Dominic V. McGrath

Modification of symmetrically substituted phthalocyanines using click chemistry: Phthalocyanine nanostructures by nanoimprint lithography

Phthalocyanines (Pcs) are commonly applied to advanced technologies such as optical limiting, photodynamic therapy (PDT), organic field-effect transistors (OFETs), and organic photovoltaic (OPV) devices, where they are used as the p-type layer. An approach to Pc structural diversity and the incorporation of a functional group that allows fabrication of solvent resistant Pc nanostructures formed by using a newly developed nanoimprint by melt processing (NIMP) technique, a variant of standard nanoimprint lithography (NIL), is reported. Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), a click chemistry reaction, serves as an approach to structural diversity in Pc macrocycles. We have prepared octaalkynyl Pc 1b and have modified this Pc using the CuAAC reaction to yield four Pc derivatives 5a-5d with different peripheral substituents on the macrocycle. One of these derivatives, 5c, has photo-cross-linkable cinnamate residues, and we have demonstrated the fabrication of robust cross-linked photopatterned and imprinted nanostructures from this material.

Phosphonic Acid Functionalized Asymmetric Phthalocyanines: Synthesis, Modification of Indium Tin Oxide, and Charge Transfer

Metalated and free-base A(3)B-type asymmetric phthalocyanines (Pcs) bearing, in the asymmetric quadrant, a flexible alkyl linker of varying chain lengths terminating in a phosphonic acid (PA) group have been synthesized. Two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents are reported, and their synthesis and characterization through NMR, combustion analysis, and MALDI-MS are described. We also demonstrate the modification of indium tin oxide (ITO) substrates using the PA functionalized asymmetric Pc derivatives and monitoring their electrochemistry. The PA functionalized asymmetric Pcs were anchored to the ITO surface through chemisorption and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA structure on the thermodynamics and kinetics of charge transfer. Ionization energies of the modified ITO surfaces were measured using ultraviolet photoemission spectroscopy.

Synthesis and characterization of new amine-imine ligands based on trans-2,5-disubstituted pyrrolidines

Abstract We present a modular synthesis of a new class of chiral N,N-chelating ligands containing the C2-symmetrictrans-2,5-disubstituted pyrrolidine moiety linked to a pyridine ring. (−)-2-[(2R,5R)-2,5-Dimethylpyrrolidin-1-ylmethyl]pyridine (11, (R,R)-MePMP), (−)-2-[2-((2R,5R)-2,5-dimethylpyrrolidin-1-yl)ethyl]pyridine (12, (R,R)-MePEP), and (+)-2-[(2R,5R)-2,5-diphenylpyrrolidin-1-ylmethyl]pyridine (13, (R,R)-PhPMP) have been prepared. The X-ray structure of the (η3-allyl)Pd complex of (R,R)-MePMP (11) is reported.

Electron-transfer processes in zinc phthalocyanine-phosphonic acid monolayers on ITO: Characterization of orientation and charge-transfer kinetics by waveguide spectroelectrochemistry

Using a monolayer of zinc phthalocyanine (ZnPcPA) tethered to indium tin oxide (ITO) as a model for the donor/transparent conducting oxide (TCO) interface in organic photovoltaics (OPVs), we demonstrate the relationship between molecular orientation and charge-transfer rates using spectroscopic, electrochemical, and spectroelectrochemical methods. Both monomeric and aggregated forms of the phthalocyanine (Pc) are observed in ZnPcPA monolayers. Potential-modulated attenuated total reflectance (PM-ATR) measurements show that the monomeric subpopulation undergoes oxidation/reduction with ks,app = 2 × 10(2) s(-1), independent of Pc orientation. For the aggregated ZnPcPA, faster orientation-dependent charge-transfer rates are observed. For in-plane-oriented Pc aggregates, ks,app = 2 × 10(3) s(-1), whereas for upright Pc aggregates, ks,app = 7 × 10(2) s(-1). The rates for the aggregates are comparable to those required for redox-active interlayer films at the hole-collection contact in organic solar cells.

Energy Harvesting in Synthetic Dendrimer Materials

In the past two and a half decades, dendrimers have emerged as a distinct branch ofmacromolecular chemistry. Tailoring of dendrimer structure yields precise placement of chromophoresthat can serve as energy harvesters, mimicking photosynthesis. The unique architecture afforded bydendrimers allows for multiple energy harvesters that can transfer their energy to a single core,which is important for optoelectronic applications such as organic light emitting diodes (OLEDs).This review emphasizes the energy transfer characteristics that these dendrimers provide rather thentheir synthesis.

Mild and convenient oxidation of aromatic heterocyclic primary alcohols by 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium perchlorate

Hydroxymethyl substituted aromatic heterocycles, including pyridines, furans, and thiophenes, are oxidized to the corresponding aldehydes in excellent yields by 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium perchlorate (1) with minimal workup.

An approach to highly functionalized dendrimers from chiral, non-racemic synthetic monomers

Abstract An approach to dendrimers with highly functional interiors constructed from chiral, non-racemic hydrobenzoin monomer units is presented. An optically pure monomer unit is prepared using asymmetric dihydroxylation (AD) and a representative dendrimer is constructed by a convergent growth strategy.

Vanillin and o-vanillin oligomers as models for dendrimer disassembly

Linear analogs have been synthesized to model disassembling dendrimers. These linear analogs provide a facile synthesis to molecules that can be used to test new trigger groups and cleavage vectors. Vanillin and o-vanillin were used as the monomer units of these analogs and two trigger groups, allyl and o-nitrobenzyl, were chosen to test the disassembly process. Allyl triggered analogs 1a–d and 3a–d and o-nitrobenzyl triggered analogs 2a–c and 4a–c showed good to excellent disassembly as followed by the evolution of p-nitrophenoxide reporter ion by UV-Visible spectroscopy. The rate and yield of disassembly was shown to depend on experimental conditions as well as length of the cleavage vector.

Peripheral Substitution of a Near‐IR‐Absorbing Soluble Phthalocyanine Using “Click” Chemistry

A series of near-IR-absorbing soluble phthalocyanines (Pcs) with eight alkyne moieties as side chains of the chromophore have been synthesized. One of these Pcs has been used as a scaffold for functional group modification using alkyne-azide click chemistry with various azides. This led to a small library of Pcs with photo and thermal crosslinkable, dendritic, and hydrophilic moieties starting from a single Pc molecule. A patterned thin film was fabricated by photocrosslinking one of these Pc derivatives.

Non-aggregating octasubstituted dendritic phthalocyanines

Eight poly(aryl) ether dendritic wedges attached to the periphery of a phthalocyanine significantly decreases self-association of these chromophores in solution and the condensed state.