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

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

• ’ conPET, this Review will also cover deviating variants such as neutral (acridine) radical conPET as well as polysulfide or ‘tandem’ photoredox catalysis that similarly rely on the absorption of two photons to access activated catalyst states that engage redox-inert substrates. Other two-photon processes

• a two-photon process. DBU was found to quench the steady-state fluorescence of *PC1 with a quenching rate constant two orders of magnitude smaller than the diffusion rate constant in DMSO at 298 K and one order of magnitude greater under the borylation reaction conditions (i.e., 0.20 M DBU) than the

• single-photon process when only taking the absorption of PC1 into account but gave a reasonable value (Φprod = 8.2%) for the two-photon process involving excitation of both PC1 and PC1•−. Electron transfer from *PC1•− (*E1/2 = −2.25 V vs SCE) to 1d is thermodynamically favored. While 1d does not quench

Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

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

Dyes in modern organic chemistry

• Heiko Ihmels

Beilstein J. Org. Chem. 2019, 15, 2798–2800, doi:10.3762/bjoc.15.272

• , two-photon absorption probes or chemosensors [24][25][26][27][28][29][30]. After all, dye chemistry is literally an "evergreen" in scientific research, and consequently, its significant contributions to scientific developments and breakthroughs is well-documented in several Nobel prizes that are

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• lanthanides’ spectroscopic properties (regular level spacing and long excited states lifetimes), one emitting ion can undergo several energy transfer processes before relaxing radiatively [15], making the overall process fundamentally different form second harmonic generation or two-photon absorption

• two-photon excitation that requires very high local power density, the upconversion process is based on multiple, noncoherent, “single photon” successive absorptions. As the molar extinction coefficient of the sensitizer ytterbium is weak (ca. 3 mol L−1 cm−1), the exciting beam is moderately

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• electron-transfer phenomena or two-photon absorption [32][33][34][35][36]. As part of our research program we have developed arylisoquinolines that integrate a boronic acid ester [37][38][39] or a BMes2 unit [6][40]. The presence of the boron-substituent confers interesting photophysical properties to

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• , belonging to the hydrazone family. The outstanding properties of this molecule, involving fluorescence toggling, bistability, high isomerization quantum yield and non-negligible two-photon absorption cross section, make it very promising for numerous applications. Here we show that the light induced Z/E

• emission component in the 500–520 nm spectral range, attributed to the Z-isomer, and a very short living blue-shifted emission, attributed to the E-isomer. Finally, transient absorption measurements performed upon far-red excitation are employed as an alternative method to determine the two-photon

• fluorescence techniques with the aim of better characterizing the actinic step of its operation. Furthermore, we employ time resolved spectroscopy to evaluate the two-photon absorption cross section of the molecule and, by comparing the results with those previously obtained using a fluorescence method, we

Fluorescent phosphorus dendrimers excited by two photons: synthesis, two-photon absorption properties and biological uses

• Anne-Marie Caminade,
• Artem Zibarov,
• Eduardo Cueto Diaz,
• Aurélien Hameau,
• Maxime Klausen,
• Kathleen Moineau-Chane Ching,
• Jean-Pierre Majoral,
• Jean-Baptiste Verlhac,
• Olivier Mongin and
• Mireille Blanchard-Desce

Beilstein J. Org. Chem. 2019, 15, 2287–2303, doi:10.3762/bjoc.15.221

• Different types of two-photon absorbing (TPA) fluorophores have been synthesized and specifically functionalized to be incorporated in the structure of phosphorus dendrimers (highly branched macromolecules). The TPA fluorophores were included in the periphery as terminal functions, in the core, or in the

• the mechanism of action of anticancer compounds, and for safer photodynamic therapy. Keywords: bioimaging; dendrimer; fluorescence; phosphorus; two-photon absorption; Introduction Natural luminescence phenomena such as the bioluminescence of fireflies or of certain marine microorganisms, or the

