Highly self-motivatied PhD with an interdisciplinary background in conjuncton with a demonstrated research prowess in the field of organic electronics and polymeric semiconductor chemistry. With a rich experience in experimental techniques, and computation modelling along with strong interpersonal skills.
This research project proposes that quantum dots be used as the active components in photoelectrochemical and electrochemical sensors to detect toxic and hazardous gases and to measure endogenously produced gaseous signaling molecules. The proposed research will focus on the synthesis, functionalization, and characterization of quantum dots followed by design and characterization in photoelectrochemical and electrochemical sensors. Quantum dots are highly tunable with numerous valuable properties; in conjunction with these types of sensors they are considered convenient and practical, having received significant attention in academia and in industry. Photoelectrochemical and electrochemical sensors are low-cost, easily miniaturized, reliable, and robust and have been reported to measure a multitude of analytes. With growing public concern of the potential risks and hazards of many airborne chemicals or the implication of endogenously produced gaseous signaling molecules in human related diseases, new types of sensors are required to detect such analytes at much lower concentrations with greater response times than what current technology can offer. The main contribution expected is related to achieving appropriate functionalization of quantum dots for selectivity and sensitivity to target analyte(s).
Synthesis of nanoparticles
Fabrication and characterization devices for sensing
This research project focused on the surface modifications of polydimethylsiloxane (PDMS) elastomer. PDMS was hydrophilized by poly(acrylicacid) (PAAc) using Surface Initiated Atomic Transfer Radical Polymerization (Si-ATRP). The ATRP initiator chosen was ((chloromethyl)phenylethyl)trichlorosilane, which was immobilized on the surface of the PDMS through a simple but innovative method of drop-coating, in contrast to the commonly used vapor deposition and solution-immersion methods. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and X-Ray Photoelectron Spectroscopy (XPS) were employed to examine surface properties of modified PDMS and confirm the presence of the PAAc chains covalently bonded to the PDMS surface. Physical properties and topography of the modified samples were characterized by water contact angle measurement and Atomic Force Microscopy (AFM). It was shown that the drop-coating of the silane initiator for ATRP modification with PAAc can result in good surface hydrophilization while causing minimum damage to the PDMS preserving its desired optical transparency. The resultant hydrophilic PDMS is stable in air and has film lubrication behavior in aqueous conditions and may be used in the development of advanced microfluidic devices and sensors where both surface hydrophilicity and bulk transparency are desired.
Surface modification of polydimethylsiloxane (PDMS)
Research conducted in several product lines.
Supported the development of P-INK device (Electrically Active Colour-Based Battery Tester)
Helped with technical problems with other product lines
Synthesized nanoparticles on demand
Developed and constructed an electronic voltage tuner (potentiometer) for P-INK devices
Responsible for the design, construction and maintenance of company website
Thesis Abstract: The concept of an organic thin film transistor was first introduced in the late 1980s and research was directed toward two key merits of performance, field-effect mobility and current ON/OFF ratio. Today these two key merits of performance are still highly sought after; however, a shortcoming associated with most organic semiconductors is their susceptibility to chemical interactions and photo-excitation; to name but a few of their caveats. Consequently, the development of organic semiconductors with high charge carrier transport as well as good air stability is still desired. Nature provides a vast diversity of materials and looking for natural or nature inspired semiconductors appears to be a promising route towards interesting and pertinent materials.
