-like mechanism involving doubly excited or charge transfer states that participate in the process in a virtual way. In addition, the systems investigated provide insight into the roles that built-in geometrical constraints and the electronic structure of the spacer play in the intramolecular singlet fission process.

3.
J Phys Chem Lett ; 9(20): 5979-5986, 2018 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-30257561

RESUMO

We investigate the dynamics of intramolecular singlet fission in a dimer consisting of two pentacene-based chromophores covalently bonded to a phenylene spacer using an approach that combines high-level ab initio multireference perturbation theory methods and quantum dynamical simulations. The results show that the population of the multiexcitonic state, corresponding to the first step of singlet fission, is facilitated by the existence of higher-lying doubly excited and charge transfer states that participate in a superexchange-like way. The important role played by high-frequency ring-breathing molecular vibrations in the process is also discussed.

4.
ACS Omega ; 3(11): 15829-15836, 2018 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-31458231

RESUMO

This work presents a pioneering multidisciplinary approach toward enhancing biohybrid light-emitting diodes (BioHLEDs), merging synthetic biology tools, polymer chemistry, and device engineering to design a thin color down-converting coating with a single white-emitting fluorescent protein (WFP). In particular, the WFP consists of fused red-, green-, and blue-emitting FPs following the so-called protein superglue approach. This WFP shows an efficient and stable white emission originated from a Förster resonance energy transfer between FP moieties. The emission chromaticity is, in addition, easily controlled by the rigidity of the polymer matrix of the coating, reaching photoluminescence quantum yields of 26% that stand out among intrinsic white-emitting materials. The WFP single-component color down-converting packaging was applied to fabricate BioHLEDs featuring efficient neutral white emission that is stable over 400 h. This represents the most stable BioHLED reported to date. Thus, this work is a landmark for the use of synthetic biology tools to design tailored luminescent biomaterials for lighting applications.

5.
Angew Chem Int Ed Engl ; 57(29): 8826-8836, 2018 07 16.
Artigo em Inglês | MEDLINE | ID: mdl-29288605

RESUMO

Over the last decades, fluorescent proteins (FPs) have been extensively employed for imaging and tracing in cell biology and medicine. However, their application for lighting devices like light-emitting diodes (LEDs) and lasers has recently started. The interest of FPs is the result of their good photoluminescence features (high emission efficiency with a narrow spectrum and a high photon-flux saturation), good photostability, sustainable production by bacteria, and eco-friendly recycling. Their low stability at high temperatures as well as the need for an aqueous environment have, however, strongly limited their use in optoelectronics. This has recently been circumvented with new coating systems that are paving the way for the entrance of FPs into the LED field. In this Minireview, we summarize the first steps taken by a few groups towards the development of bio-hybrid white LEDs (Bio-HWLEDs) with a focus on using FPs as color down-converters, highlighting the state of the art and challenges associated with this emerging field.


Assuntos
Substâncias Luminescentes/química , Proteínas Luminescentes/química , Dispositivos Ópticos , Animais , Desenho de Equipamento , Fluorescência , Lasers , Luz , Iluminação/instrumentação , Modelos Moleculares , Semicondutores
6.
Nat Commun ; 8: 15171, 2017 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-28516916

RESUMO

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

7.
Nanoscale ; 9(21): 7217-7226, 2017 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-28513712

RESUMO

We investigate charge transport in C60-based single-molecule junctions with graphene electrodes employing a combination of density functional theory (DFT) electronic structure calculations and Landauer transport theory. In particular, the dependence of the transport properties on the conformation of the molecular bridge and the type of termination of the graphene electrodes is investigated. Furthermore, electron pathways through the junctions are analyzed using the theory of local currents. The results reveal, in agreement with previous experiments, a pronounced dependence of the transport properties on the bias polarity, which is rationalized in terms of the electronic structure of the molecule. It is also shown that the edge states of zigzag-terminated graphene induce additional transport channels, which dominate transport at low voltages. The importance of the edge states for transport depends profoundly on the interface geometry of the junctions.

8.
Dalton Trans ; 45(34): 13284-8, 2016 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-27363542

RESUMO

The syntheses, photophysical/electrochemical characterizations of different metallated porphyrins -i.e., Zn(2+), Pt(2+), Pd(2+), and Sn(4+) porphyrins - as well as their first application in light-emitting electrochemical cells are provided. A direct comparison demonstrates that depending on the metallation either efficient (Pt-por) or stable (Zn-por) devices are achieved, demonstrating that the choice of the metal core is a key aspect for future developments.

9.
Nanoscale ; 8(19): 10113-23, 2016 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-27122097

RESUMO

We show unambiguous and compelling evidence by means of pump-probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 10(12) s(-1), respectively, in room temperature solutions.

