2017-2

A Smart Network Polymer with Bis(piperidyl)naphthalene Cross-linkers: Selective Fluorescence Quenching and Photodegradation in the Presence of Trichloromethyl–Containing Chloroalkanes
S. Sasaki, Y. Sugita, M. Tokita, T. Suenobu, O. Ishitani, G. Konishi*
Macromolecules, 50, ASAP (2017).
DOI: 10.1021/acs.macromol.7b00213
Link
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Abstract: 1,4-Bis(piperidyl)naphthalene (1,4-BPN) was employed as a cross-linker for poly(n-butyl methacrylate) gels to generate soft materials that exhibit selective fluorescence quenching and photodegradation in 1,1,1-trichloromethyl-containing chloroalkanes. In chloroform and 1,1,1-trichloroethane, 1,4-BPN is subject to efficient fluorescence quenching via the formation of exciplexes, which results in rapid photodegradation. Similarly, poly(n-butyl methacrylate) gels cross-linked with 1,4-BPN were highly fluorescent and stable in various organic solvents and chloroalkanes but exhibited less intense fluorescence and rapid photodegradation in 1,1,1-trichloromethyl-containing chloroalkanes. Upon swelling in 1,1,1-trichloroethane, these gels exhibited a steep drop in the storage modulus during first 10 s of photoirradiation (λ = 365 nm). Further photoirradiation for 10–30 min led to the decomposition of the gels. Thus, we propose that the 1,4-BPN-based cross-linker can be used for the facile preparation of diverse polymeric materials with synergistic fluorescence, detection, and photodecomposition properties toward unreactive and neutral analytes.

[PR]

# by konishi_lab | 2017-04-28 23:30 | 2017(2)

2017-1

Open Access
Thermo-responsive fluorescence of AIE-active
poly(N-isopropylacrylamides) labeled with highly twisted
bis(N,N-dialkylamino)arenes

S. Sasaki, G. Konishi*
RSC Adv., 7, 17403-17416 (2017).
DOI: 10.1039/C7RA01212H
Link
b0202136_11142443.jpg

Highly twisted bis(N,N-dialkylamino)arenes, which represent a new class of viscosity-sensitive fluorophores with aggregation-induced emission (AIE) luminogens, were introduced as co-monomers and cross-linkers into poly(N-isopropylacrylamides) (PNIPAMs). Despite the excellent performance of these bis(N,N-dialkylamino)arenes as fluorophores that are sensitive to the steric environment, synthetic methods to endow them with other reactive groups have not yet been reported. This study presents short synthetic pathways to 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) and 1,4-bis(N,N-dialkylamino)-2,3-dimethylnaphthalenes (DMe-BDANs) with hydroxyl groups at their alkyl chains. These hydroxyl groups were acylated to afford methacrylate moieties, which were subsequently used for the co-polymerization with N-isopropylacrylamide. At T = 20 °C, the resulting BDAA-containing PNIPAMs exhibited faint fluorescence (Φfl ≈ 0.05) in THF, whereas DMe-BDAN-containing PNIPAMs showed substantially stronger fluorescence in THF (Φfl ≈ 0.32) and water (Φfl ≈ 0.55) relative to the corresponding monomers. Moreover, BDAA-containing PNIPAMs featured a sharp increase of fluorescence intensity and quantum yield at T = 27–35 °C, while DMe-BDAN-containing PNIPAMs exhibited a continuous decrease of fluorescence intensity and Φfl with increasing temperature.

[PR]

# by konishi_lab | 2017-03-22 08:08 | 2017(2)

2016-7

Open Access
The design of liquid crystalline bistolane-based materials with extremely high birefringence

Y. Arakawa, S. Kang, H. Tsuji, J. Watanabe, G. Konishi*
RSC Adv., 6, 92845-92851 (2016).
DOI: 10.1039/C6RA14093A
Link
b0202136_11295550.jpg

We designed three new bistolanes with alkylsulfanyl groups. A symmetric derivative contains short terminal methylsulfanyl groups (-SC3) on both ends, while two asymmetric derivatives contain a methylsulfanyl group on one end, as well as a highly polarizable cyano (-CN) or isothiocyanate (-NCS) group on the other end. These materials exhibited a well-defined enantiotropic nematic phase, as well as an extremely high birefringence (Δn > 0.6). Most notably, the NCS derivative achieves an extremely high value of 0.77 at 550 nm. These results should be helpful for the design and synthesis of novel nematic materials with high birefringence.

