Formation Of Charge Transfer State Research Articles

Adsorption patterns of caffeic acid on titania: affinity, charge transfer and sunscreen applications

ABSTRACTSeveral photo-induced processes contribute to titania-catalysed photodegradation of organic UV-absorbing compound, caffeic acid (CA), utilised as skin photoprotector in sunscreens containing titania. Optical transitions, channels of photoexcitations, and charge transfer state formation in anatase TiO2 nanowire sensitised by CA are computed and analysed. Trends of charge transfer state formation are explored through modelling of non-adiabatic dynamics using reduced density matrix approach combined with density functional theory with Perdew–Burke–Ernzerhof functional, in the basis of plane waves, using Vienna Ab initio Simulation Package software. The electronic structure of the explored model shows signatures of quantum confinement of TiO2 nanowire. A change of excitation energy provides control of either one of the possible channels for photoexcitations: (1) local excitation at either nanowire or CA-adsorbate or (2) photo-induced electron transfer from CA-adsorbate to titania. The conclusions obtained from this computational modelling deliver further understanding of the adsorption of catechol groups on the surface of titania nanowire that will help in designing titania-based materials least damaging to CA and skin.

The postfunctionalization performance with poly(N-vinylcarbazole): A nonlinear optical properties and ultrafast response study

In this work, poly(N-vinylcarbazole)(PVK) together with two dispersed red one (DR1) based compounds DR1-T (T is short for triphenylamine), DR1-PVK, were investigated to study the effect of postfunctionalization performance on the nonlinear absorption and ultrafast response of dispersed red one dyes. Femtosecond Z-scan and pump-probe measurement were carried out at room temperature. The postfunctionalization performance on PVK was proved to efficiently meliorated nonlinear optical properties of chromophore DR1. DR1-PVK show very large two photon absorption up to 11371GM and good optical limiting property. The ultrafast dynamics show a fast photoresponse about 1ps, which reflect the formation of the intra-molecular charge transfer (ICT) state, another relative long decay process is attributed to the relaxation of the ICT state.

Time-Resolved Charge-Transfer State Emission in Organic Solar Cells: Temperature and Blend Composition Dependences of Interfacial Traps

Charge-transfer (CT) states across organic heterojunctions play an important role in determining the efficiency of organic solar cells. These states can be the precursors of free charges or lead to geminate recombination losses. Here, we use time-resolved photoluminescence measurements to study charge-transfer states in a sequence of polythiophene:fullerene derivative blends with different mixing ratios, over the temperature range from 10 to 290 K, and after excitation with various photon energies. Our results show that (1) excess fullerene leads to a higher probability of CT state formation per absorbed photon and (2) the CT emission intensity is temperature-dependent whereas its emission lifetime is temperature-independent. Observation 1 cannot be explained solely by the increased fraction of excitations formed on fullerene-derivatives in the fullerene-rich blends, suggesting that disruption of the polymer packing at high fullerene loadings can negatively influence charge separation. Observation 2 suggests that relaxed, emissive CT states are formed in this system through a short-lived intermediate state whose separation into free-charges or relaxation into a bound CT state is temperature-dependent. Analysis of the temperature dependence suggests that there is no single activation energy for the CT*-to-CS transition, but rather a wide variety of different sites ranging in activation energy.

Solvation-driven charge transfer and localization in metal complexes.

