Excitation Transfer Research Articles

Excited-State Charge Transfer Coupling from Quasiparticle Energy Density Functional Theory.

The recently developed Quasiparticle Energy (QE) scheme, based on a DFT calculation with one more (or less) electron, offers a good description of excitation energies, even with charge transfer characters. In this work, QE is further extended to calculate electron transfer (ET) couplings involving two excited states. We tested it with a donor-acceptor complex, consisting of a furan and a 1,1-dicyanoethylene (DCNE), in which two low lying charge transfer and local excitation states are involved. With generalized Mülliken-Hush and fragment charge-difference schemes, couplings from the QE approach generally agree well with those obtained from TDDFT, except that QE couplings exhibit better exponential distance dependence. Couplings from half-energy gaps with an external field are also calculated and reported. Our results show that the QE scheme is robust in calculating ET couplings with greatly reduced computational time.

A theoretical study of the photochemistry of 1,3-cyclopentadiene and its cyano derivatives bound to a water dimer: Assessing reactivity of ionized clusters and possible photoproducts

We theoretically investigate the photoionization scenarios of molecular complexes involving cyclopentadiene and cyanocyclopentadiene bound to water dimers. Using electronic structure calculations within density-functional theory (DFT) and time dependent DFT (TD-DFT), we explore the potential photochemical pathways following ionization, and determine the charge transfer excitations related to the possible subsequent reactions. Our findings suggest that the investigated photochemical pathways of the hydrated complexes take place in two well-defined ultraviolet regions: (i) 8.2–9.5 eV for the cyclic compounds and (ii) 11.2–11.4 eV for the bound water dimer. We quantify how H-bonding effects can influence the photoionization channels. Before forming possible photoproducts, we also examine the regiospecificity of OH addition to 1,3-cyclopentadiene and its cyano derivatives We analyze our results in light of photoionization studies of jet-cooled molecular complexes and possible implications in astrochemical environments.

Unveiling the molecular symphony - A DFT exploration of structure, electronic dynamics, and excited state electron transfer in D-π-A systems, enhanced by TeO2@GQD multi-junctions for solar energy conversion in DSSC

Graphene and graphene-derived materials have sparked a lot of interest because of their unique physico-chemical features, that have positioned graphene as a promising material for future opto-electronics, and energy-harvesting devices. Graphene possesses outstanding mechanical characteristics and chemical inertness, as well as great mobility and optical transparency. Single-layer graphene has a high optical transmissivity that allows it to pass through a wide variety of light wavelengths, making it a popular material for optically conducting windows. Graphene-based metal and metal oxide nanocomposites require substantial investigations to understand the fundamental interactions between nanostructures and the graphene surface in DSSC, for understanding the characteristic features of such nanocomposites. In the present study different donor-π-acceptor, systems were used, which are different in the type of the π –spacer units only. This D-π-A system was then decorated on a (TiO2)9 semiconductor leading to shifting of the absorption wavelength, the absorbed wavelength was further shifted upon interaction with tellurium–oxide@graphene, thereby exploring its application in solar energy harvesting devices. The result of such substitution was assessed in terms of various parameters such as highest occupied molecular orbital (HOMO), least unoccupied molecular orbital (LUMO), energy gap (Egap), maximum wavelength (λmax), the free energy of electron injection efficiency (ΔGinject), open-circuit voltage (Voc), reorganization energy (Δreorg), etc by the DFT method with Gaussian 09 set of codes. The study can prove beneficial for understanding the mechanism of high optical absorption over a broad spectrum in such multijunction systems, the feature which makes them promising materials for efficient optical, electronic, and light-harvesting devices.

Multifold Enhanced Photon Upconversion in a Composite Annihilator System Sensitized by Perovskite Nanocrystals.

Photon upconversion via triplet-triplet annihilation (TTA-UC) provides a pathway to overcoming the thermodynamic efficiency limits in single-junction solar cells by allowing the harvesting of sub-bandgap photons. Here, we use mixed halide perovskite nanocrystals (CsPbX3, X = Br/I) as triplet sensitizers, with excitation transfer to 9,10-diphenylanthracene (DPA) and/or 9,10-bis[(triisopropylsilyl)ethynyl]anthracene (TIPS-An) which act as the triplet annihilators. We observe that the upconversion efficiency is five times higher with the combination of both annihilators in a composite system compared to the sum of the individual single-acceptor systems. Our work illustrates the importance of using a composite system of annihilators to enhance TTA upconversion, demonstrated in a perovskite-sensitized system, with promise for a range of potential applications in light-harvesting, biomedical imaging, biosensing, therapeutics, and photocatalysis.

