Time-resolved Emission Spectra Research Articles

Color tuning from green to orange-red in SrBPO5: UO22+/Pr3+ phosphor via energy transfer for solid-state lighting applications

SrBPO5 doped with Pr3+, UO22+, Pr3+ and UO22+ were prepared through the conventional solid-state reaction route. PXRD and Raman spectroscopy studies confirmed the phase purity of these synthesized phosphors. The particle shape, size and distribution of dopants were studied using SEM and EDX. DFT calculations were carried out to check the suitability of the SrBPO5 host for the phosphor applications. The optical bandgap of the phosphors was obtained from the recorded diffuse reflectance spectra. The orange-red emission of Pr3+ got enhanced significantly in the presence of UO22+ codopant due to energy transfer from UO22+ to Pr3+. Interestingly, the UO22+ codoping resulted in Stark splitting of Pr3+ emission. The lifetime decay measurements confirmed the energy transfer and the Time-resolved emission spectra suggested dual-site occupancy of the uranyl ion in the SrBPO5 host.

Dynamics of electron transfer in melanin-trinitrofluorenone system

The kinetics of photoluminescence (PL) and time-resolved emission spectra (TRES) of melanin solutions with an effective electron acceptor 2,4,7-trinitrofluorenone (TNF) have been studied. Based on the analysis of the kinetic decay curves and TRES, the fast and slow PL decay components can be distinguished, which characterize the processes of a relaxation of excited states and charge transfer in the melanin-TNF molecular system. In this paper, the observed dependences have been analyzed and the model to explain such behavior of PL dynamic characteristics has been proposed.

Earth as an Exoplanet. I. Time Variable Thermal Emission Using Spatially Resolved Moderate Imaging Spectroradiometer Data

Abstract Among the more than 4000 exoplanets known today, some terrestrial planets have been detected in the so-called habitable zone of their host stars and their number is expected to increase in the near future, energizing a drive to understand and interpret the eagerly awaited wealth of data to identify signs of life beyond our solar system. So far, Earth remains the best and only example of a habitable (and inhabited) world. Although, it seems extremely unlikely that any other exoplanets will be true Earth twins, it is important to explore and understand the full range of spectral signatures and variability of Earth in order to inform the design of future instruments and missions, and understand their diagnostic power as well as potential limitations. In this work we use Earth observation data collected by the MODIS instrument aboard the Aqua satellite. The complete data set comprises 15 years of thermal emission observations in the 3.66–14.40 μm range for five different locations on Earth (Amazon Rainforest, Antarctica, Arctic, Indian Ocean, and the Sahara Desert). We then determine flux levels and variations as a function of wavelength and surface type (i.e., climate zone and surface thermal properties) and investigate whether periodic signals indicating Earth’s tilted rotation axis can be detected. Our findings suggest that (1) viewing geometry plays an important role when thermal emission data is analyzed as Earth’s spectrum varies by a factor of three and more depending on the dominant surface type underneath; (2) typically strong absorption bands from CO2 (15 μm) and O3 (9.65 μm) are significantly less pronounced and partially absent in data from the polar regions implying that estimating correct abundance levels for these molecules might be challenging in these cases; and (3) the time-resolved thermal emission spectrum encodes information about seasons/planetary obliquity, but the significance depends on the viewing geometry and spectral band considered.

Regulation of an Ambient‐Light‐Induced Photocyclization Pathway (Norrish–Yang Versus 6π) by Substituent Choice

A series of donor/acceptor chromophores 1d-3d containing two types of photoresponsive motifs, namely an electron-deficient BF2-chelated ketone fused with an electron-rich thiophene have been synthesized and their photochromic performance are investigated. The results reveal that simple variation of R substituents on the diaryl moiety allows one to control the intramolecular photocyclization mechanism with high photochemical selectivity, e.g., under ambient light, methyl-substituted 1d and 2d undergo 6π photocyclization, whereas ethyl-substituted 3d exclusively undergoes Norrish-Yang photocyclization. Single-crystal X-ray analysis of Norrish-Yang cyclization products reveals the formation of four pairs of conformational enantiomers differing in the dihedral angle between benzothiophene and the BF2 core. The UV-vis absorption spectra of 1d-3d cover a broad visible light region (380-572 nm), while theoretical calculations reveal that absorption in this region is dominated by the charge transfer (CT) transition from the thiophene-centered HOMO to the LUMO of the electron-deficient π-conjugated BF2-chelated unit. The spatial separation of the HOMO and LUMO of these dyes promotestriplet state generation and self-photosensitizes intramolecular photocyclization in the visible light region. Three-dimensional time-resolved and steady-state emission spectra of 3d show that the Norrish-Yang photocyclization takes place within milliseconds with excellent conversion efficiency (96%).

