Pendant Photochromic Conjugated Polymers Incorporating a Highly

Subscriber access provided by Karolinska Institutet, University Library

Article

Pendant Photochromic Conjugated Polymers Incorporating a Highly Functionalizable Thieno[3,4-b]thiophene Switching Motif Garvin M Peters, and John D. Tovar J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 23, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society

Pendant Photochromic Conjugated Polymers Incorporating a Highly Functionalizable Thieno[3,4-b]thiophene Switching Motif Garvin M. Peters[1] and John D. Tovar[1,2]* [1] Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States [2] Department of Materials Science and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.

*Corresponding author email: [email protected] ABSTRACT The ability to externally modulate conjugated polymer optoelectronic properties is an important challenge for modern organic electronics. One attractive approach entails the incorporation of stimuliresponsive molecular systems, such as diarylethenes (DAEs), into polymeric materials. Our approach involves the design of polymers possessing photochromic moieties pendant to the main conjugated chain to allow for electronic influence along the polymer backbone while avoiding substantial conformational demands that may affect solid-state performance. Herein we report the synthesis of a series of thieno[3,4-b]thiophene (TT) -based photochromes that demonstrate drastically different optoelectronic properties upon cyclization. Experimental and computational investigations into arylextended model compounds provided crucial insight into the interplay between electronic structure and photochromic activity, thus allowing for the realization of pendant photoswitchable conjugated copolymers that reflect the activity found in the related model systems.

ACS Paragon Plus Environment

Journal of the American Chemical Society 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Introduction Molecular switches represent a rapidly expanding area of chemistry that has provided access to a wide breadth of stimuli-responsive systems, including versatile hydrazones,1 switchable rotaxanes,2 and molecular tweezers.3 Amongst these are diarylethenes (DAEs), which represent a class of photochromic compounds that reversibly isomerize between a relatively localized “open” state and a more-delocalized “closed” state, each possessing its own structural and electronic properties. These isomerizations proceed through well-established electrocyclizations.4 Both the thermal irreversibility of the open and closed states and the electronic diversity in switchable substrates make DAE-based switches promising candidates for functional stimuli-responsive materials. Synthetic modifications to both the ethene bridge and the (hetero)aryl moieties led to the realization of hundreds of unique DAE photochromes with engineered molecular properties (fatigue resistance5-6 and sensitization7) that have enabled biological and material applications such as fluorescent biosensors,8-9 memory storage,10 actuation,11-12 and photoacid generation.13

Figure 1. Representative polymers featuring pendant (a) and main chain (b,c) photochromic moieties.


Page 2 of 17

Page 3 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


DAEs can also be incorporated into polymeric structures, either as main-chain components or as side-chain pendants. Typically, DAEs within non-conjugated polymer matrices exhibit photochromism with minimal spectral influence from the polymer backbone. For example, Branda et. al. developed pendant DAE polymers through ring-opening metathesis polymerization (ROMP), in which the open and closed state of the monomer possessed nearly identical spectral features as the corresponding polymer (Figure 1a).14 Much less study has been devoted to DAEs as part of π-conjugated polymers, in which reversible isomerization of the photochromes along the conjugated chain would be expected to have a more dramatic impact on the electronic properties of the polymer.15-16 Following the first report of a dithienylethene (DTE)-based conjugated polymer by Stelacci et al. that displayed unique on and off spectral features,17 switchable electrical conductivity in main-chain photochromic polymers has been observed, where increases in conductivity are achieved upon conversion to the more delocalized closed ring isomers (Figure 1b, c).18-20 These results further confirm diarylethene’s importance in stimuliresponsive conjugated materials. The latter two examples represent the more common situation where the entirety of the DTE π-conjugation pathway is directly coincident with the conjugation pathway of the resulting π-electron polymer. Exhaustive switch cyclizations in these latter types of polymers require severe macromolecular reorganization, a requirement that would potentially impact the kinetics of these processes in the solid state. Indeed, Kawai et. al.21 noted that irradiated and bleached polymer showed substantially different molecular weights according to GPC. This indicates that, while individual diarylethene moieties exhibit small conformational changes upon isomerization, there may be a large change in hydrodynamic radius of the polymer when several switches are being converted simultaneously (Figure 2a).