[PR]

# by konishi_lab | 2016-12-08 09:52 | 2016 (7)

News

Our new home page has been uploaded.
Japanese
http://www.op.titech.ac.jp/polymer/lab/konishi/index.html
English
http://www.op.titech.ac.jp/polymer/lab/konishi/en/index.html
List of Publications: This blog

Lab News (Japanese): Link (another blog)


Gen-ichi KONISHI lab, Tokyo Institute of Technology

Postdoctoral Positions
Only fellowship holders or applicants for externally funded fellowships can be considered at this time.

International Internship
Not avialble now

[PR]

# by konishi_lab | 2016-09-12 15:50 | News

2016-6

Highly twisted N,N-dialkylamines as a design strategy for turn of typical aromatic hydrocarbons as steric environment-sensitive fluorophores
S. Sasaki, S. Suzuki, W. M. C. Sameera, K. Igawa, K. Morokuma, G. Konishi*
J. Am. Chem. Soc., 138, 8194–8206 (2016).
DOI: 10.1021/jacs.6b03749
Link

This paper is highlighted in Cutting-Edge Chemistry, American Chemical Society (ACS)
Organic, Organometallic, and Metallic Luminogens (15 Aug, 2016)

b0202136_12512046.jpg

The steric-environment sensitivity of fluorescence of 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) was studied experimentally and theoretically. A new design strategy to tune simple aromatic hydrocarbons as efficient aggregation-induced emission (AIE) luminogens and molecular rotors is proposed. For a variety of BDAAs, prominent Stokes shifts and efficient solid-state fluorescence were observed. Calculations on BDAA-methyl suggested that in the ground state (S0) conformations, the pyramidal amine groups are highly twisted, so that their lone-pair orbitals cannot conjugate with the anthracene π orbitals. Fluorescence takes place from the S1 minima, in which one or both amine groups are planarized. The stability of the S1 excited state minima as well as destabilization of the S0 state is the origin of large Stokes shift. Experimental measurement of the non-adiabatic transition rate suggests that para disubstitution by dialkylamino (or strongly electron-donating) groups is a key for fast internal conversion. Minimum energy conical intersection (MECI) between S1 and S0 states was found to have a Dewar-benzene like structure. Although this can be reached efficiently in liquid phase for fast internal conversion, a large amplitude motion is required to reach this MECI, which is prohibited in the solid state and caused efficient AIE. This strategy is used to find experimentally that naphthalene analogues are also efficient AIE luminogens. The flexibility of alkyl chains on amino groups is also found to be important for allowed charge-transfer transition. Thus, three points (1. highly twisted N,N-dialkylamines, 2. substitution at the para positions 3. with flexible alkyl groups) were proposed for activation of small aromatic hydrocarbons.

[PR]

# by konishi_lab | 2016-07-06 18:01 | 2016 (7)

2016-4

Photo-induced Reactions of Diruthenium Tetrahydride Complexes: Carbon–Hydrogen Bond Cleavage of Tetrahydrofuran Leading to Bridging Cyclic Fischer-Type Carbene Complexes
R. Shimogawa, G. Konishi, T. Takao, H. Suzuki
Organometallics, 35, 1446–1457 (2016).
DOI: 10.1021/acs.organomet.6b00070
Link
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Photochemical reactions of diruthenium tetrahydride complexes containing cyclopentadienyls as auxiliary ligands, CpsRu(μ-H)4RuCps (1) (a: Cps = C5Me5 (Cp*), b: C5EtMe4 (CpEt), and c: 1,2,4-C5(t-Bu)3H2 (Cp‡)), with tetrahydrofuran were studied for elucidation of the reaction mode of dinuclear complexes containing multiple bridging hydrides. Complexes 1a–c reacted with tetrahydrofuran under UV irradiation (365 nm) to produce bridging cyclic Fischer-type carbene complexes, {CpsRu(μ-H)}2(μ-cyclo-CCH2CH2CH2O−)(μ-H)2 (5), via consecutive C–H bond cleavage at the α-position of the oxygen atom. The characteristic cyclic structures of the bridging carbene ligands were unambiguously confirmed by X-ray diffraction studies. Line-shape analysis of the variable-temperature 1H NMR spectra of 5c demonstrated the rotation of the bridging carbene ligand.

