Excited Donor Research Articles

Stokes and anti-Stokes emission characteristics of Er3+/Yb3+ co-doped zinc tellurite glasses under 377 and 1550 nm excitations for solar energy conversion application

One of the best rare earth combinations for down- and up-converting the solar photons is Er3+/Yb3+. Therefore, at present, by using the traditional melt quench technique, zinc tellurite glasses doped with Er3+ and Er3+/Yb3+ were characterised. Several methods of down-conversion that result in the emission of 1000 nm from the acceptor (Yb3+) under excitation of donor (Er3+) were studied. On the other hand, the impact of acceptor (Yb3+) concentration and excitation pump power on the excited state absorption and its influence on the up-conversion emission (1000 nm) properties were investigated in detail under 1535 nm excitation. The studies on emission and decay results are discovered to be very significant. Suggesting that these glasses when used as conversion layers, can append the conversion efficiency of Si-based solar cells.

A General Photoactive H‐Bonding EDA Complex Model Drives the Selective Hydrothiolation and Hydroxysulfenylation of Carbonyl Activated Alkenes

AbstractExcitation of photoactive electron donor−acceptor (EDA) complexes to generate radical is a promising approach in radical chemistry. In this study, we introduce a new model of H‐bonding EDA complexes for the selective hydrothiolation and hydroxysulfenylation of carbonyl‐activated alkenes with diverse thiols under visible light conditions. The reliability of this H‐bonding EDA complex model has been confirmed by meticulous experimental and theoretical calculations. Mechanistic investigations have revealed the significant influence of the solvent in determining whether the excitation of photoactive H‐bonding EDA complex leads to charge transfer (CT) or energy‐charge transfer (En‐CT), thereby controlling Markovnikov and anti‐Markovnikov selectivity. Notably, the Quantum Theory of Atoms in Molecules (QTAIM) analysis clearly shows that the excited state of the C=O−H−S EDA complex involves closed‐shell partially covalent interactions.

Femtosecond Dynamics of the Excited Primary Electron Donor in Reaction Centers of the Purple Bacterium Rhodobacter sphaeroides.

Femtosecond transient absorption spectroscopy was used to study the dynamics of the excited primary electron donor in the reaction centers of the purple bacterium Rhodobacter sphaeroides. Using global analysis and the interval method, we found a correlation between the vibrational coherence damping of the excited primary electron donor and the lifetime of the charge-separated stateP+BA-, indicating the reversibility of electron transfer to the primary electron acceptor, theBA molecule. In the reaction centers, the signs of superposition of two electronic states of P were found for a delay time of less than 200fs. It is suggested that the admixture value of the charge transfer statePA+PB- with the excited primary electron donorP* is about 24%. The results obtained are discussed in terms of the two-step electron transfer mechanism.

Unexplored Exciplex Formation by Dual Excitation of Donor and Acceptor Layers Optically and Electrically

AbstractElectron donor and acceptor interactions are the fundamentals for the emergence of optoelectronic functions in most organic devices. In particular, exciplexes, which hold the possibility to utilize dark triplets, are widely investigated in organic light‐emitting diodes. However, the relatively low radiative decay rate with a low photoluminescence quantum yield poses further advanced challenges. Traditionally, it is well recognized that exciplexes are formed through a charge transfer process, i.e., direct electron transfer, by photoexciting either a donor or an acceptor component. In this study, the focus is on a long‐range exciplex system where tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA) and 2,4,6‐tris[3‐(diphenylphosphinyl)phenyl]−1,3,5‐triazine (PO‐T2T) serve as the donor and acceptor, respectively. Moreover, 1,2‐bis(triphenylsilyl) benzene (UGH2) and bis[2‐(diphenylphosphino)phenyl]ether oxide (DPEPO), having a wide energy gap and a high triplet energy level, are employed as the double insulating layer to suppressing direct electron transfer between the donor and acceptor. The indirect through‐space exciplex formation is demonstrated by the simultaneous excitation of both donor and acceptor layers optically and electrically, providing a new route for exciplex formation.

Excited Charge Transfer Promoted Electron Transfer in all Perylenediimide Derived, Wide-Band Capturing Conjugates: A Mimicry of the Early Events of Natural Photosynthesis.