Far-red emitting Mg2La3NbO9:Mn4+ powder phosphor: Synthesis and luminescence properties

Novel Mg2La3NbO9:Mn4+ powder phosphors are successfully synthesized by the high-temperature solid-state reaction method under ambient air. The crystal structure, morphology, decay lifetimes, time-resolved emission spectra, and luminescence properties are investigated. The excitation spectrum of Mg2La3NbO9:Mn4+ phosphor monitored at 708 nm is observed in the region from 210 nm to 600 nm. Mg2La3NbO9:Mn4+ phosphor with excitation at the ultraviolet (UV) and blue light can emit the far-red emission with the emission band peaking at ~708 nm because of the 2E → 4A2 transition of Mn4+ and the corresponding chromaticity coordinates (0.7322, 0.2678). The optimal doping concentration of Mn4+ ion is ~0.6 mol%. The decay lifetime of Mg2La3NbO9:xMn4+ phosphors decrease from 1.143 ms to 1.099 ms with increasing the Mn4+ ion concentration from 0.2 mol% to 1.0 mol%. The good thermal stability of Mg2La3NbO9:Mn4+ phosphor is confirmed by the temperature-dependent emission spectra. The luminous mechanism of Mg2La3NbO9:Mn4+ phosphor is explained by using the Tanabe Sugano energy level diagram of Mn4+ ion. All the experimental results imply that Mg2La3NbO9:Mn4+ phosphor has a potential application in the white light-emitting diodes (LEDs) field.

Monitoring the Assembly and Aggregation of Polypeptide Materials by Time-Resolved Emission Spectra.

Polypeptide assembly and aggregation are the common forms of its physiological and pathological activity, and monitoring them on a molecular level is critical for resolving numerous medical (e.g., onset of neurodegenerative diseases) or biological problems. Sensitivity of the intrinsic fluorescence of protein to its assembly, aggregation, or complexation offers a noninvasive methodology for identifying and determining different stages of these processes. In this protocol, we present the approach based on the time-resolved emission spectra (TRES), which reveals the number of fluorescent residues, the presence of dielectric relaxation, and the changes in fluorescence kinetics during aggregation.

Coumarin Partitioning in Model Biological Membranes: Limitations of log P as a Predictor.

Time-resolved fluorescence measurements were used to quantify partitioning of three different 7-aminocoumarin derivatives into DPPC vesicle bilayers as a function of temperature. The coumarin derivatives were structurally equivalent except for the degree of substitution at the 7-amine position. Calculated log P (octanol: water partitioning) coefficients, a common indicator that correlates with bioconcentration, predict that the primary amine (coumarin 151 or C151) would experience a ∼40-fold partition enrichment in polar organic environments (log PC151 = 1.6) while the tertiary amine's (coumarin 152 or C152) concentration should be >500 times enhanced (log PC152 = 2.7). Both values predict that partitioning into lipid membranes is energetically favorable. Time-resolved emission spectra from C151 in solutions containing DPPC vesicles showed that within detection limits, the solute remained in the aqueous buffer regardless of temperature and vesicle bilayer phase. C152 displayed a sharp uptake into DPPC bilayers as the temperature approached DPPC's gel-liquid crystalline transition temperature, consistent with previously reported results ([ J. Phys. Chem. B 2017, 121, 4061-4070]). The secondary amine, synthesized specifically for these studies and dubbed C151.5 with a measured log P value of 1.9, partitioned into the bilayer's polar head group with no pronounced temperature dependence. These experiments illustrate the limitations of using a gross descriptor of preferential solvation to describe solute partitioning into complex, heterogeneous systems having nanometer-scale dimensions. From a broader perspective, results presented in this work illustrate the need for more chemically informed tools for predicting a solute tendency for where and how much it will bioconcentrate within a biological membrane.

