Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• , dimethylamino-substituted α-pyrones, as donor–acceptor systems, display remarkable photophysical properties, such as strongly red-shifted absorption and emission maxima with daylight fluorescence and fluorescence quantum yields up to 99% in solution and around 11% in the solid state, as well as pronounced

• synthesized a series of α-pyrone derivatives with emission maxima between 400 and 675 nm in the solid state and between 486 and 542 nm in chloroform [16][24][25][26], including fluorescence quantum yields as high as 95% in solution and 58% in the solid state [16][24]. While these fluorophores were synthesized

• luminescence characteristics (Table 5, entries 2, 4, 6 and 7). The Stokes shifts fall in a range between 5000 and 6100 cm−1 and the fluorescence quantum yields of the 1H-pyridines 5 account between 1 and 3%. Besides solution fluorescence all 1H-pyridines 5 also luminesce in the solid state (Figure 3, bottom

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• intense as the emitted energy increases, (iii) the intensities of the emission lines but not their wavelength vary with the UCNP size, as the surface quenching becomes the most efficient deactivation path for small nanoparticles. Therefore, the assessment of the upconversion quantum yields (UCQY) is a hot

• reliability. Recently, an accurate determination of photochemical quantum yields (QY) [26] was achieved for a commercially available diarylethene 1,2-bis(2,4-dimethyl-5-phenylthien-3-yl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene, labelled 1. Since then, this dye has been used as actinometer in the visible range

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• couplings and then transformed into boronic acid esters by employing an Ir(I)-catalyzed reaction. The chromophores show dual emission behavior, where the long-wavelength emission band can reach maxima close to 600 nm in polar solvents. The fluorescence quantum yields of the dyes are generally in the range

• ], BASHY dyes [10][11] or Boranils [12][13]) often feature quite rigid structures which contribute to high fluorescence quantum yields. These dyes have been applied for example in optoelectronics [14][15][16], sensing [17][18][19][20], and bioimaging [6][20][21][22][23][24][25][26]. On the other hand

• quantum yields (Φfluo) of the dyes, the highest values were determined for the compounds 16 and 18, being in the range of 0.35–0.59 in the investigated solvents. The dyes 17 and 19 show smaller values for Φfluo (ca. 0.15–0.30). The fluorescence lifetime of the SW emission was measured as 300–900 ps, being

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• a widespread use of the most commonly employed systems have indeed often be related to low quantum yields or poor photochemical stability, low fatigue resistance, or difficult synthesis. Furthermore, in the specific case of biological applications, inappropriate absorption wavelength is often an

Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

• Andrey G. Lvov,
• Max Mörtel,
• Anton V. Yadykov,
• Frank W. Heinemann,
• Valerii Z. Shirinian and
• Marat M. Khusniyarov

Beilstein J. Org. Chem. 2019, 15, 2428–2437, doi:10.3762/bjoc.15.235

• cyclohexenone bridges show good cycloreversion quantum yields of 0.20–0.32. The thermal stability of closed-ring isomers reveals half-lives of up to 20 days in solution at room temperature. The ligands were used to explore coordination chemistry with iron(II) targeting photoswitchable spin-crossover complexes

• spectra, see section VI in Supporting Information File 1). This allowed us to determine the quantum yields of photochemical reactions. Cyclopentene (4) and cyclopentenone (3) derivatives show the highest photocyclization quantum yields up to 0.42 in toluene. In polar acetonitrile the cyclization quantum

• yield is lower [40]. The quantum yields for cyclohexenone derivatives 6 and 7 are in the 0.22–0.27 range. Similar to some other cyclopentene derivatives [41], diarylethene 4 possesses low cycloreversion quantum yields at 4–6%. However, in accordance with previous results on imidazole derivatives [42], 3

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• ][31][32][33][34][35][36][37]. The photoisomerization of stiff stilbenes involves a complex potential energy surface with several excited species in equilibria, eventually reaching the cis or trans ground state [2]. Macroscopic parameters such as extinction coefficients and quantum yields also affect

