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Search for "excited state" in Full Text gives 250 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
Thiazolidinones: novel insights from microwave synthesis, computational studies, and potentially bioactive hybrids
Beilstein J. Org. Chem. 2025, 21, 2618–2636, doi:10.3762/bjoc.21.203
- greater charge separation in the excited state, which is more stabilized in polar solvents, typical of compounds that undergo an ICT upon excitation [86]. The use of EtOAc showed a hypochromic effect with a decrease in fluorescence emission. Similar results for chlorinated solvents (CH2Cl2, CHCl3) were
- observed, however, with an increase in fluorescence emission. Interestingly, in DMSO, a bathochromic effect was observed alongside a significant increase in fluorescence intensity. In aqueous medium, a pronounced red shift was verified, likely due to stabilization of the excited state by water molecules
- through intramolecular hydrogen bonding. By comparing the data for λabs and λem, it is evident that the compounds exhibit significant Stokes shifts with values above 2,100 cm−1, reflecting their stability in the excited state [87][88][89]. The highest values of Stokes shifts were observed in polar protic
Visible-light-driven NHC and organophotoredox dual catalysis for the synthesis of carbonyl compounds
Beilstein J. Org. Chem. 2025, 21, 2584–2603, doi:10.3762/bjoc.21.200
- presence of NHC (20 mol %), 4CzIPN (2 mol %) under mild conditions, producing corresponding unsymmetrical ketone derivatives 8 in up to 95% yield. An Ir-based photocatalyst was initially selected because its excited state is a strong oxidant (E1/2[Ir*III/II] = +1.21 V). Although 4-ethylanisole exhibits a
- higher oxidation potential (E1/2 = +1.52 V). This reaction was examined using different solvents, and it was found that toluene and 1,4-dioxane gave low yields (4–5% yield). Under blue LED irradiation, Ir-based PC is photoexcited, and its excited state is reductively quenched by the electron-rich arene
- photocatalysts such as fluorescein, alizarin red S, rhodamine B, and eosin Y. Since photoexcited organophotocatalyst rhodamine 6G (Rh6G*) possesses a sufficiently positive reduction potential in its singlet excited state S1 (Ered* = +1.18 V vs SCE*). The reduced form of Rh6G•– subsequently reduces BrCCl3 to
Conformational effects on iodide binding: a comparative study of flexible and rigid carbazole macrocyclic analogs
Beilstein J. Org. Chem. 2025, 21, 2369–2375, doi:10.3762/bjoc.21.181
- peaks appeared, indicating that photoelectron transfer occurred between iodine ions and the macrocycles [27][28], and fluorescence quenching was due to the photoinduced electron transfer (PET) effect between iodine ions and acceptors, resulting in non-radiative dissipation of excited state energy rather
- than the formation of new excited state complexes. As the I− content continued to increase, the fluorescence emission intensity of PBG continued to decrease at 354 nm and 364 nm. Similarly, the fluorescence emission intensity of WDG at 356 nm and 369 nm decreases as the I− content increases
Recent advances in Norrish–Yang cyclization and dicarbonyl photoredox reactions for natural product synthesis
Beilstein J. Org. Chem. 2025, 21, 2315–2333, doi:10.3762/bjoc.21.177
- spin-center-shift (SCS) process in forming the core of septosone B (47) [32][33]. The influence of Lewis acids is partially attributable to two effects: (1) the observed elongation of the lifetime of the singlet excited state (from 0.846 ± 0.015 ns to 0.912 ± 0.014 ns), which reduces undesired
Understanding the origin of stereoselectivity in the photochemical denitrogenation of 2,3-diazabicyclo[2.2.1]heptene and its derivatives with non-adiabatic molecular dynamics
Beilstein J. Org. Chem. 2025, 21, 2007–2020, doi:10.3762/bjoc.21.156
- two possible S1/S0-MECIs. Our dynamics simulations illustrate that inversion begins in the excited state immediately after the first σCN bond breaks. This inversion is driven by the atomic momenta acquired after the bond breaks. These dynamical effects promote the formation of the inverted housane
