Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• large fluorescence quantum yield, compound SyOTh1 emerged as a candidate for single-molecule based super-resolution fluorescence microscopy. Keywords: diarylethenes; dyes; fluorescence; organic synthesis; photochromism; photoswitching; Introduction Reversibly photoswitchable diarylethenes (DAEs) with

• fluorescence quantum yields. They exceeded lifetimes measured for the fluorescence of the unsubstituted DAE 6 by a factor of 4, and the fluorescence quantum yield of the CF of 6 was surpassed by the oxidized DAEs with thiophene side rings by a factor of 3–8 [4]. The open forms of the substituted oxidized

• – fluorescence and off-switching – compete for the depopulation of the same excited state [10]. Hence, the ratio of fluorescence quantum yield and off-switching quantum yield is proportional to the number of emitted photons (Nph) per cycle or per incursion into the fluorescent state (i.e., before off-switching

Synthesis of a dihalogenated pyridinyl silicon rhodamine for mitochondrial imaging by a halogen dance rearrangement

• Jessica Matthias,
• Thines Kanagasundaram,
• Klaus Kopka and
• Carsten S. Kramer

Beilstein J. Org. Chem. 2019, 15, 2333–2343, doi:10.3762/bjoc.15.226

• the use in multimodal (PET/OI) medical imaging of mitochondria in cancerous cells. Results: A dihalogenated fluorinatable pyridinyl rhodamine could be successfully synthesized with the high yield of 85% by application of a halogen dance (HD) rearrangement. The near-infrared dye shows a quantum yield

• features with their optical properties and control the latter by rational dye design [15][24][25][26]. These investigations led to new silicon rhodamine dyes with enhanced and fine-tuned properties (quantum yield, lifetime, brightness, absorption and emission maxima). A recent review compared the

• photophysical properties of numerous silicon rhodamines leading to further insights into the correlation of the dyes’ chemical structure with their fluorogenic behavior [27]. Regarding the quantum yield, Hanaoka et al. have shown that introduction of methyl, methoxy or dimethylamine groups into the benzene

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• dimer and 33% for the G1 dendrimer, but a 15% decrease of the TPA response was measured for the G2 dendrimer [53]. In addition, in that case, also the fluorescence quantum yield was found to decrease dramatically with an increasing number of fluorophores. TPA fluorophore as core of dendrimers None of

• has a large influence on the λmax of the fluorescence for the dendrimer with P(S)Cl2 terminal functions, which ranges from 443 nm in AcOEt to 501 nm in DMSO. Furthermore, the quantum yield (Φf) of the dendrimer with ammonium terminal groups was 0.42 in DMSO (to be compared with 0.78 for the

• G2 PEG. Thus, both compounds exhibit similar performances, the lower quantum yield being counter-balanced by a higher TPA cross-section, and vice versa [45]. TPA fluorophores at two levels of the dendrimer’s structure Having in hand the methods to introduce TPA fluorophores either on the surface, at

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• quantum yield (Φf) of 0.027. The fluorescent emission spectra of 1o in several solvents were shown in Figure 4, and λmax of the emission spectra and the fluorescence quantum yields in the solvents are summarized in Table 2. These emission spectra of 1o were largely red-shifted, indicating the ESIPT

• mm quartz cell, which was then placed in the integral sphere. The quantum yield was calculated using an installed software. The solid-state absorption spectrum was obtained by Kubelka–Munk conversion of a diffractive reflectance spectrum of the above mixture measured on a JASCO FP-6600

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• solution of 7 in CHCl3/CH3OH (3:1, v/v), a remarkable naked-eye recognizable color change from red to orange was observed. According to fluorescence spectroscopy, the emission intensity of PDI increased considerably (quantum yield enhancement factor of 57%). Anions are recognizable by catenane 7 at low

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• less bright fluorophores. Thus, the dialkylamino-substituted analogue of 5a (A3-ADOTA+) has a reported quantum yield as high as 64% in acetonitrile [17], on par with A3-TOTA+ and A2-TOTA+ which display quantum yields from 50–100% depending on the solvent [31]. A similar reduction in fluorescence

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• have only little influence on the optical properties but significantly modulate the solubility in DMF. This result agrees with other cNDIs in literature [47][48][58]. NDI 1 shows weak fluorescence in CH2Cl2 with a maximum at 384 nm and a quantum yield of 7%. The Stokes’ shift is small (413 cm−1). Based

• quantum yield of 48%. The Stokes’ shift is rather large (715 cm−1). The excitation energy E00 of cNDI 6 in the singlet state is approximately 1.98 eV and is significantly smaller than that of NDI 1 due to the visible light excitation which delivers less energy to the excited state. The redox potentials of

Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye libraries

• Xiao Xie,
• Michela Zuffo,
• Marie-Paule Teulade-Fichou and
• Anton Granzhan

Beilstein J. Org. Chem. 2019, 15, 1872–1889, doi:10.3762/bjoc.15.183

• ] or its 4-isomer, as optimal fluorescent light-up probes characterized by high fluorimetric response (I/I0 of up to 550-fold), excellent selectivity with respect to double-stranded DNA or single-stranded RNA controls, high quantum yield in the presence of G4 analytes (up to 0.32), large Stokes shift

• and quantum yield, low background fluorescence) are still poorly understood, mostly due to the lack of comparative studies. To explore this aspect, we report the synthesis and systematic study of a library of 61 di- and mono-styryl dyes, as potential “light-up” probes for G4 structures. The study aims

• varying content of guanine and a wealth of duplex structures, and (2) discriminating G4 structures based on their topology, with the exception of a few notable cases presenting structural peculiarities. Quantum yield and brightness of the probes Four highly responsive and G4-selective dyes, namely 1p, 1u

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes

• Keiichi Imato,
• Toshiaki Enoki,
• Koji Uenaka and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2019, 15, 1712–1721, doi:10.3762/bjoc.15.167

• exhibit significant fluorescence solvatochromic properties, that is, the two dyes show a significant decrease in the fluorescence quantum yield (Φf) in a polar solvent such as DMF (Φf = 0.59, 0.14 and 0.09 for OUY-2, OUK-2 and OUJ-2, respectively), although in relatively low polar solvents OUK-2 and OUJ-2

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• derivatives (P5A-DPA and P5A-Py) bearing bulky fluorophores were obtained in high yield by click reaction. The photophysical properties of both compounds were investigated in detail. P5A-DPA with two 9,10-diphenylanthracene (DPA) pigments grafted on the pillar[5]arene showed a high fluorescence quantum yield

• of 89.5%. This is comparable to the monomer DPA-6, while P5A-Py with two perylene (Py) pigments grafted on the pillar[5]arene showed a significantly reduced quantum yield of 46.4% vs 78.2% for the monomer Py-6. The oxygen-through-annulus rotation of the phenolic units was inhibited for both compounds

• quantum yield are beneficial for the application of pillar[5]arene in these fields. Perylene (Py) and 9,10-diphenylanthracene (DPA) are well known for their desirable absorption and high fluorescence quantum yield. These chromophores possess unique photophysical properties and have been widely used as

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• precious metal chloride complexes. The UV–vis absorption spectrum was shown in Figure S21 (Supporting Information File 1), and the absorption maxima are located at 241 nm and 290 nm. However, the optimal excitation wavelength is at 310 nm with a quantum yield of 6.6% in dichloromethane. The emission

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• internal conversion from S1 to S0 is responsible for the increase in the fluorescence quantum yield in these hydrophobic environments [44][45]. The fluorescence intensity of 2,6-TNS was extremely low with a maximum emission wavelength at 495 nm in aqueous solution [46]. Its fluorescence was dramatically

N-doped carbon dots covalently functionalized with pillar[5]arenes for Fe³⁺ sensing

• Jia Gao,
• Ming-Xue Wu,
• Dihua Dai,
• Zhi Cai,
• Yue Wang,
• Wenhui Fang,
• Yan Wang and
• Ying-Wei Yang

Beilstein J. Org. Chem. 2019, 15, 1262–1267, doi:10.3762/bjoc.15.123

• nm and 365 nm, which coincides with the blue light emission. The obvious blue shift was due to the modification of CP[5], which led to the increase of n–π* transition energy with the formation of new amide bonds [4][25]. The PL quantum yield (QY) of the CCDs aqueous solution was determined to be 4

Remarkable effect of alkynyl substituents on the fluorescence properties of a BN-phenanthrene

• Alberto Abengózar,
• David Sucunza,
• Patricia García-García and
• Juan J. Vaquero

Beilstein J. Org. Chem. 2019, 15, 1257–1261, doi:10.3762/bjoc.15.122

• impressive effect of the presence of alkynyl substituents on the fluorescence quantum yield, which improved from 0.01 in the parent compound to up to 0.65 in derivatives containing a triple bond. Keywords: alkyne; BN-phenanthrene; cross-coupling; fluorescence; heterocycles; Introduction BN-polycyclic

• , whose emission maxima are slightly red-shifted (395 and 392 nm vs 356 nm for unsubstituted 1a). In contrast, 7-alkynyl-substituted BN-phenanthrenes 1e and 1f show emission maxima analogous to that of the parent BN-phenanthrene 1a. With regard to the fluorescence quantum yield, phenyl and morpholine

