Photocatalysis and photochemistry in organic synthesis

• Timothy Noël and
• Bartholomäus Pieber

Beilstein J. Org. Chem. 2025, 21, 1645–1647, doi:10.3762/bjoc.21.128

• ; photochemistry; Soon after its first reported synthesis in 1936 [1], [Ru(bpy)3]Cl2 (bpy = 2,2'-bipyridine) and its derivatives attracted significant attention due to their photophysical properties [2][3][4]. These complexes can efficiently absorb visible light through a metal-to-ligand charge transfer (MLCT

Transition-state aromaticity and its relationship with reactivity in pericyclic reactions

• Israel Fernández

Beilstein J. Org. Chem. 2025, 21, 1613–1626, doi:10.3762/bjoc.21.125

• both deformed reactants, and the orbital interaction (ΔEorb) that accounts for charge transfer and polarization, the stronger interaction computed for the AlCl3-catalyzed does not result from stronger orbital interactions (as traditionally viewed) but exclusively from a less destabilizing Pauli

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

• 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

• demonstrate that precise electronic and geometric design can enable controllable excited-state behavior in orthogonal molecular systems. Keywords: charge transfer; electron transfer; molecular dyad; transient absorption; Introduction Photoinduced electron transfer and charge separation are fundamental

• charge separation and spin–orbit charge-transfer intersystem crossing (SOCT-ISC), leading to unique excited-state behavior. An important aspect of D–A systems is the interplay between the locally excited (LE) and the charge-transfer (CT) states (denoted as diabatic states). A thermal equilibrium between

Synthesis of an aza[5]helicene-incorporated macrocyclic heteroarene via oxidation of an o-phenylene-pyrrole-thiophene icosamer

• Yusuke Matsuo,
• Aoi Nakagawa,
• Shu Seki and
• Takayuki Tanaka

Beilstein J. Org. Chem. 2025, 21, 1561–1567, doi:10.3762/bjoc.21.119

• primarily localized on the aza[5]helicene moieties, while the orbital coefficients are distributed to the bridging thiophene and o-phenylene units in LUMO, indicating a charge-transfer (CT)-like transition. However, further optical characterization of compound 5 was limited due to its poor solubility in

General method for the synthesis of enaminones via photocatalysis

• Paula Pérez-Ramos,
• Raquel G. Soengas and
• Humberto Rodríguez-Solla

Beilstein J. Org. Chem. 2025, 21, 1535–1543, doi:10.3762/bjoc.21.116

• this process, UV–vis studies were carried out. Thus, upon addition of PS1 and 7a to a solution of NiBr2-dmbpy, a charge transfer (CT) band at 688 nm was visible in the UV–vis spectrum (Figure S2, Supporting Information File 1). This observation is consistent with the formation of a six-coordinate

Advances in nitrogen-containing helicenes: synthesis, chiroptical properties, and optoelectronic applications

• Meng Qiu,
• Jing Du,
• Nai-Te Yao,
• Xin-Yue Wang and
• Han-Yuan Gong

Beilstein J. Org. Chem. 2025, 21, 1422–1453, doi:10.3762/bjoc.21.106

• nm) attributed to reversible intramolecular charge transfer [20]. In parallel, several groups explored the functional versatility of heterohelicenes in device-oriented and sensing applications. Crassous’s group synthesized bipyridine-embedded helicenes via the Mallory reaction, enabling coordination

• value of 0.28. Upon coordination with tris(4-bromophenyl)aminium hexachloroantimonate (BAHA), a new absorption band emerged around 900 nm, extending to 1300 nm, indicative of charge-transfer processes. The enantiomers of 13 displayed mirror-image CD signals and showed excellent dispersibility in polar

• | values of approximately 3.0 × 10−3, offering new architectures for CPL-active helicenes [40]. Singh’s group developed fluorophore-conjugated aza[7]helicenes 27a–d, with 27b demonstrating pronounced intramolecular charge transfer (ICT), a high ΦF of 0.71 and an extended fluorescence lifetime (τ) of 15.5