ConspectusIn any physicochemical process in liquids, the dynamical response of the solvent to the solutes out of equilibrium plays a crucial role in the rates and products: the solvent molecules react to the changes in volume and electron density of the solutes to minimize the free energy of the solution, thus modulating the activation barriers and stabilizing (or destabilizing) intermediate states. In charge transfer (CT) processes in polar solvents, the response of the solvent always assists the formation of charge separation states by stabilizing the energy of the localized charges. A deep understanding of the solvation mechanisms and time scales is therefore essential for a correct description of any photochemical process in dense phase and for designing molecular devices based on photosensitizers with CT excited states.In the last two decades, with the advent of ultrafast time-resolved spectroscopies, microscopic models describing the relevant case of polar solvation (where both the solvent and the solute molecules have a permanent electric dipole and the mutual interaction is mainly dipole–dipole) have dramatically progressed. Regardless of the details of each model, they all assume that the effect of the electrostatic fields of the solvent molecules on the internal electronic dynamics of the solute are perturbative and that the solvent–solute coupling is mainly an electrostatic interaction between the constant permanent dipoles of the solute and the solvent molecules. This well-established picture has proven to quantitatively rationalize spectroscopic effects of environmental and electric dynamics (time-resolved Stokes shifts, inhomogeneous broadening, etc.). However, recent computational and experimental studies, including ours, have shown that further improvement is required.Indeed, in the last years we investigated several molecular complexes exhibiting photoexcited CT states, and we found that the current description of the formation and stabilization of CT states in an important group of molecules such as transition metal complexes is inaccurate. In particular, we proved that the solvent molecules are not just spectators of intramolecular electron density redistribution but significantly modulate it.Our results solicit further development of quantum mechanics computational methods to treat the solute and (at least) the closest solvent molecules including the nonperturbative treatment of the effects of local electrostatics and direct solvent–solute interactions to describe the dynamical changes of the solute excited states during the solvent response.

Inter/Intrachain Interactions Behind the Formation of Charge Transfer States in Polyspirobifluorene: A Case Study for Complex Excited-State Dynamics in Different Polarity Index Solvents

In this work, we demonstrate the complex excited-state nature of the conjugated polymer, polyspirobifluorene (PSBF), using steady-state and time-resolved spectroscopy techniques to understand the origin of excited charge transfer state (CT) formation and their contribution to the total photoluminescence (PL). The measurements were compared in two solvents with different polarity, for example, methyl cyclohexane (MCH) and 2-methyltetrahydrofuran (2-MeTHF), which allow us to reveal solvent quality and temperature dependent CT state formation arising from “inter/intrachain” interaction phenomena. The inter/intrachain interactions are explained by means of spatial conformational changes of the polymer chain configuration, such as coiling and collapse of the backbone with concomitant side chain reorganization. It has been found that the PL emission at room temperature (RT) demonstrates a mixed state configuration containing contributions from 1(π, π*) excited states along with the CT states contribution, with the spectra arising from a mixture of the two emissive species. However, with decreasing temperatures to ca. 145 K (prior to the freezing point) in 2-MeTHF, the two emissive species become separated, with the emission from the CT state showing a red-shift with decreasing temperature. At 145 K, we observe the formation of an unstructured, wholly new emission band, which is strongly red-shifted relatively to the 1(π, π*) excited-state and shows classic Gaussian line shape. This emission is attributed to the formation of “inter/intrachain” CT states. In the case of frozen solutions (∼90 K), the spectra dramatically blue-shifts and loses all contribution from the “inter/intrachain” species, and emission then arises completely from the pure “intrachain” CT excitonic state. The behavior of the polymer is strongly dependent on both solvent quality and temperature effects on the excited state geometry relaxation by means of the local solvent–solute interactions that stabilize the CT states, due to solvation of the new charge distribution, and also changes on the transition states via manipulating energy barriers.

Mechanism of the intramolecular charge transfer state formation in all-trans-β-apo-8'-carotenal: influence of solvent polarity and polarizability.

In this work we analyzed the infrared and visible transient absorption spectra of all-trans-β-apo-8'-carotenal in several solvents, differing in both polarity and polarizability at different excitation wavelengths. We correlate the solvent dependence of the kinetics and the band shape changes in the infrared with that of the excited state absorption bands in the visible, and we show that the information obtained in the two spectral regions is complementary. All the collected time-resolved data can be interpreted in the frame of a recently proposed relaxation scheme, according to which the major contributor to the intramolecular charge transfer (ICT) state is the bright 1Bu(+) state, which, in polar solvents, is dynamically stabilized through molecular distortions and solvent relaxation. A careful investigation of the solvent effects on the visible and infrared excited state bands demonstrates that both solvent polarity and polarizability have to be considered in order to rationalize the excited state relaxation of trans-8'-apo-β-carotenal and clarify the role and the nature of the ICT state in this molecule. The experimental observations reported in this work can be interpreted by considering that at the Franck-Condon geometry the wave functions of the S1 and S2 excited states have a mixed ionic/covalent character. The degree of mixing depends on solvent polarity, but it can be dynamically modified by the effect of polarizability. Finally, the effect of different excitation wavelengths on the kinetics and spectral dynamics can be interpreted in terms of photoselection of a subpopulation of partially distorted molecules.