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

• asymmetric DAEs with oxidized 2-ethylbenzo[b]thiophene-3-yl units have high cycloreversion quantum yields (a desirable feature for super-resolution RESOLFT microscopy), large Stokes shifts and acceptable absorptivity [5]. Yet unknown asymmetric “thiophenylated” DAEs may have unique properties

• side ring). As expected, in MeCN quantum yields of nonoxidized compounds with a bithiophene side chain were higher (ca. 8% compared to 1% for a monothiophene derivative), but still moderate. Fluorescence lifetimes were short (0.2 ns), in accordance with moderate quantum yields. The oxidized compounds

• the benzothiophene core. Oxidized DAEs with monothiophene units as side chains exhibited higher fluorescence quantum yields than the structurally related DAEs with bithiophenes (>35% compared to <20%). Longer fluorescent lifetimes (1.3–1.9 ns) of the oxidized DAEs (CFs) correspond to the better

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

• quantum yield. In Scheme 1 we compile silicon rhodamines with high quantum yields as well as their structural analogues with lower quantum yields. Silicon fluoresceins were excluded from this compilation, although “2-COOH DCTM” [31], “2-COOH DFTM” [31], and “Maryland red” [32] are representatives with

• quantum yields up to 0.67. As described previously, azetidine substituents at the xanthene moiety of 5, 7, and 9 lead to an improved quantum yield and to a red shift in comparison to the N,N-dimethylaniline analogues 1, 3, and 4 (Table 1, entry 1 vs 5, 3 vs 7, and 4 vs 9). In contrast, the 4

• –benzene bond leads to a drastic improvement of the quantum yield from 0.10 to 0.31 (Table 1, entry 2 vs 3). Accordingly, rhodamines like 3, 4, 11, or 12 bearing 2’-substituents with A-values between a proton and a methyl group (such as F and Cl) show quantum yields from 0.19 (for F) [23] to 0.30 (for Cl

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

• fluorophores are more protected by the PEG groups of the second generation G2 than by the ammonium groups of the third generation G3 as indicated by the quantum yields Φf = 0.24 (G3 ammonium) and 0.39 (G2 PEG). However, the TPA cross-section measurements gave σ2max = 13,600 GM for G3 ammonium, and 8,400 GM for

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

• summarized in Table 1. The quantum yields of cyclization and cycloreversion reactions of 1o in THF are obtained to be 0.31 and 6.2 × 10−3, respectively. They are a little bit smaller than those of simple diarylethene switches having thiophene rings as aryl groups [26]. It may be due to the connection with an

• ESIPT moiety. Only slight changes were observed in absorption spectra as well as photochromic quantum yields in two solvents. In the protic solvents including methanol, 1o and 1c did not emit fluorescence, while only 1o emitted in aprotic solvent, i.e., in hexane, orange fluorescence with a fluorescence

• 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

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

• environments with high levels of autofluorescence, constantly challenges chemists to develop new dyes with improved or special properties. In the design of simple dyes parameters such as molar absorption coefficients (ε), absorption/emission wavelengths [8][9], fluorescence quantum yields (Φfl) [10][11], and

• –130,000 M−1·cm−1), high fluorescence quantum yields (Φfl > 50%) and fluorescence lifetimes of 3–4 ns. All properties that agree well with their structural resemblance to rhodamines and fluoresceines, and triangulenium dyes such as A3-TOTA+ and H-TOTA+ (Figure 1a) can be viewed as extended symmetric

• and intensities? And how do they affect fluorescence quantum yields in these new dye systems? To the extent possible we will compare the new sulfur-functionalized dyes to known analogues with -OR or -NR2 donor groups in the same positions. The sulfur-substituted triarylmethylium dyes 1, 2 and 3

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

• fluorescence quantum yields are rather low and fluorescence lifetimes are rather short due to ISC into the triplet state [50][51]. NDIs are reversibly reducible and their stable radical anions absorb in the visible to NIR light range [37]. The aromatic core of NDIs can be easily modified by substituents in