Detection mechanism and solvent effects of the 3‐hydroxy‐2‐(4‐(pyrrolidin‐1‐yl)phenyl)benzo[g]quinolin‐4(1H)‐one (PBQ) probe

AbstractHydroxy‐2‐(4‐(pyrrolidin‐1‐yl)phenyl)benzo[g]quinolin‐4(1H)‐one (PBQ) is a ratiometric fluorescent probe based on excited‐state intramolecular proton transfer (ESIPT). PBQ‐1 is the reaction product following its exposure to phosgene. Density functional theory (DFT) and time dependent density functional theory (DFT) have been used to study the excited state dynamics of PBQ and PBQ‐1 in different solvents. The results show that the reaction of PBQ with a transition from charge‐transfer excitation to local excitation before and after the reaction. It becomes more difficult for PBQ in the excited state to transfer proton with increasing solvent polarity. The product PBQ‐1 undergoes a molecular structure twist, and the angle of twisting decreases with increasing solvent polarity, resulting in a lower degree of rotational freedom of the hydroxyl group (5‐OH) at the 5th carbon position, which makes it more susceptible to ESIPT reactions. Therefore, PBQ‐1 is more susceptible to ESIPT as solvent polarity increases. Our theoretical calculations also elucidate the cause of the blue shift of PBQ fluorescence and the impact of the twisting intramolecular charge transfer phenomenon on the solvent effect. Furthermore, our study provides the theoretical guidance for the designing probe based on excited state intramolecular proton transfer.

Controlled Self‐Assembly of Zn–Tetraphenylporphyrins for Efficient Photocatalytic Solar H2 Production and Simultaneous Organic Transformation to Valuable Chemicals

Herein, we have designed aqueous dispersed self‐assembled nanostructures with diverse morphologies from the zinc tetraphenyl porphyrin (ZnTPP) monomer employing a simple solution‐based coprecipitation methods. Detail morophological studies have been carried out by various electron microscopy techniques. Finally, the structural features were correlated with the underpinning photophysical processes using steady‐state and time‐resolved spectroscopy. Detailed studies suggest that control morphology and highly defined intermolecular interactions affect the overall photoinduced charge transfer process. Based on the fundamental investigations, all these different types of nanostructures have been utilized as photocatalysts for solar hydrogen production, without using any cocatalysts, and it was found that the spherical nanostructure exhibits significantly higher H2 production rates of ~1682 m mole/ g, which is few folds higher than other 1D and 2D nanostructured materials. The experimental findings were further supported by the TD‐DFT study. Furthermore, the detailed computational studies suggest that the spherical aggregates exhibited a more vital interaction between the ZnTPP molecules, causes significant electronic coupling between bright local excited and charge transfer states, which supports our experimental findings. Finally, we have selectively utilized the oxidative half‐reaction for the simultaneous transformation of glycerol to valuable chemicals along with photocatalytic H2 production through reductive half‐reaction.

Tautomeric enhancement of 2-(1H-pyrazol-5-yl)pyridine in photoinduced proton transfer by water-assisted molecules

Theoretical insight of excited state proton transfer (ESPT) in 2-(1H-pyrazol-5-yl)pyridine abbreviated as PPP interacting with water wires: PPP(H2O)n where n = 13 has been presented in both static and dynamics studies. Explicit water molecules placed around PPP have been simulated to elucidate the intermolecular hydrogen bonding interactions between them. Hydrogen bond strengthening in the excited state (S1) has been verified by shorter bond distances and redshift of IR vibrational spectra involving the proton transfer (PT) process. Furthermore, on-the-fly excited state dynamics simulations of all complexes have been performed to provide detailed information on the PT mechanism. The dynamic results show that one water molecule added to the neighboring PPP as an intermolecular hydrogen bonding bridge can promote double excited state intermolecular proton transfer up to 36% compared with its intrinsic intramolecular hydrogen bond of the PPP system. Meanwhile adding a second or third water molecule could decrease the probabilities of PT. Especially in PPP(H2O)3, a rearrangement of water molecules is observed that PT occurs via one water molecule. Hence, the models with explicit water molecules interacting with PPP as intermolecular hydrogen bonding bridge are a great representative role played by water molecules of the PT process at the molecular level.