Fundamental discoveries in electron transfer advance scientific and technological advancements. It is suggested that in plant and bacterial photosynthesis, the primary donor, a chlorophyll or bacteriochlorophyll dimer, forms an initial excited symmetry-breaking charge transfer state (1CT*) upon photoexcitation that subsequently promotes sequential electron transfer (ET) events. This is unlike monomeric photosensitizer-bearing donor-acceptor dyads where ET occurs from the excited donor or acceptor (1D* or 1A*). In the present study, we successfully demonstrated the former photochemical event using an excited charge transfer molecule as a donor. Electron-deficient perylenediimide (PDI) is functionalized with three electron-rich piperidine entities at the bay positions, resulting in a far-red emitting CT molecule (DCT). Further, this molecule is covalently linked to another PDI (APDI) carrying no substituents at the bay positions, resulting in wide-band capturing DCT-APDI conjugates. Selective excitation of the CT band of DCT in these conjugates leads to an initial 1DCT* that undergoes subsequent ET involving APDI, resulting in DCT +-APDI - charge separation product (kCS~109 s-1). Conversely, when APDI was directly excited, ultrafast energy transfer (ENT) from 1APDI* to DCT (kENT~1011 s-1) followed by ET from 1DCT* to PDI is witnessed. While increasing solvent polarity improved kCS rates, for a given solvent, the magnitude of the kCS values was almost the same, irrespective of the excitation wavelengths. The present findings demonstrate ET from an initial CT state to an acceptor is key to understanding the intricate ET events in complex natural and bacterial photosynthetic systems possessing multiple redox- and photoactive entities.

Efficient Electron Transfer Driven by Excited-State Structural Relaxation in Corrole-Perylenedimiide Dyad.

A sterically encumbered trans-A2B-corrole possessing a perylenediimide (PDI) scaffold in close proximity to the macrocycle has been synthesized via a straightforward route. Electronic communication as probed via steady-state absorption or cyclic voltammetry is weak in the ground state, in spite of the corrole ring and PDI being bridged by an o-phenylene unit. The TDDFT excited-state geometry optimization suggests after excitation the interchromophoric distance is markedly reduced, thus enhancing the through-space electronic coupling between the corrole and the PDI. This is corroborated by the strong deviation of the emission spectrum originating from both PDI and corrole in the dyad. Selective excitation of both donor and acceptor units triggers efficient sub-picosecond electron transfer and hole transfer, respectively, followed by fast charge recombination. In comparison to previously studied corrole-PDI dyads, both charge separation and charge recombination occur faster, because of the structural relaxation in the excited state.

Two pathways to understanding electron transfer in reaction centers from photosynthetic bacteria: A comparison of Rhodobacter sphaeroides and Rhodobacter capsulatus mutants

The rates, yields, mechanisms and directionality of electron transfer (ET) are explored in twelve pairs of Rhodobacter (R.) sphaeroides and R. capsulatus mutant RCs designed to defeat ET from the excited primary donor (P*) to the A-side cofactors and re-direct ET to the normally inactive mirror-image B-side cofactors. In general, the R. sphaeroides variants have larger P+HB− yields (up to ∼90%) than their R. capsulatus analogs (up to ∼60%), where HB is the B-side bacteriopheophytin. Substitution of Tyr for Phe at L-polypeptide position L181 near BB primarily increases the contribution of fast P* → P+BB− → P+HB− two-step ET, where BB is the “bridging” B-side bacteriochlorophyll. The second step (∼6–8 ps) is slower than the first (∼3–4 ps), unlike A-side two-step ET (P* → P+BA− → P+HA−) where the second step (∼1 ps) is faster than the first (∼3–4 ps) in the native RC. Substitutions near HB, at L185 (Leu, Trp or Arg) and at M-polypeptide site M133/131 (Thr, Val or Glu), strongly affect the contribution of slower (20–50 ps) P* → P+HB− one-step superexchange ET. Both ET mechanisms are effective in directing electrons “the wrong way” to HB and both compete with internal conversion of P* to the ground state (∼200 ps) and ET to the A-side cofactors. Collectively, the work demonstrates cooperative amino-acid control of rates, yields and mechanisms of ET in bacterial RCs and how A- vs. B-side charge separation can be tuned in both species.

