Distinct Interfacial Fluorescence in Oil-in-Water Emulsions via Exciton Migration of Conjugated Polymers

Commercial dyes are extensively utilized to stain specific phases for the visualization applications in emulsions and bioimaging. In general, dyes emit only one specific fluorescence signal and thus, in order to stain various phases and/or interfaces, one needs to incorporate multiple dyes and carefully consider their compatibility to avoid undesirable interactions with each other and with the components in the system. Herein, surfactant‐type, perylene‐endcapped fluorescent conjugated polymers that exhibit two different emissions are reported, which are cyan in water and red at oil–water interfaces. The interfacially distinct red emission results from enhanced exciton migration from the higher‐bandgap polymer backbone to the lower‐bandgap perylene endgroup. The confocal microscopy images exhibit the localized red emission exclusively from the circumference of oil droplets. This exciton migration and dual fluorescence of the polymers in different physical environments can provide a new concept of visualization methods in many amphiphilic colloidal systems and bioimaging.National Science Foundation (U.S.) (National Science Foundation DMR‐1410718

Functionalized Poly(3-hexylthiophene)s via Lithium–Bromine Exchange

Poly(3-hexylthiophene) (P3HT) is one of the most extensively investigated conjugated polymers and has been employed as the active material in many devices including field-effect transistors, organic photovoltaics and sensors. As a result, methods to further tune the properties of P3HT are desirable for specific applications. Herein, we report a facile postpolymerization modification strategy to functionalize the 4-position of commercially available P3HT in two simple steps–bromination of the 4-position of P3HT (Br–P3HT) followed by lithium−bromine exchange and quenching with an electrophile. We achieved near quantitative lithium–bromine exchange with Br–P3HT, which requires over 100 thienyl lithiates to be present on a single polymer chain. The lithiated-P3HT is readily combined with functional electrophiles, resulting in P3HT derivatives with ketones, secondary alcohols, trimethylsilyl (TMS) group, fluorine, or an azide at the 4-position. We demonstrated that the azide-modified P3HT could undergo Cu-catalyzed or Cu-free click chemistry, significantly expanding the complexity of the structures that can be appended to P3HT using this method.National Science Foundation (U.S.) (ECCS-0939514

Conjugated polymers and designed interfaces : conformational analysis and applications

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.Cataloged from PDF version of thesis. Pages 160 and 161 are blank.Includes bibliographical references.The conformations of conjugated polymers can be altered by nearby environments. The intrapolymer conformation and interpolymer assemblies have a crucial impact on a variety of properties such as absorption, energy migration, and fluorescence. In this dissertation, the conformational changes and their effects on photophysics in different environments will be discussed. In Chapter 1, the basic principles to understand this thesis will be reviewed, including the processes of absorption and emission, exciton migration, the Langmuir-Blodgett technique, and interfacial phenomena. In Chapter 2, the conformational control and alignment of conjugated polymers at the air-water interface and how this alignment of polymers can lead to new emissive aggregates will be presented. The emission has the characteristics of excimers with the improved fluorescence quantum yields. The transfer of the aligned aggregates to glass substrates is attempted and these excimer films undergo reorganization upon exposure to solvent vapors, which triggers the fluorescence color change from yellow to cyan, leading to fluorescence-based chemical sensors. In Chapter 3, exciton migration to low-energy emissive traps at amphiphilic interfaces will be discussed. This chapter will deliver the design of interfaces and how the exciton migration can occur at the air-water interface and the hydrocarbon-water interface in lyotropic liquid crystals. To expand this interfacial exciton migration to more generalizable interfaces, Chapter 4 will show the fabrication of oil-in-water emulsions and how exciton migration in oil-in-water emulsion can produce distinct fluorescences between solution and interfaces. Chapter 5 will discuss the structural variations of novel functional conjugated polymers and how substituents can change the conformation of the polymer backbones. Additionally, how this conformational change affects the electronic and optical properties of polymers will be examined.by Byungjin Koo.Ph. D

Vanillin-Based Polymers via Ring-Opening Metathesis Polymerization

Biobased polymer synthesis is becoming an indispensable research area aimed at addressing environmental pollution and the depletion of petroleum resources. Vanillin, which can be sustainably obtained from lignin biomass, is a phenolic compound that is widely used as a food additive. We herein report our study of polymer synthesis using vanillin through ring-opening metathesis polymerization (ROMP). Our initial step involves the chemical transformation of vanillin into vanillin 5-norbornene-2-carboxylate (VN), a polymerizable monomer. This ROMP monomer has the capability to form poly(vanillin 5-norbornene-2-carboxylate) using a Grubbs catalyst. This glassy homopolymer has a molecular weight of 49,000 g/mol with a Đ of 1.23. To explore its potential in copolymers, we performed triblock copolymerization to create ABA-type thermoplastic elastomers. To achieve this, we synthesized three ROMP monomers serving as soft blocks, each containing different alkyl chains. Through a sequential addition of monomers (VN, soft block, and VN in that order), we successfully synthesized six vanillin-based triblock copolymers with molecular weights of 32,000–61,200 g/mol and Đ values of 1.24–1.40. These synthesized polymers exhibit excellent mechanical properties, including a Young’s modulus of 28 MPa, surpassing commercial thermoplastic elastomers. Atomic force microscopy (AFM) reveals microphase separation consistent with the two distinct glass transition temperatures

Interfacial Pressure/Area Sensing: Dual-Fluorescence of Amphiphilic Conjugated Polymers at Water Interfaces