Figure 2. The spatial effect of photoisomerization along polymers featuring a main-chain (a) or pendant (b) diarylethene motif. We envisioned an alternative polymer design whereby the diarylethene switch elements were pendant, but still conjugated to, the polymer backbone. Here, local electronic changes upon switch cyclization would extend to, and ultimately perturb, the delocalization pathway along the conjugated polymer (Figure 2b). However, the pendant nature would result in less main-chain polymeric reorganization upon irradiation. Herein, we report the design and synthesis of a series of thieno[3,4b]thiophene (TT) based photochromes using a novel synthetic route that allows for selective functionalization at each location around the fused TT ring. Aryl-extended model systems were synthesized to observe the effect of gradually extending what would be the conjugated π-electron backbone of the polymer. Computational insights helped to elucidate structural features that would result in switch-localized transitions to prevent competitive absorbance with the oligomeric/polymeric backbone. Finally, polymers were designed with specific architectures that would preserve the photochromic activity found in the small-molecule counterparts. Results and Discussion


Page 4 of 17

Page 5 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Design and Synthesis. Photochromic diarylethenes have a local interior hexatriene moiety that, upon irradiation with ultraviolet or visible light, proceeds through a 6-π electrocyclization to yield a cyclohexadiene ring22. Although extensive studies explored perfluorocyclopentene systems, several (hetero)arene-bridged photochromes demonstrate excellent photochromic response,23-24. To realize a pendant photochromic monomer, the core from which it is built must be able to accommodate both a pendant photoswitchable motif and allow for di-halogenation or di-metallation from which polymerization can occur. Thieno[3,4-b]thiophene (TT) meets these criteria, while also possessing additional desirable features that have been exploited for many contemporary conjugated polymer studies (e.g. low band-gap25 and optical transparency26). We envisioned building the switching motif from the 2- and 3- positions of the TT core, leaving the 4- and 6- positions available for further functionalization akin to most studies that incorporate TT into extended π-conjugated materials (Figure 3). Since the switching arms are typically introduced through coupling procedures, this necessitates selective functionalization of the less reactive 2- and 3- positions prior to subsequent arylation/polymerization. Our initial synthetic attempts involved synthesizing TT according to literature methods,27-28 followed by protections of the 4- and 6- positions with various silyl groups. Attempts to halogenate the remaining open thiophene carbons proved fruitless, resulting in either deprotection and simultaneous bromination for smaller silyl groups, or no reaction for larger groups. Additionally, efforts to functionalize intermediates throughout Sotzing et. al.’s29 alternative TT synthesis prior to final aromatization with DDQ were also unsuccessful.

Figure 3. Numbering scheme and locations for functionalization for thieno[3,4-b]thiophene.



This, coupled with the limited literature precedent for the functionalization of arguably the least reactive 3- position (akin to the beta position of thiophene), led us to develop a novel route towards TT coupling procedures and efficient iodine-mediated electrophilic ring closure using Larock’s methods.30 While electrophilic cyclizations have been used to assemble a wide range of fused (hetero)aromatics,31-33 this marks its first application in the synthesis of a synthetically versatile thieno[3,4-b]thiophene.

Scheme 1. Synthesis of thieno[3,4-b]thiophene monomers and photochromic derivatives. The synthesis begins with the lithium-halogen exchange of commercially available 3,4dibromothiophene followed by quenching with dimethyl disulfide, yielding 1 which possesses one of the prerequisite appendages for eventual cyclization (Scheme 1). The subsequent Sonogashira coupling can be accomplished with the bromine substituent present on 1, but we found a two-fold increase in βposition cross-coupling yields when substituted instead with iodine. Thus, a second lithiation and quench with diiodoethane was performed to obtain the more reactive substrate 2. Several different switching components were then installed through in situ-deprotection/Sonogashira cross coupling to obtain intermediates 3a-c. The thiomethyl appendage adjacent to the alkyne moiety enabled iodinemediated electrophilic ring closure: slow addition of iodine to 3 resulted in efficient cyclization to obtain


