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

• + and 660 nm for [Os(phen)3]2+ [15]. In a same way, spin–orbit coupling, stemming from the relativistic effects, can be exploited in photoredox-catalyzed reaction [16]. Spin–orbit coupling promotes intersystem crossing (ISC) between the singlet and triplet excited states, and even allows for direct

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

• of non-planarity [40], where the helical structure allows for mixing between the singlet and triplet π,π*-states [41][42]. In addition, the insertion of heteroatoms such as nitrogen further enhances ISC due to a spin-orbit coupling between n,π*-states and π,π*-states [40], as stated by El Sayed’s

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

• ) were measured. The significant difference in the quantum yield values between the compounds was attributed to the increase in the population of triplet excited states because of spin–orbit coupling by bromine atoms. On the contrary with previous studies, it was found that the effect of proton and

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

• understanding of the TADF mechanism are highly important tasks in this research field. The singlet–triplet energy splitting between the S1 and T1 states (ΔEST) and spin–orbit coupling (SOC) play key roles in manifesting the TADF character of an organic compound. To boost the rISC process, ideally, the ΔEST is

• D–A–D compound. This is indeed the case, as the average spin–orbit coupling for the T1 to S1 transition in the D–A compound 1 is 0.462 meV, whereas for the D–A–D compound POZ-DBPHZ it is 0.177 meV. However, the average energy gap taken from all geometries in the nuclear ensemble for this transition

• is 0.37 eV for the D–A–D compound and 0.71 eV for the D–A molecule. As such, the higher similarity in electronic character between the singlet and triplet states of the D–A–D molecule was enough to decrease the average energy gap without compromising significantly the spin–orbit coupling, resulting

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

• them into emissive singlets via a reverse intersystem crossing (RISC) mechanism. This mechanism is operational when the energy gap (ΔEST) between the lowest-lying singlet and triplet excited states (S1 and T1) is sufficiently small and spin-orbit coupling (SOC) is non-negligible [4][5][6][7]. This

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

• states between S1 and T1, thus likely leading to a very efficient reverse intersystem crossing in these compounds. Keywords: DFT calculation; pentafluorosulfanyl; spin-orbit coupling; TADF; trifluoromethoxy; trifluoromethylthio; Introduction Organic thermally activated delayed fluorescence (TADF

• happen by hyperfine coupling when the ΔEST is sufficiently small (<10 meV) or spin orbit coupling (SOC), which requires different symmetry between the two states coupled with a relatively small singlet–triplet energy gap, ΔEST, (<300 meV) [8][9]. The ΔEST is directly dependent on the magnitude of the

• groups so as to localized the HOMO on the electron-donating moiety and to confine the LUMO on the electron-withdrawing moiety [12][13]. According to the Fermi’s golden rule, the reversed intersystem crossing rate (krISC) can be expressed as [14][15]: Where |VSOC|2 is the spin-orbit coupling matrix

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• 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

• state that collides with nearby molecules to reach its lowest vibrational energy state. Another fate of T1{PS}, permitted by spin–orbit coupling, is the radiative process of phosphorescence. If a molecule exhibits a high triplet quantum yield (rapid ISC and slow phosphorescence), this state is long

Et₃N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

• Dharmender Singh,
• Vipin Kumar and
• Virender Singh

Beilstein J. Org. Chem. 2020, 16, 1740–1753, doi:10.3762/bjoc.16.146

• . The quantum yields were calculated based on Equation 1. where R means reference and S sample, respectively. Generally weak fluorescence emissions were observed for the thiophene-based chromophores due to a remarkable spin–orbit coupling which is originating from the heavy atom effect of sulfur [73][74

Clickable azide-functionalized bromoarylaldehydes – synthesis and photophysical characterization

• Dominik Göbel,
• Marius Friedrich,
• Enno Lork and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2020, 16, 1683–1692, doi:10.3762/bjoc.16.139

• ,π*) excited states, owing to the poor orbital overlap, resulting in a decreased spin-orbit coupling. Quenching processes of triplet states, induced by molecular motions, oxygen, or humidity, restrict the versatile application of such organic materials [24]. Thus, low temperatures [25][26][27] or

• inert conditions [28] are necessary to facilitate an afterglow emission. Most phosphorescence studies are focused on metal complexes due to a strong heavy atom-induced spin-orbit coupling [29][30][31][32][33]. Considering the high price and the toxicity of many metal complexes, pure organic phosphors

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• novel material design can overcome typical limitations of organic semiconductors to produce more efficient photocatalysts with an enhanced charge transport. The authors did not discuss the formation of triplet excitons through intersystem crossing, which is facilitated by sulphur spin–orbit coupling, as

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• fluorinated benzils to emit phosphorescence, which may arise from immediate spin-orbit coupling involving the 1(n, π)→3(π, π) transition, unlike the case of fluorinated or nonfluorinated bisbenzil analogues. These findings offer a useful guide for developing novel pure organic room-temperature phosphorescent

• phosphorescence owing to a significant acceleration of spin-orbit coupling based on the El-Sayed rule involving the 1(n, π)→3(π, π) transition [25][26]. Over the past few years, our group has intensively investigated fluorinated 1,4-bis(2-phenylethyn-1-yl)benzenes (1), a structural class known as bistolanes