[PR]

# by konishi_lab | 2016-05-27 20:14 | 2016 (5)

2016-5

Amphiphilic gels of solvatochromic fluorescent poly(2-oxazoline)s containing D–π–A pyrenes
C.-H. Chen, Y. Niko, G. Konishi*
RSC Adv., 6, 42962-42970 (2016).
DOI: 10.1039/C6RA06251B
Link
b0202136_18441393.jpg

Herein, we report amphiphilic, fluorescent, solvatochromic poly(2-methyl-2-oxazoline) (POZO-py) and poly(2-ethyl-2-oxazoline) (PEtOZO-py), which contain D–π–A pyrene dye units in their side chains. These new fluorescent polymers display solvatochromism and bright fluorescence in a variety of solvents, ranging from toluene (475 nm) to methanol (515 nm) and water (535 nm). Furthermore, amphiphilic gels (amphigels) of POZO-py and PEtOZO-py were synthesized by cross-linking the amine sites of partially hydrolyzed POZO-py and PEtOZO-py. Amphigels were formed rapidly when bridging ethyleneimine moieties were used for POZO-py and PEtOZO-py. These amphigels swell in various solvents, resulting in a solvatochromic shifts of the fluorescence emission. We furthermore determined the relationship between the swelling process, the solvatochromic properties, and the polymer structure of the POZO-py and PEtOZO-py gels. The different swelling properties led to different amphigel structures in water and hence, to different maximum fluorescence wavelengths. For example, a POZO-py amphigel with 10% ethyleneimine bridging exhibited the same solvatochromic behavior as POZO-py in solution. These results are significant in order to evaluate the solvatochromic properties of pyrene chromophores in polymers and to investigate gel structures and functional group interactions in gels.

[PR]

# by konishi_lab | 2016-05-03 17:54 | 2016 (5)

2016-3

Open Access Review
Recent advances in Twisted Intramolecular Charge Transfer (TICT) fluorescence and related phenomena in materials chemistry
S. Sasaki, G. P. C. Drummen, G. Konishi
J. Mater. Chem. C, 4, 2731–2742 (2016).
DOI: 10.1039/C5TC03933A
Link
Themed Collections: Shape-Responsive Fluorophores
Themed Collections: 2016 Journal of Materials Chemistry C Most Accessed Manuscripts
"Highly Cited Papers" in Web of Science (Thomson Reuters)
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Twisted intramolecular charge transfer (TICT) is an electron transfer process that occurs upon photoexcitation in molecules that usually consist of a donor and acceptor part linked by a single bond. Following intramolecular twisting, the TICT state returns to the ground state either through red-shifted emission or by nonradiative relaxation. The emission properties are potentially environment-dependent, which makes TICT-based fluorophores ideal sensors for solvents, (micro)viscosity, and chemical species. Recently, several TICT-based materials have been discovered to become fluorescent upon aggregation. Furthermore, various recent studies in organic optoelectronics, non-linear optics and solar energy conversions utilised the concept of TICT to modulate the electronic-state mixing and coupling on charge transfer states. This review presents a compact overview of the latest developments in TICT research, from a materials chemistry point of view.

[PR]

# by konishi_lab | 2016-04-01 23:56 | 2016 (7)

2015 Journal of Materials Chemistry B & C Most Accessed Manuscripts

Our two papers were selected as Most Accessed Arctiles in RSC jounals.
2015 Journal of Materials Chemistry B Most Accessed Manuscripts
Y. Niko et al., J. Mater. Chem. B, 3, 184–190 (2015). Open Access

2015 Journal of Materials Chemistry C Most Accessed Manuscripts
S. Sasaki et al., J. Mater. Chem. C, 2015,3, 5940-5950. Open Access

[PR]

# by konishi_lab | 2016-03-10 18:56 | News

2016-2

Development of novel bistolane-based liquid crystalline molecules with an alkylsulfanyl group for highly birefringent materials
Y. Arakawa, S. Kang, J. Watanabe, G. Konishi*
RSC Adv., 6, 16568–16574 (2016).
DOI: 10.1039/C5RA25122B
Link
b0202136_13011086.jpg