Synthesis and characterization of novel semiconductive polymers for use in organic thin film transistors (OTFTs)
Computational studies employing density functional theory (DFT) calculations
Fabrication and characterization of OTFTs as bio-and chemosensors
Thesis Abstract: Both reduced zirconocene ("Cp2Zr") and zero valent lithium are known to induce coupling of alkynes to form dimers, oligmers, and polymers. Established work from Fagan et al., Tilley et al., and Eisch et al. was used as the basis for the synthesis of desired targets. First, the attempted syntheses of novel Group IV metalloles from a zirconocene intermediate were studied. There was no conclusive data to state that 2,3,4,5-tetraphenylzirconacyclopentadiene will undergo metallacycle transfer with CrCl3 and FeCl3. The presence of zirconocene dichloride suggests that metallacycle transfer may have occurred, which warrants further investigation. Monomers, 1-bromo-4-hex-1-ynyl-benzene, 1-bromo-3-(phenylethynyl)benzene, and p-dihex-1-ynylbenzene, were synthesized successfully via Sonogashira coupling. Attempts to synthesize novel monomers via lithium and "Cp2Zr" had mixed results. 1H NMR acquisition of the hydrolyzed product from zirconocene-coupling of 1-bromo-3-(phenylethynyl)benzene appeared to be successful. Lastly, lithium and "Cp2Zr" induced polymerization of novel monomers and known monomers were attempted. Metallacycle transfer from the zirconocene intermediate polymers to thiophene, thiopheneoxide, thiophenedioxide, and phosphole were attempted. However, limited characterization was completed. 1H NMR acquisitions suggest polymer by the loss of resolution and broadening of resonance signals, but further characterization via GPC is required. Monomers, and polymers were characterized using various means such as 1H, 13C, 31P, 119Sn NMR spectroscopy, UV-Vis spectroscopy, AIMS AccuTOF-DART mass spectrometry and GPC.
Thesis Abstract: This thesis reviews the steps required to work towards the synthesis of metal-containing inverse crown macrocycles based on zirconocene-coupling of diynes. Particular focus was on developing a new diyne precursor, 1,4-bis(hexynyldimethylsilyl)benzene, which could potentially promote inverse crown formation during macrocyclization of the polymer and/or during metallacycle transfers. Moreover, the new diyne offers other benefits such as increased safety, and the use of readily available and lower-cost reagents over the original diyne precursor, 1,4-bis(propynyldimethylsilyl)benzene, which Tilley et al. reported using. The newly synthesized diyne 1,4-bis(hexynyldimethylsilyl)benzene was discussed and compared to 1,4- bis(propynyldimethylsilyl)benzene. Subsequent developments were to establish a new route to new main group 13 metalloles, such as gallole and aluminole, via stannole intermediates. Work based on Eisch et al., and Fagan et al. were utilized as a basis to develop a new route to new main group 13 metalloles. Results show that the proposed route in this thesis is a potential route to developing new main group 13 metalloles. Aliquots of stannole solutions treated with either aluminum trichloride or gallium trichloride were discussed and compared.
The Computer Programming and Analysis program provides you with a rigorous theoretical background in object-oriented methodology, particularly in program design and system analysis. Integration of web concepts and focus on the development of dynamic database-driven web applications on a variety of operating system platforms was taught.
A (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (IBDF)-based small bandgap donor–acceptor (D–A) polymer (PIBDFBTO-HH) was synthesized, which contains a strategically chosen solubilizing electron-rich building block, 3,3'-bis(dodecyloxy)-2,2′-bithiophene (BTO) as a donor. PIBDFBTO-HH has a very small band gap of 0.95 eV, absorbing up to 1700 nm in the near-infrared (NIR) region, which enables its application in NIR photodetection. This polymer exhibits efficient ambipolar charge transport properties with balanced hole and electron mobilities of up to 0.16 cm2 V−1 s−1 and 0.14 cm2 V−1 s−1, respectively, in organic thin film transistors (OTFTs) in the absence of light. In the p-channel operation regime, the organic phototransistor (OPT) devices based on PIBDFBTO-HH demonstrated photosensitivities (P) of 130 and 40 under the illumination of 850 nm and 940 nm LED light sources, respectively. The photoresponsivity (R) under the 940 nm LED reached 450 mA W−1. In contrast, in the n-channel operation regime, a negative photoresponse, namely a decrease in the drain current, was observed, which accounted for the increased number of trapped electrons that offset the applied gate bias.