Ionic Bonding between Artificial Atoms

Conventional solids are prepared from building blocks that are conceptually no larger than a hundred atoms. While van der Waals and dipole-dipole interactions also influence the formation of these materials, stronger interactions, referred to as chemical bonds, play a more decisive role in determining the structures of most solids. Chemical bonds that hold such materials together are said to be ionic, covalent, metallic, dative, or otherwise a combination of these. Solids that utilize semiconductor nanocrystal quantum dots as building units have been demonstrated to exist; however, the interparticle forces in such materials are decidedly not chemical. Here we demonstrate the formation of charge transfer states in a binary quantum dot mixture. Charge is observed to reside in quantum confined states of one of the participating quantum dots. These interactions lead to materials that may be regarded as the nanoscale analog of an ionic solid. The process by which these materials form has interesting parallels to chemical reactions in conventional chemistry.

Polarization Imaging of Emissive Charge Transfer States in Polymer/Fullerene Blends

Photoexcitation of conjugated polymer–fullerene blends results in population of a local charge transfer (CT) state at the interface between the two materials. The competition between recombination and dissociation of this interfacial state limits the generation of fully separated free charges. Therefore, a detailed understanding of the CT states is critical for building a comprehensive picture of the organic solar cells operation. We applied a new fluorescence microscopy method called two-dimensional polarization imaging to gain insight into the orientation of the transition dipole moments of the CT states, and the associated excitation energy transfer processes in TQ1:PCBM blend films. The polymer phase was oriented mechanically to relate the polymer dipole moment orientation to that of the CT states. CT state formation was observed to be much faster than energy transfer in the polymer phase. However, after being formed an emissive CT state does not exchange excitation energy with other CT states, sugges...

A Detailed Analysis of Multiple Photoreactions in a Light-Harvesting Molecular Triad with Overlapping Spectra by Utrafast Spectroscopy

The photoreactions that occur in a molecular triad composed of derivatives of boron-dipyrromethene (BOD), diketopyrrolopyrrole (DPP), and of triphenylamine (TPA) specifically designed for the use as a possible donor material for organic solar cells are studied by ultrafast fluorescence and transient absorption spectroscopy with hyper spectral coverage (300–900 nm). While the latter is often sufficient to reveal the reaction scenario in mono- or bicomponent organic molecules, the overlap of ground state absorption and fluorescence spectra of the components present in the TPA-DPP-BOD triad requires a careful and accurate characterization of the excited state differential absorption spectra and kinetics of the individual isolated moieties. In addition, the absorption spectra of the TPA cation and the DPP and BOD anions are determined by in situ spectroelectrochemical experiments. Picosecond fluorescence demonstrates efficient excited state quenching of both DPP and BOD, with downhill energy transfer from TPA occurring in a subpicosecond time scale, leading to its complete excited state quenching. Additionally, an analysis of the multiexponential fluorescence decay indicates the existence of reactive (quenched) and nonreactive (radiative) subpopulations of DPP and BOD, most probably due to structural heterogeneities. In order to treat this complexity of multiple reaction pathways, the transient absorption data are analyzed by a combination of global fitting, providing decay-associated differential spectra (DADS), and a reconstitution of these DADS by linear combinations of the characteristic difference spectra of all molecular species and excited states. This allows us to disentangle the photoreactions that the TPA, DPP and BOD excited state subpopulations undergo on time scales ranging from 200 fs to a few ns, and to clarify the contribution of TPA as an electron donor in the formation of an intramolecular charge transfer (CT) state. DPP has a dual role as an ancillary light-harvesting unit capable of performing ultrafast energy transfer to BOD, and as an electron acceptor for the CT state. The latter has a remarkably long lifetime of 0.5 ns. We conclude that the triad could act as a very efficient electron-donor material in a blend with commonly used acceptors such as phenyl-C61-butyric acid methyl ester (PCBM).

TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4′-dimethylaminoflavonol in ethanol solvent

Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4′-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF–EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3–C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule.

Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins.

Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450–550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16–0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10–3, in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0–5.5 ps and then decays via recombination to the triplet or ground states in 0.9–3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11–22 ps.

