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

• . A study confirmed that with appropriate molecular design, the π-conjugation relationship between the donor and acceptor moieties in TCBDs and DCNQs can be retained despite their non-planarity [14]. Diederich et al. synthesized a plethora of push–pull chromophores by employing anilino groups as EDGs

Biphenylene-containing polycyclic conjugated compounds

• Cagatay Dengiz

Beilstein J. Org. Chem. 2023, 19, 1895–1911, doi:10.3762/bjoc.19.141

• for use in cutting-edge technologies. In particular, acenes, a subgroup of polycyclic aromatic compounds, are sought-after synthetic targets due to their remarkable optoelectronic properties which stem from their π-conjugation and planar structure. Despite all these promising characteristics, acenes

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

• study raises a concern regarding the performance of dyes with tert-butyl substituted DPQ acceptors, either containing benzene (Qx74) or thiophene (Qx75) as a π-conjugation linker and their benzotriazole analogue. While the incorporation of the Qx enhances the interaction between the donor and acceptor

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

• extended π-conjugation lengths which eventually favor the undesired formation of poorly emissive molecular aggregates must be overcome. Alternatively, donor–acceptor (D–A)-type organic fluorophores have been introduced and successfully exploited for the development of fluorophores with DR/NIR emissions

• without lengthy extension of their π-conjugation systems due to a broadening of both the valence and the conduction bands and a consequent narrowing of the energy gap [22][23][24][25]. The D–A characters also offer a tunability of optoelectronic properties such as energy levels, optical bandgap (Eg), and

• controlling the CT component in the HLCT state [54]. A suitable twisted angle (40–80°) allocated an appropriate tuning between the complete π‐conjugation and the pure CT transition character to form the HLCT state. As depicted in Figure 1a, the optimized structure of TPECNz revealed a twisted molecular

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

• materials [74]. In 2000, they received the Nobel Prize in Chemistry. Typical conductive polymer structures have π-conjugation (Scheme 9A) [75]. They can be synthesized by various methods such as electrochemical and chemical methods. Oxidative polymerization and chain-growth polymerization are also good ways

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

• benzoguanidine donor and compare it with the benchmark carbazole-based material (4CzIPN). Extended π-conjugation in 4BGIPN material results in yellow-green luminescence at 512 nm with a fast radiative rate of 5.5 × 10−5 s−1 and a photoluminescence quantum yield of 46% in methylcyclohexane solution. Such a

•  1. Benzoguanidine has an extended π-conjugation compared with carbazole and is more nitrogen-rich (three N-atoms vs one in carbazole). Thompson et al. recently reported a series of carbene–metal–amide (CMA) (metal = Cu, Ag, Au) emitters employing a benzoguanidine ligand [10]. The extended π

• , the LUMO isosurface in Figure 6, vide infra). Therefore, the higher reduction potential for 4BGIPN suggests that the benzonitrile core has a lower electron density, which is likely associated with extended π-conjugation and two additional electron withdrawing aza-type nitrogen atoms in the

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

• spectroscopy. The preliminary photophysical results revealed a significant red-shift in their absorption and emission spectra as compared to the meso-tetrakis(4-methylphenyl)porphyrins due to the extended π-conjugation. Keywords: bathochromic shift; benzo[f]chromeno[2,3-h]quinoxalinoporphyrins; catalysis

• other materials applications [4][5][6][7]. Among the previously synthesized synthetically modified porphyrinoids, β,β’-fused meso-tetraphenylporphyrins have gained a considerable importance because of their red-shifted absorption and emission due to the extended π-conjugation. In particular, β,β’-fused

• ; Zn-TMPP, Soret band at 425 nm) due to the extended π-conjugation after the fusion of the benzo[f]chromeno[2,3-h]quinoxaline moiety at the β-pyrrolic positions of the porphyrin macrocycle. In the fluorescence spectra, free-base benzo[f]chromeno[2,3-h]quinoxalinoporphyrins 9–13 showed emission bands at

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

• for this kind of emitters is an electron donor–acceptor dyad, and the molecular geometry is usually orthogonal, i.e., the planes of the π-conjugation systems of the electron donor and acceptor are perpendicular to each other. As a result, the highest occupied molecular orbital (HOMO) and lowest

• /Fc+) [49]. By directly connecting the NI and PTZ unit through a C–N single bond, the π-conjugation plane of the NI and PTZ units adopts a perpendicular geometry which is beneficial for SOCT-ICS (Scheme 1). Previously we observed TADF with an analogue of NI-PTZ-C5 (the difference of the molecular

• N atom of the PTZ unit [59][60]. Further, the NI-PTZ-F-O and NI-PTZ-Ph-O compounds adopt an orthogonal geometry, and the N atom in the PTZ unit is not in π-conjugation with NI moiety due to a conformational restriction [55]. Thus, it is not the ordinary intramolecular charge transfer (ICT) state