- ; stereoselectivity; Introduction Photochemical reactions utilize light as a sustainable energy source and are considered to be ‘green’ reactions [1][2]. Organic chromophores absorb light, accessing higher-lying excited state(s) that exhibit distinct reactivities, leading to bond breaking and formation, irreversibly
- static MEP calculation, the experimental quantum yield (Φ = 0.97–1.00) is inconsistent with this static analysis, since it suggests a non-productive and fluorescence pathway. We hypothesize that these S1 minima are shallow excited-state minima that can be escaped towards a productive region of the
Photochemical reduction of acylimidazolium salts
Beilstein J. Org. Chem. 2025, 21, 1973–1983, doi:10.3762/bjoc.21.153
- research has demonstrated that NHCs are also capable of stabilizing radical or excited-state species [12][13]. In 2020, our group reported the concept of photo-NHC catalysis where direct excitation of acylazolium intermediates generated from o-toluoyl fluoride substrates with UV-A light resulted in a novel
- attention turned to a consideration of the reaction mechanism. As has been well documented in the photoredox literature [47][48][49][50][51][52][53], excitation of a photocatalyst ([PC]) in the presence of DIPEA can result in reductive quenching of the excited state, affording the corresponding
- direct excitation of the benzoylazolium salt with the excited state species 1*, which subsequently reacts with TESH. Comparison of the redox potential of the silane (+1.54 V vs ferrocene) with the estimated excited-state potential of the azolium salt 1* (+1.70 V vs ferrocene) suggest that direct electron
Photoswitches beyond azobenzene: a beginner’s guide
Beilstein J. Org. Chem. 2025, 21, 1808–1853, doi:10.3762/bjoc.21.143
- ). Shining light will bring the molecule to a generic excited state (which is different for different photoswitch classes and substitution patterns and will not be treated in detail), which can then relax back to the ground state in either of the two wells. In cases where the two absorption spectra of the
- conjugated with the chromophore structure, will influence its absorption spectrum and stability [4]. The solvent will also affect the properties, as it can stabilise or destabilise either the ground or the excited state, resulting in a red- or blue shift of the spectra. The thermal half-life (t1/2) measures
- , which characterises this subclass with negative photochromism. Unsubstituted indigo (60) does not undergo photochemical isomerisation, due to much faster relaxation through excited-state proton transfer 60* followed by tautomerisation 60’ (Scheme 17). The first proof of the existence of Z-indigo was
Photocatalysis and photochemistry in organic synthesis
Beilstein J. Org. Chem. 2025, 21, 1645–1647, doi:10.3762/bjoc.21.128
- ) transition, resulting in a long-lived charge-separated species. In this excited state, [Ru(bpy)3]Cl2 is both a more potent oxidant and reductant than in its ground state. This reactivity, in combination with the reversible redox behavior of the metal complex, enables reductive or oxidative quenching cycles
- in the presence of electron donors and acceptors. Furthermore, [Ru(bpy)3]Cl2 can engage in Förster and Dexter energy transfer processes, enabling the transfer of excited-state energy to molecules that do not themselves absorb visible light. This versatility is arguably the reason for the tremendous
On the aromaticity and photophysics of 1-arylbenzo[a]imidazo[5,1,2-cd]indolizines as bicolor fluorescent molecules for barium tagging in the study of double-beta decay of 136Xe
Beilstein J. Org. Chem. 2025, 21, 1627–1638, doi:10.3762/bjoc.21.126
- (S0) and first singlet excited state (S1) are reported in Figure 3B. Using geometric criteria, we computed the HOMA [21][22] for 1 at the ground state, according to the following expression: In this equation, n is the number of covalent bonds, k describes the type of bond (CC or CN), stands for the
- rigid, with only small modifications on going from the ground state to the first single excited state (Figure 6). However, the presence of the two perchlorate anions results in additional coordination with Ba2+, thus resulting in larger values of the Ba–N distances, as well as of the average Ba–O and Ba