Preparation of anthracene-based tetraperimidine hexafluorophosphate and selective recognition of chromium(III) ions

• Qing-Xiang Liu,
• Feng Yang,
• Zhi-Xiang Zhao,
• Shao-Cong Yu and
• Yue Ding

Beilstein J. Org. Chem. 2019, 15, 2847–2855, doi:10.3762/bjoc.15.278

• paramagnetic nature of chromium(III) can cause fluorescence quenching of the fluorophore via the enhancement of spin–orbit coupling [30][31][32][33][34][35]. So far, only a few successful examples of fluorescence enhancement sensors for Cr3+ have been reported [36][37][38][39][40]. Thus, developing new and

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• properties, also in terms of electrochemistry. Additionally, the presence of a heavy metal atom induces spin-orbit coupling (SOC) effects to such an extent that intersystem crossing (ISC) processes become thus competitive over other radiationless deactivation pathways owing to relaxation of spin rules. In

Two novel blue phosphorescent host materials containing phenothiazine-5,5-dioxide structure derivatives

• Feng-Ming Xie,
• Qingdong Ou,
• Qiang Zhang,
• Jiang-Kun Zhang,
• Guo-Liang Dai,
• Xin Zhao and
• Huai-Xin Wei

Beilstein J. Org. Chem. 2018, 14, 869–874, doi:10.3762/bjoc.14.73

• simultaneously harvest both the singlet and triplet (75%) excitons through spin-orbit coupling (SOC), and obtain nearly 100% of the internal quantum efficiency (IQE). Thus, most of researchers have focused on phosphorescent organic light-emitting diodes (PhOLEDs) all over the world [7][8]. With the deepening of

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• spin–orbit vibronic coupling, in addition to the small ΔEST. Indeed, a small ΔEST is not sufficient to ensure for a TADF material an efficient RISC which is a vibronically coupled, spin–orbit coupling process with the involvement of the charge transfer state. To remain efficient, the spin–orbit

• coupling should still have a significant value, even if the separation of the HOMO and LUMO wavefunctions remain a requirement to minimize ΔEST. At present, systematic investigations examining the correlation between the spin–orbit coupling and RISC are still scarce [26][27][28][29]. Considering that the

Thiophene-forming one-pot synthesis of three thienyl-bridged oligophenothiazines and their electronic properties

• Dominik Urselmann,
• Konstantin Deilhof,
• Bernhard Mayer and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2016, 12, 2055–2064, doi:10.3762/bjoc.12.194

• state [57][79]. Also the fluorescence quantum yields Φf with 15 to 18% essentially remain constant within this series, although, the increasing number of sulfur-containing heterocycles suggests an increase in fluorescence deactivating spin–orbit coupling. In comparison to the consanguineous

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

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

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

• Sergei V. Chapyshev,
• Denis V. Korchagin,
• Patrik Neuhaus and
• Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

• ES values of trinitrene 18 by only 6% (Table 2). The breakdown of DS and ES into DSS, DSO, ESS, and ESO reveals that the BLYP/EPRII calculations are especially good in estimations of the spin–orbit coupling contributions ESO to the small parameters ES of septet trinitrenes (Table 3). By analogy with

• predissociation states. Despite the lack of symmetry, trinitrene 18 shows a small parameter of ES = −0.0034 cm−1 due to a large positive value of the spin-orbit coupling parameter ES SO (≈0.005 cm−1). In overall, the ZFS parameters of 18 are very close to the ZFS parameters of previously studied C2v symmetric

• direct spin–spin (SS) coupling DSS and spin–orbit coupling (SO) DSO parts of the D tensors were performed by using the McWeeny–Mizuno and Pederson–Khanna approaches, respectively [42]. EPR spectra: (a) simulated spectrum for a mixture of five nitrenes with (i) S = 1, g = 2.003, DT = 1.026 cm−1 and ET = 0

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

• research than has NMR. SCO compounds of iron(III), iron(II), and cobalt(II), which are the 3d transition metal elements most actively studied with EPR, typically reveal characteristic spectra that are sufficiently well resolved in both HS and LS states. There is no spin–orbit coupling in SCO compounds of

• at all accessible. EPR spectroscopy of paramagnetic iron(II) is impossible at higher temperatures, because spin–orbit coupling within the 5T2 state produces short spin-lattice relaxation times. EPR spectra can only be measured at 20 K or lower, at which the relaxation times are longer due to a

• 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

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

• 1,4-diradical. Ring-close of the latter gives an oxetane. The higher selectivity observed for the triplet reaction is rationalized by the optional conformation of the intermediate 2-oxabutane-1,4-diyl for ISC to the singlet diradical, which is preferentially controlled by spin-orbit coupling, thus

Synthesis, electronic properties and self-assembly on Au{111} of thiolated (oligo)phenothiazines

• Adam W. Franz,
• Svetlana Stoycheva,
• Michael Himmelhaus and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2010, 6, No. 72, doi:10.3762/bjoc.6.72

• considerable fluorescence with emission of greenish-blue light and large Stokes shifts (Figure 1, Δ 6400–6600 cm−1). While the absence of fluorescence of monophenothiazines 2a, 2b, and 4 with heavy atom substitution and consequently, increased spin–orbit coupling is not too surprising, the presence of a