Diketopyrrolopyrrole (DPP) derivatives are among the most efficient materials studied for both polymer solar cells (PSCs) and organic field-effect transistors (OFETs) applications. We report here the synthesis of new fluorinated dithienyldiketopyrrolopyrrole (fDT-DPP) monomers suitable for direct heteroarylation polymerization. fDT-DPP copolymers were then prepared to probe the effect of the fluorination. It was found that they feature deeper HOMO energy levels and smaller bandgaps than their non-fluorinated analogues. Moreover, some fDT-DPP copolymers show ambipolar behavior when tested in OFETs. For example, P2 shows hole mobility up to 0.8 cm2 V–1 s–1 and electron mobility up to 0.5 cm2 V–1 s–1. Inverted PSCs with power conversion efficiency (PCE) up to 7.5% were also obtained for P5. These results reported here (OFETs and PSCs) confirm that the fluorination of dithienyl-DPP moieties improves the performance of organic electronics devices. This study is also evidencing the strength of the direct heteroarylation polymerization and fDT-DPP as a new class of conjugated polymers.
We report the photoresponse characteristics of a pyrimido[4,5-g]quinazoline-4,9-dione (PQ) based polymer, PPQ2T-BT-24, which served as an active channel layer in organic phototransistors (OPTs). OPTs using this polymer showed very short rise time of 3 ms and fall time of 59 ms, photoresponsivity (R) of 0.24 and external quantum efficiency (EQE) of 50%. When PC61BM was incorporated into PPQ2T-BT-24, a significantly shortened fall time of 8 ms along with a much-improved rise time of 1 ms were realized. These response times are among the best values reported for OPTs. The R and EQE of the devices using this polymer blend also increased to 0.88 A W−1 and 189%, respectively.
This review highlights recent major progress in the development of organic semiconductors as electron transport n-channel materials in organic field effect transistors (OFETs). Three types of materials are discussed: (1) small molecules, (2) polymers, and (3) n-doped small molecules and polymers. Much effort has been made in the modification of known building blocks, development of novel building blocks, and optimization of materials processing and device structures. These efforts have resulted in the achievement of record high electron mobilities for both small molecules (12.6 cm2 V−1 s−1) and polymers (14.9 cm2 V−1 s−1), which are approaching the highest hole mobilities achieved by p-type small molecules and polymers so far. In addition, n-doping of ambipolar and p-type organic semiconductors has proven to be an efficient approach to obtaining a greater number of n-type organic semiconductors. However, it is found that n-type organic semiconductors, in general, still lag behind p-type organic semiconductors in terms of carrier mobility and air stability. Further exploration of new building blocks for making novel materials and optimization of processing conditions and device structures are needed to improve the performance, particularly air stability.
Direct (hetero)arylation polymerization (DHAP) has emerged as a valuable and atom-economical alternative to traditional cross-coupling methods for the synthesis of low-cost and efficient conjugated polymers for organic electronics. However, when applied to the synthesis of certain (hetero)arene-based materials, a lack of C–H bond selectivity has been observed. To prevent such undesirable side-reactions, we report the design and synthesis of new, bulky, phosphine-based ligands that significantly enhance selectivity of the DHAP process for both halogenated and non-halogenated electron-rich and electron-deficient thiophene-based comonomers. To better understand the selectivity issues, density functional theory (DFT) calculations have been performed on various halogenated and non-halogenated electron-rich and electron-deficient thiophene-based comonomers. Calculations showed that the presence of bromine atoms decreases the energy of activation (Ea) of the adjacent C–H bonds, allowing undesirable β-defects for some brominated aromatic units. Both calculations and the new ligands should lead to the rational design of monomers and methods for the preparation of defect-free conjugated polymers from DHAP.
Two donor–acceptor (D–A) polymers based on (3E,8E)-3,8-bis(2-oxoindolin-3-ylidene)naphtha-[1,2-b:5,6-b′]difuran 2,7(3H,8H)-dione (INDF) and substituted regioisomeric bithiophene (BT) units with different side chain positions (head-to-head, HH, and tail-to-tail, TT) were synthesized. PINDFBT-(HH) achieved electron (μe) and hole (μh) mobilities as high as 0.33 cm2 V−1 s−1 and 0.15 cm2 V−1 s−1, respectively, while PINDFBT-(TT) showed an order of magnitude lower mobilities with μe of 0.07 cm2 V−1 s−1 and μh of 0.02 cm2 V−1 s−1. The distinctly different electrical performance of these two polymers originates from their different side chain placements on the bithiophene units and consequently different electronic structures, backbone coplanarity, chain packing, and thin film morphology. Our results showed that a bithiophene unit with an HH substitution pattern is much more favoured in terms of the charge transport property of the polymers.