- between the free and bound states. The corresponding signed errors are gathered in Figure 7. The behavior of the different functionals resulted to be very variable, although the ground state and excited state geometries were very similar. In the case of absorption wavelengths, wB97XD, BHandHHLYP and CAM
Transition-state aromaticity and its relationship with reactivity in pericyclic reactions
Beilstein J. Org. Chem. 2025, 21, 1613–1626, doi:10.3762/bjoc.21.125
- defined by Doering and Detert [6], this concept has been extended well beyond benzenoid molecules to organometallic, inorganic, and even saturated molecules. As a result, besides classical π-aromaticity, other aromaticity types such as Möebius, spherical, or excited-state aromaticity (to name a few) have
Thermodynamic equilibrium between locally excited and charge transfer states in perylene–phenothiazine dyads
Beilstein J. Org. Chem. 2025, 21, 1577–1586, doi:10.3762/bjoc.21.121
- Issei Fukunaga Shunsuke Kobashi Yuki Nagai Hiroki Horita Hiromitsu Maeda Yoichi Kobayashi Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, Japan 10.3762/bjoc.21.121 Abstract We report the excited-state dynamics of π-orthogonal
- the PTZ moiety and the photoinduced charge-transfer (CT) state. Femtosecond to microsecond transient absorption spectroscopy reveals that this equilibrium is facilitated not simply by enhanced donor ability, but presumably by excited-state planarization of the PTZ moiety, which lowers the energy of
- the LE state of the PTZ moiety. In contrast, Pe-Ph–PTZ(TPA)2, in which the donor–acceptor distance is increased by a phenyl spacer, does not show clear equilibrium behavior. These results underscore the crucial role of excited-state structural relaxation in tuning photoinduced charge separation, and
Synthesis of an aza[5]helicene-incorporated macrocyclic heteroarene via oxidation of an o-phenylene-pyrrole-thiophene icosamer
Beilstein J. Org. Chem. 2025, 21, 1561–1567, doi:10.3762/bjoc.21.119
- structural relaxation in the excited state. The fluorescence quantum yield (ΦF) was determined as 0.078 (λex = 300 nm), and the fluorescence lifetime (τ) using biexponential decay model fitting as 1.7 and 4.4 ns. The partially fused structure of 5 exhibited a well-defined lowest-energy absorption band peaked
- at 399 nm (Figure 5b). A broad emission was observed at 528 nm, resulting in a relatively large Stokes shift of 6100 cm−1, which can be attributed to the structural relaxation in the excited state, as inferred by the observed broad 1H NMR spectrum at room temperature. Due to the thermal energy loss
General method for the synthesis of enaminones via photocatalysis
Beilstein J. Org. Chem. 2025, 21, 1535–1543, doi:10.3762/bjoc.21.116
- . Simultaneously, acridinium photocatalyst PC1 absorbed energy and transitioned from the ground state to excited state under visible-light irradiation. This excited state PC1* is quenched by the amine, generating the amine radical cation and PC1 radical via a single-electron transfer (SET) process. Then, the C−Br
Advances in nitrogen-containing helicenes: synthesis, chiroptical properties, and optoelectronic applications
Beilstein J. Org. Chem. 2025, 21, 1422–1453, doi:10.3762/bjoc.21.106
- displays red-shifted emission and prolonged fluorescence lifetimes as solvent polarity increases, indicating enhanced excited-state stabilization. Collectively, these studies offer valuable strategies for stabilizing long π-extended helicenes and finely tuning their chiroptical and emissive properties
- and high BCPL of 66.5 M−1 cm−1 underscore its potential for advanced chiral photonic applications. Heteroatom engineering in double helicenes has emerged as a powerful strategy for tuning chiroptical properties and excited-state dynamics. In 2021, Sakamaki’s group synthesized a novel double N,O-hetero
- sensitivity of chiral excited-state properties to heteroatom substitution within the helicene framework. Extending this design principle, the group reported a double N,S-hetero[5]helicene 58 constructed from two benzo[b]phenothiazine units in 2023 [73]. Compared to the N,O-analogue 57b, this new compound
Tautomerism and switching in 7-hydroxy-8-(azophenyl)quinoline and similar compounds
Beilstein J. Org. Chem. 2025, 21, 1404–1421, doi:10.3762/bjoc.21.105