• of two photons (of same or different energy), but this phenomenon was not observable until the advent of lasers. Two-photon excited (TPE) fluorescence is a third-order nonlinear optical process, which was first experimentally observed only in 1961 [3]. It provides intrinsic spatial selectivity in

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

• Yu-Ying Wang,
• Yong Kong,
• Zhe Zheng,
• Wen-Chao Geng,
• Zi-Yi Zhao,
• Hongwei Sun and
• Dong-Sheng Guo

Beilstein J. Org. Chem. 2019, 15, 1394–1406, doi:10.3762/bjoc.15.139

• intramolecular charge-transfer dyes. Phosphated tetraphenylethylene was involved as the classical aggregation-induced emission dye. Sulfonated acedan representing one example of two-photon fluorescent probes, was also investigated. A ruthenium(II) complex with carboxylated bipyridyl ligands was included as a

• charge-transfer dyes. P-TPE was included in the study as a classical aggregation-induced emission (AIE) dye and TPS as a representative of a two-photon fluorescent probe. Ru(dcbpy)3 was involved as a member of luminescent transition-metal complexes. Of our special interest in the present study is to

• opportunity to construct organic luminescent materials and could be engaged in the manufacture of high-performance supramolecular dye lasers [24][48]. The complexation of GC5A with the two-photon fluorescent probe Two-photon excitation microscopy is a fluorescence imaging technique utilizing near-infrared

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• , Japan Department of Molecular and Internal Medicine, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Hiroshima 734-8551, Japan 10.3762/bjoc.15.84 Abstract Novel caged nitroxides (nitroxide donors) with near-infrared two-photon (TP) responsive

• counterparts (65.8% vs 85.5%). Keywords: caged compound; nitroxide; photolysis; radical; theranostics; two-photon; Introduction Nitroxides (aminoxyl radicals) possess a delocalized unpaired electron and exhibit negligible dimerization reactivity, making them persistent open-shell species [1][2][3][4]. In

• issues can be solved by using the NIR-two-photon (TP) excitation technique [44], in which a molecule is electronically excited to the same state generated by one-photon (OP) excitation in the UV–vis region [45]. In addition to the advantages of TP excitation, three-dimensional control of the electronic

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• ion. This was one of the features to use N-phenylphenothiazine for the photoactivation of SF6 for the pentafluorosulfanylation of styrenes [2]. This two photon concept can further be extended to the photoredox catalytically generation of hydrated electrons as very powerful reductants (E = −2.8 V (vs

Structure–property relationships and third-order nonlinearities in diketopyrrolopyrrole based D–π–A–π–D molecules

• Jan Podlesný,
• Lenka Dokládalová,
• Oldřich Pytela,
• Adam Urbanec,
• Milan Klikar,
• Numan Almonasy,
• Tomáš Mikysek,
• Jaroslav Jedryka,
• Iwan V. Kityk and
• Filip Bureš

Beilstein J. Org. Chem. 2017, 13, 2374–2384, doi:10.3762/bjoc.13.235

• utilized in two-photon excited fluorescence microscopy and bioimaging [13][14], most often upon their further structural tuning towards higher polar character and solubility in water [20][21][22]. Their linking to porphyrins proved to be a useful strategy for two-photon photodynamic therapy [23][24][25

• ]. Moreover, some DPP derivatives also showed aggregation induced emission (AIE) [13][14] and the ability to selectively sense fluoride ions [26][27][28]. The modern era of DPP chromophores has been opened by Gryko et al. [3][11][12][18][20][21][29] who have demonstrated their large and tunable two-photon

• eventually intramolecular charge-transfer (ICT) [9][10] from the peripheral donors to the central DPP acceptor. Due to their generally D–π–A–π–D character and thus resulting centrosymmetric arrangement, the DPP derivatives were most frequently studied as third-order optical NLOphores, in particular as two

Multivalent dendritic polyglycerolamine with arginine and histidine end groups for efficient siRNA transfection