In order to generate high-birefringence liquid crystal (LC) materials, the introduction of highly polarisable groups into the terminal positions of the mesogen represents one of the most important design strategies. Even though the alkylsulfanyl group is a potentially interesting option for this purpose, it has so far been very difficult to obtain enantiotropic mesophases for LCs containing this group. Herein, we report novel high-birefringence LC molecules based on 1,4-bis(2-phenylethynyl)benzene (bistolane) with alkylsulfanyl groups in the terminal positions. The incorporation of a fluorine atom into the central benzene ring of an alkylsulfanyl-substituted bistolane led to the formation of a well-defined enantiotropic nematic phase. In contrast, the nonfluorinated analogue with alkylsulfanyl groups did not exhibit a mesophase. In comparison with an alkoxy-substituted derivative, the birefringence of the alkylsulfanyl-substituted analog was substantially higher (delta n = 0.42 at 550 nm). Furthermore, the birefringence properties of the alkylsulfanyl-substituted derivative were observed to be proportional to the order parameter and largely temperature dependent over the entire temperature range. These results thus provide not only fundamental insights into structure-reactivity relations, but also furnish practical design principles for the synthesis of new sulfur-containing, rod-shaped LC materials with optical applications.


[PR]

# by konishi_lab | 2016-02-10 07:54 | 2016 (4)

2016-1

Open Access
Bright and photostable push-pull pyrene dye visualizes lipid order variation between plasma and intracellular membranes
Y. Niko, P. Didier, I. Mely, G. Konishi, A. S. Klymchenko
Sci. Rep., 6, 18870 (2016).
DOI: 10.1038/srep18870
Link
b0202136_19502031.jpg

Imaging lipid organization in cell membranes requires advanced fluorescent probes. Here, we show that a recently synthesized push-pull pyrene (PA), similarly to popular probe Laurdan, changes the emission maximum as a function of lipid order, but outperforms it by spectroscopic properties. In addition to red-shifted absorption compatible with common 405 nm diode laser, PA shows higher brightness and much higher photostability than Laurdan in apolar membrane environments. Moreover, PA is compatible with two-photon excitation at wavelengths >800 nm, which was successfully used for ratiometric imaging of coexisting liquid ordered and disordered phases in giant unilamellar vesicles. Fluorescence confocal microscopy in Hela cells revealed that PA efficiently stains the plasma membrane and the intracellular membranes at >20-fold lower concentrations, as compared to Laurdan. Finally, ratiometric imaging using PA reveals variation of lipid order within different cellular compartments: plasma membranes are close to liquid ordered phase of model membranes composed of sphingomyelin and cholesterol, while intracellular membranes are much less ordered, matching well membranes composed of unsaturated phospholipids without cholesterol. These differences in the lipid order were confirmed by fluorescence lifetime imaging (FLIM) at the blue edge of PA emission band. PA probe constitutes thus a new powerful tool for biomembrane research.

[PR]

# by konishi_lab | 2016-01-11 19:53 | 2016 (5)

2015-10

1-, 3-, 6-, and 8-Tetrasubstituted Asymmetric Pyrene Derivatives with Electron-Donors and -Acceptors: High Photostability and Regioisomer-Specific Photophysical Properties
Y. Niko, S. Sasaki, K. Narushima, D. K. Sharma, M. Vacha, G. Konishi*
J. Org. Chem., 80, 10794–10805 (2015).
DOI: 10.1021/acs.joc.5b01987
Link

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The systematic synthesis of five 1-, 3-, 6-, and 8-tetrasubstituted asymmetric pyrenes with electron-donor and -acceptor moieties is presented, together with an examination of their photophysical properties. Pyrene derivative PA1, containing one formyl and three piperidyl groups, showed bright solvatochromic fluorescence from green (λem = 557 nm, ΦFL = 0.94 in hexane) to red (λem = 648 nm, ΦFL = 0.50 in methanol), suggesting potential applications for PA1 as an environmentally responsive probe. Although the synthesis of simple 1- and 3-disubstituted pyrene derivatives is considered difficult, PA13, with two formyl groups at the 1- and 3-positions and two piperidyl groups at the 6- and 8-positions, could be synthesized successfully. PA13 exhibited less pronounced solvatochromism, but displayed a narrow fluorescent band with high ΦFL in all solvents (ΦFL > 0.75). Moreover, its absorption band displayed an exceptional bathochromic shift compared to the other derivatives (e.g. λabs = 480 nm and 522 nm in ethanol for PA1 and PA13, respectively), suggesting that such modifications of pyrene may be quite important for the modulation of its energy gap. Additionally, all compounds exhibited exceptionally high photostability, which highlights the advantage of these new dyes and provides new insights on the design of photostable fluorophores.