Page 6 of 17

Page 7 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the 2-arylated 3-iodinated thieno[3,4-b]thiophenes 4a-c. This halogenation was performed in cooled solutions to avoid double addition of iodine across the alkyne. While in our cases “Ar” corresponds to various switching motifs, a wide variety of substituted alkynes can be used to obtain the desired functionality at the 2- position in TT (Figure 3). The second switching component was then added through standard heterogeneous Suzuki cross coupling, resulting in switch cores TT1-TT3. Bromination of these photochromes was accomplished with NBS initially at low temperatures to avoid overbromination of any unsubstituted thienyl β-positions on thiophenes. Di-brominated TT1-3 were used as precursors to π-extended models and for polymers. Stille couplings were employed for the synthesis of the model compounds TTn-Ph , but did not translate well to polymers. Suzuki polycondensations were found to be the highest yielding conditions, and were thus used to synthesize polymeric materials P-TTn (Scheme 2). A common issue encountered is the instability of the di-halogenated cores TTn-Br, which are subject to 4-position dehalogenation under normal coupling conditions, leading to the mono-coupled product or polymer capping during polycondensations.

Scheme 2. Synthesis of polymeric species P-TT(1-3) under common Suzuki polycondensation conditions. P-TT1 Mw:12213; Mn: 7340; Đ: 1.66. P-TT2 Mw:5352; Mn: 4689; Đ: 1.14. P-TT3 Mw:6946; Mn: 4791; Đ: 1.44. Core Switches and Diarylated Model Systems. The structures of the photochromic cores under investigation (TT1-TT3, Scheme 1) differ in the substituents on the pendant thiophene rings. TT1 features the classical 2,5-dimethylthiophene switching motif and serves as the simplest model system.



TT2 contains a bistrifluoromethylated phenyl extension that was synthesized to address fatigue resistance concerns, as this motif is one of several that allows the switch to go through several rounds of cyclization and cycloreversion with minimal conversion into the irreversibly cyclized byproduct.5 TT3 was synthesized as a visible-light only switch, possibly removing the need for high energy irradiation of potential polymeric materials due to the fact that the terthiophene switching motif strongly redshifts the absorbance compared to the classical mono-thiophene example.34 The photochromic responses of these three core molecules are shown in Figure 4. The extended conjugation within the switching motif in this series is reflected in the progressively red-shifted absorption maxima moving from TT1 to TT3. In the open form, the λmax shifts from ca. 243 nm in TT1 to 370 nm in TT3, with the latter having an absorption extending well above 400 nm, allowing it to be effectively switched using exclusively visible light. The bathochromic shift is more pronounced in the closed forms, where new absorbance bands due to the extended conjugation stretches out from 525 nm in TT1 to 685 nm in TT3. The gradual red shift is also accompanied by a drastic increase in extinction coefficient, increasing by an order of magnitude between the closed forms of TT1 and TT3.


Page 8 of 17

Page 9 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Absorption spectra and solution appearance for both the “open” and “closed” photochromic switch cores TT1 (36 μM), TT2 (21 μM), and TT3 (14 μM) in acetonitrile. The insets show the naked-eye response before and after irradiation of concentration solutions of the respective TT switches.

To observe the effect of gradually extending what would be the conjugated polymer backbone, the α-dibrominated cores (TTn-Br) were coupled with phenyl tributyl stannane to produce 4,6diphenylated switch cores (TTn-Ph, Scheme 1). All TTn-Phs featured a new absorption band at ca. 375 nm with minimal change to the rest of the absorption profile. This new lower-energy transition can be attributed to the “2,5-diphenylthiophene”-like portion of TTn-Ph (Figure 5a-c). This absorption band is, for the most part, lower in energy than those of the TT1 and TT2 switches, but overlaps substantially with that of TT3.

Figure 5. Absorption spectra for di-phenylated model compounds TT1-Ph (34 μM), TT2-Ph (25 μM), and TT3-Ph (15 μM) in acetonitrile. The short π-extension in TT1-Ph produced a highly fluorescent yellow compound but also resulted in complete loss of photochromic activity once coupled (Figure 5a). Prolonged UV irradiation only led to slow degradation of the compound. TT2-Ph, however, was found to be weakly photochromic, demonstrating relatively subtle changes in higher energy absorbance upon irradiation along with the evolution of a weak lower energy profile (Figure 5b). While interconversion between the open and closed forms could be accomplished for this π-extended derivative, conversion to the closed form is substantially diminished compared to the parent switch core. The high energy similarities before and