Trap‐Assisted Recombination via Integer Charge Transfer States in Organic Bulk Heterojunction Photovoltaics

Organic photovoltaics are under intense development and significant focus has been placed on tuning the donor ionization potential and acceptor electron affinity to optimize open circuit voltage. Here, it is shown that for a series of regioregular‐poly(3‐hexylthiophene):fullerene bulk heterojunction (BHJ) organic photovoltaic devices with pinned electrodes, integer charge transfer states present in the dark and created as a consequence of Fermi level equilibrium at BHJ have a profound effect on open circuit voltage. The integer charge transfer state formation causes vacuum level misalignment that yields a roughly constant effective donor ionization potential to acceptor electron affinity energy difference at the donor–acceptor interface, even though there is a large variation in electron affinity for the fullerene series. The large variation in open circuit voltage for the corresponding device series instead is found to be a consequence of trap‐assisted recombination via integer charge transfer states. Based on the results, novel design rules for optimizing open circuit voltage and performance of organic bulk heterojunction solar cells are proposed.

Photophysics of a Coumarin in Different Solvents: Use of Different Solvatochromic Models

This study reported the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid N-succinimidyl ester (7-DCCAE) in different neat solvents of varying polarity using steady-state absorption, fluorescence emission and picosecond time-resolved spectroscopy. In nonpolar solvents, the dye molecule predominantly exists in nonpolar structure and exhibits very low value of nonradiative decay rate constant (k(nr)), demonstrating the emission takes place from S(1) -LE to S(0) ground state. The fluorescence quantum yields, lifetime values of 7-DCCAE in different solvents are rationalized on the basis of intramolecular charge transfer (ICT) followed by twisted intramolecular charge transfer state formation (TICT) as well as specific solute-solvent interactions. Several solvatochromic models (such as Lippert, Dimroth, Kamlet-Taft, Catalán 3P and Catalán 4P models) were used to analyze the solvatochromic shift of 7-DCCAE in different solvents. The different empirical models show that the observed results are better correlate for nonchlorinated solvents and provide statistically significant best-fit result. A comparison was done between comparatively new solvatochromic model (Catalán 3P and Catalán 4P model) with Kamlet-Taft model. The ground state structure of the said molecule was optimized by using Density Functional Theory (DFT).

Electrochromic properties of novel chalcones containing triphenylamine moiety

A series of novel electrochromic chalcones containing triphenylamine units were synthesized by Aldol reaction and characterized by NMR, IR and MS. Their optical, electrochemical properties were investigated using UV–vis, photoluminescence spectra and cyclic voltammetry. The molecular orbital energy levels and excitation energies were calculated by quantum chemical calculation. It was found that the fluorescence intensity is decreasing with formation of charge-transfer state. The existence of electron donating group on triphenylamine unites caused a significant bathochromic shift of the UV absorption maximum and increased EHOMO and ELUMO. The electrochromic property of the synthesized compounds was studied by spectroelectrochemical experiments. The results showed that the chalcones containing triphenylamine moiety presented good electrochromic stability, with a color change from yellow to blue as applied potentials ranging from 0.0 to 2.8 V. The coloring and bleaching time was in the range of 2.9–4.2 s and 1.7–3.3 s, respectively.

Acetylacetone anchoring group for NiO-based dye-sensitized solar cell

In this article, the viability of the first push–pull (nitrophenyl and hexyl-thiophene as acceptor and donor unit respectively) sensitizer functionalized with acetylacetone (acac) anchoring group was assessed for application in p-type dye sensitized solar cells (NiO-based). An effective synthetic strategy to introduce the acac directly to an aryl moiety was developed. Then, the UV–visible absorption, emission and electrochemical properties of this new sensitizer were determined. FT-IR spectroscopy revealed an effective binding of the acac group to NiO surface while time-dependent density functional theory (TD-DFT) calculations predicted a strong charge-transfer transition with no component of the LUMO centred on the acac. Ultrafast hole injection (<200 fs) from the dye excited state into the valence band (VB) of NiO was experimentally demonstrated by transient absorption spectroscopy studies. It was also shown that excitation of the sensitizer leads to the formation of a twisted intramolecular charge transfer (TICT) state. Finally, the photovoltaic performances of this dye were investigated in NiO based solar cells using the iodide/triiodide electrolyte. We measured promising power conversion efficiencies higher than that of the coumarin C343 benchmark reference albeit with a weaker light harvesting efficiency.