Exciton migration to emissive defects in π-conjugated polymers is a robust signal amplification strategy for optoelectronic sensors. Herein we report end-capped conjugated polymers that show two distinct emissions as a function of interpolymer distances at the air–water and hydrocarbon–water interfaces. Amphiphilic poly­(phenylene ethynylene)­s (PPEs) end-capped with perylene monoimides display two distinct emission colors (cyan from PPE and red from perylene), the relative intensity of which depends on the surface pressure applied on the Langmuir monolayers. This behavior produces a ratiometric interfacial pressure indicator. Relative quantum yields are maintained at the different surface pressures and hence display no sign of self-quenching of the excitons in an aggregated state. These polymers can be organized at the micelle–water interface in lytropic liquid crystals, thereby paving the way for potential applications of end-capped amphiphilic conjugated polymers in biosensors and bioimaging

Employing outlier and novelty detection for checking the integrity of BIM to IFC entity associations

Although Industry Foundation Classes (IFC) provide standards for exchanging Building Information Modeling (BIM) data, authoring tools still require manual mapping between BIM entities and IFC classes. This leads to errors and omissions, which results in corrupted data exchanges that are unreliable and compromise the interoperability of BIM models. This research explored the use of two machine learning techniques for identifying anomalies, namely outlier and novelty detection to determine the integrity of IFC classes to BIM entity mappings. Both approaches were tested on three BIM models, to test their accuracy in identifying misclassifications. Results showed that outlier detection, which uses Mahalanobis distances, had difficulties when several types of dissimilar elements existed in a single IFC class and conversely was not applicable for IFC classes with insufficient number of elements. Novelty detection, using one-class SVM, was trained a priori on elements with dissimilar geometry. By creating multiple inlier boundaries, novelty detection resolved the limitations encountered in the former approach, and consequently performed better in identifying outliers correctly

Application of Vibration Signal Processing Methods to Detect and Diagnose Wheel Flats in Railway Vehicles

This paper studied two useful vibration signal processing methods for detection and diagnosis of wheel flats. First, the cepstrum analysis method combined with order analysis was applied to the vibration signal to detect periodic responses in the spectrum for a rotating body such as a wheel. In the case of railway vehicles, changes in speed occur while driving. Thus, it is difficult to effectively evaluate the flat signal of the wheel because the time cycle of the flat signal changes frequently. Thus, the order analysis was combined with the existing cepstrum analysis method to consider the changes in train speed. The order analysis changes the domain of the vibration signal from time domain to rotating angular domain to consider the train speed change in the cepstrum analysis. Second, the cross correlation analysis method combined with the order analysis was applied to evaluate the flat signal from the vibration signal well containing the severe field noise produced by the vibrations of the rail irregularities and bogie components. Unlike the cepstrum analysis method, it can find out the wheel flat size because the flat signal linearly increases to the wheel flat. Thus, it is more effective when checking the size of the wheel flat. Finally, the data tested in the Korea Railroad Research Institute were used to confirm that the cepstrum analysis and cross correlation analysis methods are appropriate for not only simulation but also test data

Highly Emissive Excimers by 2D Compression of Conjugated Polymers

Interactions between π-conjugated polymers are known to create ground-state aggregates, excimers, and exciplexes. With few exceptions, these species exhibit decreased fluorescence quantum yields relative to the isolated polymers in liquid or solid solutions. Herein, we report a method to assemble emissive conjugated polymer excimers and demonstrate their applicability in the detection of selected solvent vapors. Specifically, poly­(phenylene ethynylene)­s (PPEs) with amphiphilic side chains are organized in a Langmuir monolayer at the air–water interface. Compression of the monolayer results in the reversible conversion from a face-on organization of the π-system relative to the water to what appears to be an incline-stack conformation. The incline-stack organization creates a bright yellow emissive excimeric state with increases of 28% in relative fluorescence quantum yields to the face-on monolayer conformation. Multilayers can be transferred onto the glass substrate via a Langmuir–Blodgett method with preservation of the excimer emission. These films are metastable and the fluorescence reverts to a cyan color similar to the spectra obtained in solution and spin-cast films after exposure to selected solvent vapors. This behavior has practical utility as a fluorescence-based indicator for selected volatile organic compounds

Highly Emissive Excimers by 2D Compression of Conjugated Polymers

Interactions between π-conjugated polymers are known to create ground-state aggregates, excimers, and exciplexes. With few exceptions, these species exhibit decreased fluorescence quantum yields relative to the isolated polymers in liquid or solid solutions. Herein, we report a method to assemble emissive conjugated polymer excimers and demonstrate their applicability in the detection of selected solvent vapors. Specifically, poly­(phenylene ethynylene)­s (PPEs) with amphiphilic side chains are organized in a Langmuir monolayer at the air–water interface. Compression of the monolayer results in the reversible conversion from a face-on organization of the π-system relative to the water to what appears to be an incline-stack conformation. The incline-stack organization creates a bright yellow emissive excimeric state with increases of 28% in relative fluorescence quantum yields to the face-on monolayer conformation. Multilayers can be transferred onto the glass substrate via a Langmuir–Blodgett method with preservation of the excimer emission. These films are metastable and the fluorescence reverts to a cyan color similar to the spectra obtained in solution and spin-cast films after exposure to selected solvent vapors. This behavior has practical utility as a fluorescence-based indicator for selected volatile organic compounds