Energetic Factors Research Articles

Determinants of reef fish assemblages in tropical Oceanic islands

Diversity patterns are determined by biogeographic, energetic, and anthropogenic factors, yet few studies have combined them into a large‐scale framework in order to decouple and compare their relative effects on fish faunas. Using an empirical dataset derived from 1527 underwater visual censuses (UVC) at 18 oceanic islands (five different marine provinces), we determined the relative influence of such factors on reef fish species richness, functional dispersion, density and biomass estimated from each UVC unit. Species richness presented low variation but was high at large island sites. High functional dispersion, density, and biomass were found at islands with large local species pool and distance from nearest reef. Primary productivity positively affected fish richness, density and biomass confirming that more productive areas support larger populations, and higher biomass and richness on oceanic islands. Islands densely populated by humans had lower fish species richness and biomass reflecting anthropogenic effects. Species richness, functional dispersion, and biomass were positively related to distance from the mainland. Overall, species richness and fish density were mainly influenced by biogeographical and energetic factors, whereas functional dispersion and biomass were strongly influenced by anthropogenic factors. Our results extend previous hypotheses for different assemblage metrics estimated from empirical data and confirm the negative impact of humans on fish assemblages, highlighting the need for conservation of oceanic islands.

Energetic Factors of a Frequency-Controlled Synchronous Electric Drive

As compared to asynchronous frequency-controlled electric drives, synchronous drives are characterized by lower power losses, rigid mechanical characteristics without speed feedback and by the simplest law of frequency control (when the voltage changes proportionally to the frequency). An analytical study of energy factors (power loss, efficiency, power factor) of frequencycontrolled synchronous motor with electromagnetic ignition and with excitation caused by permanent magnets has been fulfilled. The efficiency of the power converter, in this case (i. e. in the case of the frequency converter), depends on the structure of the converter (single-link or two-link), on the power semiconductor devices being used, on additional elements (i. e. chokes, capacitors, transformers, active resistance, etc.). The efficiency of a synchronous electric motor (which is a cofactor of general efficiency of a controlled synchronous electric drive) is of an interest in the scalar frequency control of the mentioned synchronous motor, since there are almost no publications on this subject. Therefore, the energy conversion efficiency of the synchronous motor, which receives energy from the frequency converter at different frequencies and converts to mechanical energy, has been considered. For the convenience of analytical research, we used the widely used concept of relative frequency as the ratio of the current value of the voltage frequency to the nominal one. It is demonstrated that the maximum efficiency is shifted in the direction of a lower load factor with a decrease in the relative frequency of the motor supply voltage. The method of calculating the energy performance of variable frequency synchronous motor that has been developed is illustrated by the graphs of efficiency and cosj for the engine of the SD3 13-34-6 type of the capacity of 500 kW and of a voltage of 6 kV and for a synchronous motor with permanent magnets of the YGT132S4 type of a capacity of 5.5 kW.

Ontogenetic Changes in the Diet and Head Morphology of an Omnivorous Tropidurid Lizard (Microlophus thoracicus)

Ontogenetic shifts from an insectivorous diet towards an herbivorous one are well known in lizards. Energetic, behavioral and morphological factors have been linked to this pattern, but the latter have received less attention, especially with respect to head morphology. It is known that robust heads are related to stronger bite forces, consequently facilitating the consumption of harder or tougher, more fibrous items such as plants. In this study the ontogeny of diet and head morphology of the omnivorous tropidurid lizard Microlophus thoracicus are described. We found a significant ontogenetic shift from a mainly insectivorous diet in juveniles to a mainly herbivorous one in adults. In parallel, we measured the length, height and width of the head of the studied individuals. We found that adult individuals showed proportionally taller and wider heads when compared to juveniles, and that these increases in proportional head dimensions were significantly correlated with the increase in plant material in the diet that we observed. Additionally, we compared the morphologies of adults and juveniles of M. thoracicus and two other Microlophus species known to be insectivorous. These comparisons showed that M. thoracicus adults have proportionally more robust heads when compared to their insectivorous congeners, which is in agreement with the hypothesized link between head morphology and diet characteristics. The results of this study suggest that the known relationship between herbivory and head morphology is maintained even in an ontogenetic context, but further study is needed to determine the effect of other selective pressures which influence these changes in morphology.