- molecules good candidates for molecular switches [50]. Recently, we have developed a series of 7-hydroxyquinoline Schiff bases, where the tautomeric proton transfer causes intramolecular twisting upon irradiation [51]. The process happens in the excited state and the competition between proton transfer and
- forms, allowing long-range proton transfer starting from the enol, azo, (E) and finishing to the end keto form K. As described in similar compounds, ideally for switching, the process begins with excitation of E, which, in the excited state, exhibits excited-state proton transfer (PT) to KE*. This
- part is flexible, the excitation of E can lead to E/Z isomerization, which competes with the initial excited-state PT process, reducing its efficiency [52]. The theoretical data, collected in Table 1, can shed light on the potential energy landscape in the ground state for the studied compounds
Recent advances in amidyl radical-mediated photocatalytic direct intermolecular hydrogen atom transfer
Beilstein J. Org. Chem. 2025, 21, 1306–1323, doi:10.3762/bjoc.21.100
- pathway initiates with ground-state complexation 90 between HRP-12 and HFIP via hydrogen bonding. Following visible-light excitation of 90, intersystem crossing (ISC) from the S1(LE) to T2 state generates the catalytically competent triplet excited state 91. This N-centered radical species subsequently
Recent advances and future challenges in the bottom-up synthesis of azulene-embedded nanographenes
Beilstein J. Org. Chem. 2025, 21, 1272–1305, doi:10.3762/bjoc.21.99
- , it was reported that PAH 126 exhibits anti-Kasha fluorescence [80] from the S3 state in the range of 410–470 nm upon excitation at 370 nm. This was well verified by femtosecond time-resolved absorption spectroscopy (fs-TAS), with corresponding high-energy excited state absorption bands observed at
Recent advances in oxidative radical difunctionalization of N-arylacrylamides enabled by carbon radical reagents
Beilstein J. Org. Chem. 2025, 21, 1207–1271, doi:10.3762/bjoc.21.98
- intermediate B. Intermediate B undergoes cyclization to form the N-radical intermediate C, which can be further oxidized to the final product 35a by releasing a proton. Alternatively, intermediate C can be reduced by excited-state Ir(ppy)3, leading to the formation of the nitranion intermediate D. The Ir(III
- reaction mechanism was proposed (Scheme 26). The process begins with the generation of a difluoromethyl radical from S-(difluoromethyl)sulfonium salt 49 under the influence of an excited-state photocatalyst. This radical then adds to the double bond of N-arylacrylamide, forming intermediate radical 51
- -carbonyl bromide 67 through photoreduction by the excited state of the photocatalyst [IrIII*] (Scheme 33). The generated radical then undergoes addition to the diene, followed by 6-endo cyclization and deprotonation, ultimately forming the lactam product 68a. Notably, this process highlights the
Biobased carbon dots as photoreductants – an investigation by using triarylsulfonium salts
Beilstein J. Org. Chem. 2025, 21, 1024–1030, doi:10.3762/bjoc.21.84
- biocompatibility. The electrochemical properties of such materials have been then evaluated by cyclic voltammetry (CV). For all the properties mentioned above, CDs emerged as low-cost and sustainable photocatalysts. Indeed, upon visible-light irradiation, the generated excited state CD* can operate as either
On the photoluminescence in triarylmethyl-centered mono-, di-, and multiradicals
Beilstein J. Org. Chem. 2025, 21, 964–998, doi:10.3762/bjoc.21.80
- excitation wavelength (see Figure 1c). Excitation at 374 nm or 544 nm both lead to fluorescence with an identical fluorescence decay profile and identical ϕ of ≈2% (see Figure 1c). This behavior hints at the fact that the relaxed excited state, from which the emission occurs, is the same for excitation at
- the excited state dynamics, there is evidence for this fast relaxation in donor-functionalized TTM radicals [26]. Moreover, transient absorption has been employed to elucidate the formation of a non-luminescent side-product in trityl radicals. During photodegradation, two halogens are lost and two
- the molecule remains mostly planar in the excited state [37]. As a result, we observe weak emission in the yellow to red spectrum, because the respective transition remains symmetry forbidden. Circularly polarized photoluminescence PTM has been developed prior to TTM, as the first stable
