Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• the donor and the acceptor. Compounds 2, 4, and 5 were very poorly luminescent and so their emission could not be quantified. Compound 3 exhibited a broad and unstructured emission in a degassed DCM solution (λPL = 550 nm), characteristic of an excited state with significant CT character. The

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• the differences observed, differences in the excited-state profiles and quantum yields for the photoisomerization pathway may also contribute to the lack of correlation between band overlap and photoisomerization efficiency [35]. Conclusion We aimed to combine two features now known to significantly

• the lowest-lying singlet excited state and the ground state at the transition state geometry for 4pzH and 4pzMe. Theoretical calculations at the PBE0-D3/6-31G** level indicate that the lowest-lying S1 state lies >1 eV above in energy with respect to the ground state, and therefore the DFT approach is

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• excited state [59]. Plotting Stokes shifts Δν̃ against the orientation polarizabilities Δƒ of the respective solvents (Lippert plot) [60] gives a reasonable linear correlation with a moderate fit of r2 = 0.970 (Figure 13). The orientation polarizabilities Δƒ were calculated according to Equation 1 where

• εr is the relative permittivity and n the optical refractive index of the respective solvent. The change in dipole from the ground to the excited state can be calculated according to the Lippert–Mataga equation (Equation 2) where ν̃abs represents the absorption and ν̃em the emission maxima (in m−1

• the solid state. This finding suggests that by restricting intramolecular motion and vibration, which enables radiation-less deactivation of the excited state [61], an AIE (aggregation‐induced emission) or AIEE (aggregation-induced enhanced emission), might become operative [62][63][64]. The AIE or

Plasma membrane imaging with a fluorescent benzothiadiazole derivative

• Pedro H. P. R. Carvalho,
• Jose R. Correa,
• Karen L. R. Paiva,
• Daniel F. S. Machado,
• Jackson D. Scholten and
• Brenno A. D. Neto

Beilstein J. Org. Chem. 2019, 15, 2644–2654, doi:10.3762/bjoc.15.257

• agreement with the experimental data and helped to understand the stabilizing intramolecular charge-transfer process from the first excited state. The new fluorescent derivative could be applied as selective bioprobe in several cell lines and displayed plasma-membrane affinity during the imaging experiments

• and first excited state S1 (∆ρ = ρS1 − ρS0), as shown in Figure 4D, highlights the directionality of the electron density transfer with a great deal of ICT between the cationic heterocycle and the BTD core, which stabilizes the excited state of the synthesized chromophore. These theoretical results

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

• Aydan Yadigarli,
• Qimeng Song,
• Sergey I. Druzhinin and
• Holger Schönherr

Beilstein J. Org. Chem. 2019, 15, 2552–2562, doi:10.3762/bjoc.15.248

• the phenomenon is still far from accurate. Fortunately, a contribution of solute to the large amplitude motion of the diethylamino group (twisting) in intramolecular charge transfer excited state of NR, postulated in references [21][24][25] was later associated with an artefact [26]. However, the

• fluorescence (Figure 2a). This behavior for NR [35] is similar to donor–acceptor-substituted stilbenes [36][37], benzenes [38][39] and aminocoumarins [35][40][41]. This effect is caused by solvent relaxation around dipolar solutes that possess in the lowest excited state a substantially higher dipole moment

• observed in the fluorescence spectrum (1570 cm−1) indicates a higher dipole moment in the excited state (μe > μg) and a larger negative slope in Equation 1 ~μe(μe − μe) than in Equation 2 ~μg(μe − μg). This solvatochromic plot with its slope of −4730 cm−1 resembles plot according to Equation 1 in Figure 3a

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• , leaving the long-wavelength absorption available for bimolecular PICT. Moreover, the LW is sufficiently more reducible that, even accounting for its lower excitation energy, the LW excited state, LW*, is more reducible than SW*, making LW the more potent photooxidant of the two. However, for practical use

• likely be the first singlet excited state (S1), T0 and S1 possess equivalent orbital occupancy and differ only in their spin state. Our rationale for using T0 rather than S1 is that ignoring electron-exchange interaction introduces substantially less error than using different computational methods when