Bond Length Equalization with molecular aromaticity—A new measurement of aromaticity

A new method to measure the amount of aromaticity is presented through the process of Bond Length Equalization (BLE). Degree of Aromaticity (DOA), a two-dimensional intensive quantity including geometric and energetic factors, as a new measurement of aromaticity is proposed. The unique characteristic of DOA and the formation of DOA will be displayed. The calculation of the geometrical optimization, DOA, Nucleus Independent Chemical Shifts (NICS) and Ring Stretching Vibration Raman Spectroscopy Frequency (RSVRSF) for the aromatic ring molecules – GnHnm(G = C, Si, Ge, n = 3, 5–8, m = +1, −1, 0, +1, +2) were calculated using the method of Density Functional Theory (DFT). The correlation between radius angle and molecular energy is absolute quadratic in the process of BLE. As the increasing of the number of ring atoms, the value of DOA decreasing gradually, the aromaticity decreased gradually, which was a same conclusion as NICS and RSVRSF concluded.

Study of functioning of heat exchanger in soils with different thermal diffusivity

It was found with the help of mathematical model of the process of heat exchange between the air moving in vertical heat exchanger and the massif of soil, which connects energetic factors of the soil heat exchanger with its parameters as well as natural-climatic conditions that effective thermal energy during the term of heat exchanger functioning depends linearly on thermal diffusivity of soil both for separate heat exchanger and for two heat exchangers located at 4m between axes. Calculative experiment was conducted with application of the packet of calculative hydrodynamics ANSYS Fluent. Temperature field of the air being cooled and of the massif of soil has been detected for the soils with different thermal diffusivity. It has been found that temperature diffusivity of the soil is a determinative factor of energy potential of soil and has a dramatic effect on the effective thermal capacity especially for long-term functioning of soil heat exchanger. From the soil with temperature diffusivity 2,68 m 2 /s we can obtain approximately 3,6 times as more effective thermal energy while heat exchanger is functioning than from the soil with temperature diffusivity 0,83 m 2 /s.

Rational tailoring of C275 towards promising organic dyes: Enhancing light absorption and charge separation

Designed with electron-donating and electron-withdrawing moieties as donors and acceptors, respectively, a series of novel organic dyes for dye-sensitized solar cells (DSCs) are simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods The interacting dye/TiO2 systems are also studied to further explore the interfacial injection process of photo-excited electron. The model dye C275 is featured with donor/acceptor (D/A) molecular architecture, which is primary to achieve the easy charge-transfer excitation and suitable energy levels alignment. To date, considerable efforts are devoted to the design and synthesis of D/A type organic dyes, and the initial configurations are typically comprised of N-annulated perylene donor, porphyrin linker, and carboxylic acid acceptor. Our results show that, the electronic levels and optical absorption properties can be tuned gradually by introducing auxiliary donor units or electron-deficient spacer in acceptor groups. Moreover, the designed dyes also exhibit good performance in terms of photoinduced charge transfer, electron injection, and dye regeneration, etc. Through structural modification of donor moieties, the new tailored dyes provide appropriate energy levels, strong light-harvesting and easy charge separation. Meanwhile, the distinct red-shift of optical absorption and large amount of transferred charges are also obtained by structural tailoring of acceptor groups, whereas the large values of injection time may be harmful for the interfacial photoelectron injection. Therefore, comparing with donor modification, it should be more carefully to choose appropriate acceptor group with the balance of various energetic and kinetic factors for the rational design of high-efficient organic dyes.

Evaluation of adhesion strength of protective coatings with Al powder by adhesion work of initial suspension towards metal surface

The influence of energetic factors upon surface properties of suspensions on the basis of Na-CMC with aluminum powder, used to produce anticorrosion coatings, is revealed. It is shown that relative adhesion work, got by measuring the extent of suspensions surface strain and the angles of wetting the steel surface with suspensions, correlate with adhesion strength of coatings containing aluminum powder.