Structural Requirements for Surface-Induced Aromatic Stabilization

ABSTRACTSurface-induced aromatic stabilization (SIAS), a recently proposed mechanism leading to a formation of charge-transfer (CT) states at organic/metal (O/M) interfaces [G. Heimel, et al., Nat. Chem.5, 187 (2013)], was investigated for an aromatic hydrocarbon, diindenoperylene (DIP), by means of synchrotron radiation-based ultraviolet photoelectron spectroscopy (UPS). By employing DIP and noble metal substrates (Ag and Cu), we confirmed the formation of CT states, indicating that an inclusion of a specific functional group with a hetero-atom within adsorbate molecules as suggested before is not necessarily required for the formation of CT states mediated by the SIAS. With a comparison of the mother and analogue molecules, perylene and PTCDA, we discuss the structural requirement for the realization of the SIAS.

Dynamics of the Formation of a Charge Transfer State in 1,2-Bis(9-anthryl)acetylene in Polar Solvents: Symmetry Reduction with the Participation of an Intramolecular Torsional Coordinate

We have studied 1,2-bis(9-anthryl)acetylene as a model compound for the characterization of the process of solvent-mediated symmetry reduction in an excited state. Thanks to the acetylenic bridge that joins the two anthracenic moieties, this system maintains minimal steric hindrance between the end chromophores in comparison with the classic 9,9'-bianthryl model compound. The acetylenic bridge also allows for significant electronic coupling across the molecule, which permits a redistribution of electron density after light absorption. Femtosecond resolved fluorescence measurements were used to determine the spectral evolution in acetonitrile and cyclohexane solutions. We observed that, for 1,2-bis(9-anthryl)acetylene, the formation of a charge transfer state occurs in a clear bimodal fashion with well separated time scales. Specifically, the evolution of the emission spectrum involves a first solvent-response mediated subpicosecond stage where the fluorescence changes from that typical of nonpolar solvents (locally excited) to an intermediate, partial charge transfer state. The second stage of the evolution into a full charge transfer state occurs with a much longer time constant of 37.3 ps. Since in this system the steric hindrance is minimized, this molecule can undergo much larger amplitude motions for the torsion between the two anthracenic moieties associated with the charge redistribution in comparison with the typical model compound 9,9'-bianthryl. Clearly, the larger range of motions of 1,2-bis(9-anthryl)acetylene gives the opportunity to study the electron transfer process with a good separation of the time scales for the formation of a partial charge transfer state, determined by the speed of solvent response, and the intramolecular changes associated with the formation of the fully equilibrated charge transfer state.

The Influence of Push–Pull States on the Ultrafast Intersystem Crossing in Nitroaromatics

The photochemistry of nitro-substituted polyaromatic compounds is generally determined by the rapid decay of its S1 state and the rapid population of its triplet manifold. Previous studies have shown that such an efficient channel is due to a strong coupling of the fluorescent state with specific upper receiver states in the triplet manifold. Here we examine variations in this mechanism through the comparison of the photophysics of 2-nitrofluorene with that of 2-diethylamino-7-nitrofluorene. The only difference between these two molecules is the presence of a diethylamino group in a push-pull configuration for the latter compound. The femtosecond-resolved experiments presented herein indicate that 2-nitrofluorene shows ultrafast intersystem crossing which depopulates the S1 emissive state within less than a picosecond. On the other hand, the amino substituted nitrofluorene shows a marked shift in its S1 energy redounding in the loss of coupling with the receiver triplet state, and therefore a much longer lifetime of 100 ps in cyclohexane. In polar solvents, the diethylamino substituted compound actually shows double peaked fluorescence due to the formation of charge transfer states. Evaluation of the Stokes shifts in different solvents indicates that both bands correspond to intramolecular charge transfer states in equilibrium which are formed in an ultrafast time scale from the original locally excited (LE) state. The present study addresses the interplay between electron-donating and nitro substituents, showing that the addition of the electron-donating amino group is able to change the coupling with the triplet states due to a stabilization of the first excited singlet state and the rapid formation of charge transfer states in polar solvents. We include calculations at the TD-DFT level of theory with the PBE0 and B3LYP functionals which nicely predict the observed difference between the two compounds, showing how the specific S(π-π*)-T(n-π*) coupling normally prevalent in nitroaromatics is lost in the push-pull compound.