• Fatemeh Sheikhi Mehrabadi,
• Hanxiang Zeng,
• Mark Johnson,
• Cathleen Schlesener,
• Zhibin Guan and
• Rainer Haag

Beilstein J. Org. Chem. 2015, 11, 763–772, doi:10.3762/bjoc.11.86

• aperture oil immersion planapochromat objective. A 559 nm helium–neon laser, a SMD640 dichroic mirror, and a 575–620 nm band-pass barrier filter were used to obtain the images of Cy3-labeled siRNA. Images of the stained nuclei were acquired using a 780 nm two-photon excitation light, a 635 nm dichroic

Synthesis and spectroscopic properties of 4-amino-1,8-naphthalimide derivatives involving the carboxylic group: a new molecular probe for ZnO nanoparticles with unusual fluorescence features

• Laura Bekere,
• David Gachet,
• Vladimir Lokshin,
• Wladimir Marine and
• Vladimir Khodorkovsky

Beilstein J. Org. Chem. 2013, 9, 1311–1318, doi:10.3762/bjoc.9.147

• (3H)-yl)benzoic acid (4) was found to be a sensitive molecular probe for ZnO nanoparticles. We investigated in detail one- and two-photon absorption properties of this fluorophore. In nonpolar solvents, the acid 4 absorbs at about 400 nm and fluoresces at 500 nm with a fluorescence lifetime of about 7

• patterns. Keywords: fluorescence; hydrogen bond; 1,8-naphthalimide; one- and two-photon absorption; zinc oxide; Introduction 1,8-Naphthalimide derivatives are useful for a variety of applications owing to their strong fluorescence, electroactivity and photostability. These compounds can be employed as

• -substituted naphthalimide dyes are important yellow components of daylight fluorescent pigments and can be employed as fluorescent dichroic dyes in liquid-crystal displays [1][2][11]. In this paper, we report on the synthesis [12], characterization and one- and two-photon spectroscopic properties of

A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• effects. What about these caged Glu probes? Chemist: It is much harder to give a clear-cut answer to this question. At the high concentrations that are used for two-photon experiments (range 3–12 mM) all classes of caged neurotransmitters are reported to block GABA-A receptors to some extent [33][36][37

• does not make much difference to the question we are addressing. One type of experiment one could imagine performing where it may be important is the combination of two-photon uncaging of glutamate with optogenetic activation of GABA receptors from genetically selected neurons. In such a paradigm the

• uncaging only requires a concentration of 1 mM (maximally), and quite often, much lower concentrations work very well [46][47][48][49]. As we have already noted, two-photon uncaging normally requires significantly higher concentrations [30][50][51][52][53], so for these experiments solubility becomes more

Molecular switches and cages

• Dirk Trauner

Beilstein J. Org. Chem. 2012, 8, 870–871, doi:10.3762/bjoc.8.97

• , more importantly, re-uptake systems). In terms of their biological application, especially in neurobiology, they are much further developed than reversibly switchable molecules. For instance, two-photon activation, which allows for very precise localization, is fairly well established with caged

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• through a thiazole-styryl π-linker (Figure 4). Whereas the series 5a–c and 7a–c showed promising optical nonlinearities, high thermal stability, excellent solubility, and good transparency, molecules 8a–d were investigated as two-photon absorbing chromophores (Table 2). Bu and co-workers also investigated

• (Figure 5, Table 3). Imidazoles 12 (DIYSP, δ = 41 GM, [38][39]) and 13 (FD3, δ = 1556 GM, [40]) were developed as two-photon absorbing and fluorescent A-π-A’ chromophores, which undergo photopolymerization or can be applied as fluorescent sensors for (homo)cysteine. Donor 4,5-disubstituted imidazole

• -photon absorbing molecules with blue upconversion fluorescence [68]. These imidazole derivatives proved to be potent two-photon absorbing molecules with TPA cross-section δ up to 20.65 GM at 800 nm. The molecular structure of chromophore 60 was also confirmed by X-ray analysis. Similar derivatives 61