Thermodynamic equilibrium between locally excited and charge transfer states in perylene–phenothiazine dyads

• Issei Fukunaga,
• Shunsuke Kobashi,
• Yuki Nagai,
• Hiroki Horita,
• Hiromitsu Maeda and
• Yoichi Kobayashi

Beilstein J. Org. Chem. 2025, 21, 1577–1586, doi:10.3762/bjoc.21.121

• time constants were found to be 77, 46, 135, and 63 μs for Pe–PTZ, Pe–PTZ(TPA), Pe–PTZ(TPA)2, and Pe–Ph–PTZ(TPA)2, respectively. The transient absorption spectral features closely matched those of the triplet state of perylene, indicating that the 3LE state of the Pe moiety is generated in all of these

On the photoluminescence in triarylmethyl-centered mono-, di-, and multiradicals

• Daniel Straub,
• Markus Gross,
• Mona E. Arnold,
• Julia Zolg and
• Alexander J. C. Kuehne

Beilstein J. Org. Chem. 2025, 21, 964–998, doi:10.3762/bjoc.21.80

• investigated by DFT analysis. The position of the spin-quartet is in part dictated by the triplet state of the donor moiety. For example, strong donors like benzocarbazole exhibit low lying triplet states, which in combination with the TTM unit lead to the Q1 state being reduced in energy below the D2 states

• ground state; however, singlet states should not produce EPR signals (see Figure 12b). The yet obtained EPR signal indicates that the triplet state is thermally accessible, which is reasonable considering the small ΔEST of <0.1 kcal mol−1 (as determined by us on the UB3LYP/def2-SVP level of theory as

• part of this review, see Table 3). Cooling leads to a reduction of the intensity of the central EPR signal, fine structure, and significant diradical anisotropy, indicating that the triplet state becomes less and less populated (see Figure 12b) [95]. By contrast, the TTM-TTM analogue without chlorine

Substituent effects in N-acetylated phenylazopyrazole photoswitches

• Radek Tovtik,
• Dennis Marzin,
• Pia Weigel,
• Stefano Crespi and
• Nadja A. Simeth

Beilstein J. Org. Chem. 2025, 21, 830–838, doi:10.3762/bjoc.21.66

• found. We thus suspect that the substituents play a crucial role in in the population of the respective exited state and we can at this state not rule out a contribution also from the triplet state. Moreover, we could not find a quantitative correlation between the R-substituents and ΦE→Z, however, some

• triplet state [48], appear to play a role. Specifically, the rotation mechanism does not explain the low activation entropy observed in azobenzene systems [49] sparking new discussions on the possibility of alternative isomerization pathways [34]. Recently, Reimann et al. computationally showed that the

• involvement of a triplet state mechanism, which crosses the transition state for the Z→E relaxation, could explain the low values of the activation entropy. The same authors also showed experimental evidence for this proposal by an external heavy atom effect on Z→E isomerization. To understand the thermal Z→E

Unprecedented visible light-initiated topochemical [2 + 2] cycloaddition in a functionalized bimane dye

• Metodej Dvoracek,
• Brendan Twamley,
• Mathias O. Senge and
• Mikhail A. Filatov

Beilstein J. Org. Chem. 2025, 21, 500–509, doi:10.3762/bjoc.21.37

• suggest potential triplet-state formation, which is involved in the proposed mechanism for the cycloaddition reaction. Although Me4B could theoretically form triplet states, given its fluorescence quantum yield of 51.7–67.3%, its crystallographic structure is not conducive to this reaction, regardless of

• proposed pathway begins with the excitation of a bimane molecule to its singlet-excited state, followed by intersystem crossing (ISC) to the triplet state. The triplet state then forms an excimer complex with a neighboring bimane molecule, leading to the formation of a single bond and generating a triplet

Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• a Kohn–Sham molecular orbital analysis together with an energy decomposition analysis (Figure S1 in Supporting Information File 1). To form the broken bonds, both fragments have two unpaired electrons (at their triplet state). The interaction between both fragments amounts to −227.9 kcal mol−1

Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

• excitation to the triplet state from the ground state S0. This effect mitigates rapid back-electron transfer from the singlet excited state to the ground state, extending the excited-state lifetime of the photocatalyst. Since the T1 → S0 transition is spin-forbidden, the process increases the overall

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• photochemistry, porphyrins are mainly used for the generation of singlet oxygen (1O2) or other reactive oxygen species. Porphyrins in the triplet excited state can relax to the ground state by transferring energy to molecular oxygen (triplet state) forming 1O2 (Figure 13b) [67]. Photosensitized singlet oxygen