New insights into the adsorption of crystal violet dye on functionalized multi-walled carbon nanotubes: Experiments, statistical physics and COSMO–RS models application

Two multi–walled Carbon Nanotubes (MWCNTs) adsorbents, chemically functionalized by either OH (MWCNTs–OH) or COOH (MWCNTs–COOH), were adopted to study the adsorption of Crystal Violet (CV) dye from aqueous solutions. A series of CV dye adsorption isotherms was recorded at different temperatures ranging from 298 to 328K. Experimental results demonstrated that the adsorbents have similar performances, even if the sample functionalized by COOH (MWCNTs–COOH) shows slightly higher adsorption capacity. In light of the statistical physics, a model was developed and applied to explain the adsorption mechanism and to describe the role of adsorbent functionalization through model parameters. Mathematically, this model was defined by three parameters reflecting the main physicochemical aspects of the adsorption process such as, the number of dye molecules linked per site of adsorbent (nd), an energetic coefficient (w) and the number of occupied receptor site (Km). A very good accordance between the experimental results and the proposed model was observed. The difference in nd values for the two adsorbents can be attributed to the intensity of interactions between dye and the specific functional groups of the adsorbents. An energetic characterization of the systems was carried out by calculating three specific interaction energies of CV dye with the functionalized carbon nanotubes (the electrostatic misfit energy; EMF, the hydrogen–bonding energy; EHB and the Van der Waals energy; EvdW) by application of conductor–like screening model for real solvents (COSMO–RS). The COSMO–RS model clearly indicated that the hydrogen–bonding interaction is the dominant energetic factor in CV dye adsorption. Finally, a good complementarity was retrieved between the results of statistical physics and COSMO–RS models.

Unraveling protein folding mechanism by analyzing the hierarchy of models with increasing level of detail.

Taking protein G with 56 residues for a case study, we investigate the mechanism of protein folding. In addition to its native structure possessing α-helix and β-sheet contents of 27% and 39%, respectively, we construct a number of misfolded decoys with a wide variety of α-helix and β-sheet contents. We then consider a hierarchy of 8 different models with increasing level of detail in terms of the number of entropic and energetic physical factors incorporated. The polyatomic structure is always taken into account, but the side chains are removed in half of the models. The solvent is formed by either neutral hard spheres or water molecules. Protein intramolecular hydrogen bonds (H-bonds) and protein-solvent H-bonds (the latter is present only in water) are accounted for or not, depending on the model considered. We then apply a physics-based free-energy function (FEF) corresponding to each model and investigate which structures are most stabilized. This special approach taken on a step-by-step basis enables us to clarify the role of each physical factor in contributing to the structural stability and separately elucidate its effect. Depending on the model employed, significantly different structures such as very compact configurations with no secondary structures and configurations of associated α-helices are optimally stabilized. The native structure can be identified as that with lowest FEF only when the most detailed model is employed. This result is significant for at least the two reasons: The most detailed model considered here is able to capture the fundamental aspects of protein folding notwithstanding its simplicity; and it is shown that the native structure is stabilized by a complex interplay of minimal multiple factors that must be all included in the description. In the absence of even a single of these factors, the protein is likely to be driven towards a different, more stable state.

Energy, exergy and exergoeconomic analysis of a cogeneration system for power and hydrogen production purpose based on TRR method and using low grade geothermal source

In this research, a modified organic Rankine cycle (ORC) with a regeneration is used to generate power along with hydrogen. For hydrogen production purpose, a proton exchange membrane (PEM) electrolyzer is used, taking its required heating and power from the ORC. The proposed system is driven by geothermal energy. A comprehensive thermodynamic modelling (energy and exergy analysis) and exergoeconomic analysis are carried out for the proposed cycle, using various working fluids (i.e., R245fa, R114, R600 and R236fa) in order to compare their influences on performance of the integrated system. For this purpose, Engineering Equation Solver (EES) software is used in all conducted simulations which is proven to be the most professional and commercial software in thermodynamics. In addition, a comprehensive parametric study is carried out for investigating the effects of main thermodynamic flow parameters on the energetic, exergetic and economic factors of the integrated system. The results showed that R245fa had the highest energy and exergy efficiencies of 3.511% and 67.58%, respectively. Furthermore, it is the most cost-efficient working fluid with 11.54 $/GJ and 4.921 $/GJ average costs per exergy unit for output power and hydrogen production, respectively. Regarding their operational features and cost effectiveness, the working fluids R114, R600 and R236fa ranked successively after R245fa. Also R245fa had the lowest cost associated with the exergy destruction. Moreover, the results of parametric study showed that increasing of the evaporator pressure results in increasing of the output power, hydrogen production, and energy and exergy efficiencies, whereas the costs of output power and hydrogen production decreased. In addition, increasing the geothermal fluid temperature increases the output power, hydrogen production, and also their costs, while decreases the energy and exergy efficiencies. It is also found that an increase in the turbine extracted steam pressure (mean pressure) will increase the exergy efficiency, costs of produced power and hydrogen, whereas decrease the output power, hydrogen production, and energy efficiency.