From light to hydrogen: the complete life cycle of free charges in photocatalytic nanoparticles

A complete picture of charge generation over 11 orders of magnitude in time in the high-performance PM6:Y6 organic-semiconductor blend from donor and acceptor excitation is obtained using ultrafast spectroscopy and kinetic modeling.

A point-of-care aptasensor based on the upconversion nanoparticles/MoS2 FRET system for the detection of Pseudomonas aeruginosa infection.

The rapid detection of Pseudomonas aeruginosa (P. aeruginosa) is of great significance for the diagnosis of medical infection. In view of the above, a novel aptasensor based on fluorescence resonance energy transfer (FRET) was developed. It contained aptamer-coupled upconversion nanoparticles (UCNPs-apt) as a donor (excitation 980nm) and molybdenum disulfide (MoS2) nanosheets as an acceptor. The upconversion fluorescence aptamer system was investigated to obtain the optimal parameters of MoS2 concentration, the incubation time of UCNPs-apt/MoS2 and P. aeruginosa, and pH. Based on the optimal parameters, a linear calibrationequation (emission 654nm) with a wide detection range 8.7 × 10 ~ 8.7 × 107cfu/mL, a high coefficient of determination R2 0.9941, and a low limit of determination (LOD) 15.5cfu/mL were established. The method was validated with P. aeruginosa infected foci of mouse wound. The advantage of this aptasensor isthat analysisresults can be obtained within 1.5h, which was much faster than that ofthe standard method (18-24h). Furthermore, combined with a portable instrument, it can be used as a point-of-care testing for the early detection of P. aeruginosa infection, which is useful for selecting the correct antibiotics to achieve good therapeutic effects. Additionally, it also has a broad application prospect in food and environmental areas.

Anionic clay surface facilitates electron transfer between an excited donor encapsulated within a cationic capsule and a cationic electron acceptor

Fluorescence quenching of an excited guest encapsulated within a cationic host by a cationic molecule was examined on an anionic inorganic surface. Repulsion between the host and the quencher was overcome by adsorbing both an anionic surface. Dimethyl stilbene (DMS), octa amine (OAm216+), viologen derivatives (VD2+) and saponite are used as guest, cationic capsule, cationic electron acceptor and anionic inorganic surface, respectively. The fluorescence behavior of DMS within OAm216+ (denoted as DMS@OAm216+) was observed by steady-state and time-resolved fluorescence measurements. As a result of electron transfer the fluorescence of DMS@OAm216+ was quenched by VD2+ under the presence of saponite, while no quenching was observed in the absence of saponite. Those results indicate that the dynamic electron transfer between DMS@OAm216+ and VD2+ which are electrostatically repulsive, can be observed in the (DMS@OAm216+)-VD2+-saponite triad supramolecular system where the two cationic systems are brought closer by the anionic clay sheet.

FRET Based Biosensor: Principle Applications Recent Advances and Challenges.

Förster resonance energy transfer (FRET)-based biosensors are being fabricated for specific detection of biomolecules or changes in the microenvironment. FRET is a non-radiative transfer of energy from an excited donor fluorophore molecule to a nearby acceptor fluorophore molecule. In a FRET-based biosensor, the donor and acceptor molecules are typically fluorescent proteins or fluorescent nanomaterials such as quantum dots (QDs) or small molecules that are engineered to be in close proximity to each other. When the biomolecule of interest is present, it can cause a change in the distance between the donor and acceptor, leading to a change in the efficiency of FRET and a corresponding change in the fluorescence intensity of the acceptor. This change in fluorescence can be used to detect and quantify the biomolecule of interest. FRET-based biosensors have a wide range of applications, including in the fields of biochemistry, cell biology, and drug discovery. This review article provides a substantial approach on the FRET-based biosensor, principle, applications such as point-of-need diagnosis, wearable, single molecular FRET (smFRET), hard water, ions, pH, tissue-based sensors, immunosensors, and aptasensor. Recent advances such as artificial intelligence (AI) and Internet of Things (IoT) are used for this type of sensor and challenges.

Efficient Energy Transfer in a Rylene Imide-Based Heterodimer: The Role of Intramolecular Electronic Coupling.