A donor-acceptor polymer of (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b : 4,5-b′]difuran-2,6(3H,7H)-dione (IBDF) and bithiophene (BT) exhibits typical ambipolar charge transport behaviour in organic thin film transistors. Using the electron rich triphenylamine as an end capping group, a notable suppression of hole transport is observed. This interesting phenomenon is accounted for by the hole trapping effect of the triphenylamine end-capper. Thus, this study provides a novel and facile approach to tuning the charge carrier polarity of a polymer semiconductor from ambipolar to n-type dominant.
We report the synthesis of an aromatic amine-containing polymer (PDPAT-12) and the use of this polymer as an effective additive to an ambipolar polymer semiconductor (PIBDFBT-e37) to realize unipolar n-type charge transport in organic thin film transistors (OTFTs). With 10 wt% PDPAT-12 addition to PIBDFBT-e37, the OTFTs achieved unipolar n-type charge transport with electron mobility of up to 0.42 cm2 V−1 s−1 in nitrogen and 0.19 cm2 V−1 s−1 in air. Moreover, the polymer blend demonstrated improved stability towards ambient air (retaining 50% of its initial electron mobility after exposed in air for 28 days) than the pristine PIBDFBT-e37 (retaining 13% of its initial electron mobility under the same conditions) and the PIBDFBT-e37:PEI (polyethylenimine) blend, which lost transistor behaviour almost instantly once exposed to ambient air. Our results show that the use of this aromatic amine-containing polymer as an additive can convert an ambipolar polymer into an n-type unipolar polymer in OTFTs with much improved air stability.
A series of new donor–acceptor–donor (D–A–D) small-molecule compounds, with 3,3′-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) as an electron acceptor building block coupled with various electron donor end-capping moieties (thiophene, bithiophene and benzofuran), were synthesized and characterized. When the fused-ring benzofuran is combined to EBI (EBI-BF), the molecules displayed a perfectly planar conformation and afforded the best charge transport properties among these EBI compounds with a hole mobility of up to 0.02 cm2 V−1 s−1. All EBI-based small molecules were used as donor material along with a PC61BM acceptor for the fabrication of solution-processed bulk-heterojunction (BHJ) solar cells. The best performing photovoltaic devices are based on the EBI derivative using the bithiophene end-capping moiety (EBI-2T) with a maximum power conversion efficiency (PCE) of 1.92%, owing to the broad absorption spectra of EBI-2T and the appropriate morphology of the BHJ. With the aim of establishing a correlation between the molecular structure and the thin film morphology, differential scanning calorimetry, atomic force microscopy and X-ray diffraction analysis were performed on neat and blend films of each material.
We systematically varied the degree of fluorination along the backbone of a series of highly regioregular 3-hexylthiophene-based polymers, P3HT-50F, P3HT-33F, and P3HT-25F, in which 50%, 33%, and 25% of the thiophene units within the polymer chain contain fluorine atoms in the available 4-position, respectively. These materials were homopolymerized using the Kumada catalyst transfer polycondensation method from a set of mono-fluorinated bi-, ter-, and quarterthiophenes to ensure high polymer regioregularity and evenly spaced fluorine atoms along the conjugated thiophene backbone. The monomers were obtained from a synthetic route consisting of iterative Migita–Stille couplings of fluorinated and non-fluorinated 3-hexylthiophenes. The effect of the fluorine atoms on both polymer structure and properties is presented, with supporting quantum mechanical calculations that rationalize the intrinsic conformation preferences of the three P3HT derivatives. P3HT-50F (M̅n = 34 kg/mol, 98.5% rr), P3HT-33F (M̅n = 46 kg/mol, 98% rr), and P3HT-25F (M̅n = 53 kg/mol, 95% rr) displayed HOMO levels of −5.34, −5.26, and −5.24 eV, bandgaps of 1.98, 1.98, and 1.97 eV, and average field-effect transistor hole mobilities of 4.5 × 10–3, 2.7 × 10–2, and 1.2 × 10–2 cm2 V–1 s–1, respectively.