Tautomerism and switching in 7-hydroxy-8-(azophenyl)quinoline and similar compounds

• Lidia Zaharieva,
• Vera Deneva,
• Fadhil S. Kamounah,
• Nikolay Vassilev,
• Ivan Angelov,
• Michael Pittelkow and
• Liudmil Antonov

Beilstein J. Org. Chem. 2025, 21, 1404–1421, doi:10.3762/bjoc.21.105

• knowledge about the relative stabilities of E and KE in 3, it can be stated that electron-acceptor substituents in the phenyl ring shift the equilibrium towards KE, while electron donors do the same in direction of E. In this charge transfer model, the N=N group plays a role of acceptor, stabilized by

• switching if the K tautomer is considered as off-state and the E one as on-state. The predicted spectra of the terminal E and K tautomers of compounds 4 and 7 are compared with those of compound 1 in Figure S13 in Supporting Information File 1. The increased charge-transfer character of compound 4 compared

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

• stabilized and a remarkably high ϕ of 91% can be recorded. This high value is explained by a reduction of the non-radiative pathways by inclusion of the 3I-PTM into the rigid 3I-PTM-H crystal, and a charge transfer (CT) from the high bandgap 3I-PTM-H matrix to the 3I-PTM radical, which is further supported

• bathochromically shifted for mono- and bis-para-nitrile TTM radicals, successive nitrilation increases the ϕ to 4.6% and 7.4% (in cyclohexane) [53]. This improvement is most likely induced by symmetry breaking, resulting in excited states with some charge-transfer character. Moreover, the photostability of such

• the charge transfer state [37]. This substantial conformational change between the ground and excited states could also be responsible for the comparably long fluorescence lifetimes τ, which are in the range of 30–50 ns, which is long even for CT excited states [68]. The steric demand as well as

Study of tribenzo[b,d,f]azepine as donor in D–A photocatalysts

• Katy Medrano-Uribe,
• Jorge Humbrías-Martín and
• Luca Dell’Amico

Beilstein J. Org. Chem. 2025, 21, 935–944, doi:10.3762/bjoc.21.76

• 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

• solvatochromism analysis (see Supporting Information File 1, Figure S4). The structural characteristics of compound 5a conferred the biggest value in terms of Stokes shift parameter, indicating an increased excited state's charge transfer (CT) character (Table 1). Similarly, this behavior was observed

• Stokes shift values for the classical nitrogen donors (c, d, and e) demonstrate a more pronounced CT character with respect to 5a and 5b (Table 1, entry 8), also corroborated by the theoretical descriptor Δr (Table 1, entry 11) that describes the charge transfer character [32][33]. Moreover, this CT

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 a given substrate or a sacrificial species. In the case of the metal-based complexes, the absorption band associated to the metal-to-ligand charge transfer (MLCT) is generally addressed even though other types of excitations like ligand-to-metal charge transfer, ligand- and metal-based excitation

• , where the low-lying excited state often corresponds to the metal-to-ligand charge transfer (MLCT) transition. As the atomic number increases, relativistic effects become more pronounced, leading to the contraction of s and p orbitals while the d and f orbitals expand and become more diffuse. While these

• effects play a role in reducing the energy of the d orbitals and improving their overlap with the ligand orbitals, thereby facilitating electron transfer, the occurrence of metal-to-ligand charge transfer (MLCT) is also strongly influenced by other factors. Specifically, MLCT competes with metal-centered

Synthesis and characterizations of highly luminescent 5-isopropoxybenzo[rst]pentaphene

• Islam S. Marae,
• Jingyun Tan,
• Rengo Yoshioka,
• Zakaria Ziadi,
• Eugene Khaskin,
• Serhii Vasylevskyi,
• Ryota Kabe,
• Xiushang Xu and
• Akimitsu Narita