Role of Solvent on Charge Transfer in 7-Aminocoumarin Dyes: New Hints from TD-CAM-B3LYP and State Specific PCM Calculations.

Time-dependent B3LYP and CAM-B3LYP calculations have been used to investigate the absorption and emission energies as well as to shed light on the formation of the twisted intramolecular charge transfer state (TICT) in Coumarin-152 (C152) embedded in cyclohexane, acetonitrile, and water solvents. The bulk solvent effects have been included by using the linear-response (LR) and State-Specific (SS) models in the framework of the so-called polarizable continuum method (PCM). The results demonstrate that the choice of the exchange-correlation functional and of the PCM model is critical to reproduce the experimental data in the most accurate way. In particular, it has been observed that both the solvatochromic and Stokes' shifts are well reproduce by CAM-B3LYP/SSPCM calculations performed on the S0 and S1 geometries of C152 optimized at the B3LYP/LRPCM level of theory, whereas not accurate Stokes' shifts are computed with CAM-B3LYP/SSPCM calculations carried out on the CAM-B3LYP/LRPCM optimized structures. This is attributed to the incorrect (underestimated) solvation energy provided by LRPCM, which could lead to misleading results especially for charge-transfer excited state structures in polar solvents. Instead, B3LYP/LRPCM excited state optimizations seem to provide a reasonable geometry for a simple 'error cancellation' effect due to the balance among the B3LYP overstabilization of charge transfer states and the LRPCM underestimation of the solute-solvent binding energy when the former is in a polar solvent. Finally, CAM-B3LYP/SSPCM calculations, in very good agreement with experimental evidence, show that the formation of an accessible TICT state is possible for C152 and that the crossing between S0 and S1 states at a dihedral angle of around 70° occurs only in polar solvents.

Vibrational Spectroscopy of Electronic Processes in Emerging Photovoltaic Materials

Molecules affect the electronic properties of many emerging materials, ranging from organic thin film transistors and light emitting diodes for flexible displays to colloidal quantum dots (CQDs) used in solution processed photovoltaics and photodetectors. For example, the interactions of conjugated molecules not only influence morphological and charge transport properties of organic photovoltaic (OPV) materials, but they also determine the primary photophysical events leading to charge generation. Ligand-nanocrystal interactions affect the density and energetic distributions of trap states, which in turn influence minority carrier transport in CQD photovoltaics. Therefore, it is critical for scientists to understand how the underlying molecular structures and morphologies determine the electronic properties of emerging materials. Recently, chemists have used vibrational spectroscopy to study electronic processes in emerging materials, and been able to directly measure the influence molecular properties have on those processes. Time-resolved vibrational spectroscopy is uniquely positioned to examine molecular species involved in electronic processes because it combines ultrafast time resolution with measurement of the vibrational spectra of molecules. For instance, molecules at the electron donor/acceptor interfaces in OPV materials have unique vibrational features because vibrational frequencies of molecules are sensitive to their local molecular environments. Through ultrafast vibrational spectroscopy, researchers can directly examine the dynamics of charge transfer (CT) state formation and dissociation to form charge separated states specifically at donor/acceptor interfaces. Vibrational modes of ligands are also sensitive to their bonding interactions with nanocrystal surfaces, which enables chemists to directly probe the molecular nature of charge trap states in colloidal quantum dot solids. Because of the ability to connect electrical properties with the underlying molecular species, scientists can use ultrafast vibrational spectroscopy to address fundamental challenges in the development of emerging electronic materials. In this Account, we focus on two applications of vibrational spectroscopy to examine electronic processes in OPV and CQD photovoltaic materials. In the first application, we examine archetypal classes of electron acceptors in OPV materials and reveal how their molecular structures influence the dynamics and energetic barriers to CT state formation and dissociation. In the second application, we discuss the surface chemistry of ligand-nanocrystal interactions and how they impact the density and energetic distribution of charge trap states in CQD photovoltaic materials. Through direct observations of the vibrational features of ligands attached to surface trap states, we can obtain valuable insights into the nature of charge traps and begin to understand pathways for their elimination. We expect that further examination of electronic processes in materials using ultrafast vibrational spectroscopy will lead to new design rules in support of continued materials development efforts.