Spectroscopic studies of the excited-state intramolecular proton and electron transfer processes of methyl benzoate derivatives in cucurbit[7]uril nanocage

The encapsulation of four methyl benzoate derivatives (I-IV) in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB[7]) was studied using steady-state, time-resolved and 1H NMR spectroscopic techniques. The significant changes in the steady-state and time-resolved fluorescence spectra (and calculated from them fluorescence decay times) were attributed to the formation of a well-defined, stable 1:1 inclusion complex. To understand the mechanism of supramolecular solvation dynamics, the time-dependent fluorescence Stokes' shifts, represented by the normalized spectral response function c(t), were studied. Our studies have shown that solvation dynamics of water are significantly inhibited inside a cucurbit cavity. The experimental results were also used to calculate, according to Benesi-Hildebrand plot and nonlinear least-squares regression analysis, equilibrium constants of the formed inclusion complex. For all investigated dyes, the K1 value is significantly larger than this previously calculated for I-IV inclusion into cyclodextrins (CDs), indicating the superior host abilities of CB[7] as compared to CDs. The position of the guest molecule inside the host cavity was investigated by 1H NMR experiment. The nature of the 1H NMR shifts for different protons is qualitatively different for methoxy derivative-CB[7] complex (I-CB[7] and III-CB[7] systems) and hydroxy derivative-CB[7] complex (II-CB[7] and IV-CB[7] systems), which indicates that the inclusion complexes of hydroxy and methoxy derivatives with CB[7] are of a difference in nature. The CB[7]-induced chemical shifts clearly demonstrate that for II-CB[7] and IV-CB[7] complexes, benzene ring is fully embedded in the interior of CB[7], while for I-CB[7] and III-CB[7] complexes, only the part of the benzene ring is located within the CB[7] cavity. Finally, 1H NMR chemical shifts and evolution of the steady-state and time-resolved emission spectra clearly indicate that -NMe2 group attached to the III and IV is located outside of the CB[7] portal.

Total Emission Time Resolved Decay: a Method for Measurement and Resolution of Broad-Band Emission.

This article reports a time-resolved fluorescence data acquisition technique termed as "Total Emission Time Resolved Decay" (TETRD). TETRD is recorded by using zero-order diffraction of emission grating in TCSPC instrument. TETRD decay curve has entire wavelength dependent decay information buried in it. Cut-off filters are used to avoid scattering contamination. Two existing approaches are used for analysing the interconnected TETRD data. (i) First, global analysis: for discretely decaying multiple components, TETRD dataset is analyzed using global analysis. The normalized pre-exponentials (αi) and relative amplitudes (fi) recovered from global analysis reflect the individual component emission more faithfully and resembles with steady-state spectral data as well. (ii) Second, stretched exponential fitting (StrEF): for continuous lifetime distribution systems, StrEF (I(t) = I0 exp[-(t/τ)1/h]) has been used to analyse TETRD data. The average lifetime (τ) of StrEF matches well with the average lifetime of multi-exponential fitting, the heterogeneity factor (h) of StrEF is an additional parameter, which informs about local heterogeneity in the system. It is shown that the lifetimes obtained with TETRD matches well with the lifetimes obtained using conventional time resolved emission spectra (TRES). TETRD holds advantage in rapid data acquisition and facilitates inclusion of another variable (like concentration, solvent composition, pH, excitation wavelength etc.) into experimental design. Further, with the use of an appropriate data analysis tool, the multi-component decay profiles can be resolved conveniently.

A New Near‐Infrared Long Persistent Luminescence Material with Its Outstanding Persistent Luminescence Performance and Promising Multifunctional Application Prospects

AbstractIn this work, a novel near‐infrared (NIR) persistent luminescence (PersL) material Na2CaGe5SiO14 (NCGSO):Cr3+ is designed and prepared. The phase composition and crystal structure are analyzed by X‐ray diffraction (XRD) and Rietveld structural refinement. The band gap of NCGSO is calculated to be 4.245 eV by density functional theory (DFT) and confirmed by diffuse reflection spectroscopy (DRS). It is determined by the photoluminescence (PL) spectra, X‐ray absorption near‐edge spectroscopy (XANES), and time‐resolved emission spectra (TRES) that three Ge4+ sites can be superseded simultaneously when Cr3+ ions are doped. In addition, the PL, photoluminescence excitation (PLE), and PersL performance are analyzed systematically. Under the radiation of 254 nm ultraviolet (UV) lamp, the samples exhibit excellent PL and PersL performance in the range of 600–900 nm, and the optimal afterglow duration lasts for more than 10 h. According to results, a possible mechanism is proposed to explain the PersL phenomenon. In the end, a set of information encrypted digital labels is designed and biological tissue penetration experiments are performed. The results reveal the potential of NCGSO:Cr3+ for information encryption and biological imaging applications.