The development of antenna molecules with simplified structures can effectively avoid the complex exciton dynamics resulting from conformational mobility. Two distinct heterodimers TP and TBP comprising a perylenediimide (PDI) donor and terrylenediimide (TDI) acting as an energy sink were investigated. Tuned by varying functionalization positions, the bay-to-bay-linked TP offers a strong chromophore coupling, while the bay-to-N-linked TBP exhibits a weak chromophore coupling. Using transient absorption spectroscopy, we found that TP underwent ultrafast vibrational relaxation (τVR < 400 fs) from upper vibrational energy levels of the singlet states after pumping at 490 nm, and followed by electron transfer (ET, τET = 2.5 ps) from TDI to PDI. TBP exhibited ultrafast excitation energy transfer (EET, τEET = 0.48 ± 0.1 ps) from the excited PDI donor to TDI acceptor, and the subsequent charge transfer (CT) process was almost quenched. This result provides insight into designing novel small molecules capable of efficient energy transfer.

Improved estimation of the ratio of detection efficiencies of excited acceptors and donors for FRET measurements.

Förster resonance energy transfer (FRET) is a radiationless interaction between a donor and an acceptor whose distance dependence makes it a sensitive tool for studying the oligomerization and the structure of proteins. When FRET is determined by measuring the sensitized emission of the acceptor, a parameter characterizing the ratio of detection efficiencies of an excited acceptor versus an excited donor is invariably involved in the formalism. For FRET measurements involving fluorescent antibodies or other external labels, this parameter, designated by α, is usually determined by comparing the intensity of a known number of donors and acceptors in two independent samples leading to a large statistical variability if the sample size is small. Here, we present a method that improves precision by applying microbeads with a calibrated number of antibody binding sites and a donor-acceptor mixture in which donors and acceptors are present in a certain, experimentally determined ratio. A formalism is developed for determining α and the superior reproducibility of the proposed method compared to the conventional approach is demonstrated. Since the novel methodology does not require sophisticated calibration samples or special instrumentation, it can be widely applied for the quantification of FRET experiments in biological research.

Fluorescence lifetime analysis of smFRET with contribution of PIFE on donor and acceptor.

Single-molecule fluorescence resonance energy transfer (FRET) is a powerful technique based on dipole-dipole interaction between donor and acceptor fluorophores to observe inter- and intra-molecular dynamics in real time with sensitivity to macro-molecular distances (∼2.5-10 nm). That said, some fluorophores have an inherent characteristic known as protein induced fluorescence enhancement (PIFE). PIFE is a photo-physical feature of dyes undergoing cis-trans transitions and occurs for protein-dye interactions closer than 3 nm where FRET is less sensitive. Here, the challenge is uncoupling the PIFE effect in the FRET data. Ignoring the PIFE effect in the analysis of the FRET data may lead to misinterpretation of the system under investigation. As a solution to this problem, we develop a computational framework based on Bayesian statistics to analyze the fluorescence lifetime signals of the donor and acceptor channels which allows us to uncouple the PIFE effects from the FRET. Our framework can extract any changes in the FRET efficiency simultaneously with any changes in the fluorescence lifetimes of the donor and acceptor due to the PIFE effect. In addition, our framework can provide other parameters, such as the donor and acceptor excitation rates, background photon rates, and detectors’ cross-talk ratios. Our framework extracts all these parameters by analyzing a single photon arrival time trace with only a few thousand photons.

Ultrasensitive inner filter effect fluorescence sensing platform for alkaline phosphatase based on arginine surface-engineered gold nanoclusters