after irradiation suggest only minor cyclization progress in the photostationary state. At the other extreme, TT3-Ph demonstrated excellent photochromic response upon irradiation (Figure 5c). The varying photochromic response seen in these systems can be attributed to the differences in the extent of conjugation along the pendant switching motif relative to the pseudo-oligomeric backbone. Since the energy gap corresponding to the excitation of the α-diphenylated thiophene is roughly fixed, gradual πextension (as in TT1 to TT3) of the DAE portion will eventually narrow the energy gap to the point where it becomes the favorable low-energy transition and hence restores photochromism. Although Kasha’s rule35 indicates that the most likely radiative transition occurs from the lowest excited state (in this case, the energy gap corresponding to the “diphenylthiophene” backbone), we initially believed that the pendant DAE switching motif would be far enough removed from this system to act independently of this π-extended region, i.e. proceed through cyclization similar to the parent photochromic cores TT1-3. However, the lack of photochromic response for TT1-Ph suggests that the electronic structure of these systems should be treated globally, where the two photoresponsive regions effectively compete for the lowest energy transitions, one of which leads to cyclization through the conical intersection while the other leads to emission of a photon. Time-dependent density functional theory (TD-DFT) calculations provided support for this idea, where key transitions were calculated for TT(1-3)Ph as well as for their isolated competing chromophores: the 4- 6- diphenylated thieno[3,4-b]thiophene (TT-Ph) and the 2- 3- disubstituted switch cores TT(1-3) (Figure 6). Examining both the TT switch core and the competing “oligomeric” backbone independently would allow ready correlation of key transitions with the diarylated model compounds under investigation. As expected, the frontier molecular orbital (FMO) topologies for TT1-Ph more closely resemble that of TT-Ph, indicating that the HOMO-LUMO transition is associated with the αdiphenylated thiophene portion while DAE-involved transitions are excluded (Figure 6b). It is not until


Page 10 of 17

Page 11 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the LUMO+1 that it reflects TT1’s LUMO, with densities distributed over the switching motif. Although each system is in a different electronic environment, the calculated HOMO-LUMO and HOMO-LUMO+1

Figure 6. Energy gaps and frontier molecular orbital topologies for “phenyl-thienothiophene-phenyl” model system TT-Ph (a) compared to unsubstituted and substituted photochromes TT1 (b), TT2 (c), and TT3 (d). Calculated HOMO-LUMO energy levels can be found in the supporting information. energy gaps for the hybrid molecule TT1-Ph also agree well with the segregated systems TT-Ph and TT1, respectively, indicating that the relevant switch transition is energetically out of reach in the presence of the conjugated backbone. A similar investigation into the TT2-Ph system was performed, although a clear distinction between the transitions is not apparent (Figure 6c). FMO topologies now show the reverse situation as in the TT1 series, with strong LUMO similarities between TT2-Ph and TT2. Both the energies and oscillator strengths, however, indicate that the relevant orbitals are heavily mixed, with significant contributions from both regions of the molecule. This helps to explain the weak photochromic response experimentally observed in TT2-Ph upon irradiation. A major difference between the TT1 and TT2 systems is the extended conjugation present in the pendant switch units of



the TT2 series, which may have resulted in competitive energetics that led to mild photochromic response. The terthiophene-based switching motif in TT3 (Figure 6d) possessed desirable excited state transitions that were localized on the DAE switch portion of the molecule. The HOMO topology for TT3Ph differs from the previous two model systems in that it is almost completely localized across the switching motif, with little to no distribution across the TT-Ph backbone. The LUMO and LUMO+1 are close in energy, and together their FMO surfaces mirror the LUMO of the switch core itself. The further energetically removed LUMO+2 is almost identical in energy gap and FMO distribution to that of TT-Ph. In the TT3 systems, the absorbance of the switching motif heavily overlaps with that of the delocalized backbone, whereas in TT1 and TT2, their analogous peak is noticeably higher in energy. Thus, both computational and experimental data reveals that key transitions can be localized on the switching motif through rational molecular engineering, thus leading to efficacious photoswitching.

