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

• benzene (Figure 3). This indicates that in addition to structure I, which is traditionally used to depict indigo, intraionic resonance structures II and III with single C–O bonds and double C=N bonds make a pronounced contribution in the ground state of indigo (Figure 3) [13][14]. In the excited state

• hypsochromic shifts of the absorption maxima [24]. These effects can be easily explained considering the direction of the charge transfer in the H-chromophore of indigo upon excitation. Thus, in the excited state, the electron density shifts from the N towards the O atom (Figure 4). Therefore, an increase in

• interest and, therefore, has been investigated comprehensively. To understand the photochemical and photophysical properties of indigo, a great number of theoretical and experimental studies [25][26][27][28][29][30][31][32][33][34][35] have been performed so far, which allowed to characterize excited state

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

• of 63 in toluene revealed that the lowest singlet excited state (S1) decays mono-exponentially to the ground state (S0) within approximately 1 ps, suggesting the existence of an accessible CI between S1 and S0. In the S1 minimum conformation of 63, the PCBD moiety adopted a planar orientation

• room-temperature solution (dichloromethane) and as a frozen matrix at 77 K [123]. This is in contrast with the typical homoleptic phenanthroline-based CuI complexes renowned for their emissions from a triplet metal-to-ligand charge transfer excited state. The absence of luminescence may be attributed

• the plausible energy transfer from the local charge-separated (CS) state of the push–pull chromophore (namely N,N-diethylanilino (DEA)•+–TCBD•−) to the singlet excited state of C60 (1C60*). In transient absorption spectral measurements conducted via the femtosecond laser-flash photolysis of compound

Photoinduced in situ generation of DNA-targeting ligands: DNA-binding and DNA-photodamaging properties of benzo[c]quinolizinium ions

• Julika Schlosser,
• Olga Fedorova,
• Yuri Fedorov and
• Heiko Ihmels

Beilstein J. Org. Chem. 2024, 20, 101–117, doi:10.3762/bjoc.20.11

• by the reaction with C-radicals 4 and 5 to give peroxides such as 6 (Scheme 4), by cycloaddition of 1O2 to alkene and diene units, or by deactivation of the excited state in a triplet-triplet annihilation [90], all of which leading to a reduced photocleavage efficiency. However, with much longer

Electron-beam-promoted fullerene dimerization in nanotubes: insights from DFT computations

• Laura Abella,
• Gerard Novell-Leruth,
• Josep M. Ricart,
• Josep M. Poblet and
• Antonio Rodríguez-Fortea

Beilstein J. Org. Chem. 2024, 20, 92–100, doi:10.3762/bjoc.20.10

• analyzed the interaction between C60 and the nanotube within the peapod. Next, we have found that some dimeric C60–C60 fullerene structures inside the carbon nanotube are thermodynamically favorable. Experiments indicate that, besides C60 sensitization via a singlet excited state, the [2 + 2] cycloaddition

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• : if photoinduced cleavage occurs we would expect the scope of RX cleavage to be more-or-less limited by the reducing strength of D• (E(D+/D•) = ca. −2.4 V for both species used here), whereas the singlet excited state of the dimer, D2*, should be more reducing, allowing more challenging substrates to

• longer-time spectra with Cyc-DMBI• having a blue-shifted absorption relative to N-DMBI•, consistent with the observed features arising from the monomeric radicals. Intersystem crossing (ISC) from the singlet to triplet excited state is also a possibility and TD-DFT calculations suggest that the dimer T1

Thienothiophene-based organic light-emitting diode: synthesis, photophysical properties and application

• Recep Isci and
• Turan Ozturk

Beilstein J. Org. Chem. 2023, 19, 1849–1857, doi:10.3762/bjoc.19.137

• (excitation at λmax), respectively, leading to a mega Stokes shift (>100 nm) of 109 nm, which could be explained to be due to a fast relaxation from the excited state to the ground state as a result of a powerful intramolecular energy transfer between the TPA and boron groups through the thieno[3,2-b

Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• − (−1.67 V) is plausible, albeit the difference is not high. Estimation of the redox potentials of the excited state of PS (Eox* and Ered*) was done assuming that the energy difference (E00) between the energies of the excited and ground states, both at their zero levels, is the same as the emission

• accumulation of the reduced PS− species. We propose the following mechanism (Scheme 1). The PS absorbs a photon (420 nm) and in its excited state is quenched by BIH, which is deprotonated by the base (TEA) and forms a radical (BI·). Since this radical is highly reducing, it can happen that this species can