Excited-State Proton Transfer in 8-Azapurines I: A Kinetic Analysis of 8-Azaxanthine Fluorescence.

A super-continuum white laser with a half-pulse width of ~75 ps was used to observe the kinetics of a postulated excited-state proton transfer in 8-azaxanthine and its 8-methyl derivative. Both compounds exhibited dual emissions in weakly acidified alcoholic media, but only one band was present in aqueous solutions, exhibiting an abnormal Stokes shift (>12,000 cm−1). It was shown that long-wavelength emissions were delayed relative to the excitation pulse within alcoholic media. The rise time was calculated to be 0.4–0.5 ns in both methanol and deuterated methanol. This is equal to the main component of the fluorescence decay in the short-wavelength band (340 nm). Time-resolved emission spectra (TRES) indicated a two-state photo-transformation model in both compounds. Global analysis of the time dependence revealed three exponential components in each compound, one of which had an identical rise-time, with the second attributed to a long-wavelength band decay (6.4 ns for aza-xanthine and 8.3 ns for its 8-methyl derivative). The origin of the third, intermediate decay time (1.41 ns for aza-xanthine and 0.87 ns for 8-methyl-azaxanthine) is uncertain, but decay-associated spectra (DAS) containing both bands suggest the participation of a contact ion pair. These results confirm the model of phototautomerism proposed earlier, but the question of the anomalous isotope effect remains unsolved.

Europium-Doped Ceria-Gadolinium Mixed Oxides: PARAFAC Analysis and High-Resolution Emission Spectroscopy under Cryogenic Conditions for Structural Analysis.

Gadolinium-doped ceria or gadolinium-stabilized ceria (GDC) is an important technical material due to its ability to conduct O2- ions, e.g., used in solid oxide fuel cells operated at intermediate temperature as an electrolyte, diffusion barrier, and electrode component. We have synthesized Ce1-xGdxO2-y:Eu3+ (0 ≤ x ≤ 0.4) nanoparticles (11-15 nm) using a scalable spray pyrolysis method, which allows the continuous large-scale technical production of such materials. Introducing Eu3+ ions in small amounts into ceria and GDC as spectroscopic probes can provide detailed information about the atomic structure and local environments and allows us to monitor small structural changes. This study presents a novel approach to structurally elucidate europium-doped Ce1-xGdxO2-y:Eu3+ nanoparticles by way of Eu3+ spectroscopy, processing the spectroscopic data with the multiway decomposition method parallel factor (PARAFAC) analysis. In order to perform the deconvolution of spectra, data sets of excitation wavelength, emission wavelength, and time are required. Room temperature, time-resolved emission spectra recorded at λex = 464 nm show that Gd3+ doping results in significantly altered emission spectra compared to pure ceria. The PARAFAC analysis for the pure ceria samples reveals a high-symmetry species (which can also be probed directly via the CeO2 charge transfer band) and a low-symmetry species. The GDC samples yield two low-symmetry spectra in the same experiment. High-resolution emission spectra recorded under cryogenic conditions after probing the 5D0-7F0 transition at λex = 575-583 nm revealed additional variation in the low-symmetry Eu3+ sites in pure ceria and GDC. The total luminescence spectra of CeO2-y:Eu3+ showed Eu3+ ions located in at least three slightly different coordination environments with the same fundamental symmetry, whereas the overall hypsochromic shift and increased broadening of the 5D0-7F0 excitation in the GDC samples, as well as the broadened spectra after deconvolution point to less homogeneous environments. The data of the Gd3+-containing samples indicates that the average charge density around the Eu3+ ions in the lattice is decreased with increasing Gd3+ and oxygen vacancy concentration. For reference, the Judd-Ofelt parameters of all spectra were calculated. PARAFAC proves to be a powerful tool to analyze lanthanide spectra in crystalline solid materials, which are characterized by numerous Stark transitions and where measurements usually yield a superposition of different contributions to any given spectrum.