Figure 7. Absorption spectra for pendant diarylethene polymers P-TT1, P-TT2, and P-TT3. Pendant Polymeric Photoswitches. While extended conjugation along the pendant aryl groups of the DAE restored photochromic function to TT3-Ph, this strategy likely cannot be generalized to the analogous polymers, where the longer effective conjugation pathway will typically have the lowest energy transition. Thus, we sought a different approach to distort the polymer backbone and interrupt this long-range conjugation, thus allowing in the pendant switch chromophore to remain the dominant lowest-energy transition. We prepared sterically congested polymers P-TT1, P-TT2, and P-TT3 by way of Suzuki polycondensation with a dialkylated phenylene comonomer, where the alkyl groups were


Page 12 of 17

Page 13 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


expected to provide enough backbone distortion to limit the effective conjugation length along the polymer (Scheme 2). The absorption profiles (Figure 7) for these polymers are very similar to their analogous model compounds (Figure 5), in which an absorbance band can be seen around ca. 375 nm, again attributed to the α-diphenylated thiophene (TT-Ph) segment. As in previous delocalized systems, P-TT1 demonstrated no photoisomerization upon irradiation. The small degree of steric hindrance imposed on the polymer by the 2,5-dimethylthiophene units may not be enough to further interrupt extended conjugation along the polymer. Calculations also suggest that it only takes two planarized flanking benzenes around the TT1 core to lead to inactivity. Both P-TT2 and P-TT3 were photochromic. The larger switching motifs in P-TT2 and P-TT3 lead to more congested systems that may not be able to accommodate a planarized backbone over multiple repeat units. While both experimental and computational results demonstrate that these two switch cores can tolerate local planarity of flanking benzene subunits and still respond productively to irradiation, the added steric congestion in P-TT2 facilitated out-of-plane distortion, leading to a relatively stronger photochromic response. Analogous to an experiment performed by Kawai et. al.,21 the GPC profiles for P-TT2 and P-TT3 were performed for both the bleached state and the irradiated photostationary state. There was no significant difference between the polymer molecular weights between the two isomeric forms, indicating no substantial polymer expansion or contraction following isomerization. Thus, we propose that there is little to no conformational impact on the polymer backbone featuring pendant switching motifs compared to its main-chain counterparts. Conclusion A novel synthetic route towards thieno[3,4-b]thiophene has allowed for the synthesis of photochromic cores that can be functionalized to serve as key precursors for pendant photochromic polymers. Aryl-extended models were first synthesized to observe the effect of gradual π-extension of the conjugated backbone, which had different manifestations based on the switching motif under



investigation. The model system containing the 2,5-dimethylthiophene switching motif (TT1-Ph) were photochromically inactive, whereas TT2-Ph showed weak photochromism. TD-DFT calculations for hybrid and segregated systems indicated that the TT-Ph backbone has competing excitations that interfered with the photochrome’s ability to switch. Computational insights led to the development of terthiophene based switch TT3, which had key excited state transitions localized on the switching motif as opposed to the backbone. To transition to polymers, conjugated backbone distortion was introduced to limit the extent of delocalization and ultimately localizing key transitions to the pendant photochrome. This was accomplished by introducing a sterically congested di-alkylated co-monomer, leading to polymers P-TT1, P-TT2, and P-TT3. The smaller switching motif in P-TT1 was not enough to restore photochromic activity in this compound, though the relatively larger subunits in P-TT2 and P-TT3 led to functional pendant photochromic polymers. We have demonstrated that novel photochromic monomers based on the TT heteroarene core can be incorporated into switchable π-conjugated materials. These compounds represent the first photochromic polymers that contain pendant DAE moieties cross-conjugated to π-conjugated main chains thereby minimizing the macromolecular reorganization necessary for photochromism. ASSOCIATED CONTENT Supporting Information General information, synthesis, quantum mechanical methods, and GPC chromatograms, and NMR spectra. The supporting information is available free of charge on the ACS Publications website. AUTHOR INFORMATION Corresponding Author [email protected] ORCID Garvin M. Peters: 0000-0003-0139-7049 John D. Tovar: 0000-0002-9650-2210


Page 14 of 17

Page 15 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ACKNOWLEDGEMENT This work was supported by Johns Hopkins University and the National Science Foundation (CHE1607821). References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16.

