A new synthetic protocol for coumarin amino acid

• Xinyi Xu,
• Xiaosong Hu and
• Jiangyun Wang

Beilstein J. Org. Chem. 2013, 9, 254–259, doi:10.3762/bjoc.9.30

• applications related to it [2][3][4][5][6][7][8]. Compound 1a is of great interest to scientists because the 7-hydroxycoumarin moiety has a high fluorescence quantum yield and a large Stokes shift. Its excellent fluorescence properties make it a great candidate to substitute green fluorescent protein (GFP) in

A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• called a rate. The former is simply a way of measuring the quantum yield by determining the half-time (hence “rate”) of photolysis under some set of defined irradiation conditions. However, even with the former measurement care must be taken. The chemical reactions of release can be quite complex, so the

• than MNI-Glu [27] (ε = 4,300/M/cm). The second property is the quantum yield of photolysis (chemists use the symbol Φ for this). This measures how many excited molecules give a product, with the normal maximum being 1. Photochemical efficiency is ε·Φ. So, to some extent, a large ε can make up for a

Hydrophobic analogues of rhodamine B and rhodamine 101: potent fluorescent probes of mitochondria in living C. elegans

• Laurie F. Mottram,
• Safiyyah Forbes,
• Brian D. Ackley and
• Blake R. Peterson

Beilstein J. Org. Chem. 2012, 8, 2156–2165, doi:10.3762/bjoc.8.243

• -shifted absorbance and emission spectra (5–9 nm), modest reductions in molar extinction coefficent and quantum yield, and enhanced partitioning into octanol compared with aqueous buffer of 10-fold or more. Comparison of living C. elegans (nematode roundworm) animals treated with the classic fluorescent

• [43] molar extinction coefficient of rhodamine B (5) of 106,000 M−1 cm−1 (at 545 nm in ethanol) with HRB (9, 83,000 M−1 cm−1 at 555 nm in methanol). Additionally, a modest reduction in quantum yield of ~0.3 for both fluorophores was observed. Spectroscopic studies revealed that HRB 9 and HR101 10 are

• not as bright as the carboxylate-containing parent dyes. However, because the fluorescence intensity is directly proportional to the product of the extinction coefficient and the quantum yield at excitation levels below saturation, these analogues represent very bright fluorophores for imaging

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• -pressure lamp, if operating at 30% efficiency will have a total UV power of 4.5 W at 254 nm. According to Equation 3 this corresponds to a photon flux of 34 mmol photons per hour. When multiplied by the quantum yield of a reaction driven by 254 nm UV, a figure is obtained that represents the maximum

• described earlier. For example, when 80% of the available photons are delivered to the solution to drive a reaction with a quantum yield of just 10%, the productivity can be estimated as 2.7 mmol/h. The photons are acting as a “reagent” but not one that can be added all at once; rather, they are introduced

• as a stream (flux). As the reactant solution is also introduced as a stream, the flow rate can be precisely tailored to match the photon flux of the lamp and the quantum yield of the substrate. The main aim of this review is to illustrate the advances made in flow photochemistry over the last 10

A simple and efficient dual optical signaling chemodosimeter for toxic Hg(II)

• Sabir H. Mashraqui,
• Sapna A. Tripathi,
• Sushil S. Ghorpade and
• Smita R. Britto

Beilstein J. Org. Chem. 2012, 8, 1352–1357, doi:10.3762/bjoc.8.155

• a quantum yield (ФF) of 0.021, calculated with respect to anthracene (ФF = 0.27) [61]. Fluorimetric titration (Figure 3) revealed linear enhancements in the emission intensity with a significant 17-fold enhancement observed at a limiting 5.1 × 10−5 M of Hg2+ [60]. Based on the linear response

Interaction of cyclodextrins with pyrene-modified polyacrylamide in a mixed solvent of water and dimethyl sulfoxide as studied by steady-state fluorescence

• Akihito Hashidzume,
• Yongtai Zheng and
• Akira Harada

Beilstein J. Org. Chem. 2012, 8, 1312–1317, doi:10.3762/bjoc.8.150

• one to construct functional systems that convert photo energy based on molecular recognition. Among aromatic compounds, pyrene is the most examined as a fluorescence probe or label because it shows a relatively high fluorescence quantum yield and a relatively long fluorescence lifetime in both monomer