• to a marked increase in the fluorescence quantum yield (0.44 and 0.65), particularly when the triple bond is bonded to a phenyl ring (1f). A similar increase (Φf = 0.45) is observed when the alkynyl group is attached to C1 (5), thus indicating that the positive influence of the triple bond on the

Precious metal-free molecular machines for solar thermal energy storage

• Meglena I. Kandinska,
• Snejana M. Kitova,
• Vladimira S. Videva,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• Stanislav B. Baluschev,
• Silvia E. Angelova and
• Aleksey A. Vasilev

Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106

• higher energy form has to be with quite small molar absorptivity in comparison to the lower one; (iv) the quantum yield of the photoisomerization has to be as high as possible, which requires the design of MOST systems with completely suppressed or minimal fluorescence, intramolecular charge transfer or

• that in neat CD3CN (Supporting Information File 1, Figure S9 and Figure S10). A common behavior demonstrated in Figure 2 was observed: the fluorescence quantum yield of all dyes (Table 1) decreases if the concentration of the Ba2+ ions increases, i.e., the formation of the trans-dye–Ba2+ complexes

• ranging from 1 × 10−5 M to 5 × 10−1 M in ACN. Emission spectra were recorded on FluoroLog3-22, Horiba Jobin Yvon spectrofluorometer with Quanta–φ accessory having a large 150 mm integrating sphere for the quantum yield measurements. All spectra we recorded using quartz cells of 1 cm path length. The

Diaminoterephthalate–α-lipoic acid conjugates with fluorinated residues

• Leon Buschbeck,
• Aleksandra Markovic,
• Gunther Wittstock and
• Jens Christoffers

Beilstein J. Org. Chem. 2019, 15, 981–991, doi:10.3762/bjoc.15.96

• (CH2Cl2), this material shows strong fluorescence (quantum yield 57% with emission at 495 nm, absorption maximum at 420 nm). The other compound (57% yield over three steps) possesses a propylene spacer between the ALA and the DAT units for electronic decoupling, thus, bathochromic shifts are observed

• (absorption at 514 nm, emission at 566 nm). The quantum yield is, however, lower (4%). Self-assembled monolayers on a gold surface of both compounds were prepared and characterized by high-resolution XPS of the C 1s, O 1s, S 2p, N 1s and F 1s emissions. The high signal-to-noise ratios of the F 1s peaks

• , target compound 3 has the highest (0.57), target compound 7 the lowest (0.04) quantum yield. XPS characterization of SAMs. SAMs were prepared from compounds 3 and 7 exploiting the strong binding affinity of the ALA residue to gold surfaces [52]. The resulting layers of compound 3 (SAM 3) and 7 (SAM 7

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• was 80% after 10 min irradiation in benzene under air atmosphere (Figure 2g). Secondary photoreaction of TEMPO gradually decreased the chemical yield of TEMPO. The quantum yield (Φ) for photochemical release of the TEMPO radical was 2.5% at ≈1% conversion in the photolysis of 2a in benzene under

• irradiation (Figure 2h). In DMSO, the quantum yield for the formation of TEMPO increased significantly to 13.1% (from 2a) and 12.8% (from 2b) at ≈1% conversion of 2 under atmospheric conditions (Figure 1). The notable effect of the solvent on the TEMPO generation may be due to the increase in the lifetime of

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• to increased fluorescence quantum yield (74%) in THF solution. The compounds exhibit low cytotoxicity and as such are useful for the cell labelling studies in the future. Keywords: 7-deazapurines; fluorescence; nucleophilic aromatic substitution; purines; push–pull systems; pyrrolo[2,3-d]pyrimidines

• The optical properties of the synthesized compounds were assessed by performing absorption and fluorescence spectroscopy and fluorescence quantum yield measurements. The quantum yields were determined using a fluorescence standard of quinine sulfate in 0.1 M H2SO4 as a reference [53]. Absorption and

• fluorescence quantum yield to 74% in the case of 7-deazapurine derivative 11c. The solvent change provided a fluorescence shift from dark blue (≈440 nm) to orange (≈620 nm) color. Finally, the purines and 7-deazapurines were tested in live cell imaging on breast cancer cell lines MCF-7 and MDAMB231. They are

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• chain mechanism was further confirmed by calculating the quantum yield (Φ) because a chain process provides multiple equivalents of product per photon absorbed by the photocatalyst (Φ > 1). The photon flux of blue LED (λmax = 469 nm) was determined using the potassium ferrioxalate actinometer [57][58

• presence of 1a in degassed DMSO recorded at different delay times, respectively (excitation wavelength = 355 nm). UV–vis absorption spectrum of 1a (1 mM solution in DMSO). Degenerative radical transfer of xanthates to olefins. Photocatalytic RAFT polymerization of xanthate 4. Determination of quantum yield