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

• images of dyes in the absence and in the presence of selected DNA samples are shown in Figure 10. All dyes display moderate to good quantum yields and brightnesses upon complexation with both G4 analytes. In more detail, distyryl dyes 1p and 1u prove more performant in this sense, displaying higher

• quantum yield and brightness (Φ = 0.12 to 0.32, B = (4.0–11.4) × 103 cm−1 M−1) than mono-styryl dyes (Φ = 0.040–0.085, B = (1.1–2.3) × 103 cm−1 M−1). It must be noted that the increase of fluorescence quantum yields observed in the presence of G4-DNA (Φ/Φ0) is significantly lower (up to five-fold) than

• potential of dyes, rendering the photoinduced electron-transfer reaction with guanine residues in DNA energetically disfavored and resulting in higher fluorescence quantum yields. However, in the absence of redox potential data, this assumption could not be experimentally verified. Finally, we showed that

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

• Quentin Huaulmé,
• Cyril Aumaitre,
• Outi Vilhelmiina Kontkanen,
• David Beljonne,
• Alexandra Sutter,
• Gilles Ulrich,
• Renaud Demadrille and
• Nicolas Leclerc

Beilstein J. Org. Chem. 2019, 15, 1758–1768, doi:10.3762/bjoc.15.169

• phthalocyanines [10][11], organic push–pull compounds [12], and boron-dipyrromethene [13] (BODIPY®). BODIPY dyes are one of the most extensively studied class of fluorophores due to their unique properties, including high absorption coefficients in the visible and NIR ranges, high fluorescence quantum yields, and

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

• NMR spectrometer. Photoabsorption spectra were measured with a Hitachi U-2910 spectrophotometer, and fluorescence spectra were measured with a Horiba FluoroMax-4 spectrofluorometer. The fluorescence quantum yields in solution were determined by a Horiba FluoroMax-4 spectrofluorometer by using a

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

• light, and under excitation with a UV lamp (365 nm). b) Emission (blue line) and excitation (black line) spectra of the CN-dots in water, and emission (pink line) and excitation (red line) spectra of the CCDs in water. Quantum yields of c) CCDs and d) CN-dots. Experimental conditions: Slit widths: Ex. 5

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

• fluorescence quantum yield of BN-phenanthrene seems to be a general effect, irrespective of its position. It should be noted that the introduction of ethynyl groups into the all-carbon phenanthrene skeleton results in a slight increase in the fluorescence quantum yields compared to that of phenanthrene [27

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

• improvements and brings the scientists nearer to the identification of the “perfect” MOST system. In this connection we identified crown ether-containing styryl dyes [14][15] as promising substances due to their ability to undergo trans-to-cis photoisomerization (E/Z) with very high quantum yields. In addition

• causes the observed fluorescence decrease. The optical parameters of all 4 dyes, including absorption maxima (λmax,abs), fluorescence emission maxima (λmax,f), hypsochromic shift of the absorption maxima (Δλmax), and fluorescence quantum yields (Φf) for different excitation wavelengths, obtained for the

• was tuned within the region of λexc = 400–550 nm. Generally one of the advantages of the presented Ba2+–crown ether containing styryl dye complexes as a MOST material is the extremely low intrinsic fluorescence which can be a precondition for higher quantum yields of the cis–trans photoisomerization

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

• dyes [1][2] with outstanding properties such as high quantum yields and pronounced stability against photobleaching [3][4][5]. Although being structurally relatively simple, this class of dyes is so far underrated in the literature. The chromophore, which is accessed from succinyl succinates and

• quantum yields (i.e., "turn-on effect") [11][12][13]. Modification of solid surfaces by defined layers of organic compounds raised significant interest in the last century. Those modifications can be fairly simple as in the case of alkanethiolate layers on gold [18] yet have a number of applications in

• bathochromic shift is observed towards the absorption at 451–473 nm (514 nm for compound 7, which is exceptionally high) and emission at 547–567 nm. The quantum yields of compounds 1–4 range between 0.21 and 0.57, for compounds 5–8 with propylene linker, the quantum yields are between 0.04–0.13. Interestingly