Two donor–acceptor (D–A) conjugated polymers, PIDTOBT and PIDTOBTz, based on thiophene-S,S-dioxidized indophenine (IDTO) as the acceptor building block are synthesized for solution processed organic thin-film transistors (OTFTs). The influences of the donor unit on the photophysical, electrochemical and electron-transport properties were investigated. These polymers possess very deep highest-occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels due to the strong electron accepting capability of the IDTO moiety. In OTFT devices, both polymers exhibited unipolar n-type charge transport characteristics with electron mobility up to 0.18 cm2 V−1 s−1.
A trimer of diketopyrrolopyrole (DPP), Tri-BTDPP, was synthesized and characterized. Tri-BTDPP has a HOMO level of −5.34 eV, a low band gap of 1.33 eV, and a hole mobility of ∼10−3 cm2 V−1 s−1 in organic field effect transistors (OFETs). Organic photovoltaic (OPV) devices using the donor/acceptor blends of Tri-BTDPP and PC71BM exhibited low power conversion efficiencies (PCE) of up to 0.72%, even though the desirable optical and electronic characteristics of this compound as a donor semiconductor for achieving high performance for OPV. Through an intensive study of the active layer using AFM, XRD, and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix and formed oversized Tri-BTDPP phases, resulting in poor charge separation. Some guidance on how to improve the OPV performance of Tri-DPP compounds is provided.
Two bisthienyl diketopyrrolopyrrole (DPP)-bithiazole based copolymers were synthesised via two different direct (hetero)arylation polymerization (DHAP) routes. When a bisthienyl DPP and 5,5′-dibromo-2,2′-bithiazole were used as monomers, the resulting polymer PA-1 showed poor solubility, ill-organized chain ordering and low performance in organic thin film transistors (OTFTs). Surprisingly, the synthetic route using a dibrominated bisthienyl DPP and 2,2′-bithiazole as monomers produced a polymer PB-1 with improved solubility, much higher crystallinity and excellent charge transport performance in OTFTs. The electron and hole mobilities of up to 0.53 cm2 V−1 s−1 and 0.06 cm2 V−1 s−1, respectively, achieved for PB-1 are more than one order of magnitude higher than those of PA-1 and also better than the mobilities reported for a similar polymer synthesized via Stille coupling polymerization. The dramatically different carrier mobilities observed for these two polymers are accounted for by their different amounts of α–β coupling linkages and branched (and lightly cross-linked) structure defects formed in the respective synthetic routes. This work also demonstrated for the first time that 2,2′-bithiazole is a suitable monomer for the construction of conjugated polymers with good electron transport performance via DHAP.
We report the synthesis of a novel electron acceptor building block, fluorene-fused triphenodioxazine (FTPDO), and a donor-acceptor polymer based on FTPDO and bithiophene, PFTPDOBT. This new polymer possesses a narrow band gap (1.66 eV) with low-lying frontier energy levels and exhibits hole transport characteristics in organic thin film transistors (OTFTs). Thin films of PFTPDOBT show remarkable thermal stability in air at temperatures of up to 250 °C with no noticeable differences in UV–Vis absorption characteristics in comparison to the films annealed in nitrogen. Surprisingly, OTFTs with the polymer thin films annealed in air and measured in air outperform significantly the devices annealed and measured in nitrogen.
A novel acceptor building block, 3,7-bis((E)-2-oxoindolin-3-ylidene)-3,7-dihydrobenzo[1,2-b:4,5-b′]dithiophene-2,6-dione (IBDT), is developed to construct a donor-acceptor polymer PIBDTBT-40. This polymer has favorable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for balanced ambipolar charge transport. Organic thin film transistors (OTFTs) based on this polymer shows well-balanced ambipolar characteristics with electron mobility of 0.14 cm2 V−1 s−1 and hole mobility of 0.10 cm2 V−1 s−1 in bottom-gate bottom-contact devices. This polymer is a promising semiconductor for solution processable organic electronics such as CMOS-like logic circuits.