Amino-acid composition after loop deletion drives domain swapping.

Rational engineering of a protein to enable domain swapping requires an understanding of the sequence, structural and energetic factors that favor the domain-swapped oligomer over the monomer. While it is known that the deletion of loops between β-strands can promote domain swapping, the spliced sequence at the position of the loop deletion is thought to have a minimal role to play in such domain swapping. Here, two loop-deletion mutants of the non-domain-swapping protein monellin, frame-shifted by a single residue, were designed. Although the spliced sequence in the two mutants differed by only one residue at the site of the deletion, only one of them (YEIKG) promoted domain swapping. The mutant containing the spliced sequence YENKG was entirely monomeric. This new understanding that the domain swapping propensity after loop deletion may depend critically on the chemical composition of the shortened loop will facilitate the rational design of domain swapping.

Predicting Protein\u2013protein Association Rates using Coarse-grained Simulation and Machine Learning

Protein–protein interactions dominate all major biological processes in living cells. We have developed a new Monte Carlo-based simulation algorithm to study the kinetic process of protein association. We tested our method on a previously used large benchmark set of 49 protein complexes. The predicted rate was overestimated in the benchmark test compared to the experimental results for a group of protein complexes. We hypothesized that this resulted from molecular flexibility at the interface regions of the interacting proteins. After applying a machine learning algorithm with input variables that accounted for both the conformational flexibility and the energetic factor of binding, we successfully identified most of the protein complexes with overestimated association rates and improved our final prediction by using a cross-validation test. This method was then applied to a new independent test set and resulted in a similar prediction accuracy to that obtained using the training set. It has been thought that diffusion-limited protein association is dominated by long-range interactions. Our results provide strong evidence that the conformational flexibility also plays an important role in regulating protein association. Our studies provide new insights into the mechanism of protein association and offer a computationally efficient tool for predicting its rate.

Mechanistic Insights into Oxygen Reduction and Evolution Reactions in Non-Aqueous Metal-Air Batteries

Non-aqueous metal-air batteries have generated strong research interest because they possess much greater theoretical gravimetric energy storage density than today’s rechargeable battery technologies.1-4 This has re-kindled research into the fundamentals of oxygen reduction and evolution reactions (ORR and OER) in non-aqueous electrolytes because they are the central electrochemical processes at metal-air cathodes. Understanding the reaction mechanisms is critical to improving cycling efficiency and making rechargeable metal-air batteries a reality. We will present the results of a series of electrochemical studies of the ORR/OER on a gold electrode in strictly dry, non-aqueous dimethyl sulfoxide (DMSO) electrolytes containing different cations, including H+, Li+, and Na+,5,6 using in situ spectroelectrochemistry and first-principles calculations and theoretical modeling. Significantly the ORRs share a common characteristic, namely the superoxide anion (O2 -), the one-electron reduction product of O2, is the first O2 reduction product to form. It has several important consequences: O2 - thus controls the onset potential of the ORR, and its solubility in the electrolyte makes solution-phase reactions involving O2 - an integral part of the electrode processes at low overpotentials, including the formation of superoxides and peroxides (via disproportionation of the superoxides) away from the cathode. On the other hand, there is a clear contrast between Li+ and Na+: Whereas the main reduction product is Li2O2 for Li+, which requires a high overpotential to be oxidized, the reduction product for Na+ is predominantly NaO2, whose high solubility in DMSO alleviates solid buildup on the electrode and also facilitates the oxidation of NaO2. Consequently the Na+ O2 cathode is much more reversible than its Li+ counterpart. The energetic factors controlling the formation of O2 -, solution vs. surface reaction pathways, and the lack of Na2O2 formation will be discussed. Overall, our studies reveal that the ORR/OER mechanisms depend intimately on the cation, potential, and electrolyte, and contribute new mechanistic understanding to the eventual realization of reversible metal-air battery technologies. 1. P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nat. Mater. 2012, 11, 19. 2. J. Lu, L. Li, J.-B. Park, Y.-K. Sun, F. Wu, K. Amine, Chem. Rev. 2014, 114, 5611. 3. A.C. Luntz, B.D. McCloskey, Chem. Rev. 2014 , 114, 11721. 4. R. Black, B. Adams, L.F. Nazar, Adv. Energy Mater. 2012, 2, 801 5. Z. Peng, Y. Chen, P.G. Bruce, Y. Xu, Angew. Chem. Int. Ed. 2015, 54, 8165. 6. Y. Zhang, X. Zhang, J. Wang, W.C. McKee, Y. Xu, Z. Peng, J. Phys. Chem. C 2016, 120, 3690.