Su, X.; Aprahamian, I. Hydrazone-based switches, metallo-assemblies and sensors. Chemical Society Reviews 2014, 43 (6), 1963-1981. Nygaard, S.; Leung, K. C. F.; Aprahamian, I.; Ikeda, T.; Saha, S.; Laursen, B. W.; Kim, S.-Y.; Hansen, S. W.; Stein, P. C.; Flood, A. H.; Stoddart, J. F.; Jeppesen, J. O. Functionally Rigid Bistable [2]Rotaxanes. Journal of the American Chemical Society 2007, 129 (4), 960-970. Leblond, J.; Gao, H.; Petitjean, A.; Leroux, J.-C. pH-Responsive Molecular Tweezers. Journal of the American Chemical Society 2010, 132 (25), 8544-8545. Houk, K. N.; Li, Y.; Evanseck, J. D. Transition Structures of Hydrocarbon Pericyclic Reactions. Angewandte Chemie International Edition in English 1992, 31 (6), 682-708. Herder, M.; Schmidt, B. M.; Grubert, L.; Patzel, M.; Schwarz, J.; Hecht, S. Improving the Fatigue Resistance of Diarylethene Switches. Journal of the American Chemical Society 2015, 137 (7), 2738-2747. Pariani, G.; Quintavalla, M.; Colella, L.; Oggioni, L.; Castagna, R.; Ortica, F.; Bertarelli, C.; Bianco, A. New Insight into the Fatigue Resistance of Photochromic 1,2-Diarylethenes. The Journal of Physical Chemistry C 2017, 121 (42), 23592-23598. Fredrich, S.; Göstl, R.; Herder, M.; Grubert, L.; Hecht, S. Switching Diarylethenes Reliably in Both Directions with Visible Light. Angewandte Chemie International Edition 2016, 55 (3), 1208-1212. Zou, Y.; Yi, T.; Xiao, S.; Li, F.; Li, C.; Gao, X.; Wu, J.; Yu, M.; Huang, C. Amphiphilic Diarylethene as a Photoswitchable Probe for Imaging Living Cells. Journal of the American Chemical Society 2008, 130 (47), 15750-15751. Osakada, Y.; Fukaminato, T.; Ichinose, Y.; Fujitsuka, M.; Harada, Y.; Majima, T. Live Cell Imaging Using Photoswitchable Diarylethene-Doped Fluorescent Polymer Dots. Chemistry – An Asian Journal 2017, 12 (20), 2660-2665. Irie, M.; Fukaminato, T.; Matsuda, K.; Kobatake, S. Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators. Chemical Reviews 2014, 114 (24), 1217412277. Kobatake, S.; Takami, S.; Muto, H.; Ishikawa, T.; Irie, M. Rapid and reversible shape changes of molecular crystals on photoirradiation. Nature 2007, 446 (7137), 778-781. Terao, F.; Morimoto, M.; Irie, M. Light-Driven Molecular-Crystal Actuators: Rapid and Reversible Bending of Rodlike Mixed Crystals of Diarylethene Derivatives. Angewandte Chemie International Edition 2012, 51 (4), 901-904. Nakashima, T.; Tsuchie, K.; Kanazawa, R.; Li, R.; Iijima, S.; Galangau, O.; Nakagawa, H.; Mutoh, K.; Kobayashi, Y.; Abe, J.; Kawai, T. Self-Contained Photoacid Generator Triggered by Photocyclization of Triangle Terarylene Backbone. Journal of the American Chemical Society 2015, 137 (22), 7023-7026. Myles, A. J.; Branda, N. R. Novel Photochromic Homopolymers Based on 1,2-Bis(3thienyl)cyclopentenes. Macromolecules 2003, 36 (2), 298-303. Luo, Q.; Cheng, H.; Tian, H. Recent progress on photochromic diarylethene polymers. Polymer Chemistry 2011, 2 (11), 2435-2443. Harvey, C. P.; Tovar, J. D. Main-chain photochromic conducting polymers. Polymer Chemistry 2011, 2 (12), 2699-2706.



17. 18. 19. 20. 21. 22. 23. 24.

25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.