• formation (KPy) can be calculated as where [Py]0 is the total concentration of Py residue and x as given in Equation 2. Here, A1,376, A1,480, A2,376, and A2,480 are constants corresponding to the products of the molar extinction coefficient and the fluorescence quantum yield (subscripts 1 and 2 indicate

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• and S2←S0 excitations and cis–trans isomerization by exciting into the S1 or S2 state [21]. The sum of the quantum yields is different to unity, which indicates multiple pathways for isomerization. In stilbene, the isomerization occurs exclusively by rotation and the quantum yield equals unity [22

• (azo-15) may be useful as a molecular switch, because the photoisomerization of azo-fullerene 14 leads to only 8% of the cis-isomer. Although, the quantum yield obtained for cis-14 is not very high, this proportion is significant, given the speed with which energy transfer to the fullerene unit occurs

The effect of the formyl group position upon asymmetric isomeric diarylethenes bearing a naphthalene moiety

• Renjie Wang,
• Shouzhi Pu,
• Gang Liu and
• Shiqiang Cui

Beilstein J. Org. Chem. 2012, 8, 1018–1026, doi:10.3762/bjoc.8.114

• fluorescence quantum yield. The cyclization quantum yields of these compounds increased in the order of para < ortho < meta, whereas their cycloreversion quantum yields decreased in the order of meta > para > ortho. Additionally, all of these diarylethenes functioned as effective fluorescent switches in both

• different from those with an electron-donating methoxy group [14][50][51]. The cycloreversion quantum yields of diarylethenes 1–3 increased in the order of ortho (Φc-o = 0.11) < para (Φc-o = 0.12) < meta substitution (Φc-o = 0.15) by the formyl group. However, the cyclization quantum yield of the para

• evidently increased. When anthracene was used as the reference, the fluorescence quantum yields of 1o–3o were determined to be 0.012, 0.018, and 0.059, respectively, indicating that the formyl group on the terminal benzene ring could notably enhance the fluorescence quantum yield and remarkably influence

Synthesis of dye/fluorescent functionalized dendrons based on cyclotriphosphazene

• Aurélien Hameau,
• Sabine Fuchs,
• Régis Laurent,
• Jean-Pierre Majoral and
• Anne-Marie Caminade

Beilstein J. Org. Chem. 2011, 7, 1577–1583, doi:10.3762/bjoc.7.186

• fluorescence quantum yield is slightly sensitive to the nature of the A functionality (Table 1). Dendrons 8 and 9 are soluble in organic solvents, as is dendron 10, but in the case of 10 it is also soluble in water in contrast to the others, thus we also studied its fluorescence in water. We observed a notable

• decrease of its fluorescence quantum yield (Φ) in water upon going from pure dioxane (Φ = 51) to pure water (Φ = 17), which cannot be related to protonation, as indicated from the UV–vis spectrum [10]. An analogous phenomenon was already described for a dansyl derivative of adenosine in solution in water

• fluorescent dendrons were synthesized and their fluorescence properties studied. One of them, 10 is both soluble in organic solvents and in water, and displays novel behaviour in mixtures of solvent (dioxane/water). Variations in the fluorescence quantum yield of its dansyl groups must be related to

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• Scheme 1, the maximum quantum yield of 0.50 along with the DFT activation barriers at the triplet hypersurface suggest that 5-exo-trig attack of electrophilic vinyl radical at the remaining 1,4-CHD double bond is the most likely subsequent step. Because this photocycloaddition occurs from the triplet

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• species involved. Mattay has shown that the quantum yield of the photocycloaddition of 1,3-dioxoles with benzene is halved for all three occurring modes (ortho, meta and para) if the reaction is carried out under an atmosphere of xenon rather than argon [22]. Xenon accelerates the singlet–triplet

• intramolecular reaction was shown to be very efficient when three atoms tethers were employed, but the quantum yield drops considerably when four atoms tethers are involved [40], apart from some exceptional cases when the freedom of the tether is restricted and a suitable conformation can be found [41]. The

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• photophysical and photochemical properties of N-phthaloylvaline methyl ester (1) have been studied by nanosecond laser flash photolysis (λexc = 248 or 308 nm) [5]. The quantum yield of fluorescence is low (ФF = 10−2), whereas that of phosphorescence at −196 °C is large (0.5). The triplet properties of 1 at room