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• ). In general, if a molecule is to participate in a reaction in the S1 state, its τf must be greater than 1 ns; N.B. the diffusion rate constant (kdiff) is ≈1–2 × 1010 s−1. The fluorescence quantum yield (Φf) is another key parameter to consider when determining whether the S1 state of a molecule is

• likely to be involved in PET. A molecule with a low Φf will be unlikely to be found in the S1 state, as this state will be highly susceptible to other decay pathways in the timescale of PET. For a molecule to undergo PET when in the T1 state, the intersystem crossing quantum yield (ΦISC) must be

Rational design of boron-dipyrromethene (BODIPY) reporter dyes for cucurbit[7]uril

• Mohammad A. Alnajjar,
• Jürgen Bartelmeß,
• Robert Hein,
• Pichandi Ashokkumar,
• Mohamed Nilam,
• Werner M. Nau,
• Knut Rurack and
• Andreas Hennig

Beilstein J. Org. Chem. 2018, 14, 1961–1971, doi:10.3762/bjoc.14.171

• fluorescence from biological samples, and it would have a high fluorescence quantum yield in either bound or unbound state with a large difference in fluorescence intensity between both. In addition, a tuneable hydrophobicity to render the dye–CB complex membrane permeable or not, and a tuneable affinity for

• protonated, or at high pH values above the pKa value of the BODIPY•CB7 complex (see below) had no effect on the spectroscopic properties of the dyes. For example, the fluorescence quantum yield of 2 was identical in absence and presence of CB7 at pH 1.5. At intermediate pH values, however, the fluorescence

Synthesis of 9-arylalkynyl- and 9-aryl-substituted benzo[b]quinolizinium derivatives by Palladium-mediated cross-coupling reactions

• Siva Sankar Murthy Bandaru,
• Darinka Dzubiel,
• Heiko Ihmels,
• Mohebodin Karbasiyoun,
• Mohamed M. A. Mahmoud and
• Carola Schulzke

Beilstein J. Org. Chem. 2018, 14, 1871–1884, doi:10.3762/bjoc.14.161

• ][65][66]. The effect of the donor substituent on the emission quenching was supported by the strong increase of the emission quantum yield of 2c upon protonation of the amino group, that is, by the transformation of the donor to an acceptor substituent (Figure 5) [34]. Considering the water solubility

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• luminescence lifetime and determined the quantum yield of luminescence under air and argon atmosphere for conjugate 9 and reference [Ru(TAP)2phen]2+ in water with 5% DMSO in order to avoid any formation of aggregates. The data gathered in Table 1 clearly indicate that the tethering of the [Ru(TAP)2phen]2

• ). Emission quantum yields were determined by integrating the corrected emission spectra over the frequencies. [Ru(bpy)3]2+ in water under air was chosen as the standard luminophore (quantum yield of 0.042 under argon). The luminescence lifetimes were measured by the time-correlated single photon counting (TC

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• tuneable over the entire visible spectrum and beyond; together with compounds with photoluminescence quantum yield (PLQY) approaching unity. These peculiar features have greatly fuelled the still growing interest in luminescent TMCs for its potential employment in applications and real-market technology

• properties (Figure 6) [37]. The intermolecular interaction was finely tuned as a function of the steric hindrance of the acac-type ancillary ligand, which had a profound impact on the emission quantum yield. Characterization of the electroluminescence performances of these complexes in mixed-matrix OLED led

D–A–D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies

• Lin Gan,
• Xianglong Li,
• Xinyi Cai,
• Kunkun Liu,
• Wei Li and
• Shi-Jian Su

Beilstein J. Org. Chem. 2018, 14, 672–681, doi:10.3762/bjoc.14.55

• property according to the energy gap law [16] as vibrational relaxation and intersystem crossing (IC) processes can consume the energy in S1, leading to increased nonradiative deactivation [17], reduced PL quantum yield, and thus reduced singlet exciton utilization. On the contrary, the geometry of 2 is

• -1,1’-biphenyl (CBP) were vacuum co-deposited at a concentration of 8 wt % for photoluminescence quantum yield (PLQY) and time-resolved transient photoluminescence decay measurements. The concentration of the doped films was optimized to ensure complete energy transfer between the host and the guest

• [5][7][16]. where kr, knr, kisc, and krisc represent the rate constant of radiative, nonradiative, intersystem crossing and reverse intersystem crossing, respectively; Φ, ΦPF, ΦTADF, τPF and τTADF represent the photoluminescence quantum yield, quantum yield of the prompt component, quantum yield of