Electronic Couplings and Conversion Dynamics between Localized and Charge Transfer Excitations from Many-Body Green's Functions Theory.

We investigate the determination of electronic coupling between localized excitations (LEs) and charge-transfer (CT) excitations based on many-body Green's functions theory in the GW approximation with the Bethe-Salpeter equation (GW-BSE). Using a small molecule dimer system, we first study the influence of different diabatization methods, as well as different model choices within GW-BSE, such as the self-energy models or different levels of self-consistency, and find that these choices affect the LE-CT couplings only minimally. We then consider a large-scale low-donor morphology formed from rubrene and fullerene and evaluate the LE-CT couplings based on coupled GW-BSE-molecular mechanics calculations. For these disordered systems of bulky molecules, we observe differences in the couplings based on the Edmiston-Ruedenberg diabatization compared to the more approximate Generalize Mulliken-Hush and fragment charge difference diabatization formalisms. In a kinetic model for the conversion between LE and CT states, these differences affect the details of state populations in an intermediate time scale but not the final populations.

A near-infrared fluorescent probe with thiadiazole unit as key skeleton for ICT and ESIPT mechanism and effective detection of Cu2+

Fluorescent probe L-I was synthesized to demonstrate that 1,3,4-thiadiazole is an attractive moiety and could be utilized as positive hydrogen bond acceptor for excited state intramolecular proton transfer (ESIPT) processes, guider of electrons movement for intramolecular charge transfer (ICT) process and identify group for mental ions. Furthermore, dicyanoisophorone framework was employed to improve the fluorescence characteristics and near-infrared (NIR) fluorescent emission at 695 nm accompanied by a Stoke's shift as large as 260 nm was obtained. L-I could selectively detect Cu2+ over other analytes taking advantages of high sensitivity, fast response within 30 s and low detection limit (0.026 μM). More important, L-I exhibited good performance for detection of Cu2+ in actual water samples, food products, traditional Chinese medicine and for cell imaging which demonstrates practical significance in the fields of environmental monitor, food safety and biotechnology.

Photoluminescence Study of Undoped and Eu-Doped Alkali-Niobate Aluminosilicate Glasses and Glass-Ceramics.

In this study, the photoluminescence (PL) behavior of two aluminosilicate glass series containing alkali-niobates ranging from 0.4 to 20 mol% was investigated. The glasses exhibit an intense visible emission centered at ~18,400 cm-1 for the peralkaline series and at higher energies (~19,300 cm-1) for the metaluminous glasses. However, the photoluminescence emission intensity varies significantly with the niobate content and the bulk chemistry. PL and fluorescence lifetime measurements indicate that the broad emission bands result from the overlap of different niobate populations, whose distribution changes with niobate content. The distinct PL behavior in the two glass series was related to the structural evolution of the niobate units upon niobium addition. An enhancement of the visible emission was observed for a higher fraction of distorted [NbO6] units. Eu-doping was carried out as a structural probe of the glass network, and also to determine if these glasses could be used as potential rare earth element (REE) activators. The crystal field strength around Eu ions is strongly dependent on the bulk chemistry and the niobate content. Furthermore, the peralkaline series showed energy transfer from the host [NbO6] to Eu3+, confirming the feasibility of exploring niobate glasses and glass-ceramics as lanthanide ion-activated luminescent materials. In addition, glass-ceramics (GCs) containing alkali-niobate phases with a perovskite-like structure were developed and studied to verify the optical performance of these materials. It was verified that the bulk chemistry influences crystallization behavior, and also the photoluminescence response. The transparent GC from the metaluminous series exhibits a quenching of the Eu3+ emission, whereas an enhanced emission intensity is observed for the peralkaline GC. The latter shows a strong excitation-dependent PL emission, suggesting energy transfer and migration of electronic excitation from one Eu population to another. Additionally, Eu3+ emissions arising from the D15 and D25 excited states were observed, highlighting the low phonon energy achievable in niobo-aluminosilicate hosts.