Beilstein J. Org. Chem. 2025, 21, 270–276, doi:10.3762/bjoc.21.19

• (13%). BPP-dione, when compared to the parent BPP, also displayed improved absorption and emission from the first excited singlet (S1) state with a PLQY of 62% and an intramolecular charge-transfer character. The rod-like nano- to microcrystals as well as longer wires of these BPPs were also revealed

• by scanning electron microscopy. The intriguing optical properties of BPP and its derivatives may lead to their application as fluorophores. Keywords: benzo[rst]pentaphene; intramolecular charge transfer; nanocrystals; photoluminescence; polycyclic aromatic hydrocarbon; Introduction Polycyclic

• singlet (S1) state [21]. Notably, a dimer of BPP, 5,5'-bibenzo[rst]pentaphene (BBPP), exhibited an enhanced PLQY of 44% through intensity borrowing from its bright S2 state as well as intriguing symmetry-breaking charge transfer between two BPP units. Moreover, the substitution of BPP with two electron

Quantifying the ability of the CF₂H group as a hydrogen bond donor

• Matthew E. Paolella,
• Daniel S. Honeycutt,
• Bradley M. Lipka,
• Jacob M. Goldberg and
• Fang Wang

Beilstein J. Org. Chem. 2025, 21, 189–199, doi:10.3762/bjoc.21.11

• oxygen lone pairs (LPs) of Me3PO with the H–CF2Ar antibonding orbital (σ*). Such hyperconjugative interactions indicate the magnitudes of the charge transfer from the LPs to the σ* orbitals and are considered the major contributors to hydrogen bonding [57]. Using this analysis, strong linear correlations

Hydrogen-bonded macrocycle-mediated dimerization for orthogonal supramolecular polymerization

• Wentao Yu,
• Zhiyao Yang,
• Chengkan Yu,
• Xiaowei Li and
• Lihua Yuan

Beilstein J. Org. Chem. 2025, 21, 179–188, doi:10.3762/bjoc.21.10

• adopted a nonplanar conformation, with one aromatic residue protruding out of the macrocyclic skeleton plane. Adopting such a conformation rendered it possible for the π-electron-rich phenyl ring to interact strongly with π-electron-deficient guest molecules G1 by means of charge–transfer interactions and

Recent advances in electrochemical copper catalysis for modern organic synthesis

• Yemin Kim and
• Won Jun Jang

Beilstein J. Org. Chem. 2025, 21, 155–178, doi:10.3762/bjoc.21.9

• (IV) species 113 coordinates with carboxylic acid and undergoes photoinduced ligand-to-metal charge transfer (LMCT) and regeneration of the Ce(III) species to produce a benzylic radical 115. The chiral Cu(II) catalyst 117 reacts with benzylic radical 115 to yield Cu(III) intermediate 118, which then

Synthesis, characterization, and photophysical properties of novel 9‑phenyl-9-phosphafluorene oxide derivatives

• Shuxian Qiu,
• Duan Dong,
• Jiahui Li,
• Huiting Wen,
• Jinpeng Li,
• Yu Yang,
• Shengxian Zhai and
• Xingyuan Gao

Beilstein J. Org. Chem. 2024, 20, 3299–3305, doi:10.3762/bjoc.20.274

• recent years, and they are mostly based on purely organic electron donor−electron acceptor (D−A) or D−A−D systems with significant intramolecular charge transfer interactions for frontier molecular orbital separation [28][29][30]. Due to the electron-accepting properties, PhFlOP can clearly act as an

• * transitions associated with the conjugated system, while the band at around 340 nm is attributed to intramolecular charge transfer processes. The low-energy absorption bands of 7-t-Bu (λmax = 345 nm, Table 2) and 7-Cz-2 (λmax = 342 nm) are slightly redshifted compared to 7-H (λmax = 338 nm), and larger