Pyrazino[2,3-g]quinoxaline-2,7-dione (PQx) was used as a building block for π-conjugated polymer semiconductors, which demonstrated a strong acid affinity by showing marked bathochromic shifts in their absorption spectra. These polymers exhibited semiconductor performance in organic thin film transistors (OTFTs). Copolymers of PQx and bithiophene exhibited electron-dominant ambipolar transport characteristics with electron mobilities of up to 4.28 × 10−3 cm2 V−1 s−1 and hole mobilities of up to 5.22 × 10−4 cm2 V−1 s−1, while copolymers of PQx and thieno[3,2-b]thiophene exhibited hole-dominant ambipolar transport characteristics with hole mobilities of up to 4.82 × 10−2 cm2 V−1 s−1 and electron mobilities of up to 3.95 × 10−3 cm2 V−1 s−1.
We report two novel π-conjugated polymers, PPQ2T-TVT-24 and PPQ2T-TT-24, containing the pyrimido[4,5-g]quinazoline-4,9-dione moiety and thieno[3,2-b]thiophene (TT) and (E)-1,2-bis(thiophen-2-yl)ethene (TVT), respectively, via the Stille cross-coupling reaction. Both polymers displayed good thermal stability and promising field effect transistor performance with hole mobilities of up to 3.08 × 10−3 cm2 V−1 s−1 for PPQ2T-TT-24 and 5.34 × 10−3 cm2 V−1 s−1 for PPQ2T-TVT-24. The ambient air stability of the organic thin film transistors based on these two polymers along with another previously reported PQ polymer containing bithiophene (BT) units, PPQ2T-BT-24, was studied. It was found that the moisture (H2O) in the ambient air is a detrimental component responsible for the degradation of the device performance, while oxygen, in contrast, could enhance the carrier mobility. Our study showed that the electron donor comonomer unit significantly influenced the stability of these polymers towards moisture in the stability order of TT > BT ≫ TVT. It was shown that the interaction between H2O and PPQ2T-TT-24 is physisorption and the device performance could be fully recovered, while the interaction of H2O with two other polymers involved chemical reactions, leading to permanent damages to the polymers and only partially recovered device performance upon removal of moisture.
Three thiophene-S,S-dioxidized indophenine (IDTO) isomers, 3 a (E,E,E), 3 b (Z,E,E), and 3 c (Z,E,Z), were synthesized by oxidation of an indophenine compound. 3 b and 3 c could be converted into the most-stable 3 a by heating at 110 °C. An IDTO-containing conjugated polymer, PIDTOTT, was prepared using 3 a as a comonomer through a Stille coupling reaction, and it possesses a narrow band gap and low energy levels. In organic field effect transistors (OFETs), PIDTOTT exhibited unipolar n-type semiconductor characteristics with unexpectedly high electron mobility (up to 0.14 cm2 V−1 s−1), despite its rather disordered chain packing.