Influence of Solvents and Halogenation on ESIPT of Benzimidazole Derivatives for Designing Turn-on Fluorescence Probes.

This work reports a theoretical investigation of the solvent polarity as well as the halogenation of benzimidazole derivatives during excited state intramolecular proton transfer (ESIPT). It details how the environment and halogen substitution may contribute to the efficiency of ESIPT upon keto-enol tautomerism and exploits this effect to design fluorescence sensing. For this purpose, we first examine the conformational equilibrium of benzimidazole derivatives containing different halogen atoms, which results in intramolecular proton transfer, using density-functional theory (DFT) combined with the polarizable continuum model (PCM). Then we evaluate the fluorescence of the benzimidazole derivatives in different dielectric constants within time-dependent DFT (TD-DFT) approaches. Our results quantitatively allow the determination of large Stokes shifts in nonpolar solvents around 100 nm. These theoretical results are in agreement with experimental solvatochromism studies of benzimidazoles. The effect of halogenation, with fluorine, chlorine, and bromine, is less important than solvent polarization when ESIPT takes place. Thus, halogenation can be properly chosen depending on the interest of the synthesis of benzimidazole-based turn-on fluorescence in appropriate solvents.

Concerning for the solvent-polarity-dependent conformational equilibrium and ESIPT mechanism in Pz3HC system: A novel insight

In this report, we propose a new insight into the interaction between the solvent-polarity-dependent conformational equilibrium and excited state intramolecular proton transfer (ESIPT) behavior of Pz3HC system in four different polar solvents (polarity order: ACN > THF > TOL > CYC). Using quantum chemistry method, we first announce a coexistence mechanism between Pz3HC-1 and Pz3HC-3 in the ground state in four solvents based on the Boltzmann distribution. In particular, Pz3HC-1 is the principal configuration in non-polar solvent, but Pz3HC-3 is the principal configuration in polar solvent. In addition, the simulated fluorescence spectra interprets the negative solvatochromism effect of Pz3HC-1 and Pz3HC-3 in four solvents. The evidence from intramolecular hydrogen bonding (IHB) parameters and electronic perspective collectively confirms the light-induced IHB enhancement and intramolecular charge transfer (ICT) properties in Pz3HC-1 and Pz3HC-3, which raises the likelihood of the ESIPT process. Combining the calculation of potential energy curve (PEC) and intrinsic reaction coordinate (IRC), we demonstrate that the ESIPT ease of Pz3HC-1 in different polar solvents obeys the order of CYC > TOL > THF > ACN, while the order of ESIPT ease in Pz3HC-3 is opposite. Notably, the ESIPT process of Pz3HC-3 in CYC solvent is accompanied by the twisted intramolecular charge transfer (TICT) process. In addition, we also reveal that the enol* and keto* fluorescence peaks of Pz3HC-3 in CYC solvent are quenched by ISC and TICT process, respectively. Our work not only provides a satisfactory explanation of the novel dynamics mechanism for Pz3HC system, but also brings light to the design and application of new sensing molecules in the future.

A single excitation dual emission semi-salamo type multi-functional probe for sensitive pH and Cu2+ detection

pH and Cu2+ ion concentration changes are linked to disorders like Alzheimer's and cancer. Rapid detection of pH and Cu2+ ions is critical for public health and environmental concerns. The semi-salamo-type probe (E)-2-hydroxy-1-naphthaldehyde O-(2-(aminooxy)ethyl) oxime (NSS) demonstrated substantial dual-functional performance, sensing pH change and Cu2+ ions. A single excitation and double emission characteristic on the probe NSS made it distinctive. Probe NSS exhibits pH-dependent excited state intramolecular proton transfer (ESIPT), and its optical properties vary based on the pH environment. Probe NSS detects pH changes from 2 to 11 by changing the “off-on-off” of the excited state intra-molecular proton transfer (ESIPT) mechanism, exhibiting rapid, reversible, and selective responses. In addition, the luminescent salamo-like naphthalene-based probe NSS can coordinate with Cu2+ ions, achieving great selectivity and sensitivity to identify Cu2+ ions with a detection limit of 0.84 ppb (13.2 nM) Probe NSS can detect Cu2+ ions in actual water samples such as tap water and yellow river water. The test strip loaded with probe NSS enabled quick and accurate detection of Cu2+ ions in water samples. Consequently, the versatile salamo-type probe NSS lays the foundation for developing high sensitivity and fast-response dual-mode pH meters as well as Cu2+ sensing.

