Gregory T. Carroll

Control of Surface Wettability Using Tripodal Light-Activated Molecular Motors

Monolayers of fluorinated light-driven molecular motors were synthesized and immobilized on gold films in an altitudinal orientation via tripodal stators. In this design the functionalized molecular motors are not interfering and preserve their rotary function on gold. The wettability of the self-assembled monolayers can be modulated by UV irradiation.

Light-driven altitudinal molecular motors on surfaces

A Cu(I)-catalyzed 1,3-dipolar cycloaddition was used to construct a monolayer of an altitudinal molecular motor on quartz and silicon substrates, which represents the fastest light-driven molecular motor, to date, grafted to a solid surface.

On/Off Photoswitching of the Electropolymerizability of Terthiophenes

In this contribution the polymerization of terthiophene, to form an alkene bridged alpha,alpha-coupled sexithiophene polymer, is controlled by light; i.e. the electropolymerizability of the monomer 1F is switched off and on with UV and visible light, respectively. The system comprises of both bis-terthiophene and photochromic dithienylethene units. The presence of a light-switchable unit allows on-off switching of the electropolymerization of the monomer with light. Furthermore the incorporation of the dithienylethene in the polymer backbone increases dramatically the homogenity of the polymer formed (i.e., only sexithiophene units are formed). The derived films are robust and fully retain electrochromic behavior as has been demonstrated through cyclic voltammetry while spatial control (patterning) is readily achieved by applying simple optical masking techniques.

A Chiroptical Photoswitchable DNA Complex

The interesting structural, electronic, and optical properties of DNA provide fascinating opportunities for developing nanoscale smart materials by integrating DNA with opto-electronic components. In this article we demonstrate the electrostatic binding of an amine-terminated dithienylethene (DET) molecular switch to double-stranded synthetic polynucleotides. The DET switch can undergo photochemical ring-closure and opening reactions. Circular dichroism (CD) and UV-vis spectroscopy show that both the open, 1o, and the closed, 1c, forms of the switch bind to DNA. Upon addition of DNA to a solution of 1o or 1c, the UV-vis spectrum displays a hypochromic effect, indicative of an interaction between the switch and the DNA. The chirality of the DNA double-helix is transmitted to the switching unit which displays a well-defined CD signal upon supramolecular complexation to the DNA. Additionally, the CD signal of the DNA attenuates, demonstrating that both components of the complex mutually influence each others structure; the DNA induces chirality in the switch, and the switch modifies the structure of the DNA. Modulation of the chiroptical properties of the complex is achieved by photochemically switching the DET between its ring open and closed isomers. A pH dependence study of the binding shows that when the pH is increased the switches lose their binding ability, indicating that electrostatic interactions between protonated amines and the negatively charged phosphate backbone are the dominant driving force for binding to the DNA. A comparison of poly(deoxyguanylic-deoxycytidylic) acid [poly(dGdC)(2)] polynucleotides with poly(deoxyadenylic-deoxythymidylic) acid [poly(dAdT)(2)] shows distinct differences in the CD spectra of the complexes.

Controlled rotary motion of light-driven molecular motors assembled on a gold film

Using circular dichroism (CD) spectroscopy, we show that light-driven rotary molecular motors based on overcrowded alkenes can function in a self-assembled monolayer on semi-transparent gold films.

Adhesion of Photon-Driven Molecular Motors to Surfaces via 1,3-Dipolar Cycloadditions: Effect of Interfacial Interactions on Molecular Motion

We report the attachment of altitudinal light-driven molecular motors to surfaces using 1,3-dipolar cycloaddition reactions. Molecular motors were designed containing azide or alkyne groups for attachment to alkyne- or azide-modified surfaces. Surface attachment was characterized by UV-vis, IR, XPS, and ellipsometry measurements. Surface-bound motors were found to undergo photochemical and thermal isomerizations consistent with unidirectional rotation in solution. Confinement at a surface was found to reduce the rate of the thermal isomerization process. The rate of thermal isomerization was also dependent on the surface coverage of the motors. In solution, changes in the UV-vis signal that accompany thermal isomerization can be fit with a single monoexponential decay. In contrast, thermal isomerization of the surface-bound motors does not follow a single monoexponential decay and was found to fit a biexponential decay. Both one- and two-legged motors were attached to surfaces. The kinetics of thermal isomerization was not affected by the valency of attachment, indicating that the changes in kinetics from solution to surface systems are related to interactions between the surface-bound motors.

Shedding light on surfaces—using photons to transform and pattern material surfaces

The ultimate goal of surface modification is to quantitatively control surface properties by precise manipulation of surface chemical structure at the molecular level. Advances in the understanding of molecular design principles for soft matter surfaces can be combined with the available arsenal of interesting photochemical reactions to create an exciting paradigm for surface modification: the use of photons to both transform and pattern chemical functionality at soft matter surfaces. The success of the paradigm is predicated on the ability to design and synthesize “photochemical surface delivery vehicles”, complex photoactive molecules that form stable surface monolayers and subsequently deliver photoactive moieties to the surface. Shedding light onto these smart, modified surfaces brings about a wide variety of precise photochemical reactions that are preprogrammed within the surface delivery vehicle. Surface chemical patterns are formed by exposure through a mask. Some photochemical surface transformation can be considered as “green” chemistry since only photons are required as reagents. In this review, we provide a brief tutorial on photochemistry fundamentals to illustrate the nature of possible photochemical surface reactions and discuss the principles of design for photochemical surface delivery vehicles. Applications of the paradigm drawn from a variety of fields emphasize the tremendous potential for photochemical surface transformation and patterning on both hard and soft substrates.

Patterning dewetting in thin polymer films by spatially directed photocrosslinking

In this report we examine the dewetting of spin-cast poly (styrene) films in a confined geometry. We designed a platform for laterally confining PS by photo-patterning crosslinks in spin-coated thin films. Heating the patterned film above the glass transition temperature of PS results in localized dewetting patterns in regions that were not crosslinked, while the crosslinked pattern serves as a rigid barrier that confines the retraction of the uncrosslinked polymer in micron-sized domains. The barriers also provide a favorable surface that the liquid PS wets onto, forming a rim at the boundary of crosslinked and uncrosslinked polymer. The resulting patterns are shown to be dependent on the irradiation and annealing time, the dimensions of the uncrosslinked region and the thickness of the film.

Towards Dynamic Control of Wettability by Using Functionalized Altitudinal Molecular Motors on Solid Surfaces

We report the synthesis of altitudinal molecular motors that contain functional groups in their rotor part. In an approach to achieve dynamic control over the properties of solid surfaces, a hydrophobic perfluorobutyl chain and a relatively hydrophilic cyano group were introduced to the rotor part of the motors. Molecular motors were attached to quartz surfaces by using interfacial 1,3-dipolar cycloadditions. To test the effect of the functional groups on the rotary motion, photochemical and thermal isomerization studies of the motors were performed both in solution and when attached to the surface. We found that the substituents have no significant effect on the thermal and photochemical processes, and the functionalized motors preserved their rotary function both in solution and on a quartz surface. Preliminary results on the influence of the functional groups on surface wettability are also described.

Photons to illuminate the universe of sugar diversity through bioarrays

In this mini-review, we summarize the photochemical approaches for developing high-throughput carbohydrate microarray technologies. Newly established methods for photo-immobilizing unmodified monosaccharides, oligosaccharides and polysaccharides onto photoactive surfaces and coupling of photoactive carbohydrates onto polymer surfaces are reviewed.