Photochromic Intercalation Compounds

Photochromism of intercalation compounds has been investigated so far. Starting from fundamental studies on the photochromic reactions of the dyes in the presence of layered materials, the precise design of the nanostructures of intercalation compounds toward controlled photochemical reactions and the creation of novel photoresponsive supramolecular systems based on layered solids have been a topic of interests. Various layered materials with different surface chemistries have been used as hosts for the controlled orientation, and aggregation of the intercalated dyes and the states of the intercalated guests affected photoresponses. Molecular design of the photochromic dyes has also been conducted in order to organize them on layered solids with the desired manner. On the other hand, layered solids with such functions as semiconducting and magnetic have been examined to host photochromic dyes for the photoresponsive changes in the materials' properties.ArticlePHOTOFUNCTIONAL LAYERED MATERIALS. 166: 177-211 (2015)journal articl

Fast T-Type Photochromism of Colloidal Cu-Doped ZnS Nanocrystals

This paper reports on durable and nearly temperature-independent (at 298–328 K) T-type photochromism of colloidal Cu-doped ZnS nanocrystals (NCs). The color of Cu-doped ZnS NC powder changes from pale yellow to dark gray by UV light irradiation, and the color changes back to pale yellow on a time scale of several tens of seconds to minutes after stopping the light irradiation, while the decoloration reaction is accelerated to submillisecond in solutions. This decoloration reaction is much faster than those of conventional inorganic photochromic materials. The origin of the reversible photoinduced coloration is revealed to be a strong optical transition involving a delocalized surface hole which survives over a minute after escaping from intraparticle carrier recombination due to electron-hopping dissociation. ZnS NCs can be easily prepared in a water-mediated one-pot synthesis and are less toxic. Therefore, they are promising for large-scale photochromic applications such as windows and building materials in addition to conventional photochromic applications. Moreover, the present study demonstrates the importance of excited carrier dynamics and trap depths, resulting in coloration over minutes not only for photochromic nanomaterials but also for various advanced photofunctional materials, such as long persistent luminescent materials and photocatalytic nanomaterials

Controlling the Cycloreversion Reaction of a Diarylethene Derivative Using Sequential Two-Photon Excitation

Diarylethenes (DAE) are a class of photochromic molecular switches that convert between two structural isomers upon excitation with light. A great deal of research has been dedicated to elucidating the mechanisms of the reversible electrocyclic reactions to make optical memory devices with DAE compounds, but details of the fundamental reaction mechanism after one- or two-photons of light is still lacking. The primary DAE discussed in this dissertation is 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DMPT-PFCP), which is a model compound for studying the fundamental reaction dynamics using one- and two-photon excitation experiments. Pump-probe spectroscopy was used to study the low one-photon quantum yield cycloreversion reaction of DMPT-PFCP by changing the excitation wavelength, solvent, and temperature to describe the dynamics on the ground- and excited states. However, the primary goal of this work was to use sequential two-photon excitation with fs laser pulses to map out the cycloreversion reaction dynamics for DMPT-PFCP compound on the first and higher excited states. The cycloreversion quantum yield was selectively increased using sequential two-photon excitation, where after promotion to the S1 state, a second excitation pulse promotes the molecules to an even higher excited state. The mechanism of increasing the yield by promoting the molecules to a higher excited state was explored using pump-repump-probe (PReP) spectroscopy. The PReP experiments follow the excited-state dynamics as the molecules sample different regions of the S1 potential energy surface. The projection of the S1 dynamics onto the higher excited states showed that by changing the secondary excitation wavelength and the delay between excitation pulses, the cycloreversion quantum yield was selectively controlled. Future studies to obtain the specific modes involved in the ring-opening reaction coordinate on the excited-state would further improve our knowledge of the cycloreversion reaction and therefore improve the efficiency of the sequential two-photon excitation process to make very efficient optical memory devices using DAE compounds

Light-Mediated Control of Polymeric Materials

The synthesis and characterization of precision polymeric materials represents a broad research area with significant value to society. Recently, light-mediated approaches to controlled polymer synthesis have attracted significant interest due to the low cost and tremendous tunability of modern light sources. Through manipulating these various properties (wavelength, intensity, etc), researchers have made considerable progress in controlling a wide range of important polymeric properties such as molecular weight distribution, comonomer composition, and molecular architecture. However, the systems developed to date have largely focused on homogenous targets and have lacked in-depth photophysical interpretation. This dissertation describes the development of an in-situ approach to studying light-mediated chemical reactions and efforts to better understand the temporal control of state-of-the-art photopolymerizations. Furthermore, the lessons learned from these studies led to the development of a new approach to 3D printing, wherein specific wavelengths of visible light were used to independently and simultaneously define local materials properties throughout a part in a single step. This breakthrough in additive manufacturing greatly expands the potential of multi-material printing techniques. The findings of these works have broad implications for using light as a tool for the future development of synthetic approaches to advanced polymeric materials

Organometallic Materials: Ferroceno[\u3cem\u3ec\u3c/em\u3e]thiophenes and 1,2-Bisthienylmetallocenes