Study of tribenzo[b,d,f]azepine as donor in D–A photocatalysts
Beilstein J. Org. Chem. 2025, 21, 935–944, doi:10.3762/bjoc.21.76
- is a particular interest in the obtainment of organic molecules with well-balanced redox potentials in the excited state that can act as bimodal photocatalysts, facilitating their use in oxidative and reductive quenching cycles. In this sense, it is crucial to understand the molecule's structure
- density distribution in the charge transfer (CT) excited state is facilitated by the presence of an electron-rich moiety and an electron-poor part in the same molecule, increasing the lifetime in the excited state. One of the representative classes of molecules demonstrating dual use in materials
- excited state. This results in a consistently planar conformation for donor b, while donor a can exhibit either a planar or bent conformation, depending on the nature of the substituent, as previously mentioned. This duality between planar and bent shapes is significant, as it contributes to the aromatic
Recent advances in controllable/divergent synthesis
Beilstein J. Org. Chem. 2025, 21, 890–914, doi:10.3762/bjoc.21.73
- mechanistic experiments and DFT calculations, the authors proposed a possible mechanism for the reaction: first, DPZ is excited by light to form the excited state DPZ*, which then oxidizes bromide ions through single-electron transfer to generate corresponding radical anions. These radical anions undergo
Light-enabled intramolecular [2 + 2] cycloaddition via photoactivation of simple alkenylboronic esters
Beilstein J. Org. Chem. 2025, 21, 854–863, doi:10.3762/bjoc.21.69
- prohibitively high in energy for selective reactivity [5]. The inception of energy transfer catalysis (EnT) has expedited discoveries concerning the photoactivation of organic molecules [15][16][17], enabling direct access to the triplet excited state through the use of a photocatalyst (Figure 1A, top
- isomerization of alkenes [18][19], [2 + 2] cycloadditions [20][21][22][23][24], and dearomative [4 + 2] cycloadditions [25][26][27]. When considering conjugated alkenes, the triplet excited state energy and excited state lifetime are intrinsically linked to the degree of conjugation and substitution of a
- scaffold (Figure 1A, bottom), with increasing excited state energy moving from stilbenes and conjugated dienes to simple dienes, styrenes and enones (not shown) [28]. Consequently, small truncated chromophores, such as simple alkenes remain an intractable challenge for efficient EnT due to prohibitively
Substituent effects in N-acetylated phenylazopyrazole photoswitches
Beilstein J. Org. Chem. 2025, 21, 830–838, doi:10.3762/bjoc.21.66
- studies on azobenzene [32][40]. Another interesting aspect, that could point to a more complex picture in the excited state landscape of these switches, is that the QYs of NAc-PAPs with R = NO2 and R = H are lower for the π→π* than for the n→π* transition, while for the other substituents the opposite was
Photochemically assisted synthesis of phenacenes fluorinated at the terminal benzene rings and their electronic spectra
Beilstein J. Org. Chem. 2025, 21, 670–679, doi:10.3762/bjoc.21.53
- wavelength region for the corresponding parent phenacenes whereas their fluorescence bands markedly red-shifted and broadened. These observations suggest that the intermolecular interactions of excited-state F8-phenacene molecules are significantly different from those of the corresponding parent molecules
- negative (orange region) in the parent compounds, whereas the phenacene cores turned to be positive (blue) for the F8-phenacenes. Therefore, one can manipulate the polarization of the phenacene cores through the introduction of fluorine atoms without altering the electronic spectral features. The excited
- -state electronic characteristics were also calculated, and the electronic transitions for the first two vertical absorption bands are summarized in Table 2. Although the calculated S1←S0 and S2←S0 electronic transition energies were slightly overestimated to show a systematic difference between the
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