Linda A. Peteanu

Carnegie Mellon University | CMU · Department of Chemistry

Poly(3-alkylesterfurans) fold into helical conformations due to a preference for adjacent furan repeat units in the polymer backbone to adopt a syn conformation in which the oxygen atoms of the furan rings are oriented in the same direction. In this contribution, a new chiral helical poly(3-alkylesterfuran) is reported in which a cholesterol group...

In this study, the impact of ester side group regiochemistry on electronic and conformational properties of regioregular polyfurans was explored. A derivative with alternating head-to-head and tail-to-tail orientation of the side groups was synthesized and compared with its head-to-tail analogue, and these were benchmarked against the related regio...

Silicon nanoparticles (Si NPs) are of great interest to researchers due to their fluorescence properties, low toxicity, and the low cost of the Si precursor. Recent studies have shown that Si NPs surface-modified with secondary aryl amine ligands emit light at wavelengths ranging from cyan to yellow and with quantum yields of up to 90%. The predomi...

Deciphering the complicated excited-state process is critical for the development of luminescent materials with controllable emissions in different applications. Here we report the emergence of a photo-induced structural distortion accompanied by an electron redistribution in a series of gold nanoclusters. Such unexpected slow process of excited-st...

The origin of the near-infrared (NIR) photoluminescence (PL) from thiolate-protected gold nanoclusters (Au NCs, < 2 nm) has long been controversial, and the exact mechanism for the enhancement of quantum yield (QY) in many works remains elusive. Meanwhile, based upon the sole steady-state PL analysis, it is still a major challenge for researchers t...

Although bulk silicon (Si) is known to be a poor emitter, Si nanoparticles (NPs) exhibit size-dependent photoluminescence in the red or near-infrared due to quantum confinement. Recently it has been shown that surface modification of Si NPs with nitrogen-capped ligands results in bluer emission wavelengths and quantum yields of up to 90%. However,...

Molecules that undergo reverse intersystem-crossing (RISC) which enables thermally-activated delayed fluorescence (TADF) represent an important advance in the development of organic-based light emitting diodes (OLEDs). The current study focuses on two blue-emitting RISC molecules employing carbazole as the donor and benzothiazole or benzoxazole der...

Single-molecule Förster resonance energy transfer (smFRET) of freely diffusing biomolecules using confocal microscopy is a simple and powerful technique for measuring conformation and dynamics. However a spurious zero-FRET population can significantly distort the measured histograms and lead to incorrect results, particularly in measurements of int...

The aggregation of conjugated polymers in common organic solvents is investigated using fluorescence correlation spectroscopy (FCS), burst analysis, and microscopy. Poly(3-hexylthiophene) (P3HT) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) are both shown to form weakly-bonded non-emissive aggregates in toluene that persis...

It is of vital importance to theoretically understand unique nanoparticle size-tunable and excitation wavelength-dependent multiple optical properties in organic nanoparticle. In this work, we proposed a theoretical protocol to cal-culate the optical spectrum of the organic nanoparticles, which combines molecule dynamic (MD) simulation, quan-tum me...

One measure of exciton mobility in an aggregate is the efficiency of exciton-exciton annihilation (EEA). Both exciton mobilities and EEA are enhanced for aggregate morphologies in which the distances between chromophores and their relative orientations are favorable for Förster energy transfer. Here this principle is applied to gauge the strength o...

The structure of ionic liquids (ILs) surrounding solute dyes and the effects of solvent structure on solute diffusion are investigated using molecular dynamics (MD) and the experimental tools of confocal and fluorescence correlation spectroscopies. While confocal microscopy and simulations show that the local environment around solutes in ILs is he...

Photoinduced metal-free atom transfer radical polymerization (ATRP) of methyl methacrylate was investigated using sev-eral phenothiazine derivatives and other related compounds as photoredox catalysts. The experiments show that all selected catalysts can be involved in the activation step, but not all of them participated efficiently in the deactiv...