Laser-induced multiphoton and collisional ionizations in sodium-argon mixture

It is attractive to investigate the interaction mechanism between metal and rare gas atoms within ionization process, especially for the mixture of metal vapor and rare gas. In this paper, laser-induced breakdown spectroscopy is used to study the ionization and recombination kinetic processes in sodium-argon mixture. Sodium-argon excimer is formed by the atomic collision, and it plays an important role in the ionization process, sodium atoms on 3P state are produced after the dissociation of excimer, then multiphoton ionization happens, the electrons in plasma are accelerated to collide with argon atoms, electron-impact ionization of argon will take place, identified with time-resolved atomic emission spectrum. Population accumulate on 3D,4P, and 5S states after the recombination process of Na+ with electron, then most population will transit to 3P state mainly by collisional relaxation.

Energy transfer, structural and luminescent properties of the color tunable phosphor Y2WO6:Sm3+

Abstract Inorganic phosphors based on monoclinic Y2WO6 doped with Sm3+ ions were prepared via conventional solid-state reactions at high temperature. A total of six samples were obtained with different Sm3+ concentrations (0–9%). The purity of the as-prepared phases was checked by powder X-ray diffraction (PXRD). The excitation, emission, and time-resolved emission spectra were examined in detail. The experimental decay curves were fitted to the Inokuti–Hirayama model, showing that the Sm3+ ions form clusters at all compositions. Periodic hybrid density functional theory calculations were also carried out on the undoped material and on 144-atom supercells of stoichiometry Y1.9375Sm0.0625WO6 and Y1.875Sm0.125WO6. The different coordination environments at the Y1, Y2 and Y3 sites are analysed in detail. The calculated structure and band gap of Y2WO6 are in good agreement with experiment with one potentially important discrepancy in a Y3–O bond length. The thermodynamically favoured substitution sites for Sm, Y2 and Y3, in the supercell are not those observed under the preparation conditions used here, since the experimental Rietveld analysis suggests occupation of Y1 at all concentrations. Analogous calculations for the Eu-doped system highlight marked differences between Eu and Sm despite their similar ionic sizes. The calculated densities of states show the position of the 4f levels in the band gap depend on the sites occupied by the dopants and thus expect marked differences in the luminescence spectra, opening up possibilities for tuning device performance.

Investigation on OLEDs efficiency roll-off with interfacial charge storage and their time-resolved emission spectra

Abstract Organic light-emitting diodes (OLEDs) are the next generation technique of display and lighting, confronted with the bottle-neck problem of OLEDs efficiency roll-off. The nature of luminescence and efficiency roll-off of OLEDs are processes of electrons and energy, during which charge injection and storage play important roles. In order to study the mechanism of OLEDs efficiency roll-off with interfacial charge storage, organic light-emitting devices with Ir(ppy)3 doped CBP as the light-emitting layer were prepared, and PMMA layers of 5 nm, 6 nm, 8 nm and 9 nm were inserted as charge storage layers to control hole injection and hole accumulation. The OLEDs efficiency roll-off is obvious with the increase of the current density. The storage of t he interfacial charges is analyzed by transient electroluminescence measurement. Luminescence spikes occur at both forward and reverse turn-off voltages, which is caused by electron diffusion and trap carriers release, respectively. The time-resolved emission spectra prove the relationship of interfacial charges and exciton quenching. The OLEDs efficiency roll-off is positively correlated with the interfacial charge storage especially at low current density. This is due to the effect of the accumulation of the interfacial charge especially under unbalanced charge injection of OLEDs, which is of importance to improve the OLEDs performance and to decrease the OLEDs efficiency roll-off in industry.

Characterization of melanoidin formed from glucose with alanine by Fluorescence spectroscopy and redox chemistry in vitro cells

تشخيص وتوصيف الملانويدين المتشكل من السكر المختزل مع الحامض الأميني بواسطة مطيافية الفلورة كيميائيا وبيلوجيا. وأثبت الباحث أن الميلانويدين قبل الديلزة كان الاعلى امتصاص، ثم الميلانويدين بعد الديلزه، بعد ذلك الميلانويدين بعد الديلزه المعامل بايونات النحاس المعقدة على التوالي. وتم استخدام تقنية TRES في تشخيص الميلانويدين ولأول مرة، وذلك من أجل الحصول على نتائج أفضل. اختزال اللون البني وانخفاض امتصاصية الميلانويدين كان بسبب ارتفاع تركيز بيروكسيد الهيدروجين، حيث استخدمت التراكيز 100 و200مايكرولتر. أثبت الباحث أن الميلانويدين لا يستطيع اختراق خلايا CHO-K1عند إضافة المركب إلى الخلايا خلال ساعة أو ساعتين، ولكن عند مرور 24 ساعة ظهرت نتائج مثيره للاهتمام.

