Search results
Search for "triplet state" in Full Text gives 73 result(s) in Beilstein Journal of Organic Chemistry.
Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis
Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183
- principle, the photosensitizer is regenerated and therefore functions in a very similar way to a catalyst and can be deemed a photocatalyst. A common example of this concept is triplet photosensitization. The excited photocatalyst has a relatively high triplet-state energy and a long lifetime, such that it
- light and is excited from the ground singlet state S0{PS} to the excited singlet state S1{PS}. Intersystem crossing (ISC) transforms S1{PS} to its more stable triplet state, T1{PS}. ISC is a process in which a nonradiative transition of a singlet excited electronic state to a triplet excited state takes
- place at a point where the potential energy curves of these two states interset, which requires spin–orbit coupling [117]. In the absence of spin–orbit coupling, it is a forbidden transition according to the Pauli exclusion principle. The resulting triplet state, T1{PS} is in an excited vibrational
Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization
Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139
- can occur. While the latter decay (fluorescence) takes place without a change in the electron spin, phosphorescence is defined as the radiative transition from the lowest excited triplet state (T1) to the singlet ground state (S0) [18][19][20][21]. Triplet state excitons are generated by the spin
Heterogeneous photocatalysis in flow chemical reactors
Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125
Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis
Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103
- case (Scheme 1, box 2), the excited photocatalyst can engage in an EnT mechanism. Upon the excitation and intersystem crossing, the triplet state photocatalyst 3PC* can interact directly with a ground state species Sub and transfer the triplet energy to generate an excited state Sub* and the ground
- state PC. In most cases, Sub* is in the triplet state if it is an organic molecule. A common exception to this is molecular oxygen, which upon excitation attains a more reactive singlet state. In the third mode of activation, atom transfer (AT, Scheme 1, box 3), the excited state photocatalyst PC* can
- compared to other methods for radical generation [56]. Within this field, organic dyes can act as competent photocatalysts for direct HAT processes. Specifically, upon light excitation, photoactive carbonyl compounds, such as benzophenone and its derivatives, reach an electronically excited triplet state
Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches
Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83
- photocatalysts. Under light irradiation, one electron from the ground state (S0) is promoted to the excited singlet state (S1) which has a short lifetime (10−9 s). Therefore, fast intersystem-crossing of one electron gives the excited triplet state (T1) with a relatively longer lifetime (10−6 s). While the
- molecular oxygen (triplet state). In this process, well-known singlet oxygen (1O2) is generated. Singlet oxygen can be considered a very versatile reagent in organic synthesis since it promotes many mild oxidation processes instead of combustion [23][57][58][59][60]. This excited state form of molecular
Aldehydes as powerful initiators for photochemical transformations
Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76
- capable to induce other types of reactions, such as hydrogen atom abstraction (HAT) processes or triplet state energy transfer processes (EnT). Carbonyl compounds, especially diaryl ketones, have shown great potential as far as their catalytic scope is concerned. Benzophenone or acetophenone (64) and
- a nonbonding electron on the oxygen atom to the first excited singlet state. This singlet state can lead to the corresponding triplet state T1 (n,π*) through intersystem crossing. This triplet state can be quenched through various chemical transformations, like Norrish type I and Norrish type II
- dissociations (Scheme 1). However, when a possible energy acceptor is present, the triplet state energy can be transferred from the carbonyl compound to the acceptor, returning the carbonyl compound to the ground electronic state. For example, in reaction (1) of Scheme 1, the β-bond dissociation of methyl n
Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties
Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53
- triplet state can be another pathway to understand the lower emission quantum yield of the BODIPYs. However, reactive singlet oxygen species (1O2) was not observed under the aerobic conditions probed by the near-infrared photoluminescence at 1270 nm. The above spectral features were likewise shown with
Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0
Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40
- these into the triplet state and brings benefits known from UV systems to NIR systems either. This can be the generation of singlet oxygen and would enable the use of NIR absorbers in photodynamic therapy. Another benefit can be seen to increase the efficiency of photoinduced electron transfer needed in
p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies
Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33