Realization of energy efficient and cost effective electroluminescence applications of conjugated polymers, like organic light emitting diodes (OLEDs), requires a complete understanding of photo-chemical processes at metal-polymer interfaces. Therefore it is useful to study the effects of metal films on the photoluminescence of emissive organic lay...

Gold nanoclusters hold many potential applications such as biosensing and optics due to their emission characteristics, small size, and non-toxicity. However, their low quantum yields remain problematic for further applications, and their fluorescence mechanism is still unclear. To increase the low quantum yields, various methods have been performe...

The phenomenon of electric field-induced emission quenching is important in organic light-emitting diodes because operating conditions involve large electric fields. Past experimental work on light-emitting polymers and oligomers showed that field-induced quenching (FIQ) efficiencies are higher in non-rigid molecules such as poly(pphenylene vinylen...

Organic light-emitting diodes (OLEDs) have received a significant attention over the past decade due to their energy-saving potential. We have recently synthesized two novel carbazole-based donor-acceptor compounds and analyzed their optical properties to determine their suitability for use as blue emitters in OLEDs. These compounds show remarkable...

Field-induced fluorescence quenching of poly(p-phenylenevinylene)(PPV) oligomers due to non-radiative relaxation through free electron-hole pair (FEHP) states is modeled using Singles Configuration Interaction computations with the Intermediate Neglect of Differential Overlap Hamiltonian. The computations find FEHP states with energies that drop linear...

Applications of conjugated polymers in photovoltaics and displays drive the need to understand how morphology affects emission and charge migration. Due to the inherent complexity of polymers, parallel studies of oligomer aggregates are required to â€build-up' an understanding of the polymer features. Fluorescence lifetime imaging microscopy (FLIM)...

Oligomeric thiophenes are commonly-used components in organic electronics and solar cells. These molecules stack and/or aggregate readily under the processing conditions used to form thin films for these applications, significantly altering their optical and charge-transport properties. To determine how these effects depend on the substitution patt...

Conjugated systems are frequently studied in their nanoaggregate form to probe the effects of solvent and of film formation on their spectral and dynamical properties. This article focuses on the emission spectra and dynamics of nanoaggregates of alkoxy-substituted PPV oligomers with the goal of interpreting the vibronic emission envelopes observed...

The efficiency of the glutathione monolayer-protected gold nanocluster (NC) Au(25) (1.2 nm metal core diameter (d)) in quenching the emission of dyes intercalated into DNA is compared to that of 2 and 4 nm gold nanoparticles (NPs). In all cases, the DNA/dye moieties and the gold particles are not covalently attached but rather form non-covalent gro...

We have synthesized fluorescent DNA duplexes featuring multiple thiazole orange (TO) intercalating dyes covalently attached to the DNA via a triazole linkage. The intercalating dyes stabilize the duplex against thermal denaturation and show bright fluorescence in the green region of the spectrum. The emission color can be changed to orange or red b...

The use of fluorescence lifetime imaging microscopy (FLIM) is introduced as a means of directly imaging core–shell structured organic aggregates through the gradient observed in their emission wavelength and lifetime as a function of distance from their center to their exterior. The aggregates studied consist of alkoxy-substituted oligomeric PPVs (...

Fluorescein O-methacrylate was copolymerized with n-butyl acrylate by atom transfer radical polymerization in a “grafting from” reaction with a multifunctional linear macroinitiator to form pH responsive fluorescent bottlebrushes. The brush-like structure of the synthesized macromolecules was confirmed through molecular imaging by atomic force micr...

Electric field-induced fluorescence quenching has been measured for a series of conjugated polymers with applications in organic light-emitting diodes. Electrofluorescence measurements on isolated chains in a glassy matrix at 77 K show that the quenching efficiency for poly[2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is an order of...

Chain aggregation in electroluminescent materials profoundly affects their emission and charge transport. Single aggregate time-resolved fluorescence imaging studies of shorter-chain MEH-PPV oligomer aggregates reveal morphological details that rationalize their unusual emission properties.

