18 research outputs found
Investigating light-driven rotary molecular motors
No full textLight-driven rotary molecular motors based on overcrowded alkenes have been firmly established in the pantheon of artificial molecular machines. Applications range far and wide, although the impact of these versatile compounds on our fundamental understanding of chirality and molecular motion cannot be underestimated. The development of molecules with such novel properties inevitably goes hand in hand with the exploration of novel analytical methods. To demonstrate and investigate the rotational properties of overcrowded alkene-based motors and switches, we must embrace innovative ways of using common lab equipment and branch out into learning new analytical techniques. In this chapter, we aim to provide a practical guide for the study of overcrowded alkene based molecular motors and switches. We commence with an overview of the most commonly used methods to characterize these compounds, and specifically focus on our collective experimental experience in investigating rotational and/or switching behavior. In addition, we will discuss various cutting-edge techniques that have recently facilitated even further investigation into the unique properties of these fascinating molecules.</p
Controlling rotary motion of molecular motors based on oxindole
Get PDFMolecular motors are essential components of artificial molecular machines, which can be used to manipulate and amplify mechanical motion at the nanoscale to create machine-like function. Since the discovery of light-driven rotary molecular motors, the field has been widely developed, including the introduction of molecular motors based on oxindole by our group in 2019. The rotational properties of molecular motors, e.g. absorption wavelength, quantum yield and rotation speed, often critically depend on substituent effects. Up to now, the substituent effects of oxindole-based molecular motors have not yet been investigated. Herein, we present a family of oxindole-based molecular motors functionalised at three different positions on the motor core, with either CN or OMe groups. The motors prepared in this work retain the favourable features of oxindole-based motors, i.e. simple synthesis and visible light addressability. We find that functionalisation has substantial effects on the absorption wavelength of the motors, meanwhile the rotation speed is unaffected. Furthermore, we found that functionalisation of the oxindole molecular motors increases their quantum efficiency considerably in comparison to previous motors of their class
Designing light-driven rotary molecular motors
Get PDFThe ability to induce and amplify motion at the molecular scale has seen tremendous progress ranging from simple molecular rotors to responsive materials. In the two decades since the discovery of light-driven rotary molecular motors, the development of these molecules has been extensive; moving from the realm of molecular chemistry to integration into dynamic molecular systems. They have been identified as actuators holding great potential to precisely control the dynamics of nanoscale devices, but integrating molecular motors effectively into evermore complex artificial molecular machinery is not trivial. Maximising efficiency without compromising function requires conscious and judicious selection of the structures used. In this perspective, we focus on the key aspects of motor design and discuss how to manipulate these properties without impeding motor integrity. Herein, we describe these principles in the context of molecular rotary motors featuring a central double bond axle and emphasise the strengths and weaknesses of each design, providing a comprehensive evaluation of all artificial light-driven rotary motor scaffolds currently present in the literature. Based on this discussion, we will explore the trajectory of research into the field of molecular motors in the coming years, including challenges to be addressed, potential applications, and future prospects.</p
Synergistic interplay between photoisomerization and photoluminescence in a light-driven rotary molecular motor
Get PDFPhotoactuators and photoluminescent dyes utilize light to perform mechanical motion and undergo spontaneous radiation emission, respectively. Combining these two functionalities in a single molecule would benefit the construction of advanced molecular machines. Due to the possible detrimental interaction between the two light-dependent functional parts, the design of hybrid systems featuring both functions in parallel remains highly challenging. Here, we develop a light-driven rotary molecular motor with an efficient photoluminescent dye chemically attached to the motor, not compromising its motor function. This molecular system shows efficient rotary motion and bright photoluminescence, and these functions can be addressed by a proper choice of excitation wavelengths and solvents. The moderate interaction between the two parts generates synergistic effects, which are beneficial for lower-energy excitation and chirality transfer from the motor to the photoluminescent dye. Our results provide prospects towards photoactive multifunctional systems capable of carrying out molecular rotary motion and tracking its location in a complex environment
A visible-light-driven molecular motor based on barbituric acid
Get PDFWe present a class of visible-light-driven molecular motors based on barbituric acid. Due to a serendipitous reactivity we observed during their synthesis, these motors possess a tertiary stereogenic centre on the upper half, characterised by a hydroxy group. Using a combination of femto- and nanosecond transient absorption spectroscopy, molecular dynamics simulations and low-temperature 1H NMR experiments we found that these motors operate similarly to push-pull second-generation overcrowded alkene-based molecular motors. Interestingly, the hydroxy group at the stereocentre enables a hydrogen bond with the carbonyl groups of the barbituric acid lower half, which drives a sub-picosecond excited-state isomerisation, as observed spectroscopically. Computational simulations predict an excited state “lasso” mechanism where the intramolecular hydrogen bond pulls the molecule towards the formation of the metastable state, with a high predicted quantum yield of isomerisation (68%) in gas phase.</p
Coupled Rocking Motion in a Light-Driven Rotary Molecular Motor
Get PDFCoupled motion is ubiquitous in Nature as it forms the base for the direction, amplification, propagation, and synchronization of movement. Herein, we present experimental proof for the coupling of the rocking motion of a dihydroanthracene stator moiety with the light-induced rotational movement of an overcrowded alkene-based molecular motor. The motor was desymmetrized, introducing two different alkyl substituents to the stator part of the molecular scaffold, resulting in the formation of two diastereomers with opposite axial chirality. The structure of the two isomers is determined with nuclear Overhauser effect spectroscopy NMR and single-crystal X-ray analysis. The desymmetrization enables the study of the coupled motion, that is, rotation and oscillation, by 1H NMR, findings that are further supported by density functional theory calculations. A new handle to regulate the rotational speed of the motor through functionalization in the bottom half was also introduced, as the thermal barrier for thermal helix inversion is found to be largely dependent on the alkyl substituents and its orientation toward the upper half of the motor scaffold. In addition to the commonly observed successive photochemical and thermal steps driving the rotation of the motor, we find that the motor undergoes photochemically driven rotation in three of the four steps of the rotation cycle. Hence, this result extends the scope of molecular motors capable of photon-only rotary behavior