The synthesis of three new isomerically pure (E,E,E)-form thiophene-S,S-dioxidized indophenine (IDTO) compounds, (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(1-dodecyl-indolin-2-one) (4a-S1), (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(5-bromo-1-dodecyl-indolin-2-one) (4b-S1) and (3Z,3′Z)-3,3′-((E)-1,1,1′,1′-tetraoxido-5H,5′H-[2,2′-bithiophenyldene]-5,5′-diylidene)bis(6-bromo-1-dodecyl-indolin-2-one) (4c-S1), and their use as n-channel semiconductors for organic thin film transistors (OTFTs) are reported. Compared to the non-oxidized parent indophenine compound 3,3′-(5H,5′H-[2,2′-bithiophenylidene]-5,5′-diylidene)bis(1-dodecylindolin-2-one) (3a), 4a-S1 exhibited significantly lower HOMO and LUMO energy levels. Having bromine atoms at the 5,5′- (4b-S1) or 6,6′-positions (4c-S1), the HOMO and LUMO energy levels further decreased. In OTFT devices, these IDTO compounds exhibit unipolar n-type semiconductor behavior due to their significantly deeper LUMO and HOMO energy levels than those of 3a that shows ambipolar charge transport performance. The maximum electron mobilities of 4a-S1, 4b-S1 and 4c-S1 are in the order of 10−2 to 10−1 cm2 V−1 s−1, which are much higher than that of 3a (∼10−3 cm2 V−1 s−1), originating from the lower LUMO energy levels and the high isomeric purities of the former compounds. Among the three IDTO compounds, 4c-S1 shows the highest electron mobility of up to 0.11 cm2 V−1 s−1, which is likely due to its most extended π-electron delocalization on the LUMO wavefunction.
A new n-type semiconducting polymer based on indigo having thermocleavable tert-butoxycarbonyl (t-Boc) groups was synthesized and used as an active layer in organic thin film transistors (OTFTs). Twisting of the polymer main chain due to the presence of the bulky t-Boc groups renders this indigo-based polymer highly soluble. A post-deposition thermal treatment at a temperature above 170 °C could remove the t-Boc groups to retrieve the highly coplanar geometry of the unsubstituted indigo units. The thermally annealed polymer semiconductor films at 200 °C showed an electron mobility of up to ∼6 × 10−3 cm2 V−1 s−1 in OTFTs, which is a 5-fold increase compared to that of the indigo-based polymers reported previously due to the retrieved high backbone coplanarity.
In this work we report the opposite charge transport polarity observed for two regioisomeric polymer semiconductors. Previously, we observed n-type electron transport behaviour for a polymer semiconductor, 6,6′-PIDBDT, which contains 6,6′-indigo units. Electron distributions in the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of indigo calculated by density functional theory (DFT) could explain the electron transport behaviour since electrons can be delocalized along the polymer backbone through the LUMO rather than the HOMO via the 6- and 6′-positions. Serendipitously, we found that the 5- and 5′-positions of indigo are occupied by electrons in the HOMO but empty in the LUMO, opposite to the 6- and 6′-positions. This suggests that 5,5′-PIDBDT containing the 5,5′-indigo units, a regioisomer of 6,6′-PIDBDT, may exhibit the opposite p-type charge transport behaviour. To prove our assumption, we synthesized 5,5′-PIDBDT and found that this polymer indeed showed p-type semiconductor behaviour. Hence we demonstrated a novel approach to control the electron or hole charge transport polarity by simply varying the main chain regiochemical connections.
Two donor–acceptor (D–A) conjugated polymers, PINDFTT and PINDFBT, based on a novel electron acceptor, (3E,8E)-3,8-bis(2-oxoindolin-3-ylidene)naphtho-[1,2-b:5,6-b′]difuran-2,7(3H,8H)-dione (INDF), are synthesized for solution processed organic thin-film transistors. Both polymers exhibited highly balanced ambipolar characteristics with hole and electron mobilities up to 0.51 cm2 V−1 s−1 and 0.50 cm2 V−1 s−1, respectively.
A novel acceptor, (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)-5,7-dihydropyrrolo[2,3-f]indole-2,6(1H,3H)-dione, was reported. Donor–acceptor (D–A) polymer semiconductors using this new building block showed high ambipolar charge transport performance with hole and electron mobilities up to 0.19 and 0.09 cm2 V−1 s−1, respectively, in thin film transistors.
We report the development and use of a new type of branched alkyl ester side chain for donor–acceptor polymers. The synthesis of the branched alkyl ester side chain precursors is simple and the side chain's branching position and branch length can be adjusted conveniently by choosing the readily available starting materials. (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (IBDF) based donor–acceptor polymers were previously found to have poor solubility in common organic solvents. Herein, we used this new type of branched alkyl ester side chain for the copolymers of IBDF and bithiophene and explored how the branch length would impact the microstructure and charge transport properties of these polymers. With an optimal branch length, the polymer demonstrated ambipolar charge transporting characteristics with a high electron mobility of up to 0.35 cm2 V−1 s−1 and a hole mobility of up to 0.20 cm2 V−1 s−1 in organic thin film transistors (OTFTs), which is comparable to the one with branched alkyl side chains.