2-Aryl-3H-1,3-Benzazaphosphole Oxides: Synthesis, Optical Properties, and Excited State Intramolecular Proton Transfer.

Inclusion of a heteroatom to the phosphole ring is a promising strategy to intrinsically modulate the optical properties of phosphole derivatives. We report on a series of 2-aryl-3H-1,3-benzazaphosphole oxides that were efficiently prepared via sequential C-P cross-coupling, dehydrative [3+2] cycloaddition, and ring-oxidation reactions. The inclusion of one nitrogen atom into the benzophosphole framework caused red shifting of the absorption and emission maxima, reflecting the greater stabilization of the LUMO level. 2-(2-Hydroxyphenyl)benzazaphosphole oxide underwent excited state intramolecular proton transfer and emitted a weak fluorescence from the excited state of the N-H tautomer.

Orbital-Optimized Versus Time-Dependent Density Functional Calculations of Intramolecular Charge Transfer Excited States.

The performance of time-independent, orbital-optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital-optimized calculations, even when including orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. -2 eV for TD-DFT, no correlation is observed for the orbital-optimized approach. The orbital-optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with a long-range charge transfer character. Orbital-optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best-performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.

Effect of different substituted groups on excited state intramolecular proton transfer of BOHMB

AbstractThe photophysical features of 3‐(benzo[d]oxazol‐2‐yl)‐2‐hydroxy‐5‐methoxy benzaldehyde (BOHMB) were investigated through experimental (J. Phys. Chem. A 2019, 123, 10,246–10,253) and theoretical (Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2022, 266, 120,406) methods. However, the effect of substituent groups on the excited state proton transfer process has not been studied. In this work, the excited state intramolecular proton transfer (ESIPT) dynamics and photophysical properties of BOHMB with different substituent groups were investigated by density‐functional theory (DFT) and time‐dependent DFT (TDDFT) methods at CAM‐B3LYP/6‐311G(d,p) level. The primary parameters related to hydrogen bonding and infrared vibration frequency were obtained to understand the ESIPT properties of BOHMB derivatives. The results indicate that the excited‐state intramolecular hydrogen bond (ESIHB) strengthening behaviors, and the intramolecular hydrogen bond O1–H2···O3 for 1a in the S1 state is the strongest among BOHMB derivatives. From the calculated potential energy curves, it can be inferred that the substitution and position of NH2 and NO2 groups will regulate the excited‐state energy barrier and thus affect the ESIPT process. The molecular absorption peak and fluorescence peak are affected by different substituting groups and different positions.

GOALS-JWST: Mid-infrared Molecular Gas Excitation Probes the Local Conditions of Nuclear Star Clusters and the Active Galactic Nucleus in the LIRG VV 114

The enormous increase in mid-IR sensitivity and spatial and spectral resolution provided by the JWST spectrographs enables, for the first time, detailed extragalactic studies of molecular vibrational bands. This opens an entirely new window for the study of the molecular interstellar medium in luminous infrared galaxies (LIRGs). We present a detailed analysis of rovibrational bands of gas-phase CO, H2O, C2H2, and HCN toward the heavily obscured eastern nucleus of the LIRG VV 114, as observed by NIRSpec and the medium resolution spectrograph on the Mid-InfraRed Instrument (MIRI MRS). Spectra extracted from apertures of 130 pc in radius show a clear dichotomy between the obscured active galactic nucleus (AGN) and two intense starburst regions. We detect the 2.3 μm CO bandheads, characteristic of cool stellar atmospheres, in the star-forming regions, but not toward the AGN. Surprisingly, at 4.7 μm, we find highly excited CO (T ex ≈ 700–800 K out to at least rotational level J = 27) toward the star-forming regions, but only cooler gas (T ex ≈ 200 K) toward the AGN. We conclude that only mid-infrared pumping through the rovibrational lines can account for the equilibrium conditions found for CO and H2O in the deeply embedded starbursts. Here, the CO bands probe regions with an intense local radiation field inside dusty young massive star clusters or near the most massive young stars. The lack of high-excitation molecular gas toward the AGN is attributed to geometric dilution of the intense radiation from the bright point source. An overview of the relevant excitation and radiative transfer physics is provided in an appendix.