Developing a simple yet powerful method for enzyme activity monitoring is of great significance in the early diagnosis of diseases. Herein, we designed a precise spectral overlap-triggered inner filter effect (IFE) fluorescence sensing platform for alkaline phosphatase (ALP) detection. ALP could catalyze hydrolysis of p-nitrophenylphosphate (PNPP) to generate p-nitrophenol (PNP) and PNP acts as a powerful acceptor in IFE reaction system to influence the excitation of fluorescent donors. Based on this principle, a standardized procedure was proposed for rational screening of high-performance donor/acceptor pairs to maximize IFE efficiency. The results proved that perfect spectral overlap and high quantum yield of fluorescent donors synergistically contribute to maximizing IFE efficiency. In this case, a high quantum yield of 51.7% of the arginine surface-engineered gold nanoclusters (Arg/ATT-AuNCs) produced perfect spectral overlap with PNP and achieved maximal IFE efficiency, which was eventually selected as fluorescent signal tag for ALP detection. The Arg/ATT-AuNCs-based approach achieved ultrasensitive detection of ALP with a detection limit of 0.0062 U/L, which exhibited 4.2–25.8-fold improvement compared to other donors. Furthermore, the accuracy and reliability of established method in real human serum samples were verified by spiking analysis and commercial kits, thus providing a promising platform for monitoring ALP. This work aims to provide a standardized procedure for rational screening high-performance donor/acceptor pairs and to develop an ultrasensitive IFE sensing platform for biomarkers detection, which will open up a promising horizon for other biomarkers detection in clinical diagnostics.

Effect of the Push–Pull Electronic Structure of Nonfullerene Acceptor Molecules on the Interfacial Charge Dynamics in Heterojunction Organic Solar Cells

Nonfullerene acceptor (NFA) molecules have attracted significant attention in high‐efficient heterojunction organic solar cells (OSCs) due to their push–pull electronic structures. Herein, using a universal quantum model for an organic donor/acceptor interface composed of a polymer donor and an NFA molecule, effect of the NFA molecular electron push and pull ability on the interfacial charge dynamics in the case of donor excitation is focused on. It is confirmed that energy and charge transfer coexist and compete during the interfacial charge dynamics, by which an interfacial hybrid state is created, and the quantitative correlations of the generation rates for different component states (e.g., donor exciton, acceptor exciton, and charge transfer state) with the NFA molecular electron push and pull ability are separately clarified. It is found that, by strengthening the NFA molecular electron push ability, competition between charge and energy transfer presents a nonmonotonous behavior; by strengthening the electron pull ability, charge transfer is always promoted and energy transfer is inhibited. This study provides a microscopic understanding for the interfacial charge dynamics modulated by tuning the NFA molecular push–pull electronic structure and thus sheds light on further improving the performance of heterojunction OSCs by rational designs of NFA molecules.

Dynamics of the Energy Transfer Process in Eu(III) Complexes Containing Polydentate Ligands Based on Pyridine, Quinoline, and Isoquinoline as Chromophoric Antennae.

In this work, we investigated from a theoretical point of view the dynamics of the energy transfer process from the ligand to Eu(III) ion for 12 isomeric species originating from six different complexes differing by nature of the ligand and the total charge. The cationic complexes present the general formula [Eu(L)(H2O)2]+ (where L = bpcd2– = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate; bQcd2– = N,N′-bis(2-quinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate; and bisoQcd2– = N,N′-bis(2-isoquinolinmethyl)-trans-1,2-diaminocyclohexane N,N′-diacetate), while the neutral complexes present the Eu(L)(H2O)2 formula (where L = PyC3A3– = N-picolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate; QC3A3– = N-quinolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate; and isoQC3A3– = N-isoquinolyl-N,N′,N′-trans-1,2-cyclohexylenediaminetriacetate). Time-dependent density functional theory (TD-DFT) calculations provided the energy of the ligand excited donor states, distances between donor and acceptor orbitals involved in the energy transfer mechanism (RL), spin-orbit coupling matrix elements, and excited-state reorganization energies. The intramolecular energy transfer (IET) rates for both singlet-triplet intersystem crossing and ligand-to-metal (and vice versa) involving a multitude of ligand and Eu(III) levels and the theoretical overall quantum yields (ϕovl) were calculated (the latter for the first time without the introduction of experimental parameters). This was achieved using a blend of DFT, Judd–Ofelt theory, IET theory, and rate equation modeling. Thanks to this study, for each isomeric species, the most efficient IET process feeding the Eu(III) excited state, its related physical mechanism (exchange interaction), and the reasons for a better or worse overall energy transfer efficiency (ηsens) in the different complexes were determined. The spectroscopically measured ϕovl values are in good agreement with the ones obtained theoretically in this work.