10.
J Chem Theory Comput ; 11(1): 147-56, 2015 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-26574213

RESUMO

The lowest-lying electronic excited states of pentacene and its oligomers are investigated using accurate multireference wave function methods (CASPT2/CASSCF) and the many-body Greens's function approach (GW/BSE). The results obtained for dimers and trimers of different geometry reveal a complex electronic structure, which includes locally excited, charge transfer, and multiexciton states. For singlets of single-excitation character, both approaches yield excitation energies that are in good overall quantitative agreement. While the multiexciton states are located relatively high in energy in all systems investigated, charge transfer states exist in close proximity to the lowest-lying absorbing states. The implications of the results for the mechanisms of singlet fission in pentacene are discussed.

11.
Adv Mater ; 27(37): 5493-8, 2015 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-26271025

RESUMO

The first bioinspired hybrid white-light-emitting diodes (bio-HLEDs) featuring protein cascade coatings are presented. For easy fabrication a new strategy to stabilize proteins in rubber-like material was developed. The synergy between the excellent features of fluorescent proteins and the easily processed rubber produces bio-HLEDs with less than 10% loss in luminous efficiency over 100 hours.


Assuntos
Materiais Biomiméticos , Iluminação/instrumentação , Proteínas Luminescentes , Materiais Biomiméticos/química , Escherichia coli , Géis/química , Luz , Iluminação/métodos , Proteínas Luminescentes/química , Proteínas Luminescentes/isolamento & purificação , Proteínas Luminescentes/metabolismo , Polietilenoglicóis/química , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Espectrofotometria , Vácuo
12.
Proc Natl Acad Sci U S A ; 112(17): 5325-30, 2015 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-25858954

RESUMO

Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley-Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule.

13.
Nano Lett ; 15(5): 3512-8, 2015 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-25923590

RESUMO

On the way to ultraflat single-molecule junctions with transparent electrodes, we present a fabrication scheme based on epitaxial graphene nanoelectrodes. As a suitable molecule, we identified a molecular wire with fullerene anchor groups. With these two components, stable electrical characteristics could be recorded. Electrical measurements show that single-molecule junctions with graphene and with gold electrodes display a striking agreement. This motivated a hypothesis that the differential conductance spectra are rather insensitive to the electrode material. It is further corroborated by the assignment of asymmetries and spectral features to internal molecular degrees of freedom. The demonstrated open-access graphene electrodes and the electrode-insensitive molecules provide a model system that will allow for a thorough investigation of an individual single-molecule contact with additional probes.

14.
Phys Chem Chem Phys ; 16(46): 25642-8, 2014 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-25351413

RESUMO

We have investigated the non-adiabatic relaxation processes occurring in the singlet manifold of 4-(dimethylamino)benzethyne (DMABE), a molecule isoelectronic with 4-(dimethylamino)benzonitrile (DMABN) but lacking its characteristic dual fluorescence, using multireference perturbation theory methods. The results obtained point out to the existence of a two-fold decay mechanism in which the population of the initially accessed La state bifurcates towards a locally excited (LE) and a πσ* state. Further relaxation to an emitting intramolecular charge transfer (ICT) state is impeded due to the presence of pronounced energy barriers along their associated potential energy surfaces. These results provide further evidence of the role of πσ* states in the non-adiabatic relaxation processes of dialkylaminobenzonitriles.

15.
J Mol Model ; 20(4): 2163, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-24633770

RESUMO

A novel mechanism for switching a molecular junction based on a proton transfer reaction triggered by an external electrostatic field is proposed. As a specific example to demonstrate the feasibility of the mechanism, the tautomers [2,5-(4-hydroxypyridine)] and {2,5-[4(1H)-pyridone]} are considered. Employing a combination of first-principles electronic structure calculations and Landauer transport theory, we show that both tautomers exhibit very different conductance properties and realize the "on" and "off" states of a molecular switch. Moreover, we provide a proof of principle that both forms can be reversibly converted into each other using an external electrostatic field.


Assuntos
Elétrons , Modelos Teóricos , Prótons
16.
Phys Chem Chem Phys ; 15(39): 16704-12, 2013 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-23986088