The effects of aggregate formation on the photophysical properties of alkoxy and cyano-substituted polyphenylene phenylene vinylene oligomers (CN-PPVs) were studied in bulk solution to better understand the consequences of aggregation for the emission properties of the polymer. Nanoaggregates of oligomers from 5 to 13 repeat units in length were fo...

The electroabsorption spectra for the metal-to-ligand charge transfer transition in complexes containing oxalate and terephthalate bridged MM quadruply bonded units, [(MM)(pivalate)(3)](2)-mu(2)-BR, where M = Mo or W and BR = oxalate or terephthalate, are reported. The measured magnitude of the change in dipole moment (|Deltamu|) and the change in...

The effects of aggregate formation on the photophysical properties of oligomers of MEH-PPV were studied in bulk solution to better understand the effects of aggregation on the emission properties of the polymer. Nanoaggregates of oligomers from 3 to 17 repeat units in length were formed using a solvent reprecipitation method. The spectra are not re...

Fluorescence microscopy is used to probe variations in vibronic structure and emission lifetime between individual aggregates and trends with aggregate size and oligomer chain length. The results are compared to theoretical models and to polymers.

Polythiophene is a commonly used component of organic electronics and solar cells. Polythiophene chains are readily aggregated under the processing conditions used to form thin films for applications in devices. This aggregation can drastically alter the charge transfer and optical properties of the material. In order to better understand these eff...

The recent upsurge in use of conjugated polymers in photovoltaic devices and in displays drives the need for understanding how morphology affects important functional features such as emission and charge migration. Due to the inherent complexity of polymers, a parallel effort to `build-up' understanding of their features via a detailed study of imp...

Fluorescent conjugated polymers have attracted a great deal of attention among scientists and engineers for their potential use in opto-electronic devices. One of the points that remain to be fully understood, however, is the undesirable sensitivity of their charge transport efficiency and emission characteristics on variations of the polymer struc...

In a previously published study (J. Phys. Chem. B 2006, 110, 7732−7742), we reported field-induced fluorescence quenching in both poly[2-methoxy,5-(2‘-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and several model oligomers in solvent glass matrices at high dilution (<0.1% by weight). The observed quenching is not readily explained by field-ind...

Stable biodegradable nanogels cross-linked with disulfide linkages were prepared by inverse miniemulsion atom transfer radical polymerization (ATRP). These nanogels could be used for targeted drug delivery scaffolds for biomedical applications. The nanogels had a uniformly cross-linked network, which can improve control over the release of encapsul...

(Figure Presented) Reversible disruption and regeneration of block-copolymer micelles has been achieved by UV and visible-light irradiation and studied by atomic force microscopy (see picture). A hydrophobic dye encapsulated in the original polymeric micelles was released after UV irradiation. Remarkably, some of the released hydrophobic dye was re...

Fluorescent labeling of biological RNA is complicated by the narrow range of nucleoside triphosphates that can be used for biological synthesis (i.e., transcription) as well as the inability to site-specifically incorporate them into long RNA transcripts. Noncovalent strategies for labeling RNA rely on attaching fluorescent dyes to hybridization pr...

231st ACS National Meeting, Atlanta, GA, United States, PHYS-258. CODEN: 69HYEC AN 2006:249772 CAPLUS

Electrofluorescence (Stark) spectroscopy has been used to measure the trace of the change in polarizability (trDeltaalpha) and the absolute value of the change in dipole moment (|Deltamu|) of the electroluminescent polymer poly[2-methoxy,5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV) and several model oligomers in solvent glass matrixes. Fro...

Excitation localization in a nominally 3-fold-symmetric molecule is probed using electroabsorption (Stark) spectroscopy in polymer and organic glass matrixes. The absolute value of the change in dipole moment of this molecule, referred to as the trimer, is found to be nearly identical to that of a model compound consisting of one of its three arms...

Disorder-induced symmetry breaking is studied in a model dendrimer that consists of three arms arranged with C3 symmetry. Electroabsorption spectroscopy measurements in the accompanying paper (Bangal, P. R.; Lam, D. M. K.; Peteanu, L. A.; Van der Auweraer, M. J. Phys. Chem. B 2004, 108, 16834) show that the dipole moment change of the dendrimer is...