Free Energy Landscapes of Metabotropic Glutamate Receptor Ligand-Binding Domains

Metabotropic glutamate receptors (mGluRs) are dimeric class C GPCRs that mediate cellular responses to the neurotransmitter glutamate in the central nervous system. Crystal structures and single-molecule FRET results suggest that closure of the ligand-binding domains (LBDs) as well as reorientation of the dimer interface are necessary conformational transitions for receptor activation. The energetic factors that drive these coupled processes, however, are poorly understood. Here, we report free energy landscapes, or potentials of mean force (PMFs), for monomer and dimer mGluR3 LBDs in apo and glutamate-bound states. PMFs of LBD monomers suggest the LBDs are bistable: the closed and open-cleft conformations are accessible for both glutamate-bound and apo LBDs, but with the apo closed-cleft conformation destabilized relative to the glutamate-bound LBD.

A Psychoacoustic Investigation on the Effect of External Shading Devices on Building Facades

Due to energetic and natural lighting factors, building facades often present external shading devices, but the acoustic properties of such devices have not yet been well studied. This study was carried out using a full-scale model of a portion of a shading device, in a semi-anechoic chamber, using traditional and sound absorbing louvres. The psychoacoustic effects produced by the shading system were evaluated through comparisons between averaged values of loudness, roughness and sharpness levels, as well as sound pressure levels as reference. Results highlighted that the sound absorbing shading device offers good attenuation in terms of loudness, roughness and sound pressure level, with a small reduction in sharpness. The traditional shading system studied does not efficiently reduce the analysed parameters, or even worsens the situation. Several analyses of variance were carried out, one for each situation studied. The sound source position and the louvres’ tilt angle both produce statistically significant effects on almost all of the variations of the parameters studied. The analyses of the partial eta squared factors highlighted that source position and louvre tilt angle affect the variations of the parameters studied to a different degree in respect of the two types of louvres.

Molecular dynamics simulation of the sliding of distamycin anticancer drug along DNA: interactions and sequence selectivity

Molecular dynamics simulations and umbrella sampling have been used to investigate the sliding of distamycin anticancer drug along the DNA minor groove. The potential energy surface calculated for the sliding of drug shows three minima. The global minimum corresponds to the binding of drug to the AT-rich region, which is the origin of sequence selectivity of distamycin. This selectivity originates from both structural factors and energy contributions. The analysis of energy contributions of binding was performed by the MM–PBSA method. The analysis of hydrogen bonds and van der Waals, electrostatic, and solvation interactions show that structural or steric factors are more important in the selectivity of distamycin than energetic factors. The results of this study can be applied in the design of new derivatives of distamycin anticancer drug with improved properties.

Dynamic generation of supercritical water fluid in a strong electrical discharge in a liquid

A new impetus for the development of electro physics is associated with using different types of electrical discharges in biology and medicine. These applications are based on their energetic and non-toxic factors affecting the medium on a cellular level. For the study of such processes, a mathematical model of a high-current low-temperature Z-discharge in a liquid, forming by the electrical explosion of a thin-walled metal shell, connected to a pulsed high-voltage generator, has been developed. High efficiency energy conversion, introduced into the plasma discharge to the energy of fluid motion, provides various bio chemical applications of such physical processes. The investigation is conducted through numerical solution of one-dimensional single-temperature non-stationary equations of radiation magneto hydrodynamics, one way describing the evolution of hydrodynamic, thermal and electrical characteristics of the medium throughout the area under consideration. The electrical approximation based on the assumption that the electric field in the discharge has a uniform distribution. The results are presented as a function of the electric current and the plasma channel length of time, as well as the temperature and pressure distributions at different time points along the radius of the cylindrical region in which the explosion occurs.