The effect of the number of conjugated C=C bonds on the ESIPT and ICT reactions of SNCN derivatives

The electronic structure of the molecule is significantly influenced by the number of conjugated C=C bonds. In this work, the influence of the conjugated C=C bonds of the SNCN derivatives on the excited state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) properties are studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculation level is proved to be reasonable by calculating electronic spectra. The hydrogen bond parameters, infrared vibrational frequency (IR), reduction density gradient (RDG) isosurface, topological analysis and potential energy curves of SNCN derivatives in ground state (S0) and the first excited state (S1) are analyzed. According to theoretical research results, ESIPT reaction has a higher likelihood of occurring in the S1 state. Moreover, the ESIPT reaction becomes more challenging to occur with the number of conjugated C=C bonds rising. Finally, the analyses of the frontier molecular orbitals (FMOs), dipole moment and charge transfer transition confirm that the ICT effect is aided by the increased number of conjugated C=C bonds. This work indicates that the number of conjugated C=C bonds can regulate the ESIPT and ICT processes, which provides guidance for the study of fluorescent groups with similar characteristics.

Versatile aggregation induced emissive molecular probes incorporating different donor/acceptor groups for tunable multiple color fluorescence

Excited state intramolecular proton transfer (ESIPT) and aggregation induced emission active multicolour fluorescent probes for bioimaging applications has grown popularly in recent years. Herein, we report a series of different donor/acceptor units (Cl, NO2 and O–CH3) bearing anthracene-salicylaldehyde based fluorescent probes and their antibacterial activity and fluorescence imaging of E. Coli bacteria and zebrafish embryos. All the compounds (ASA1, ASA2, ASA3 and ASA4) synthesized via facile one pot condensation reaction of anthracene hydrazide with Salicylaldehyde, 5-Chlorosalicylaldehyde, 5-Nitrosalicylaldehyde, 5-methoxysalicylaldehyde and characterized using all the possible spectroscopic techniques. The noteworthy tuneable emission wavelength shifts from 471 nm to 625 nm and ESIPT characteristics of the compounds were demonstrated through photophysical experiments and single crystal X-ray diffraction analysis. All the experimental results were completely analyzed theoretically on the ground as well as the excited state using density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. Compounds ASA1-ASA4 showed fascinating different colour fluorescent (Green, Yellow and Orange) aggregation induced emission features in the THF-H2O mixture. AIE characteristics of ASA1, ASA2, ASA3 and ASA4 were recognized using absorption, emission, fluorescence quantum yield (Φ), DLS and SEM analysis. ASA1, ASA2, ASA3 and ASA4 showed excellent antibacterial activity and ROS generation against E. Coli bacteria. Further, owing to their multicolour fluorescent property all the compounds successfully applied for fluorescent imaging in E. Coli bacteria and live zebrafish embryos.

Investigating the Photophysical Aspects of a Naphthalene-Based Excited-State Proton Transfer Dye 1-(1H-Benzo[d]imidazol-2-yl)naphthalen-2-ol: pH-Dependent Modulation of Photodynamics.

The steady state and time-resolved photophysical behavior of a proton transfer dye 1-(1H-benzo[d]imidazol-2-yl)naphthalen-2-ol (H-BINO) was investigated. The excited state intramolecular proton transfer (ESIPT) reaction in H-BINO is predominant in nonpolar solutions (toluene and DCM) with a lifetime of ∼1.0 ns. However, in polar media (DMF and MeOH), the excited state photodynamics is characterized by a complex equilibrium of emission from the locally excited state (0.1-2.3 ns), the phototautomer (0.5-1.2 ns), and the anionic emission (2.1-5.4 ns). In the solid state, emission from the various aggregated states dictates the photobehavior. Interestingly, the photodynamics in aqueous solution changes starkly as a function of pH with the anionic (2.1 ns) and phototautomeric (0.5-1.0 ns) emissions guiding the photodynamics as the pH of the medium increases. Optimized structural parameters at the proton donor and acceptor sites for the enol and keto forms and the calculated potential energy curve along the proton transfer coordinate at the density functional theory (DFT) level with the B3LYP/6-311G++(d,p) theory support a favorable and barrierless ESIPT process. The current results will surely boost the ongoing research on small molecule emissive materials.