Stellacci, F.; Toscano, F.; Gallazzi, M. C.; Zerbi, G. From a photochromic diarylethene monomer to a dopable photochromic polymer: optical properties. Synthetic Metals 1999, 102 (1), 979-980. Kawai, T.; Kunitake, T.; Irie, M. Novel Photochromic Conducting Polymer Having Diarylethene Derivative in the Main Chain. Chemistry Letters 1999, 28 (9), 905-906. Choi, H.; Lee, H.; Kang, Y.; Kim, E.; Kang, S. O.; Ko, J. Photochromism and Electrical Transport Characteristics of a Dyad and a Polymer with Diarylethene and Quinoline Units. The Journal of Organic Chemistry 2005, 70 (21), 8291-8297. Kim, E.; Lee, H. W. Photo-induced electrical switching through a mainchain polymer. Journal of Materials Chemistry 2006, 16 (14), 1384-1389. Kawai, T.; Nakashima, Y.; Irie, M. A Novel Photoresponsive π-Conjugated Polymer Based on Diarylethene and its Photoswitching Effect in Electrical Conductivity. Advanced Materials 2005, 17 (3), 309-314. Hoffmann, R.; Woodward, R. B. Conservation of orbital symmetry. Accounts of Chemical Research 1968, 1 (1), 17-22. Fukumoto, S.; Nakashima, T.; Kawai, T. Photon-Quantitative Reaction of a Dithiazolylarylene in Solution. Angewandte Chemie International Edition 2011, 50 (7), 1565-1568. Wong, H. L.; Tao, C. H.; Zhu, N. Y.; Yam, V. W. W. Photochromic Alkynes as Versatile Building Blocks for Metal Alkynyl Systems: Design, Synthesis, and Photochromic Studies of DiaryletheneContaining Platinum(II) Phosphine Alkynyl Complexes. Inorganic Chemistry 2011, 50 (2), 471481. Liang, Y. Y.; Feng, D. Q.; Wu, Y.; Tsai, S. T.; Li, G.; Ray, C.; Yu, L. P. Highly Efficient Solar Cell Polymers Developed via Fine-Tuning of Structural and Electronic Properties. Journal of the American Chemical Society 2009, 131 (22), 7792-7799. Seshadri, V.; Wu, L.; Sotzing, G. A. Conjugated Polymers via Electrochemical Polymerization of Thieno[3,4-b]thiophene (T34bT) and 3,4-Ethylenedioxythiophene (EDOT). Langmuir 2003, 19 (22), 9479-9485. Brandsma, L.; Verkruijsse, H. D. An Alternative Synthysis of Thieno[3,4-b]Thiophene. Synthetic Communications 1990, 20 (15), 2275-2277. Sotzing, G. A.; Lee, K. Poly(thieno[3,4-b]thiophene): A p- and n-Dopable Polythiophene Exhibiting High Optical Transparency in the Semiconducting State. Macromolecules 2002, 35 (19), 7281-7286. Dey, T.; Navarathne, D.; Invernale, M. A.; Berghorn, I. D.; Sotzing, G. A. Versatile synthesis of 3,4b diheteropentalenes. Tetrahedron Letters 2010, 51 (16), 2089-2091. Mehta, S.; Larock, R. C. Iodine/Palladium Approaches to the Synthesis of Polyheterocyclic Compounds. The Journal of Organic Chemistry 2010, 75 (5), 1652-1658. VanVeller, B.; Robinson, D.; Swager, T. M. Triptycene Diols: A Strategy for Synthesizing Planar π Systems through Catalytic Conversion of a Poly(p-phenylene ethynylene) into a Poly(pphenylene vinylene). Angewandte Chemie International Edition 2012, 51 (5), 1182-1186. Yang, W.; Lucotti, A.; Tommasini, M.; Chalifoux, W. A. Bottom-Up Synthesis of Soluble and Narrow Graphene Nanoribbons Using Alkyne Benzannulations. Journal of the American Chemical Society 2016, 138 (29), 9137-9144. Godoi, B.; Schumacher, R. F.; Zeni, G. Synthesis of Heterocycles via Electrophilic Cyclization of Alkynes Containing Heteroatom. Chemical Reviews 2011, 111 (4), 2937-2980. Irie, M.; Eriguchi, T.; Takada, T.; Uchida, K. Photochromism of diarylethenes having thiophene oligomers as the aryl groups. Tetrahedron 1997, 53 (36), 12263-12271. Kasha, M. Characterization of electronic transitions in complex molecules. Discussions of the Faraday Society 1950, 9 (0), 14-19.


Page 16 of 17

Page 17 of 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Image


Pendant Photochromic Conjugated Polymers Incorporating a Highly

Recommend Documents