Charge carrier transport in perylene-based and pyrene-based columnar liquid crystals

• Alessandro L. Alves,
• Simone V. Bernardino,
• Carlos H. Stadtlober,
• Edivandro Girotto,
• Giliandro Farias,
• Rodney M. do Nascimento,
• Sergio F. Curcio,
• Thiago Cazati,
• Marta E. R. Dotto,
• Juliana Eccher,
• Leonardo N. Furini,
• Hugo Gallardo,
• Harald Bock and
• Ivan H. Bechtold

Beilstein J. Org. Chem. 2023, 19, 1755–1765, doi:10.3762/bjoc.19.128

• at the Colhex–Iso transition. The reduction of PL at the Cr–Colrect transition also reflects stronger molecular π-stacking of 2 in the Colrect phase compared to the crystalline state. The excited state lifetimes of 1 and 2 in chloroform solutions and spin-coated films, both excited at 401 nm, are

• within B3LYP/def-TZVP(-f) level of theory and their frontier orbitals (b). Molecular structures of compounds 1 and 2. Characteristics of 1 and 2 extracted from [17] and [18], respectively. Excited state lifetimes and relative amplitudes of 1 and 2 in chloroform solutions and spin-coated films at room

Quinoxaline derivatives as attractive electron-transporting materials

• Zeeshan Abid,
• Liaqat Ali,
• Sughra Gulzar,
• Faiza Wahad,
• Raja Shahid Ashraf and
• Christian B. Nielsen

Beilstein J. Org. Chem. 2023, 19, 1694–1712, doi:10.3762/bjoc.19.124

• high-performance red/orange TADF emitters (Qx65). The team successfully transitioned the emission type from local excited-state to charge-transfer state by carefully tuning the molecular structure and energy levels, leading to efficient TADF. The Qx65a-based orange TADF OLEDs exhibit a maximum EQE of

A deep-red fluorophore based on naphthothiadiazole as emitter with hybridized local and charge transfer and ambipolar transporting properties for electroluminescent devices

• Suangsiri Arunlimsawat,
• Patteera Funchien,
• Pongsakorn Chasing,
• Atthapon Saenubol,
• Taweesak Sudyoadsuk and
• Vinich Promarak

Beilstein J. Org. Chem. 2023, 19, 1664–1676, doi:10.3762/bjoc.19.122

• transition orbitals [31][32][33]. In these molecules, the lowest excited state still shows moderate or large oscillator strengths or a mixing of two excited-state components, locally excited (LE) state and CT excited state. This kind of excited state was later known as a hybridized local and charge transfer

• . To further figure out excited-state properties of TPECNz, the natural transition orbitals (NTOs) of singlet (S) and triplet (T) excited states were executed based on time-dependent (TD)-DFT calculations at the CAM-B3LYP/6-31G(d) level of theory. As shown in Figure 1b, the hole and particle of TPECNz

• maxima shifting towards longer wavelengths with increasing solvent polarities. Particularly, the maximum PL peaks in low polar solvents showed little shifts because of the LE character, whereas red shifts of the PL maxima apparently occurred in higher polar solvents due to CT excited state; therefore

A series of perylene diimide cathode interlayer materials for green solvent processing in conventional organic photovoltaics

• Kathryn M. Wolfe,
• Shahidul Alam,
• Eva German,
• Fahad N. Alduayji,
• Maryam Alqurashi,
• Frédéric Laquai and
• Gregory C. Welch

Beilstein J. Org. Chem. 2023, 19, 1620–1629, doi:10.3762/bjoc.19.119

• stabilization of the first excited state in relation to the stabilization of the ground state, which is observed in other PDIs when installing the electron-withdrawing nitrile group on the polycyclic aromatic core [27][28]. The molar extinction coefficients (ε) of all compounds in ethyl acetate were determined

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

• (Scheme 12B). Boydston and co-workers [91], systematically studied various pyrylium and thiopyrylium PCs (Scheme 13). It is necessary for these PCs having a high excited-state redox potential to oxidize the enol ether initiators. A range of enol ether initiators that has been successfully applied in metal

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

• aerated MCH solution. The reduction in quantum yield on exposure to oxygen is due to quenching of the triplet excited states indicating a TADF luminescence mechanism. PLQY in Zeonex films is 39% in air, which is lower than the PLQY of 87% reported for 4CzIPN [17]. The two-component excited state lifetime