A fluorescent probe for detection of Hg²⁺ ions constructed by tetramethyl cucurbit[6]uril and 1,2-bis(4-pyridyl)ethene

• Xiaoqian Chen,
• Naqin Yang,
• Yue Ma,
• Xinan Yang and
• Peihua Ma

Beilstein J. Org. Chem. 2023, 19, 864–872, doi:10.3762/bjoc.19.63

• , which provides convenience for studying the host–guest chemistry of TMeQ[6] and constructing fluorescent probes in aqueous solution [37][38]. There is a π–π conjugation effect between the carbon–carbon double bond and the pyridine ring in 1,2-bis(4-pyridyl)ethene (G), which determines its ultraviolet

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

• the extent of π-conjugation and the efficiency of particular donor–acceptor conjugation path in these new compounds. X-ray structures and absorption spectra of doubly protonated tetrafluoroborate salts of the oligomers are also discussed. Keywords: 1,8-bis(dimethylamino)naphthalene; cross-conjugated

• which although conjugated to a third unsaturated center are not conjugated to each other” [16]. It is easy to see that there are two π-conjugation paths in molecules 5: a donor–acceptor conjugation path (Figure 2, highlighted in blue) and the π-conjugation of naphthalene rings through a butadiyne linker

• , Figure 9). However, unlike salts 11a,c,d, methoxy derivative 11b demonstrates end absorption up to 415 nm and, thus, the lowest optical band gap in the series (2.99 eV). Evidently, protonation of 5b gives rise to a push–pull D–π–A–π–A–π–D system, in which the π-conjugation between the donating

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

• ). For NI-Ph-PTZ, the NI•− absorption bands in the 350–600 nm range are less resolved than for NI-PTZ. This likely comes from the effect of the π-conjugation of the phenyl ring with the NI moiety in NI-Ph-PTZ. In contrast, the PTZ•+ absorption band of NI-Ph-PTZ resembles the one of NI-PTZ, indicating

Introducing a new 7-ring fused diindenone-dithieno[3,2-b:2',3'-d]thiophene unit as a promising component for organic semiconductor materials

• Valentin H. K. Fell,
• Joseph Cameron,
• Alexander L. Kanibolotsky,
• Eman J. Hussien and
• Peter J. Skabara

Beilstein J. Org. Chem. 2022, 18, 944–955, doi:10.3762/bjoc.18.94

• , which extends the degree of π-conjugation [1]. In this way, the HOMO–LUMO gap can be narrowed [2]. Low HOMO–LUMO gaps are desirable for organic solar cells as the maximum photoflux density of the sun is at ca. 700 nm, corresponding to 1.77 eV [3]. However, fused systems have the drawback of being prone

Thiophene/selenophene-based S-shaped double helicenes: regioselective synthesis and structures

• Mengjie Wang,
• Lanping Dang,
• Wan Xu,
• Zhiying Ma,
• Liuliu Shao,
• Guangxia Wang,
• Chunli Li and
• Hua Wang

Beilstein J. Org. Chem. 2022, 18, 809–817, doi:10.3762/bjoc.18.81

• ; selenophene; thiophene; Introduction Given their esthetically pleasing helical structures, inherent helical chirality, and extended π-conjugation, helicenes have attracted extensive research attention. Helicenes are generally divided into carbohelicenes and heterohelicenes. The rapid development of

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

• -type compound (λPL = 521 nm for POZ-DBPHZ) in cyclohexane. These data indicate that the effective length of π-conjugation is not affected by the number of donors, probably due to the right D–A dihedral angle for both compounds in the ground state. In contrary, the slight blue-shift of the PL spectra of

Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

• Yelong Lei and
• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 70–76, doi:10.3762/bjoc.18.6

• p–π conjugation. This stabilization is not possible with alkyl groups, explaining why 2-alkylaziridines did not generate the corresponding products. Intermediates C undergo an intramolecular nucleophilic attack to yield ethyl (oxazolidin-2-ylidene)alkanoates D, which further isomerize to more stable

Synthesis and investigation on optical and electrochemical properties of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridines

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 2450–2461, doi:10.3762/bjoc.17.162

• 3,5-dibromoanthranilic acid (1) [61] with cyclohexanone in POCl3 through an adapted reported procedure [62] (Scheme 1). With precursor 2 in hand, we intended to expand the π-conjugation of the tetrahydroacridine core by adding diversely substituted aryl groups using the Suzuki–Miyaura cross-coupling

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• stability as well. The absorption maxima displayed by polymer 18 (409 nm) in dichloromethane solution was comparable to the above-discussed 1,3-polyazulene 5 (404 nm), however, the long alkyl substituents present at the 6-position of 19 and 20 were disrupting the effective π-conjugation along the polymer