Concentration - dependent fluorescence properties of Nile Red in TiO2 based thin films

Abstract Thin films of Nile Red in TiO2 matrix were prepared with the sol–gel method for different dye concentrations. It was found that at high dye concentration fluorescence and absorption spectra as well as fluorescence intensity decay and time-resolved fluorescence spectra exhibit strong changes. In particular, fluorescence spectra profiles are strongly shifted to the red in a way typical of aggregate formation. Fluorescence intensity decays much faster with increase in concentration in the monomer band due to Nile Red aggregate formation and excitation energy trapping. Time-resolved fluorescence spectra exhibit strong evolution. Clear formation of aggregate band at the red part of time-resolved emission spectra was observed.

Time-resolved photoluminescence study of excited states in nanostructured melanin

Time resolved emission spectra (TRES), 3D maps of photoluminescence excitation-emission (PLE maps), 3D maps of TRES, and kinetics of photoluminescence (PL) spectra of natural and synthetic melanin, as well as melanin composites with surfactant, sodium dodecyl benzenesulfonate, have been studied. The kinetics of PL and TRES for the melanin and the composites were investigated at low temperatures that allowed to discuss melanin’s intermolecular complexation, nano-aggregation and formation of charge transfer states. Particularly, the radiation of Frenkel excitons from fragments of different degrees of conjugation that are the parts of molecular nanodisks of melanin is observed. Furthermore, charge transfer excitons (CT-excitons) can be formed and observed at both room and helium temperatures. Some bands in the PL spectra of melanin, depending on temperature, behave like excimer radiation. The studies are aiming to understand the electronic properties of various melanins, particularly natural ones.

Mechanism for tunable broadband white photoluminescence of one-dimensional (C4N2H14)2Pb1-xMnxBr4 perovskite microcrystals

This work demonstrated that tunable photoluminescence of the low-dimensional hybrid halide perovskites via the doping strategy is feasible, and hence paves the way towards the investigation and application of high-performance single photoluminescence perovskite material with broadband white light emission. This work reported the first synthesis of one-dimensional (1D) (C4N2H14)2Pb1-xMnxBr4 perovskite microcrystals (MCs) with tunable broadband white-light emission and long-lived STE (self-trapped exciton) emission. The overall photoluminescence mechanism under the regulation of defect engineering of 1D (C4N2H14)2Pb1-xMnxBr4 MCs was formulated for the first time. Photoluminescence mechanism of these MCs involves competition of FE (free exciton) and STE and 4T1 states. This competitive mechanism further promotes photoluminescence tunability ranging from blue-white to white to orange-red for Mn-doped MCs. Moreover, time-resolved emission spectra show the changes of lifetime of these MCs at different emission wavelength. These perovskite MCs have a long-lived STE emission, which indicates that the more effective exciton combinations are occurring in them. For comparation, the Mn-doping strategy can regulate structural defect of these MCs, which promotes or suppresses transitions of FE→STE, FE→4T1, STE→FE and further tunes photoluminescence. This work paves the way towards the investigation and development of optoelectronic application of perovskite MCs material.

Buried Liquid Interfaces as a Form of Chemistry in Confinement: The Case of 4-Dimethylaminobenzonitrile at the Silica-Aqueous Interface.

Time-resolved fluorescence emission and resonance-enhanced second harmonic generation (SHG) spectra were collected from 4-dimethylaminobenzonitrile (DMABN) adsorbed to the aqueous-silica interface in order to identify how strongly associating solvent-substrate interactions change DMABN's photoisomerization properties. In bulk polar solution, DMABN forms an excited twisted intramolecular charge-transfer (TICT) state that emits with a distinctive, solvatochromic fluorescent signature. At the silica-aqueous interface, the TICT fluorescence disappears, similar to DMABN's behavior in nonpolar environments. SHG spectra confirm that the interface is, in fact, polar, and DMABN's unusual fluorescence emission acquired from the interface is attributed to strong hydrogen bonding associations between the water molecules and the silica surface that prevent adsorbate isomerization. Additionally, SHG spectra show a strong resonance at long wavelengths that is unexpected based on bulk absorbance spectra and selection rules for nonlinear hyperpolarizabilities. Using both Zerner's INDO semiempirical and TD-DFT calculations, this spectroscopic behavior is attributed to a combination of strong electric fields present at the aqueous-silica interface and surface-induced changes to DMABN's ground-state molecular structure.