[PR]

# by konishi_lab | 2015-11-07 10:03 | 2015 (10)

2015-9

Highly birefringent polymer films from the photo-crosslinking polymerisation of bistolane-based methacrylate monomers
Y. Arakawa, H. Kuwahara, K. Sakajiri, S. Kang, M. Tokita, G. Konishi*
Liq. Cryst., 42, 1419-1427 (2015).
DOI:10.1080/02678292.2015.1053542
Link

The photo-polymerisation of mixtures of mono- and dimethacrylates, which contained a bistolane moiety with a central fluorine-substituted benzene ring resulted in the formation of highly birefringent polymer films (Δn = 0.40), which were obtained in a nematic liquid crystal (NLC) phase. While the dimethacrylate forms enantiotropic NLCs at T = 110–138 °C, smectic phases at T = 50–138 °C, and crystallises at T = 50 °C, the monomethacrylate forms NLCs at a wider temperature range (T = 98–185 °C) and crystallises at a lower temperature (T = 98 °C). These methacrylates were infinitely miscible and a 20/80 (w/w) mixture of the dimethacrylate/monoacrylate was able to form a NLC phase over a broad temperature range (T = 73–179 °C). The mixed NLC phase exhibited a Δn value of 0.36, even though the Δn values of the mono- and dimethacrylates were determined as 0.35 and 0.25, respectively, suggesting that the Δn of the mixture follows an additivity rule. Furthermore, the Δn of the NLC phase could be increased to 0.40 by photo-polymerisation.



[PR]

# by konishi_lab | 2015-10-14 09:41 | 2015 (9)

Mr. Sasaki won the English oral presenation award from JPA

Mr. Sasaki won the English oral presenation award from the Japanese Photochemistry Association.
Congratulations!
“Photophysical properties of strongly twisted bis(N,N-dialkylamino)anthracenes”
b0202136_16110621.jpg

[PR]

# by konishi_lab | 2015-09-14 16:06 | News

2015-8

Open Access
The effect of regioisomerism on the solid-state fluorescence of
bis(piperidyl)anthracenes: structurally simple but bright
AIE luminogens

S. Sasaki, K. Igawa, G. Konishi*
J. Mater. Chem. C, 3, 5940-5950 (2015).
DOI: 10.1039/C5TC00946D
Link
PDF
This paper is highlighted by Noteworthy Chemistry, June 22 2015, a news weekly published electronically by the American Chemical Society (ACS).
Link (ACS)
2015 Journal of Materials Chemistry C Most Accessed Manuscripts
Link (RSC)
b0202136_21211300.jpg

A series of regioisomers of piperidylanthracenes (PA) and bis(piperidyl)anthracenes (BPA) were synthesized and their photophysical properties were examined in solution, suspension, and the solid state. Aggregation-induced emission (AIE) was observed only for 1,4-BPA and 9,10-BPA, in which two piperidyl groups are substituted at the anthracene moiety in para-position with respect to each other. Compared to previously reported AIE luminogens, these easily obtainable para-substituted BPAs, exhibited several unique and beneficial features, such as simple structures, bright solid-state fluorescence (Φfl = 0.49 and 0.86 for 1,4-BPA and 9,10-BPA, respectively), tunable fluorescence emission, and large Stokes shifts. Results from diffuse-reflectance and fluorescence lifetime measurements demonstrated that PAs and BPAs intrinsically possess an efficient non-radiative transition pathway in the solid state, and that 1,4-BPA and 9,10-BPA may overcome this pathway. The X-ray crystallographic analysis of 1,4-BPA revealed that undesirable interchromophoric interactions can be minimised, while TD-DFT calculations suggested that enhanced Stokes shift of 1,4-BPA arises from severe electronic repulsion between neighbouring piperidyl moieties, which presumably results in the absence of self-absorption.


[PR]

# by konishi_lab | 2015-06-23 10:04 | 2015 (10)