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• intersystem crossing (ISC) process exists for the excited chromophore 1h that directs the photoreaction predominately to the triplet pathway. The 3,5-bis(trifluoromethyl)phenyl substituent may be responsible for the ISC, because m-bis(trifluoromethyl)benzene has an ISC quantum yield of ΦISC = 0.12 (λex = 254

A new fluorescent chemosensor for fluoride anion based on a pyrrole–isoxazole derivative

• Zhipei Yang,
• Kai Zhang,
• Fangbin Gong,
• Shayu Li,
• Jun Chen,
• Jin Shi Ma,
• Lyubov N. Sobenina,
• Albina I. Mikhaleva,
• Guoqiang Yang and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2011, 7, 46–52, doi:10.3762/bjoc.7.8

• produce any change under the same conditions. The receptor 1 displayed an emission maximum at 400 nm with a fluorescence quantum yield of 0.067 (determined by comparison with 1,4-bis(5-phenyl-2-oxazolyl)benzene as the reference compound, similarly in all other cases) [12] when excited at 340 nm. The

• . The quantum yield of fluorescence was reduced to 0.031 in this case. The stoichiometry of the equilibrium was found to be 1:2 by the existence of the inflexion in the titration profile (insert) at 400 nm (Figure 7). Usually, the deprotonation of an NH moiety caused by F− includes two steps. The first

Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

• Ritesh Nandy and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2010, 6, 992–1001, doi:10.3762/bjoc.6.112

• interactions. Quantum yield of fluorescence From Figure 3 and Figure 4 it is clear that with increasing solvent polarity, the intensity of emission decreases along with the bathochromic shift of the wavelength of emission. The fluorescence intensity of molecular systems that undergo efficient ICT upon

• photoexcitation decreases due to competing electron transfer from the donor to the acceptor site that quenches the fluorescence [49][50][51]. For compounds 1c, 1f and 1g, the fluorescence quantum yield decreased upon changing the solvent from cyclohexane to DMSO (Table 1). For compounds 1a and 1b, which did not

• show strong solvatochromic emission, the reverse trend was observed. The quantum yield of fluorescence increased in DMSO compared to cyclohexane. This might be due to the increase in the viscosity of the medium which quenches the non-radiative pathways. In the cases of the carbonyl derivatives 1d and

Conjugated polymers containing diketopyrrolopyrrole units in the main chain

• Bernd Tieke,
• A. Raman Rabindranath,
• Kai Zhang and
• Yu Zhu

Beilstein J. Org. Chem. 2010, 6, 830–845, doi:10.3762/bjoc.6.92

• polymer such as P-15 (Table 2) exhibited absorption and fluorescence maxima of 510 and 585 nm, respectively, the fluorescence quantum yield being 66%. Polymer/PCBM bulk heterojunction solar cells exhibited a power conversion efficiency of 0.16%. Cao et al. [53] prepared new fluorene-DPP-phenothiazine

Functional properties of metallomesogens modulated by molecular and supramolecular exotic arrangements

• Alessandra Crispini,
• Mauro Ghedini and
• Daniela Pucci

Beilstein J. Org. Chem. 2009, 5, No. 54, doi:10.3762/bjoc.5.54

• , this complex shows thermotropic mesomorphism, with a lamello-columnar organization and, at the same time, a light-green emission with the typical high quantum yield of pentacordinated Ga(III) complexes (40% in solution) [62], has been detected. Conclusions We have selected some examples of recent works

Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane – an inverse photochromic system. (Photoactive cyclophanes 5)

• Henning Hopf,
• Christian Beck,
• Jean-Pierre Desvergne,
• Henri Bouas-Laurent,
• Peter G. Jones and
• Ludger Ernst

Beilstein J. Org. Chem. 2009, 5, No. 20, doi:10.3762/bjoc.5.20

• donor and an acceptor partner, such as a Diels-Alder reaction (see below). 3.3 Photodissociation Under the same experimental conditions, the photoproduct 4 was irradiated at 306 nm for 10 min until the starting material spectrum was recovered (Figure 8). Disappearance quantum yield of 4 at 306 nm was