In this study, electroabsorption (Stark) spectroscopy is used to determine the trace of the change in polarizability (tr (Delta x) over bar) and the absolute value of the change in dipole moment (/Delta(mu) over right arrow/) of the electroluminescent polymer poly [2-methoxy,5-(2'-ethyl-hexoxy)- 1,4-phenylene vinylene] (MEH-PPV) and several model o...

Stark spectroscopy (electroabsorption) is used to study the variation of electronic properties with the size of helical H-aggregates that are formed by the spontaneous noncovalent assembly of co-facial dimers of the cyanine dye (DiSC 2 (5)) into the minor groove of double-helical DNA. The unique and important property of these aggregates, first syn...

Electroabsorption (Stark spectroscopy) is used to measure the electronic properties of o-hydroxybenzaldehyde (oHBA) and o-hydroxyacetophenone (oHAP), two molecules that undergo excited-state intramolecular proton transfer (ESIPT) in a non-interacting organic glass matrix. We report the change in dipole moment, , and the average change in polarizabi...

We present a Stark spectroscopy study of the lowest electronic transition of MEH-PPV and a nine-ring oligomer, both in polymer glasses and solvent glass matrices. The change in polarizability on excitation, which is correlated with exciton delocalization, as well as the change in dipole moment are obtained. Our results indicate that the change in p...

Electroabsorption measures the change in polarizability and dipole moment accompanying excitation of a conjugated polymer. In this work, INDO theory is used to simulate the electroabsorption spectra of polymers and oligomers of MEH-PPV, both in solution and in glassy solids. Agreement with the observed changes in polarizability requires inclusion o...

We have investigated the photo-physics of novel helical aggregates formed by spontaneous assembly of numerous co-facial dimers of cyanine dyes to the minor groove of Poly(dI-dC) DNA. The dimensions of these helical aggregates are restricted to the width of the dye dimer due to steric constraints in the minor groove, though their length can be contr...

A complex that mimics many of the properties of the blue copper protein center that was synthesized by Holland and Tolman1 is studied using Stark spectroscopy to determine the values of two electronic properties, the change in the dipole moments (| |) and the average change in the polarizability (Δα) for excitation into the ligand-to-metal charge t...

A series of studies is presented to characterize the photophysical properties of a novel type of aggregate formed by the spontaneous noncovalent assembly of numerous cofacial dimers of cyanine dyes (DISC3+(5)) to the minor groove of poly(dI-dC) DNA. The dimensions of these helical aggregates, first synthesized and characterized by Armitage and co-w...

The electroabsorption (Stark) spectrum of the emeraldine base form of polyaniline (EB) in a polymethyl methacrylate (PMMA) matrix at room temperature is presented. For the lowest-energy (1.98 eV) band, the absolute value of the change in dipole moment on excitation (\ Delta<( )over right arrow>\) is 6.1 D and the trace of the change in polarizabili...

This Letter describes a study of the absorption and electroabsorption spectroscopy of a complex consisting of the –ReI(CO)3Cl chromophore coordinated to the 4,4′-{bis-[2,5-(dimethoxyphenyl)ethynyl]}-2,2′-bipyridine ligand. The objective of the study is to explore whether Re → bipyridine metal-to-ligand charge transfer (MLCT) excitation leads to ele...

The change in the dipole moments (|Δ→μ|) and the average change in the polarizability (〈Δα〉) upon excitation for the Cys(S)⇒Cu(II) ligand-to-metal charge-transfer (LMCT) transitions in two species of azurin, a type I blue copper protein from Alcaligenes denitrificans (AD) and Pseitdomonas aeruginosa (PA), were determined using Stark (electroabsorpt...