• charge transfer, as indicated by the λmax value of 342 nm. In addition, the effect of solvent polarity on the UV−vis absorption was studied with 7-H (Figure 2b). The spectra show that there is no significant difference in the absorption bands in different solvents, indicating that the polar environment

Tunable full-color dual-state (solution and solid) emission of push–pull molecules containing the 1-pyrindane moiety

• Anastasia I. Ershova,
• Sergey V. Fedoseev,
• Konstantin V. Lipin,
• Mikhail Yu. Ievlev,
• Oleg E. Nasakin and
• Oleg V. Ershov

Beilstein J. Org. Chem. 2024, 20, 3016–3025, doi:10.3762/bjoc.20.251

• and acceptor groups arranged in a specific sequence, such as in D–π–A chromophores. This creates the conditions for efficient intramolecular charge transfer (ICT), which plays a key role in the DSE phenomenon. Also, additional substituents can affect the geometry and conformation of the molecule

Synthesis of benzo[f]quinazoline-1,3(2H,4H)-diones

• Ruben Manuel Figueira de Abreu,
• Peter Ehlers and
• Peter Langer

Beilstein J. Org. Chem. 2024, 20, 2708–2719, doi:10.3762/bjoc.20.228

• coefficients and bathochromically shifted absorption bands which might be a result of a certain intramolecular charge transfer between the donating N,N-dimethylamino group and the electron-deficient uracil moiety. Similar effects are observed for the emission spectra. The emission maxima of N,N-dimethylamino

Photoluminescence color-tuning with polymer-dispersed fluorescent films containing two fluorinated diphenylacetylene-type fluorophores

• Kazuki Kobayashi,
• Shigeyuki Yamada,
• Motohiro Yasui and
• Tsutomu Konno

Beilstein J. Org. Chem. 2024, 20, 2682–2690, doi:10.3762/bjoc.20.225

• as electron-donating groups was shown to promote intramolecular charge transfer (ICT) and shifted the PL wavelength to longer wavelengths, resulting in yellow or orange fluorescence in the solid state [21][22]. In addition, cross-linking between the amino group and attached benzene ring effectively

• non-radiative deactivation process. On the other hand, the other derivatives, namely 1b and 1d–f, showed increased ΦPL values in the PMMA films compared with those in the crystalline state, presumably due to a suppression of the formation of non-fluorescent twisted intramolecular charge transfer (TICT

A review of recent advances in electrochemical and photoelectrochemical late-stage functionalization classified by anodic oxidation, cathodic reduction, and paired electrolysis

• Nian Li,
• Ruzal Sitdikov,
• Ajit Prabhakar Kale,
• Joost Steverlynck,
• Bo Li and
• Magnus Rueping

Beilstein J. Org. Chem. 2024, 20, 2500–2566, doi:10.3762/bjoc.20.214

Photoredox-catalyzed intramolecular nucleophilic amidation of alkenes with β-lactams

• Valentina Giraldi,
• Giandomenico Magagnano,
• Daria Giacomini,
• Pier Giorgio Cozzi and
• Andrea Gualandi

Beilstein J. Org. Chem. 2024, 20, 2461–2468, doi:10.3762/bjoc.20.210

• , enhances charge transfer by stabilizing the mesityl moiety. Conversely, the introduction of tert-butyl groups increases the life time of the excited state [52][53][54][55][56]. As a consequence, the PC IV is a strong oxidant in the excited state and displays unique oxidizing properties (E1/2[*PC+/PC

Synthesis, electrochemical properties, and antioxidant activity of sterically hindered catechols with 1,3,4-oxadiazole, 1,2,4-triazole, thiazole or pyridine fragments

• Daria A. Burmistrova,
• Andrey Galustyan,
• Nadezhda P. Pomortseva,
• Kristina D. Pashaeva,
• Maxim V. Arsenyev,
• Oleg P. Demidov,
• Mikhail A. Kiskin,
• Andrey I. Poddel’sky,
• Nadezhda T. Berberova and
• Ivan V. Smolyaninov