Development of synthetic routes toward two general organometallic frameworks was undertaken. The first project involved synthetic attempts of substituted and unsubstituted ferroceno[c]thiophene while the second one was the synthesis of 1,2-dithienylmetallocenes. The long-term goal of this work is to lay the foundations for study of electronic, electrochromic, redox, and optical properties of thiophene-based materials integrated with organometallic systems such as ferrocene, ruthenocene and cymantrene. The synthetic pathway for the target molecule in the first project involved converting 1,2-bis(hydroxymethyl)ferrocene to 1,2-bis(thiouroniummethyl)ferrocene with thiourea under acidic conditions. Refluxing the salt in base followed by acidification resulted in 1,2-bis(mercaptomethyl)ferrocene, which is oxidized to the cyclic ferroceno[d]-1,2-dithiane. Ring contraction of cyclic dithiane gave the thioether, ferroceno[c]-2,5-dihydrothiophene. Periodate oxidation of the thioether gave ferroceno[c]-2,5-dihydrothiophene-S-oxide (1), a potential precursor for ferroceno[c]thiophene via Pummerer dehydration. Attempts to dehydrate 1 and to trap the resulting thiophene in situ indicated instability of the target compound. Synthesis of ferroceno[c]thiophene with electron-donating as well as electron-withdrawing substituents at the 2,5-positions of the thiophene ring was attempted. 1,2–Dithienylethenes and their derivatives have gained increased attention due to their exceptional photochromic property. They tend to be thermally irreversible but photochemically reversible, which is a vital for their potential use in optical memories, switches and other optoelectronic applications. Inspiration of the second project was that incorporation of 1,2-dithienyl systems into metallocenes would enhance the general properties of the molecule, including stability, fatigue resistance, solid-state reactivity and higher sensitivity. 1,2-Dithienylferrocene was successfully synthesized. The synthetic pathway for 1,2-dithienylferrocene involved the reaction of α-bromo-3-acetyl-2,5-dimethylthiophene (1) with ethyl 4-(2,5-dimethylthiophen-3-yl)-3-oxobutanoate (2) to give 2,3-diarylcyclopent-2-en-1-one (3). Compounds 1 and 2 were synthesized following literature methods. Compound 3 was then converted to its cyclopentadienide form by first reducing the ketone to alcohol using LAH, followed by dehydration and then deprotonation of the substituted cyclic diene using butyllithium to give 1,2-bis(2,5-dimethylthiophene)-2,4-cyclopentadien-1-yl)lithium (4). [Fe(fluorenyl)(Cp)] was then used as a transfer reagent and reacted with 4 to yield the target compound

Multiphoton and Structural Control of 6 Pi Photocyclization in ortho-terphenyls

Multiphoton excitation and manipulation of reactant structure promises opportunities for opening new photochemical reaction pathways and controlling photoproduct distributions. In the first part of this dissertation, we demonstrate photonic control of the 6π photocyclization of ortho-terphenyl (OTP), a model system with a similar structure to diarylethenes, to make 4a,4b-dihydrotripheneylene (DHT). Using Pump-Repump-Probe spectroscopy we show that 1+1’ excitation to a high-lying reactant electronic state generates a metastable species characterized by a red absorption feature that accompanies a repump-induced depletion in the one-photon trans-dihydro product (trans-DHT); signatures of the new photoproduct are clearer for a structural analog of the reactant that is sterically inhibited against one-photon cyclization. Quantum-chemical computations support assignment of this species to cis-DHT, which is accessible photochemically along a disrotatory coordinate from high-lying electronic states reached by 1+1’ excitation. We use time-resolved spectroscopy to track photochemical dynamics producing cis-DHT. In total, we demonstrate that selective multiphoton excitation opens a new photoreaction channel in these photocyclizing reactants by taking advantage of state-dependent correlations between reactant and product electronic states. In the second part of this dissertation, we examine the impact of specific structural perturbations on the one and two-photon induced dynamics in ortho-terphenyl. Through the addition of substituent groups on pendant rings of OTP, we demonstrate improved branching efficiency for cyclization over nonreactive deactivation. Using both pump-probe and pump-repump-probe transient absorption spectroscopy, we show that nonreactive deactivation rates are largely unaffected by structural modifications, whereas those associated with cyclization to form trans-DHT decrease with increasing substituent size/mass. Based on these observations, we conclude that these deactivation channels require different scales of nuclear reorganization in low-lying electronic excited states. We have previously shown that two-photon excitation of OTP generates cis-DHT. Here we find that the cis-DHT photoproduct yield generated by a 1+1’ excitation of the reactant is impacted by dynamics in the low-lying excited-states of OTP that exhibit sensitivities to structural modification. Ultrafast spectral dynamics observed by PRP and TAS occur on significantly different timescales, indicating that these methods have different sensitivities for probing dynamics on low-lying potential energy surfaces

Computational mechanistic photochemistry: The central role of conical intersections

In this thesis, I review my own contributions in the field of computational photochemistry. This manuscript is written as an introduction to this field of research. It is not intended to be a textbook, as more emphasis has been made on illustrations rather than on methodologies and technical guidelines. In this way, I hope that it will be accessible to a large audience, from undergraduate students to more experienced scientists who would be interested in learning about this fascinating and relatively young field of research

光と熱によって動くメカニカル結晶の創製

早大学位記番号:新8191早稲田大

A new light-responsive resistive random-access memory device containing hydrogen-bonded complexes.

Acknowledgements: TSV acknowledges financial support from the Ministry of Higher Education of Malaysia through the Fundamental Research Grant Scheme [FP079-2018A]. AR acknowledges Ministerio de Economía y Competitividad (MINECO) for his PhD grant BES-2015-071235, under the project MAT2014-55205-P. VMA acknowledges the University Malaya for the grant RF004B-2018. AMF would like to thank the Royal Academy of Engineering, U.K., for the grant NRCP1516/4/61 (Newton Research Collaboration Programme), the University of Aberdeen, for the award of the grant SF10192, the Carnegie Trust for the Universities of Scotland, for the Research Incentive Grant RIG008586, the Royal Society and Specac Ltd., for the Research Grant RGS\R1\201397, and the Royal Society of Chemistry for the award of a mobility grant (M19-0000). AMF and TSV further acknowledge University Malaya for travelling support.Peer reviewedPostprin