• with prompt and delayed fluorescence is characteristic for the TADF-type luminescence [1]. The excited state lifetime of 4BGIPN has a biexponential decay with a prompt fluorescence τp = 13 ns and a delayed fluorescence τd = 1655 ns components in MCH solution. Zeonex films of 4BGIPN exhibit a similar

• spectra showing both broad and resolved components, thus supporting the assignments of the 3CT and 3LE(donor) excited states. The excited state lifetime of the broad CT component has a multiexponential decay with averaged lifetimes of 0.7 ms in MCH glass and up to 212 ms in Zeonex films, which we assigned

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• incorporated at the porphyrin periphery and different metal ions in the porphyrin core to modulate ground-state and excited-state characteristics of easily accessible meso-tetraarylporphyrins. Some of these π-extended tetrapyrrolic macrocycles have emerged as potential candidates in photodynamic therapy and

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• dioxide [16]. Excited-state PCET, which is of particular interest for interactions between hydrogen atom or hydride-donating sacrificial donors, has recently been reviewed in detail by Dempsey and co-workers [17]. To select an effective sacrificial electron donor, at least four properties need to be

• and the ground-state redox potentials of the photosensitizer [18][20], or simulated [21][22]. There are actually methods for directly measuring the excited-state redox potentials of a photosensitizer, such as photomodulated voltammetry but they often require a more elaborate experimental setup [23

• excited state. Hence, Stern–Volmer plots derived from quenching measurements and photosensitizer excited-state lifetimes measured by transient spectroscopy are crucial to understanding and optimizing the system as a whole [18]. Recently, Kientz et al. demonstrated that the dark regeneration of oxidatively

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• initial halogen-bonded complex 42, whose irradiation with blue light was proposed to produce acyclic excited state 43*, where possible bond rotation could account for the convergence of alkene isomers into a single product (40c). Radical coupling would then lead to the typical iodocyclobutane intermediate

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• UV region, side reactions and selectivity issues arise upon direct excitation of organic molecules. In recent years, two conceptually distinct but mechanistically related strategies have emerged that enable access to excited state catalysts wielding i) higher redox power than standard monophotonic

• radical anion or radical cation. As a semi-stable, higher energy ground-state entity, this can accumulate in sufficient concentration under the reaction conditions to absorb another photon and thereby generate a super-reducing or super-oxidizing excited state (Figure 2 left). In addition to ‘radical ion

• generation of super-reductants (*E1/2 > −2.0 V vs SCE) that accumulate the energy of multiple photons. Case studies will now be presented. Hereafter, while we quote the excited state redox potentials from the report in question, it should be noted that these are estimates associated with uncertainties

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

• attributed to a localized singlet excited state of 1NI* by comparison with the reported spectra of NI [58]. Within 155 fs, the system evolves to the second spectrum (blue line), for which both a sharp peak centered at 404 nm and a broad band in the range 600–750 nm were observed, which is identified as a

• Information File 1) and we did not obtain the EADS, CS, CR, and other time constants exactly. In ACN, the first transient species (black line in Figure 7d) can be recognized as a localized singlet excited state of 1NI* by comparison with the spectra reported for the parent NI [58]. Within about 178 fs, the

• nm) [39], while this positive absorption band is closer to that of NI−•, which was determined at ca. 430 nm [58]. Therefore, this absorption band is assigned to the NI radical anion. The excited state absorption (ESA) band centered at 460 nm is attributed to the 3NI state. Moreover, another positive

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• visible-light irradiation of the photoredox catalyst [Ir(dF(CF3)ppy)2(dtbpy)]PF6 to access the excited state *[Ir(dF(CF3)ppy)2(dtbpy)]PF6, which can trigger SET oxidation of 8. Rapid decarboxylation leads to α-amino radical V (and the reduced photocatalyst), which is intercepted by the pendant double bond

Synthesis of substituted 8H-benzo[h]pyrano[2,3-f]quinazolin-8-ones via photochemical 6π-electrocyclization of pyrimidines containing an allomaltol fragment

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Mikhail E. Minyaev and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2023, 19, 778–788, doi:10.3762/bjoc.19.58

• proposed. Keywords: allomaltol; dihydrobenzo[h]pyrano[2,3-f]quinazolines; 6π-electrocyclization; photocyclization; pyrimidines; Introduction Photochemical processes involve absorption of UV light leading to the generation of molecules in the excited state and subsequent chemical transformations [1][2