Hierarchical Analysis of Self-Assembled PEGylated Hexaphenylalanine Photoluminescent Nanostructures.

Despite the growing literature about diphenylalanine-based peptide materials, it still remains a challenge to delineate the theoretical insight into peptide nanostructure formation and the structural features that could permit materials with enhanced properties to be engineered. Herein, we report the synthesis of a novel peptide building block composed of six phenylalanine residues and eight PEG units, PEG8 -F6. This aromatic peptide self-assembles in water in stable and well-ordered nanostructures with optoelectronic properties. A variety of techniques, such as fluorescence, FTIR, CD, DLS, SEM, SAXS, and WAXS allowed us to correlate the photoluminescence properties of the self-assembled nanostructures with the structural organization of the peptide building block at the micro- and nanoscale. Finally, a model of hexaphenylalanine in aqueous solution by molecular dynamics simulations is presented to suggest structural and energetic factors controlling the formation of nanostructures.

Biomechanics, energetics and coordination during extreme swimming intensity: effect of performance level

ABSTRACTThe present study aimed to examine how high- and low-speed swimmers organise biomechanical, energetic and coordinative factors throughout extreme intensity swim. Sixteen swimmers (eight high- and eight low-speed) performed, in free condition, 100-m front crawl at maximal intensity and 25, 50 and 75-m bouts (at same pace as the previous 100-m), and 100-m maximal front crawl on the measuring active drag system (MAD-system). A 3D dual-media optoelectronic system was used to assess speed, stroke frequency, stroke length, propelling efficiency and index of coordination (IdC), with power assessed by MAD-system and energy cost by quantifying oxygen consumption plus blood lactate. Both groups presented a similar profile in speed, power output, stroke frequency, stroke length, propelling efficiency and energy cost along the effort, while a distinct coordination profile was observed (F(3, 42) = 3.59, P = 0.04). Speed, power, stroke frequency and propelling efficiency (not significant, only a tendency) were higher in high-speed swimmers, while stroke length and energy cost were similar between groups. Performing at extreme intensity led better level swimmers to achieve superior speed due to higher power and propelling efficiency, with consequent ability to swim at higher stroke frequencies. This imposes specific constraints, resulting in a distinct IdC magnitude and profile between groups.

Revising Intramolecular Photoinduced Electron Transfer (PET) from First-Principles

Photoinduced electron transfer (PET) plays relevant roles in many areas of chemistry, including charge separation processes in photovoltaics, natural and artificial photosynthesis, and photoluminescence sensors and switches. As in many other photochemical scenarios, the structural and energetic factors play relevant roles in determining the rates and efficiencies of PET and its competitive photodeactivation processes. Particularly, in the field of fluorescent sensors and switches, intramolecular PET is believed (in many cases without compelling experimental proof) to be responsible of the quench of fluorescence. There is an increasing experimental interest in fluorophore's molecular design and on achieving optimal excitation/emission spectra, excitation coefficients, and fluorescence quantum yields (importantly for bioimaging purposes), but less efforts are devoted to fundamental mechanistic studies. In this Account, I revise the origins of the fluorescence quenching in some of these systems with state-of-the-art quantum chemical tools. These studies go beyond the common strategy of analyzing frontier orbital energy diagrams and performing PET thermodynamics calculations. Instead, the potential energy surfaces (PESs) of the lowest-lying excited states are explored with time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations and the radiative and nonradiative decay rates from the involved excited states are computed from first-principles using a thermal vibration correlation function formalism. With such a strategy, this work reveals the real origins of the fluorescence quenching, herein entitled as dark-state quenching. Dark states (those that do not absorb or emit light) are often elusive to experiments and thus, computational investigations can provide novel insights into the actual photodeactivation mechanisms. The success of the dark-state quenching mechanism is demonstrated for a wide variety of fluorescent probes, including proton, cation and anion targets. Furthermore, this mechanism provides a general picture of the fluorescence quenching which englobes intramolecular charge-transfer (ICT), ratiometric quenching, and those radiationless mechanisms believed to be originated by PET. Finally, this Account provides for the first time a computational protocol to quantitatively estimate this phenomenon and provides the ingredients for the optimal design of fluorescent probes from first principles.