Featuring a new computational protocol for the estimation of intensity and overall quantum yield in lanthanide chelates with applications to Eu(III) mercapto-triazole Schiff base ligands

Computational studies on luminescent properties of lanthanides chelates are important for the pre-synthetic design of new luminescent materials. However, the development of suited computational methods and protocols is still in its infancy. Here we present a new computational protocol for a systematic description and analysis of luminescent properties of Ln(III) chelates. The new methodologies herein presented are divided in three major categories: (1) Utilization of local vibrational mode theory for obtaining local Ln–ligand force constants; (2) Calculation of ligand effective polarizabilities through complex localized molecular orbitals; and (3) Extended formulation of excited state donor–acceptor RL distances accounting for excited molecular orbitals weights. The protocol was applied to understand the underlying photophysical processes in two Eu(III) complexes with mercapto-triazole Schiff bases as main ligands, utilizing time-dependent density functional theory (ωB97X-D/MWB52(Eu)/Def2-TZVP). The introduction of local force constants into lanthanide spectroscopy led to a unique explanation of the inverse relationship between the Ln–ligand strength and ligand effective polarizability. This new protocol will contribute to a better understanding of Ln–ligand bond properties, to more accurate results in terms of Judd–Ofelt intensity parameters and overall quantum yield, and will bridge the current gap between available theoretical results and experimental data.

(Invited) Dynamics of Porphyrin-Fullerene Charge Transfer and Recombination Via Ultrafast Spectroscopy

Electron donor-acceptor (D-A) interactions have been the subject of intense scrutiny by the scientific community due to their role in a variety of applications, such as solar energy production, photocatalysis, and stimulus-responsive materials. We chose porphyrins and fullerenes for our fundamental studies of D-A interactions, as they are the prototypical D-A pair by virtue of their well-positioned energy levels, low reorganization energies, and the high extinction coefficients of the porphyrin ring in the visible region. Moreover, they give us the opportunity to not only choose between different bound or endohedral metal ions or clusters, but also to connect them in different ways in order to tune their behavior. We have used time-resolved spectroscopic techniques, including transient absorption, fluorescence upconversion, and time-correlated single-photon counting, to untangle charge separation and recombination dynamics upon donor excitation in the femto- to nanosecond regime to gain additional insight into the relationship between structure and behavior.

Enhanced energy transfer from diolefinic laser dyes to meso-tetrakis (4-sulfonatophenyl) porphyrin immobilized on silver nanoparticles: DFT, TD-DFT and spectroscopic studies

Porphyrin derivatives are known singlet oxygen sensitizers in photodynamic therapy (PDT). Energy transfer from a class of diolefinic laser dyes (DOLDs) as energy donors to the sodium salt of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) as the accepter of energy would extend the range of photon harvesting down to the UV-region. Energy transfer was substantially enhanced in the presence of metallic silver nanoparticles (AgNPs), as revealed by steady-state emission spectroscopy, lifetimes, and quantum mechanics. DOLDs under investigation are 2,5-distyrylpyrazine (DSP), 1,4-bis (β-pyridyl-2 vinyl) benzene (P2VB), and 1,4 bis (2-methylstyryl) benzene (MSB) as efficient donors of intense absorption in the UV-region. AgNPs enhance the rate of energy transfer from DOLDs to TPPS via bringing donor and acceptor into close- proximity with a concomitant increase in dipole–dipole interaction between excited state donor and ground-state acceptor. The DOLDs molecular structures were optimized using the DFT/CAM-B3LYP/6-311G++ (d, p) level of theory. The calculated electronic absorption spectra for the studied DOLDs in the gaseous phase and methanol solvent were studied using the time-dependent density functional theory (TD-DFT) at M06-2X/6-311G++ (2d,2p) level. The calculated absorption/emission spectra for DSP laser dye in methanol are obtained at the TD/ M06-2X/6-311G++(2d, 2p) method. Notably, all theoretical results of the molecular structures under study highly agreed with the practical optical results. Energy transfer rate constants (kET) amid energy donor/acceptor pairs were determined by Stern-Volmer constants (KSV) and donors' lifetime measurements. The KSV values indicate an enhanced Fluorescence Resonance Energy Transfer (FRET) efficiencies in the presence of negatively charged AgNPs. The critical transfer distances Ro were determined from the spectral overlap between the emission spectrum of donor and absorption spectrum of TTPS. These outcomes propose the application of designed metal-enhanced FRET for energy-transfer-based assays and photodynamic therapy (PDT) applications.