Probing multivalency in ligand–receptor-mediated adhesion of soft, biomimetic interfaces

• Stephan Schmidt,
• Hanqing Wang,
• Daniel Pussak,
• Simone Mosca and
• Laura Hartmann

Beilstein J. Org. Chem. 2015, 11, 720–729, doi:10.3762/bjoc.11.82

• (Scheme 1). It is known that benzophenone can absorb the energy of photons to excite the electron in its carbonyl group from ground state (S0) to the excited state (S1) or (S2) depending on the wavelength used. Subsequently, the excited electron can go to the triple state (T1) through intersystem crossing

A small azide-modified thiazole-based reporter molecule for fluorescence and mass spectrometric detection

• Stefanie Wolfram,
• Hendryk Würfel,
• Stefanie H. Habenicht,
• Christine Lembke,
• Phillipp Richter,
• Eckhard Birckner,
• Rainer Beckert and
• Georg Pohnert

Beilstein J. Org. Chem. 2014, 10, 2470–2479, doi:10.3762/bjoc.10.258

• . However, introduction of these heavy atom substituents in a fluorophore is challenging since it often results in decreased fluorescence due to intersystem crossing [26]. When working with reversed-phase LC–MS not only a specific isotopic pattern but also balanced polarity of the reporter is required

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• the developing anionic charge on the departing nucleofuge. The resulting biradical 31, which must be a triplet by Wigner’s spin rule [47] is formed from the chromophore while on the excited state PES. Intersystem crossing (isc) to a diradicaloid ground state intermediate 32 (vide infra) is followed by

• acidic proton (especially for singlet state reactions). The carbonyl appendage, however, must be responsible for the enhanced heterolysis efficiency [28][29][38] and may influence the formation of the triplet excited state through intersystem crossing (isc) [26] which is the origin of the heterolysis and

• intersystem crossing in the 2,6-HNA platform and strong fluorescence of the 2,6-HNA chromophore (Figure 2) also diminishes formation of the triplet and, thus, its participation in a photo-Favorskii rearrangement. Finally, an indication of the photostability of the 2,6-HNA derivatives had earlier precedence in

Synthesis of new, highly luminescent bis(2,2’-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole

• Anastasia S. Kostyuchenko,
• Vyacheslav L.Yurpalov,
• Aleksandra Kurowska,
• Wojciech Domagala,
• Adam Pron and
• Alexander S. Fisyuk

Beilstein J. Org. Chem. 2014, 10, 1596–1602, doi:10.3762/bjoc.10.165

• increasing atomic number of the heteroatom of the azole unit is a clear manifestation of the heavy atom effect [35]. The proximity and availability of higher energy 3d levels in sulfur facilitates radiationless relaxation modes of the excited electron. Enhanced spin–orbit coupling opens up intersystem

• crossing channels as well, making the thermal decay pathway accessible. The hindering of these decay modes in the oxadiazole derivatives 13 and 14 doubles their quantum yield. For the triazole derivative 18 the quantum yield is even nearly triple that of 15, but this enhancement should also be traced to

Tailoring of organic dyes with oxidoreductive compounds to obtain photocyclic radical generator systems exhibiting photocatalytic behavior

• Christian Ley,
• Julien Christmann,
• Ahmad Ibrahim,
• Luciano H. Di Stefano and
• Xavier Allonas

Beilstein J. Org. Chem. 2014, 10, 936–947, doi:10.3762/bjoc.10.92

• a dye (PS) with an electron acceptor (A) is depicted. After absorption of actinic light (hν), the PS reaches its singlet excited state (1PS*) and after intersystem crossing (kISC), its triplet excited state (3PS*). From both these excited states, an electron transfer can occur from the PS to A (with

• rate constants of singlet and triplet state deactivation to the ground state, respectively; kISC the rate constant of the intersystem crossing from 1PS to 3PS; 1kq/A, 3kq/A, (1kq/D, 3kq/D) the bimolecular electron transfer rate constant of the singlet and triplet excited state of the PS by the acceptor

• . Intersystem crossing rate constant kISC was obtained from the triplet state quantum yield and singlet state lifetime according to [59]: which leads to: and to At this RB concentration, and in the absence of quencher, the triplet state lifetime was measured around 80 µs, leading to kdes3= 1.25·104 M−1s−1

Studies on the photodegradation of red, green and blue phosphorescent OLED emitters

• Susanna Schmidbauer,
• Andreas Hohenleutner and
• Burkhard König

Beilstein J. Org. Chem. 2013, 9, 2088–2096, doi:10.3762/bjoc.9.245

• effectively convert singlet into triplet states via fast intersystem crossing. The recombination of electron–hole pairs generates singlet and triplet excitons in a ratio of 1:3 which means that the use of phosphorescent devices can give up to 4 times higher efficiencies than those based on fluorescent

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• share one common characteristic: a facile intersystem crossing (ISC) that allows the conversion of the initially formed singlet photoexcited state to the relatively long-lived triplet photoexcited state. The triplet photoexcited state’s long lifetime permits it to engage in single-electron transfer with

Topochemical control of the photodimerization of aromatic compounds by γ-cyclodextrin thioethers in aqueous solution

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2013, 9, 1858–1866, doi:10.3762/bjoc.9.217

• spin-orbit coupling interactions between states of different spin multiplicities and consequently facilitate intersystem crossing. However, supramolecular control of the packing of ACE leads to a significant improvement of the stereoselectivity. ACE was complexed in a cavitand nanocapsule [32] and in a