• splitting, high quantum yield for intersystem crossing, and long triplet state lifetime, act as robust electron mediators. This section highlights the use of metal-free porphyrins in organic photoredox catalysis. So far, mainly planar metal-free porphyrins have been explored as photoredox catalysts, paving

Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis

• Johannes Rocker,
• Till J. B. Zähringer,
• Matthias Schmitz,
• Till Opatz and
• Christoph Kerzig

Beilstein J. Org. Chem. 2024, 20, 1236–1245, doi:10.3762/bjoc.20.106

• -mentioned methods [39]. However, the longer lifetime of the triplet state usually comes at the expense of a lower energetic driving force. Helicenes in particular show an increased ISC rate compared to planar molecules, which is attributed to an enhanced spin-orbit coupling that is sensitive to their degree

• , yielding clear-cut evidence for the proposed reaction mechanism [47][48][49][50][51][52][53][54][55][56][57]. We found that quenching of the singlet-excited Aza-H by 4-cyanopyridine is the main pathway for the 3-CR, while the triplet state of our catalyst, which is formed with a quantum yield as high as

• were thus carried out and they showed short-lived fluorescence and long-lived emission (phosphorescence) that was assigned to the triplet state of Aza-H with an energy of 2.32 eV (Figure 1A). Quantum mechanical computations of the Aza-H triplet state yielded a triplet energy of 2.17 eV (adiabatic

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• photolysis in combination with steady-state measurements [59]. It was found that the E–Z photoisomerization of 9a, 9d, 9g, 9h occurred through a singlet mechanism upon direct excitation. However, the triplet state could be achieved by a sensitized reaction. At room temperature, a transient species that could

• be assigned to a triplet state was also observed for rigid molecules 10 and 16, based on the quenching experiments and the fact that the same transient species could be found under sensitized conditions. Further insight in the excited state properties of derivatives 9a, 9d, 9g, 9h and N,N

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• , the racemization was observed at 80 °C. Torres et al. performed detailed theoretical calculations and showed that the racemization observed in 59 and 60 is caused by triplet-state photogeneration, which leads to the rotation around the sterically hindered buta-1,3-diene chiral axis [132]. In fact, the

• estimated energy barrier of ≈37 kcal mol−1 is reduced to ≈15 kcal mol−1 upon the electronic excitation of 59 and 60 to the T1 state. It is reasonable to consider that the phototriggered racemization is inhibited in the presence of O2 because O2 acts as a triplet-state scavenger. Osuka et al. synthesized two

• state was observed; the subsequent internal conversion of S2 into the S1 state was also observed, from which the CS state (MP•−–D•+) emerged. Here, since the triplet state 3MP* is energetically lower than the

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• radicals on polymer surfaces. Its photoexcitation and subsequent reaction with polymers have been studied for decades [164][165][166]. When irradiated at around 360 nm, benzophenone undergoes excitation to a triplet state with biradical behavior. It then abstracts a hydrogen atom from the polymer resulting

Organic thermally activated delayed fluorescence material with strained benzoguanidine donor

• Alexander C. Brannan,
• Elvie F. P. Beaumont,
• Nguyen Le Phuoc,
• George F. S. Whitehead,
• Mikko Linnolahti and
• Alexander S. Romanov

Beilstein J. Org. Chem. 2023, 19, 1289–1298, doi:10.3762/bjoc.19.95

• : guanidine; organic; photoluminescence; TADF; yellow; Introduction Thermally activated delayed fluorescence (TADF) is a photoluminescence mechanism where excitons undergo thermally-assisted reverse-intersystem crossing from an excited triplet state to a higher-lying in energy singlet state to emit delayed

The effect of dark states on the intersystem crossing and thermally activated delayed fluorescence of naphthalimide-phenothiazine dyads

• Liyuan Cao,
• Xi Liu,
• Xue Zhang,
• Jianzhang Zhao,
• Fabiao Yu and
• Yan Wan

Beilstein J. Org. Chem. 2023, 19, 1028–1046, doi:10.3762/bjoc.19.79

• ; electron donor; intersystem crossing; TADF; triplet state; Introduction Thermally activated delayed fluorescence (TADF) compounds are promising emitters to be used in organic light-emitting diodes (OLED) [1][2][3][4][5][6][7][8][9][10][11][12]. These emitters have the advantage of low cost and high

• may also enhance the rISC in OLED devices, in which the electron–hole recombination produces mainly the triplet state (the theoretical probability is 75%, by following the spin statistic rule) [1]. Compared to the application studies, the investigation of the photophysical mechanism of TADF emitters