Beilstein J. Org. Chem. 2024, 20, 2378–2391, doi:10.3762/bjoc.20.202

• changes. This is confirmed by the appearance of an absorption maximum in the UV–visible spectrum at λ = 490 nm, which is characteristic of thiolated o-benzoquinones. This absorption band corresponds to intramolecular charge transfer between the thioether group and the o-benzoquinone fragment [36][62][63

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• binding constants, leading to higher equilibrium concentrations of the electrophilically activated substrates. The H-bonds also increased the electrostatic potential on the σ-hole of the I atom, resulting in higher charge transfer values from the ligated species. Although no comparison was made with

Benzylic C(sp³)–H fluorination

• Alexander P. Atkins,
• Alice C. Dean and
• Alastair J. J. Lennox

Beilstein J. Org. Chem. 2024, 20, 1527–1547, doi:10.3762/bjoc.20.137

• ]. The authors proposed the formation of a charge-transfer complex between the heterocycle and Selectfluor, capable of promoting an ET/PT or PCET pathway to furnish the carbon-centred radical at the heterobenzylic position. Fluorine-atom-transfer with Selectfluor then afforded the desired product

• co-workers reported a benzylic fluorination of phenylacetic acids via a charge-transfer complex (Figure 21) [62]. The authors proposed that the combination of Selectfluor and DMAP spontaneously produced the Selectfluor radical dication (TEDA2+•), which served as a radical chain carrier capable of

• with Selectfluor. Benzylic fluorination using triethylborane as a radical chain initiator. Heterobenzylic C(sp3)–H radical fluorination with Selectfluor. Benzylic fluorination of phenylacetic acids via a charge-transfer complex. NMR yields in parentheses. Oxidative radical photochemical benzylic C(sp3

Synthesis of indano[60]fullerene thioketone and its application in organic solar cells

• Yong-Chang Zhai,
• Shimon Oiwa,
• Shinobu Aoyagi,
• Shohei Ohno,
• Tsubasa Mikie,
• Jun-Zhuo Wang,
• Hirofumi Amada,
• Koki Yamanaka,
• Kazuhira Miwa,
• Naoyuki Imai,
• Takeshi Igarashi,
• Itaru Osaka and
• Yutaka Matsuo

Beilstein J. Org. Chem. 2024, 20, 1270–1277, doi:10.3762/bjoc.20.109

• assigned to the charge transfer band of the C=S bond in t-Bu-FIDS, which was stronger than that of the C=O bond in t-Bu-FIDO [30]. Interestingly, the maximum absorption band observed in t-Bu-FIDO at 432 nm, which is a characteristic feature of 58π-fullerene derivatives with a 1,2-addition pattern, was

Stability trends in carbocation intermediates stemming from germacrene A and hedycaryol

• Naziha Tarannam,
• Prashant Kumar Gupta,
• Shani Zev and
• Dan Thomas Major

Beilstein J. Org. Chem. 2024, 20, 1189–1197, doi:10.3762/bjoc.20.101

• . However, the there was no significant change in the trend in energies for both series of carbocations (Figure S5, Supporting Information File 1). NBO analysis The charge transfer between filled Lewis-type NBOs and empty non-Lewis-type NBOs can provide information regarding the relative stabilities of the

• stability trend between F-OH and H-OH. The second order perturbation energy (E(2)) value for O(LP) to C(LV) (LP = lone pair, LV = lone valence orbitals) charge transfer in F-OH is 2.9 kcal/mol, whereas there is no such charge transfer in H-OH. This explains the relative stability of F-OH compared to H-OH

• . Additionally, we carried out NBO analysis for other hedycaryol cations, and due to large bond distances between C+···OH, no such charge transfer is observed, i.e., E(2) = 0. In these cases, the interaction is likely of a classical electrostatic nature. Next, to better understand the influence of carbocation