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

• atmosphere were discovered. The quantum yields for the release of the TEMPO radical were 2.5% (2a) and 0.8% (2b) in benzene at ≈1% conversion of 2, and 13.1% (2a) and 12.8% (2b) in DMSO at ≈1% conversion of 2. The TP uncaging efficiencies were determined to be 1.1 GM at 740 nm for 2a and 0.22 GM at 730 nm

• theory (TD-DFT) calculations for 5a at the CAM-B3LYP/6-31G(d) level of theory (Supporting Information File 1, Figure S2). The fluorescence quantum yields of caged-TEMPO 2a and 2b were found to be 2.9 and 2.2% in DMSO, which are much smaller than those of 5a and 5b, respectively, suggesting the chemical

• nitroxides 2a and 2b having a TP-responsive chromophore were synthesized, and OP- and TP-induced generation of the TEMPO radical with these species was examined. The quantum yields for generation of the TEMPO radical from 2a and 2b were determined to be 2.5% and 0.8% in benzene, respectively. The quantum

Synthesis of functionalized diazocines for application as building blocks in photo- and mechanoresponsive materials

• Widukind Moormann,
• Daniel Langbehn and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 727–732, doi:10.3762/bjoc.15.68

• damage by UV light [19]. Well separated absorption bands, high switching efficiency and high quantum yields are further advantages regarding their application as switches in photoresponsive materials [19][24][26]. In contrast to spiropyrans which have been frequently used as photoswitches in materials

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

• transformed into the title compounds by CuAAC reaction. The designed compounds belong to the push–pull systems and possess promising fluorescence properties with quantum yields in the range from 28% to 60% in acetonitrile solution. Due to electron-withdrawing properties of purine and 7-deazapurine

• direction in the development of various fluorescent (7-deaza)purine derivatives [12][13][14][15][16]. The push–pull effect arises by adding electron-donating and electron-withdrawing groups at the opposite ends of π-conjugated systems. Large Stokes shifts and high quantum yields are usually characteristic

• ] and 8-heteroarylguanosine [22] derivatives which revealed good to excellent quantum yields. Useful levels of fluorescence were reported also for purine nucleos(t)ides bearing azole-type substituents at C(2) or C(6) (e.g., 6-thiazol-2-yl derivative C [23] and 2-(1,2,3-triazol)-1-yladenosines D [24][25

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• catalyst applications. Some of them exhibit high emission quantum yields, long excited-state lifetimes and high oxidation potentials adequate for photoredox catalysis [59][60][61][62]. One example of highly efficient copper complex developed for photoredox applications is [Cu(neo)(DPEphos)]BF4 also named

Synthesis of a water-soluble 2,2′-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine

• Xiayang Huang,
• Xinghua Zhang,
• Tianxin Qian,
• Junwei Ma,
• Lei Cui and
• Chunju Li

Beilstein J. Org. Chem. 2018, 14, 2236–2241, doi:10.3762/bjoc.14.198

• of isoquinoline alkaloids‘ family, P and B can produce singlet oxygen (1O2) and oxide biological substrates under light, and thereby have applications in photodynamic therapy (PDT) [48][49][50]. However, their low quantum yields limit such applications, which could be potentially improved or restored

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

• ][30]. They are characterized by narrow absorption and fluorescence emission bands with small Stokes shifts, high molar absorption coefficients, and high quantum yields. Their excitation and emission maxima are in the visible region, usually above 470 nm, and they show high thermal and photochemical

• state of the amine lone pair with the BODIPY chromophore. In accordance with this hypothesis, a positive solvatochromism with varying contents of ACN was observed (Figure S18, Supporting Information File 1). The fluorescence quantum yields of the unprotonated BODIPY dyes were determined in 30% (v/v) ACN

• sufficient for the desired sensing applications (Table 1) [20][53]. Surprisingly, and despite the hexaalkylated core was used, the fluorescence quantum yields of protonated as well as unprotonated 3 were more than 100-fold lower than the quantum yields of the other derivatives. Such reduced quantum yields