• transient species of the dyads formed upon photoexcitation, the ns-TA spectra of NI-PTZ-F in HEX were studied (Figure 8a). Upon pulsed laser excitation, a positive absorption band centered at ca. 430 nm was observed, which is inconsistent with the characteristic triplet state absorption of the NI unit (460

Naphthalimide-phenothiazine dyads: effect of conformational flexibility and matching of the energy of the charge-transfer state and the localized triplet excited state on the thermally activated delayed fluorescence

• Kaiyue Ye,
• Liyuan Cao,
• Davita M. E. van Raamsdonk,
• Zhijia Wang,
• Jianzhang Zhao,
• Daniel Escudero and
• Denis Jacquemin

Beilstein J. Org. Chem. 2022, 18, 1435–1453, doi:10.3762/bjoc.18.149

• can be controlled. The singlet oxygen quantum yield (ΦΔ) of NI-PTZ is moderate in n-hexane (HEX, ΦΔ = 19%). TADF was observed for the dyads, the biexponential luminescence lifetime are 16.0 ns (99.9%)/14.4 μs (0.1%) for the dyad and 7.2 ns (99.6%)/2.0 μs (0.4%) for the triad. Triplet state was

• : charge-transfer; electron donor; intersystem crossing; TADF; triplet state; Introduction Thermally activated delayed fluorescence (TADF) has attracted much attention in recent years, not only for its application in organic light emitting diodes (OLED) [1][2][3] but also as a mean for studying of charge

• interaction-driven ISC is slow. Recently, it was proposed that an intermediate localized triplet state (3LE) is essential to enhance the ISC and rISC, through the so-called spin-vibronic coupling effect [8][16][17][18][19]. However, the effect of the molecular geometry on the ISC and rlSC is complicated, and

Ionic multiresonant thermally activated delayed fluorescence emitters for light emitting electrochemical cells

• Merve Karaman,
• Abhishek Kumar Gupta,
• Subeesh Madayanad Suresh,
• Tomas Matulaitis,
• Lorenzo Mardegan,
• Daniel Tordera,
• Henk J. Bolink,
• Sen Wu,
• Stuart Warriner,
• Ifor D. Samuel and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2022, 18, 1311–1321, doi:10.3762/bjoc.18.136

• stabilized to 3.07 eV and 2.83 eV, respectively. The ΔEST decreases to 0.24 eV and there is no intermediate triplet state. The trend of stabilized S1 and T1 states when a donor group decorates the DiKTa core (S1 = 3.45 eV, T1 = 3.18 eV) has been previously observed in reported emitters such as Cz-DiKTa (S1

Thermally activated delayed fluorescence (TADF) emitters: sensing and boosting spin-flipping by aggregation

• Ashish Kumar Mazumdar,
• Gyana Prakash Nanda,
• Nisha Yadav,
• Upasana Deori,
• Upasha Acharyya,
• Bahadur Sk and
• Pachaiyappan Rajamalli

Beilstein J. Org. Chem. 2022, 18, 1177–1187, doi:10.3762/bjoc.18.122

• -lying triplet state T1 to the singlet excited state S1, we recorded the fluorescence and phosphorescence spectra of aggregates (90 vol % water/THF) at room temperature and 77 K, respectively (Figure 4). The structural phosphorescence band was obtained from the aggregates in 90 vol % water/THF mixtures

• (Figure 4). Additionally, the phosphorescence spectra of both compounds were recorded in THF at 77 K (Figure S3 in Supporting Information File 1). The retention of the structural phosphorescence band in THF indicates its origin from the locally excited triplet state 3LE. The ΔEST values calculated based

Comparative study of thermally activated delayed fluorescent properties of donor–acceptor and donor–acceptor–donor architectures based on phenoxazine and dibenzo[a,j]phenazine

• Saika Izumi,
• Prasannamani Govindharaj,
• Anna Drewniak,
• Paola Zimmermann Crocomo,
• Satoshi Minakata,
• Leonardo Evaristo de Sousa,
• Piotr de Silva,
• Przemyslaw Data and
• Youhei Takeda

Beilstein J. Org. Chem. 2022, 18, 459–468, doi:10.3762/bjoc.18.48

• ) occurs in the singlet excited state (1CT). An efficient rISC can be mediated by mixing the 1CT state with a locally excited triplet state on the donor (3LED) or the acceptor (3LEA) through spin–vibronic coupling [14] or non-Condon effects [15][16]. In 2016, we developed a twisted D–A–D compound POZ-DBPHZ

• compound POZ-DBPHZ, transitions to T1 display 48% probability whereas fluorescence has around 4%. The remaining probabilities are mostly distributed between transfers to T2 and T3 with about 20% each. Transfers to higher lying triplet states may end up relaxing to the lowest triplet state by means of