- affinity of selected both active and non-active derivatives. Preliminary theoretical studies were performed, in an effort to explain the reasons why some derivatives cause photocleavage and some others not, which were experimentally verified using triplet state activators and quenchers. These theoretical
- . For the dissociation reaction of compound 12 in the triplet state, the molecule passes through a very small energy barrier and dissociates finally into its photoproducts which are the two ground state radicals indicated in Scheme 2. The almost negligible change in geometry on going from T1 min to T1
- barriers are very large, 29.37 kcal/mol for T1 and 31 kcal/mol for the S1 state. Hence, 11 does not show any photoreactivity, in accordance with our experimental results. Photoexcitation in the presence of a triplet state energy activator and a triplet state quencher Triplet photosensitizers (TPSs) or
Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations
Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26
- Figure 3, E0,0 is the energy gap between the ground state and the lowest triplet state, corresponding to the band gap in semiconductors. C–H acylation Decarboxylative acylation of acetanilides: In 2015, Wang and co-workers first reported the acylation of acetanilides via C–H functionalization using
Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior
Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240
- calculating excited and ground-states, the triplet T0 state was used instead of the singlet S1 state as the photochemical intermediate (SW*) for computational purposes. Since T0 is the lowest energy triplet state, it is amenable to a ground-state computation. While the real SW* photochemical intermediate may
Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex
Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229
- of the photochromic reactions to visible light are to extend the π-conjugation and to utilize photosensitizers. Especially, triplet photosensitizers, which form the triplet state of a molecule by the triplet–triplet energy transfer, have been frequently used in photoresists, photodynamic therapy, and
Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses
Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221
- intersystem conversion towards a triplet state (T1), from which there will be emission of phosphorescence, having generally a lifetime longer than that of fluorescence. This classical one-photon excited fluorescence has led to the design of numerous types of chemical entities since the XIX century. For
Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes
Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210
- enhanced internal conversion or intersystem crossing to the triplet state. Further photophysical work will have to settle this issue and thereby suggest structural improvements and/or the best applications of these dyes. Conclusion The effective introduction of alkylthiol groups into the para-positions of
Naphthalene diimides with improved solubility for visible light photoredox catalysis
Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201
- catalysis is mainly [Ru(bpy)3]2+ [21], due to its strong MLCT (metal-to-ligand charge transfer) absorption, the excellent yield of its triplet state and the long lifetime, the versatile redox behavior (Ru3+ vs Ru+) in quenching processes and the chemical and photochemical robustness. Despite their positive
- 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
Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response
Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139
- aggregation and the shielding effect of PMCD against quenching of the TPPS triplet state [37]. Also, it has been employed in the construction of photovoltaic materials and light-harvesting systems [38][39]. The complexation of GC5A with ACQ dyes generally has the advantage of strong binding affinities
- singlet state 1MLCT can undergo ultrafast intersystem crossing leading to the formation of the triplet state 3MLCT which could emit phosphorescence. Ru(dcbpy)3 was employed as a representative candidate in this work to study the photophysical response upon complexation with GC5A. Almost no appreciable
Degenerative xanthate transfer to olefins under visible-light photocatalysis
Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283
- is initiated through triplet-sensitization of xanthates by the long-lived triplet state of the iridium-based photocatalyst. Keywords: energy transfer; olefin; photocatalysis; radical; xanthate; Introduction A degenerative radical transfer of xanthates to olefins has been developed as a robust
- report a photocatalytic degenerative radical transfer of xanthates to olefins using an iridium-based photocatalyst under blue LED irradiation (Scheme 1C). A series of mechanistic investigations identified that the process involves a triplet-sensitization of the xanthates by the long-lived triplet state
- previously been ascribed to the absorption of the xanthic acid radical formed plausibly from homolytic C–S bond cleavage of the short-lived triplet state of xanthate 1a [22]. The ns-TA spectra of photocatalyst 8 (25 μM) in the presence of xanthate 1a (40 mM) in degassed DMSO at various delay times are shown
Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region
Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282
- mechanisms. From a single or triplet state of the photoredox catalyst, an electron is transferred. According to Rehm–Weller, an electron can be transferred from the electron donor to the electron acceptor in the excited state if the free energy change ∆Get is negative. ∆Get can be calculated from the