Pyrimido[4,5-g]quinazoline-4,9-dione (PQ) was used for the first time as a building block for π-conjugated polymer semiconductors. Copolymers of PQ and bithiophene showed dramatic bathochromic shifts in their absorption spectra in the presence of protonic (acetic acid and trifluoroacetic acid) and Lewis (BBr3) acids, resulting from the strong interaction of the basic 1,6-nitrogen atoms in the PQ unit with the acid. These polymers exhibited characteristic p-type semiconductor performance with hole mobilities of up to 6.4 × 10−3 cm2 V−1 s−1 in organic thin-film transistors (OTFTs). The potential bioactivity, high sensitivity to acids, and good field effect transistor performance of these PQ-based polymers will enable their application for bio- and chemo-sensors.
A facile and moderate to high yielding protocol is reported for the synthesis of 2,7-bis(5-bromothiophen-2-yl)-3,8-bis(2-decyltetradecyl)-3,8-dihydropyrimido[4,5-g]quinazoline-4,9-dione, which can be potentially used to synthesize other pyrimido[4,5-g]quinazoline-4,9-diones. Moreover, new pyrimido[4,5-g]quinazoline-4,9-diones synthesized by this route can potentially be used as organic semiconductors.
The surface of polydimethylsiloxane (PDMS) elastomer was hydrophilized by poly(acrylic acid) (PAAc) using Surface Initiated Atomic Transfer Radical Polymerization (Si-ATRP). The ATRP initiator chosen was ((Chloromethyl) phenylethyl) trichlorosilane, which was immobilized on the surface of the PDMS through a simple but innovative method of drop coating, in contrast to the commonly used vapor deposition and solution-immersion methods. Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS) were employed to examine surface properties of modified PDMS and confirmed presence of the PAAc chains covalently bonded to the PDMS surface. Physical properties and topography of the modified sample were characterized by water contact angle measurement and Atomic Force Microscopy. It is shown that the drop-coating of the silane initiator for ATRP modification with PAAc can result in good surface hydrophilization while causing minimum damage to the PDMS preserving its desired optical transparency. The resultant hydrophilic PDMS is stable in air and has film lubrication behavior in aqueous conditions and may be used in the development of advanced microfluidic devices and sensors where both surface hydrophilicity and bulk transparency are desired.
Indigo is for the first time used as a building block to construct polymer semiconductors for organic thin film transistors (OTFTs). Two donor–acceptor polymers using indigo as the acceptor and bithiophene as the donor are synthesized via Stille coupling polymerization. Two types of acyl groups, 2-hexldecanoyl (for polymer P1) and 2-octyldodecanoyl (for polymer P2), are utilized as solubilizing side chains. These polymers possess very deep highest-occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, due to the strong electron accepting capability of the indigo moiety. In OTFT devices, characteristic n-type semiconductor performance with electron mobility of up to ∼10−3 cm2 V−1 s−1 is observed.
Visions of Science Network for Learning Inc. (VoSNL) is a charitable organization that aims to advance the educational achievements and career aspirations of youth from low-income and marginalized communities through meaningful engagement in science, technology, engineering and mathematics (STEM) fields and research.
This award was established by Dr. and Mrs. Park M. Reilly to recognize skill in research as measured by analysis of an engineering problem, planning an efficient solution of the problem and achieving the solution with superior insight into the science and/or engineering involved. The nomination of a student must originate with the PhD Examining Committee, which will submit the nomination to the Chemical Engineering Graduate Review Committee.
FAPESP’s Post-Doctoral fellowship is aimed at distinguished researchers with a recent doctorate degree and a successful research track record. The fellowship enables the development of research within higher education and research institutions located in the State of São Paulo.
The award is for academic excellence during a graduate student’s degree in polymer science/engineering.