Effect of a twin-emitter design strategy on a previously reported thermally activated delayed fluorescence organic light-emitting diode

• Ettore Crovini,
• Zhen Zhang,
• Yu Kusakabe,
• Yongxia Ren,
• Yoshimasa Wada,
• Bilal A. Naqvi,
• Prakhar Sahay,
• Tomas Matulaitis,
• Stefan Diesing,
• Ifor D. W. Samuel,
• Wolfgang Brütting,
• Katsuaki Suzuki,
• Hironori Kaji,
• Stefan Bräse and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 2894–2905, doi:10.3762/bjoc.17.197

• and T1 states is different, for example by additionally involving a third (local) triplet state with different symmetry, because otherwise SOC vanishes when the orbital types for these two states are the same, according to El-Sayed’s rule [9]. Designing a molecule able to achieve RISC and the desired

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• to its triplet state CuICN*, in which the fluoroalkyl iodides were reduced to Rf• and I−. Subsequently, the radical Rf• attacks the alkene forming a new alkyl radical species. This radical species is then trapped by CuII(CN)n to generate a CuIII intermediate, which undergoes reductive elimination to

• homolysis to produce CuI species and radical intermediates. These intermediates can initiate productive organic transformations [39]. 2.1 Visible-light-mediated Cu(I) catalytic cycle Upon the absorption of a photon (Scheme 4), CuILn forms a singlet MLCT state, which subsequently yields the excited triplet

• state CuI*Ln via rapid ISC. The excited CuI*Ln species has a lifetime to finish the chemical processes. A radical mechanism is proposed in Scheme 4. In path a (a ligand transfer cycle), CuI* is oxidized by an electrophilic reagent (haloalkane) to form CuII and the radical species R• in a single-electron

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• the triplet-state diradical 23-I. A HAT process between 23-I and the alkane substrate generates the desired carbon-centered radical 23-II with concomitant formation of ketyl radical species 23-III. The thus formed alkyl radical 23-II undergoes Giese addition to alkene 94 resulting in the radical

An initiator- and catalyst-free hydrogel coating process for 3D printed medical-grade poly(ε-caprolactone)

• Jochen Löblein,
• Thomas Lorson,
• Miriam Komma,
• Tobias Kielholz,
• Maike Windbergs,
• Paul D. Dalton and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2021, 17, 2095–2101, doi:10.3762/bjoc.17.136

• exposed PCL fibers in the PHEMA-filled MEW scaffolds. Schematic representation of the self-initiated photografting and photopolymerization (SIPGP) of 2-hydroxyethyl methacrylate (HEMA) including intersystem crossing from singlet to triplet state which is mandatory for the formation of a biradical (left

Exploring the possibility of using fluorine-involved non-conjugated electron-withdrawing groups for thermally activated delayed fluorescence emitters by TD-DFT calculation

• Dongyang Chen and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2021, 17, 210–223, doi:10.3762/bjoc.17.21

• -dependent density functional theory calculations indicate that when only two ortho-disposed carbazole donors are used (Type I molecules), the lowest-lying triplet state possesses locally excited (LE) character while the lowest-lying singlet state possesses charge-transfer character. When five carbazole

• ]. We analysed the higher excited states of the fluorinated acceptor-containing emitters in both Type I and Type II structures. For 2CzCF3, the T1 is locally excited; further, T2 (3.46 eV) to T6 (3.58 eV) all exhibited significant LE character. The lowest triplet state that exhibits charge transfer

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• /22 ratio of 1:2, which revealed that the singlet spin-state of coumarin could be involved in the photodimerization process within the CB[8] cavity and that the triplet state could be shielded from external quenchers (O2 as a triplet quencher). These results also indicated that photodimerization could

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• acid so that a Dexter energy transfer process is possible from the photocatalyst to the substrate to promote 155 into its triplet state, which can then cyclise with 156 to give enantioenriched cycloaddition products 158. The selectivity of this reaction is generally low (6 examples, up to 93:7 er, 67

• by Bach to the deracemisation of allenes rac-194 (Scheme 29) [85]. The proposed mechanism proceeds through configurationally isomeric hydrogen bonding complexes 195 and 195’, with subsequent photoexcitation of the thioxanthone chromophore leading to racemisation of the allene through a triplet state

• enantioselectivity via triplet state intermediate 200, rather than proceeding via an enantioselective rearrangement. Bifunctional hydrogen bonding photocatalysts have been developed by other groups as well. Sivaguru developed an atropisomeric thiourea-based catalyst 201 and used it for the intramolecular