- localization of the electrons on the triplet state, which upconvert to the singlet state thermally (i.e., at room temperature) and can promote a radiative decay from the singlet excited state. This property gives to TADF complex lifetime of their excited state comparable to the lifetime of the excited state of
- example [80]. The triplet excited state is obtained. From the triplet state of carbazole, similar reactions with ruthenium triplet state (reactions 1, 2, and 3 in Section 2.1.1) can be observed. Moreover, as both oxidation and reduction potential are compatible with additives presented in Scheme 1, both
Novel photochemical reactions of carbocyclic diazodiketones without elimination of nitrogen – a suitable way to N-hydrazonation of C–H-bonds
Beilstein J. Org. Chem. 2018, 14, 2250–2258, doi:10.3762/bjoc.14.200
- Michler’s ketone, with different levels of triplet state energy were tested. Furthermore, to clearly demonstrate the difference of light-induced reactions of diazo compounds 1 in the triplet and singlet excited states, the direct photolysis of diazodiketones 1a-c without sensitizers was also examined
Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)
Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18
- delayed fluorescence (TADF) emitters. As specificity, these materials can thermally repopulate the singlet state from the triplet state by reverse intersystem crossing (RISC), leading to an increase of the luminescence intensity. From the OLEDs viewpoint, TADF emitters behave by harvesting both singlet
- and triplet excitons for radiative transition, excepted that the emission occurs from the singlet state and not from the triplet state (as observed for metal complexes) and that the triplet–triplet annihilation commonly observed with phosphorescent OLEDs [10] can be drastically reduced (see Figure 1
- , demonstrating their T1 states to be 3LE states. Conversely, only a broad spectrum was obtained for T21, and its triplet state was assigned to a 3CT state. Precisely, by its large dihedral angle, T21 differs from T20, T22 and T23 by the order of its orbitals, 3LE and 3CT being inverted in this case. Analysis of
Pyrene–nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies
Beilstein J. Org. Chem. 2017, 13, 2521–2534, doi:10.3762/bjoc.13.249
- fluorescence intensity and fast decay of fluorescence were rationalized by the presence of low-energy nπ* excited states. In particular, for the lowest excited singlet state 1ππ* efficient intersystem crossing to a triplet state 3nπ* close in energy can be expected according to the El-Sayed rule. Then, this
- carbonyl compound 3 as compared to the hydroxy compound 5. The computations reveal several triplet states below the lowest singlet excited state. In particular, the carbonyl pyrene derivative 3 displays a triplet state of nπ* character being lower in energy than the emissive singlet state S1 (being a
Novel β-cyclodextrin–eosin conjugates
Beilstein J. Org. Chem. 2017, 13, 543–551, doi:10.3762/bjoc.13.52
- being excited with visible light, the PS – while reverting to the ground state – transfers the energy of its lowest excited triplet state to nearby molecular oxygen. This leads to an in situ generation of singlet oxygen (1O2), which is the main responsible species for cytotoxic reactions in cells [6
- tentatively be attributed to populations of fluorophores probably interacting in a different way with the CD cavity. As outlined in the introduction, singlet oxygen, 1O2, is the key species involved in PDT and it is generated by energy transfer from the excited triplet state of a PS and the nearby molecular
- dye in the same solvent (ΦΔ = 0.49) [31]. This result excludes any significant intra- or interencapsulation of the excited triplet state of the dye within the β-CD. If this was the case, the reduced quenching by oxygen due to steric hindrance would have resulted in a much smaller value for ΦΔ. The
A self-assembled cyclodextrin nanocarrier for photoreactive squaraine
Beilstein J. Org. Chem. 2016, 12, 2535–2542, doi:10.3762/bjoc.12.248
- appropriate wavelength. Irradiation of the PS causes its transition to the excited singlet state and, via intersystem crossing; the PS reaches its triplet state. Electron transfer occurs upon relaxation to the ground state. This process can take place in two ways distinguished as type I and II mechanisms [5
Synthesis and characterization of fluorinated azadipyrromethene complexes as acceptors for organic photovoltaics
Beilstein J. Org. Chem. 2016, 12, 1925–1938, doi:10.3762/bjoc.12.182
- fluorinated derivatives allow access to triplet state blue light-emitters [13]. This work further investigates the effects of fluorination in n-type materials for OPVs. A series of selectively fluorinated ADP derivatives based on WS3 were synthesized (Figure 2). To understand the effect of the fluorination
On the cause of low thermal stability of ethyl halodiazoacetates
Beilstein J. Org. Chem. 2016, 12, 1590–1597, doi:10.3762/bjoc.12.155
- obtain an energy difference between the singlet and triplet electronic spin state (Figure 3). The singlet–triplet energy gap is 4.1 kcal/mol in favor of the triplet state for the EDA-generated carbene. All three carbenes generated from 2a–c on the other hand have singlet ground states. The singlet
Other Beilstein-Institut Open Science Activities