General strategy for boosting the performance of speed-tunable rotary molecular motors with visible light
Get PDFLight-driven molecular rotary motors perform chirality-controlled unidirectional rotations fueled by light and heat. This unique function renders them appealing for the construction of dynamic molecular systems, actuating materials, and molecular machines. Achieving a combination of high photoefficiency, visible-light responsiveness, synthetic accessibility, and easy tuning of dynamic properties within a single scaffold is critical for these applications but remains a longstanding challenge. Herein, a series of highly photoefficient visible-light-responsive molecular motors (MMs), featuring various rotary speeds, was obtained by a convenient one-step formylation of their parent motors. This strategy greatly improves all aspects of the performance of MMs-red-shifted wavelengths of excitation, high photoisomerization quantum yields, and high photostationary state distributions of isomers-beyond the state-of-the-art light-responsive MM systems. The development of this late-stage functionalization strategy of MMs opens avenues for the construction of high-performance molecular machines and devices for applications in materials science and biological systems, representing a major advance in the synthetic toolbox of molecular machines.</p
Two-photon absorption of oxindole-based push–pull molecular motors
Get PDFFuture applications of light-driven molecular motors in bio-based systems and soft materials require their operation with benign, low-energy light irradiation. Here we report four rotary molecular motors based on oxindole units which can be driven by near-infrared light. By installing an electron-withdrawing CN group on the oxindole lower half, in direct conjugation through the alkene axle to the electron-donating OMe substituent on the upper half, our design establishes a rigid push–pull system which red-shifts the absorption maximum further into the visible region. We also show that the induced nonlinearity to the system increases their two-photon absorption cross section, and the operation of oxindole based molecular motors with 800 nm light for the very first time. The motors prepared in this work show improved performance compared to previous oxindole based motors, e.g. visible light addressability up to 530 nm and 1.5-fold increase in quantum yields in both directions, whilst retaining their desirable qualities of easy synthesis and fast rotation speed.</p
Population genetic analysis of two species of non-indigenous riparian weeds in northeast England in the context of their spatial ecology
Get PDFThe population genetic structure of two species of invasive non-indigenous riparian weeds in the Northeast of England was investigated using microsatellite markers. Heracleum mantegazzianum and Impatiens glandulifera were introduced into the UK from Asia. The first records of the species in the Tees, Tyne and Wear catchment areas were in 1944 and 1892 respectively. Both species have spread rapidly, and are present over a wide area of the catchments. The pattern of genetic variation was investigated in order to determine the importance of anthropogenic introduction, and life-history and dispersal strategies to the distribution of the species. Twelve populations of each species were sampled from the Tees, Tyne and Wear catchments as well as an independent population for comparison. Genomic libraries were constructed and screened for dinucleotide repeat microsatellite loci. Four polymorphic loci of H. mantegazzianum and three of I. glandulfera were identified, and each species was also screened for variation using one universal chloroplast microsatellite locus. A large amount of variation was found in both species as the loci of H. mantegazzianum had between nine and twenty alleles and those of I. glandulifera between eight and sixteen alleles. Results revealed greater overall variation between populations from different catchments than those in the same catchment. Within a catchment, there was evidence of isolation by distance for both species in one out of two catchments examined. Populations of I. glandulifera showed greater temporal variation and there was more variation both overall and within a catchment in this species. This is likely to be due to the larger number of individuals present, and the wider distribution of this species. Low levels of chloroplast variation were found in both species. This may reflect a lack of variation in the material introduced into the UK
Microresonators for organic semiconductor and fluidic lasers
No full textThis thesis describes a number of studies of microstructured optical resonators,
designed with the aim of enhancing the performance of organic semiconductor lasers
and exploring potential applications. The methodology involves the micro-engineering
of the photonic environment in order to modify the pathways of the emitted light and
control the feedback mechanism. The research focuses on designing new organic
microstructures using established semi-analytical and numerical methods, developing fabrication techniques using electron-beam lithography, and optically characterising the resulting structures.
Control of the feedback mechanism in conjugated polymer lasers is first investigated by studying Distributed Feedback or photonic crystal resonators based on a square feedback lattice. This study identified the diffraction to free space radiation as a major source of loss in current microstructured resonator designs. By cancelling the coupling to free space through the use of different feedback symmetries and diffraction orders, a threshold reduction by almost an order of magnitude is demonstrated.
The introduction of mid-gap defect photonic states in an otherwise uniformly periodic
structure was studied in Distributed Bragg Reflector (DBR) resonators. This enabled
GaN diode pumped polymer lasers to be demonstrated, indicating that the transition
from complex excitation sources to more compact systems is possible. Devices for
potential applications in the field of optical communications are also explored by
demonstrating a polymer DBR laser based on silicon. In this way, the potential for
integrating conjugated polymers with silicon photonics is confirmed.
Photonic crystal fibres, which have a periodic microstructure in the transverse
direction, are explored as an alternative means for controlling the optical properties of organic lasers. Fluidic fibre organic lasers were demonstrated as efficient sources with good spectral purity. In these devices, mechanisms to tune the emission wavelength
were explored and the origin of the frequency selection mechanism was investigated.The author received a Wingate Scholarship for the Si experiments