The polaron band at ∼1.4 eV of d,l-camphorsulfonic acid-doped polyaniline ((±)-HCSA-PANI) in a poly(methyl methacrylate) (PMMA) matrix was studied using electroabsorption (Stark-effect) spectroscopy at 298 K. A very small change in dipole moment on excitation (View the MathML source) in the order of 1.4±0.2 D was measured as well as an average chan...

The change in the dipole moments (| |) and the average change in the polarizability (Δα) upon excitation for the Cys(S)Cu(II) ligand-to-metal charge-transfer (LMCT) transitions in two species of azurin, a type I blue copper protein from Alcaligenes denitrificans (AD) and Pseudomonas aeruginosa (PA), were determined using Stark (electroabsorption) s...

Using Stark effect (electroabsorption) spectroscopy to study all-trans-retinal (ATR) in a variety of polymer matrices and organic glasses, we have found that the average change in polarizability upon excitation ( ) that we measure is highly dependent on the rigidity of the matrix used. In rigid polymer and organic glass matrices, the measured value...

Using Stark effect (electroabsorption) spectroscopy to study the well-known solvatochromic probe molecule coumarin 153 (C153) in a variety of polymer matrices and organic glasses, we have found that the average change in polarizability ( ) that we measure depends critically on the rigidity of the matrix used. In rigid polymer and frozen organic gla...

The science of photochemistry has greatly benefited by the constant expansion in the number of techniques suitable for probing the electronic and structural properties of molecules as well as their dynamics. The purpose of this article is to (re-)aquaint the photochemistry community with spectroscopic methods based on the Stark effect in the hope o...

Dipolar Properties of and Temperature Effects on the Electronic States of 3-Hydroxyflavone (3HF) Determined using Stark-Effect Spectroscopy and Compared to Electronic Structure Calculations Abstract HTMLFull Text HTML PDFHi-Res PDF[110 KB] PDFPDF w/ Links[174 KB] Figures Citing Articles Your current credentials do not allow retrieval of the full...

In this manuscript, a relatively simple and inexpensive INDO/SCI finite-field (FF) method for calculating polarizabilities (α) is demonstrated to give good agreement with results obtained by both the INDO/MRD/SDCI sum-over-states routine and published results using the RPA method. The FF method is as effective as the other techniques in predicting...

Electroabsorption is used to determine the difference dipole moment, ∣Δμ∣, and the difference polarizability, Δα, of HBT and HBO, two molecules that undergo excited-state intramolecular proton transfer (ESIPT). These measurements are compared to ab initio (6-31G∗) and semi-empirical (INDO1/s) calculations. Good agreement is obtained between ab init...

Three biologically active conformers of retinal, all-trans, 9- and 13-cis, and their Schiff bases (SB), are studied using a combination of electroabsorption (Stark) spectroscopy and semiempirical calculations. All of the retinal isomers studied show both a large change in dipole moment between the ground and excited states (|Δμ| greater than 8 D) a...

Stark effect (electroabsorption) spectroscopy was used to determine the changes in dipole moment and polarizability that result from excitation of o-hydroxyacetophenone (OHAP) to its first excited state. A polyethylene matrix is used to minimize the possibility of hydrogen-bonding impurities that are known to alter the properties of molecules that...

Femtosecond pump-probe experiments reveal the impulsive production of photoproduct in the primary event in vision. The retinal chromophore of rhodopsin was excited with a 35-femtosecond pulse at 500 nanometers, and transient changes in absorption were measured with 10-femtosecond probe pulses. At probe wavelengths within the photo-product absorptio...

Understanding the role of vibrational coherence in photochemical reactions is a fundamental problem in photochemistry and biology. ¹ , ² , ⁵ Vibrational coherence may play a significant role in reactions which occur on a time scale shorter than the relevant nuclear vibrational periods. One of the fastest chemical reactions is the first step in visi...

Next Section Biological sensing of small molecules such as NO, O2, and CO is an important area of research; however, little is know about how CO is sensed biologically. The photosynthetic bacterium Rhodospirillum rubrum responds to CO by activating transcription of two operons that encode a CO-oxidizing system. A protein, CooA, has been identified...