Cationic oligonucleotide derivatives and conjugates: A favorable approach for enhanced DNA and RNA targeting oligonucleotides

• Mathias B. Danielsen and
• Jesper Wengel

Beilstein J. Org. Chem. 2021, 17, 1828–1848, doi:10.3762/bjoc.17.125

• better hybridization properties than LNA-thymidine; however, only modification 22 gave significant increases in Tm relative to modification 19 used as control. This finding was ascribed to both the extended π-conjugation of the alkynyl-functionalized nucleobase and stabilizing electrostatic interactions

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli,
• Noureddine Chaaben,
• Kamel Alimi,
• Stefan Jopp and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 1629–1640, doi:10.3762/bjoc.17.115

• catalysis. With this precursor in hand, we intended to expand the π-conjugation by introducing two arylethynyl groups by Sonogashira reactions [66][67][68][69]. For the optimization, we studied the reaction of 2 with phenylacetylene (3a) and we obtained the desired product 4a in up to 72% as best yield

• )-9-chloro-5,6,7,8-tetrahydroacridine derivatives via a double Sonogashira cross-coupling method. The arylethynyl groups expand the π-conjugation of the tetrahydroacridine core. The substituents located at the aryl group influenced the photophysical properties of the prepared molecules. In particular

Recent advances in the application of isoindigo derivatives in materials chemistry

• Andrei V. Bogdanov and
• Vladimir F. Mironov

Beilstein J. Org. Chem. 2021, 17, 1533–1564, doi:10.3762/bjoc.17.111

• ][103][104][105]. Thus, two polymers 56 were obtained in which isoindigo fragments are condensed on the indacenedione scaffold [102]. Despite the presence of an extended π-conjugation system, which determines the ambipolar properties of a transistor based on these polymers, the charge mobility values

• polymers for OFETs. Isoindigoid homopolymers with differing rigidity. Isoindigo-based materials with extended π-conjugation. Poly(isoindigothiophene) compounds as sensors for ammonia. Sensor devices based on poly(isoindigoaryl) compounds. Isoindigo polymers for miscellaneous applications. Mono-, rod-like

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• electron-accepting group coupled with various donors connected via a π-conjugation bridge [31][32][33]. Such dyes offer good NLO characteristics when compared to Disperse Red 1 as well as remarkable thermal stabilities with dissociation temperatures up to 300 °C [31][32]. Schiff bases containing an

• organic NLO chromophore is related to the presence of donor (D) and acceptor (A) groups linked through a π-conjugation path and is characterized by a large first-order hyperpolarizability value (β). However, a small energy gap between the HOMO and the LUMO (Egap) is an important indicator for high NLO

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• mono-substituted sumanene derivatives 49b–d in a stereoselective manner as can be inspected from Scheme 10 [41][42]. In another event, Amaya, Ito, Katoh and Hirao reported a vital building block 53 to extend the π-conjugation bidirectionally through regioselective functionalization (Scheme 11) [43]. To

Aryl-substituted acridanes as hosts for TADF-based OLEDs

• Naveen Masimukku,
• Dalius Gudeika,
• Oleksandr Bezvikonnyi,
• Ihor Syvorotka,
• Rasa Keruckiene,
• Dmytro Volyniuk and
• Juozas V. Grazulevicius

Beilstein J. Org. Chem. 2020, 16, 989–1000, doi:10.3762/bjoc.16.88

• explained by the dihedral angle between the acridanyl and naphthyl moieties, that is the largest one among all the studied compounds, leading to a reduction of π-conjugation. This observation explains the distinct ICT character of the luminescence of compound 4. The dihedral angles in the molecules of 3 and

Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes

• Aya Yoshimura,
• Hitoshi Kimura,
• Kohei Kagawa,
• Mayuka Yoshioka,
• Toshiki Itou,
• Dhananjayan Vasu,
• Takashi Shirahata,
• Hideki Yorimitsu and
• Yohji Misaki

Beilstein J. Org. Chem. 2020, 16, 974–981, doi:10.3762/bjoc.16.86

• systems; electrochemical properties; extended π-conjugation; digital simulation analysis; tetrathiafulvalene; Introduction Tetrathiafulvalenes (TTFs) with extended π-conjugation have attracted attention as possible components of functional materials, such as molecular conductors, field-effect transistors

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• emission at 617 nm (16207 cm−1) with two equally intense bands (a characteristic of symmetric porphyrins). The nearly similar λmax of both these dimers reinforces the lack of extended π-conjugation or communication that is present in these molecules. Comparatively, the zinc dimer 9 has an increased

• dimer 9 with a gap of 2.03 eV and the butadiyne-linked dimer 20 with 1.87 eV. These values give an initial indication of the extent of π-conjugation occurring within these systems, as the more conjugation present in the system the lower the HOMO–LUMO gap. A spectroscopic comparison of the porphyrin