RESUMO

The spectroscopic properties in water solution of the different prototropic forms of the strongly fluorescent hemiacetal 4,9-dihydroxy-1,2-dihydro-4,11a-methanooxocino[4,5-b]benzofuran-5(4H)-one (1a, monardine), the aza analogue 4,9-dihydroxy-3,4-dihydro-1H-4,11a-methanobenzofuro[2,3-d]azocin-5(2H)-one (2a, azamonardine) and the respective 2-carboxyl derivatives (1b, 2b) have been studied by experimental and quantum-chemical methods. Monardine and carboxymonardine are the major products of new fluorogenic, room-temperature reactions of hydroxytyrosol or salvianic acid in aqueous solution, respectively, and present unique photophysical properties. Near neutral pH (pKa = 7.2) monardine switches from a weakly emitting, UV-absorbing (382 nm) neutral species to a VIS-absorbing (426 nm), blue emitting (464 nm) anion form, with a fluorescence quantum yield ϕF = 1 and single-exponential decay τF = 2.74 ns. This binary-like spectroscopic change from the neutral to the anionic form was interpreted based on time-dependent density functional theory (TDDFT) calculations as due to (i) the reversal of (n,π*) and (π,π*) lowest-lying singlet excited states, and (ii) a change in the triplet-state distribution accompanying monardine ionization which may abolish de-excitation via intersystem crossing. A similar fluorogenic reaction takes place with catecholamines such as dopamine and DOPA, to yield fluorescent azocines 2a and 2b which, depending on pH, may be present as cationic, neutral or anionic species. TDDFT computations of these forms were also carried out to assign the corresponding excitation transitions and emission properties. Besides the analytical interest of the fluorogenic reactions, the photochemical stability and biocompatibility of the bright-dark pH-controlled molecular switches 1a and 1b may facilitate novel labels and probes to be developed for superresolution fluorescence microscopy.


Assuntos
Azocinas/síntese química , Oxocinas/síntese química , Teoria Quântica , Água/química , Azocinas/química , Materiais Biocompatíveis/química , Fluorescência , Estrutura Molecular , Oxocinas/química
17.
J Phys Chem Lett ; 4(5): 809-14, 2013 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-26281937

RESUMO

We investigate charge transport in pentacene-graphene nanojunctions employing density functional theory (DFT) electronic structure calculations and the Landauer transport formalism. The results show that the unique electronic properties of graphene strongly influence the transport in the nanojunctions. In particular, edge states in graphene electrodes with zigzag termination result in additional transport channels close to the Fermi energy, which deeply affects the conductance at small bias voltages. Investigating different linker groups as well as chemical substitution, we demonstrate how the transport properties are furthermore influenced by the molecule-lead coupling and the energy level lineup.

18.
J Chem Theory Comput ; 9(1): 481-96, 2013 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-26589049

RESUMO

Proton/hydrogen-transfer processes have been broadly studied in the past 50 years to explain the photostability and the spontaneous tautomerism in the DNA base pairs. In the present study, the CASSCF/CASPT2 methodology is used to map the two-dimensional potential energy surfaces along the stretched NH reaction coordinates of the guanine-cytosine (GC) base pair. Concerted and stepwise pathways are explored initially in vacuo, and three mechanisms are studied: the stepwise double proton transfer, the stepwise double hydrogen transfer, and the concerted double proton transfer. The results are consistent with previous findings related to the photostability of the GC base pair, and a new contribution to tautomerism is provided. The C-based imino-oxo and imino-enol GC tautomers, which can be generated during the UV irradiation of the Watson-Crick base pair, have analogous radiationless energy-decay channels to those of the canonical base pair. In addition, the C-based imino-enol GC tautomer is thermally less stable. A study of the GC base pair is carried out subsequently taking into account the DNA surroundings in the biological environment. The most important stationary points are computed using the quantum mechanics/molecular mechanics (QM/MM) approach, suggesting a similar scenario for the proton/hydrogen-transfer phenomena in vacuo and in DNA. Finally, the static model is complemented by ab initio dynamic simulations, which show that vibrations at the hydrogen bonds can indeed originate hydrogen-transfer processes in the GC base pair. The relevance of the present findings for the rationalization of the preservation of the genetic code and mutagenesis is discussed.

19.
Phys Rev Lett ; 109(5): 056801, 2012 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-23006194

RESUMO

We analyze quantum interference and decoherence effects in single-molecule junctions both experimentally and theoretically by means of the mechanically controlled break junction technique and density-functional theory. We consider the case where interference is provided by overlapping quasidegenerate states. Decoherence mechanisms arising from electronic-vibrational coupling strongly affect the electrical current flowing through a single-molecule contact and can be controlled by temperature variation. Our findings underline the universal relevance of vibrations for understanding charge transport through molecular junctions.

20.
J Phys Chem Lett ; 3(3): 436-40, 2012 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-26285863

RESUMO

Femtosecond charge-transfer dynamics in self-assembled monolayers of cyano-terminated ethane-thiolate on gold substrates was investigated with the core hole clock method. By exploiting symmetry selection rules rather than energetic selection, electrons from the nitrogen K-shell are state-selectively excited into the two symmetry-split π* orbitals of the cyano end group with X-ray photons of well-defined polarization. The charge-transfer times from these temporarily occupied orbitals to the metal substrate differ significantly. Theoretical calculations show that these two π* orbitals extend differently onto the alkane backbone and the anchoring sulfur atom, thus causing the observed dependence of the electron-transfer dynamics on the symmetry of the orbital.

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