• < 10−3% and mainly leading to the anti-HH dimer [39]. In contrast, polar protic solvents, like water, increase both the quantum yield and the amount of the syn-HH dimer, exemplified in Table 3. The singlet state has a very short lifetime because of rapid intersystem crossing and self-quenching and it

• atom effect of the S-atoms of CD derivatives 1–7 should facilitate intersystem crossing to the triplet state and therefore support the formation of the anti-HH dimer. Because this preference does not hold true in this case, especially for host 2, the multiplicity of the excited state seems not to be

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• species, an ”automatic” labeling with nonequilibrium magnetizations is also feasible by utilizing the CIDNP [5][6][7][8][9][10] effect (chemically induced dynamic nuclear polarization). CIDNP arises through a complex interplay of nuclear-spin-selective intersystem crossing and electron-spin-selective

• . During their excursions, the differential precession of their electron spins causes intersystem crossing with a rate that depends on the spin states of their nuclei through the hyperfine interactions; upon reencounter, a chemical reaction serves to distinguish between singlet and triplet pairs (usually

• triplet energy (222 kJ/mol [32]) is only lower by less than 90 kJ/mol. Its first excited singlet state has a lifetime of 2.9 ns [32], so reacts only marginally with the millimolar sulfide concentrations used in our experiments, but its triplet state (intrinsic intersystem-crossing efficiency, 0.48 [32

Spin state switching in iron coordination compounds

• Philipp Gütlich,
• Ana B. Gaspar and
• Yann Garcia

Beilstein J. Org. Chem. 2013, 9, 342–391, doi:10.3762/bjoc.9.39

• the spin-allowed but parity-forbidden transition to the 1T1 and 1T2 ligand field states. These decay fast in two consecutive intersystem crossing processes, to the spin triplet states 3T1,2 and finally to the 5T2 state. Two factors are favorable for the occurrence of LIESST: (i) The spin triplet

• states 3T1,2 are placed energetically lower than the 1T1 and 1T2 ligand field states; (ii) The double intersystem crossing decay path is favored by spin–orbit coupling and therefore faster than the direct decay path back to 1A1. The decay of the 5T2 state to the 1A1 state is highly spin- and parity

• sample with red light (820 nm from a Krypton laser), whereby the metastable 5T2 state (“LIESST state”) is excited to the 5Eg state, which decays fast – again favored by spin–orbit coupling – by double intersystem crossing via 3T1,2 states to the LS (1A1) state [149]. The LIESST effect has mostly been

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

• photostable fluorophore [52], has been designed to function as metal ion and anion sensor [53][54][55][56][57]. In contrast to moderately fluorescent acridone, its thione analog is poorly emissive presumably on account of the intersystem crossing process of the C=S bonding [58]. Keeping this in mind, we have

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• expansion of 12, via 2H-azirine 3, affords didehydroazepine 4, which can be trapped by variety of nucleophiles to provide the corresponding azepine 5. Alternatively, intersystem crossing (ISC) of 12 gives rise to 32, which can dimerize to form diazo compound 6. Performing the reaction in the presence of

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

• photophysical step and the involvement of PET from 1,4-cyclohexadiene (1,4-CHD) to the enediyne excited singlet state. In contrast, substituents that accelerate the intersystem crossing (ISC) through a “phantom state” effect [53][54][55] direct reactivity along an alternative triplet cycloaddition pathway. Our

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

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

• intersystem crossing by the heavy-atom effect, and thus decreases the singlet excited-state lifetime of the arene. Mattay considered this as direct proof that the addition of benzene to 1,3-dioxoles takes place primarily via the singlet excited-state of benzene. Ferree et al. had earlier provided evidence

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

• photoinduced electron-transfer (PET) reactions. N-Alkylated phthalimides typically absorb in the 295 nm region with extinction coefficients around 103. The quantum yields for intersystem crossing ФISC significantly change with the substitution on the imide nitrogen, e.g., ФISC = 0.5 for N-isobutylphthalimide

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

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

• Junya Arimura,
• Tsutomu Mizuta,
• Yoshikazu Hiraga and
• Manabu Abe

Beilstein J. Org. Chem. 2011, 7, 265–269, doi:10.3762/bjoc.7.35

• oxetane 2OX after the intersystem crossing (ISC). Alternatively, 2,7-dioxabicyclo[2.2.1]hept-5-ene OBH would be formed from the 1,6-biradical form. The regioisomeric oxetane 3OX should be formed via the regioisomeric biradical BR’. Biradical BR is energetically more stable than BR’, because BR can undergo

Photocycloaddition of aromatic and aliphatic aldehydes to isoxazoles: Cycloaddition reactivity and stability studies

• Axel G. Griesbeck,
• Marco Franke,
• Jörg Neudörfl and
• Hidehiro Kotaka

Beilstein J. Org. Chem. 2011, 7, 127–134, doi:10.3762/bjoc.7.18

• about a remarkable increase in our understanding of this reaction. Especially the role of intermediary triplet 1,4-biradicals – their stability, lifetimes and intersystem crossing geometries – was crucial for a more sophisticated description [2][3][4][5], which also improved the synthetic significance

Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 119–126, doi:10.3762/bjoc.7.17

• the intersystem-crossing (ISC) rate or the triplet energy of the carbonyl functionality leading to insufficient sensitization. In addition, competing deactivation pathways of the excited ketone may be considered, such as rotation about the Car–CH2 group or reaction with the chloride counter ion

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• (singlet or triplet or both) on a ground-state olefin. For aromatic carbonyl compounds, the reaction is a triplet cycloaddition, that is, a triplet-excited carbonyl compound adding to an olefin to yield a triplet 1,4-diradical intermediate, which undergoes intersystem crossing (ISC) to produce a singlet