• pyranone ring leading to the formation of α-hydroxy-1,2-diketones. This phototransformation is initiated by an excited state intramolecular proton transfer (ESIPT) process. In most cases the resulting α-hydroxy-1,2-diketones are unstable and their further reactions open access to various original products

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

• Semyon V. Tsybulin,
• Ekaterina A. Filatova,
• Alexander F. Pozharskii,
• Valery A. Ozeryanskii and
• Anna V. Gulevskaya

Beilstein J. Org. Chem. 2023, 19, 674–686, doi:10.3762/bjoc.19.49

• monomers 6d and 6e are typical rod-like D–π–A systems. In such molecules, a photon absorption induces a shift from a D–π–A ground state to a D+–π–A− excited state. It is obvious that the actual electron transfer depends on all three components of the push–pull molecule. However, the study on the through

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• protocol in a 42% yield by using CuI and DIPEA in THF at room temperature (Scheme 11). Their photophysical studies revealed that the fluorescence of zinc porphyrin 58 is strongly quenched due to the copper-corrole 59 in the dyad 60. Also, an efficient excited-state interaction was found between zinc

• metal exchange reaction of porphyrin 90 with excess CoCl2·6H2O in an acetone/THF (1:1) mixture. The results of the photophysical investigations demonstrated that these dyads exhibit adequate electronic interactions between the sensitizer and catalyst in the excited state. In this study, NiO films were

• recombination dynamics is primarily related to the electronic properties of the conjugates, such as electron affinity, orbital energies, and excited state energies. In another report, Nikolaou et al. [51] described the synthesis of two novel porphyrin dyads 107b and 108b containing terminal carboxylic acid

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

• S33a, Supporting Information File 1), sharp excited state absorption (ESA) bands centered at 360 and 470 nm were observed in HEX, and a 63 μs lifetime was determined. For NI-PTZ, positive absorption bands centered at 360, 470, 390, and 520 nm were observed upon pulsed laser in HEX (Figure 8a). This

• , significantly below the estimated value of 2.88 eV for the CT state (approximated from the CT absorption band, Figure 1). The longer lifetime of NI-PTZ-O infers that for NI-PTZ, CT state sharing similar energy with 3LE may drain the excited state and shorten the triplet state lifetime. The ns-TA spectra of NI

• excited state potential energy surfaces leads to different scenarios for the studied compounds as shown in Table S2: a 3CT character is found for the lowest triplet excited state (T1) of NI-PTZ and a considerable 3CT character is found for the T1 of NI-N-PTZ and NI-PTZ2. Conversely, for NI-PhMe2-PTZ, NI

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

• same at 0.27 eV. The nature of S1 and T1 resemble to those of its parent DiKTa and so this compound is likely to behave as a MR-TADF emitter. The nature of the S2 state is n–π* in DiKTa-OMe. The excited state picture of DiKTa-DPA-OMe is different to that of other reported D–A-type systems containing

• = 3.35 eV, T1 = 3.09 eV) and DMAC-DiKTa (S1 = 3.43 eV, T1 = 3.17 eV) [28]. We also calculated the charge transfer character of each excited state, focussing on the distance of charge transfer (DCT). When considering the S1 excited state, there is an increase in CT character moving from DiKTa, DiKTa-OMe

• , in line with its decreased oscillator strength (vide supra). According to the calculations (vide supra), the S1 excited state is also SRCT, but with larger long-range charge transfer (LRCT) content. Owing to the relative flexibility around the DPA donor unit, the Stokes shift is larger at 75 nm (2761

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

• donor size and strength: the emitter BPy-pTC with tert-butylcarbazole (TC) as the donor and BPy-p3C with bulky tricarbazole (3C) as the donor unit. Both BPy-pTC and BPy-p3C exhibited prominent emission with TADF properties in solution and in the solid phase. The stronger excited-state charge transfer

• developed mainly by focusing on photophysical processes, such as photoinduced electron transfer (PET), excited-state intramolecular proton transfer (ESIPT), fluorescence resonance energy transfer (FRET), etc. [21][22][24][25]. Several literature reports have also demonstrated the switching of fluorescence

• molecular design and donor size in tuning ΔEST in an aggregated state and in fluorescence switching by acid–base addition. Results and Discussion Design and synthesis Several BPy derivatives have been reported to lower ΔEST in D–A pairs to promote spin upconversion from the low-lying triplet excited state