• comparing orbitals of SW* to those of SW and SW•−. Using S1 for SW* would require unbalanced ground and excited-state calculations, e.g., time-independent and time-dependent density functional theories, or single-reference and multi-reference methods. However, using T0 for SW* is a straightforward ground

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

• – Istituto Nazionale di Ottica, Largo Enrico Fermi 6, 50125 Firenze, Italy 10.3762/bjoc.15.236 Abstract In this work we apply a combination of steady state and time resolved luminescence and absorption spectroscopies to investigate the excited-state dynamics of a recently developed molecular photoswitch

• isomerization occurs on a fast <1 ps timescale in both toluene and acetonitrile, while the excited state lifetime of the Z-form depends on solvent polarity, suggesting a partial charge transfer nature of its low lying excited state. Time-resolved luminescence measurements evidence the presence of a main

• obtained lifetime value is in accordance with the excited state lifetime previously measured for the Z-isomer [29]. After complete Z/E isomerization, obtained by irradiating the solution at 440 nm, the time-resolved luminescence of the E-form was analyzed upon excitation at 350 nm. The spectral

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• sensitization of PIC expands the versatility of the rate-tunable photoswitches of PIC systems. In this study, we synthesized a novel PIC derivative conjugated with a visible-light photosensitizer (Benzil-PIC, Scheme 1) and investigated the excited state dynamics. We used a benzil framework as a photosensitizer

• , indicating that the excited state dynamics of the two isomers of Benzil-PIC after the bond breaking are identical. Therefore, the mixture solution of the two isomers was used for further time-resolved spectroscopic measurements. Nanosecond-to-microsecond transient absorption spectra To investigate the

• assigned to the excited state absorption from the lowest vibrational level of the S1 state. The transient absorption band at 531 nm gradually decreases with a time scale of nanoseconds and another transient absorption band appears at 485 nm. The transient absorption band at 485 nm was assigned to the T1

Mono- and bithiophene-substituted diarylethene photoswitches with emissive open or closed forms

• A. Lennart Schleper,
• Mariano L. Bossi,
• Vladimir N. Belov and
• Stefan W. Hell

Beilstein J. Org. Chem. 2019, 15, 2344–2354, doi:10.3762/bjoc.15.227

• – fluorescence and off-switching – compete for the depopulation of the same excited state [10]. Hence, the ratio of fluorescence quantum yield and off-switching quantum yield is proportional to the number of emitted photons (Nph) per cycle or per incursion into the fluorescent state (i.e., before off-switching

Synthesis of a dihalogenated pyridinyl silicon rhodamine for mitochondrial imaging by a halogen dance rearrangement

• Jessica Matthias,
• Thines Kanagasundaram,
• Klaus Kopka and
• Carsten S. Kramer

Beilstein J. Org. Chem. 2019, 15, 2333–2343, doi:10.3762/bjoc.15.226

• negative value of the HOMO energy level and/or the oxidation potential [15], but it is also influenced by other factors. Nonradiative quenching (e.g., bond rotation) can effectively contribute to depopulation of the fluorophore’s excited state [28], yielding a lower quantum yield. However, the rational

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

• excited state (S1). Depending on the type of molecules, two main ways can be taken to go back to the ground state: either a nonradiative decay of the energy absorbed, or the emission of fluorescence at a longer, less energetic wavelength. A third possibility (not shown in the Figure) concerns an

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• ’-dCF3bpy)PF6 (1) undergoes photoexcitation with visible light to form the highly oxidizing excited state ·Ir(III) 2. Then, SET from copper carboxylate 4, derived from carboxylic acid 3 with the Cu(II) catalyst to ·Ir(III) 2 provides Cu(III) carboxylate 5, or in the dissociated form, a carboxyl radical and

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• , diarylethene derivatives with photoswitchable fluorescent properties were prepared. They are applicable for fluorescence imaging including bio-imaging. On the other hand, a new system called “excited state intramolecular proton transfer (ESIPT)” is reported. In the system, absorption and emission bands are

• a large Stokes shift is indispensable for such a system. One of the possible choices to achieve such a large Stokes shift is to introduce the excited-state intramolecular proton transfer (ESIPT). The process of ESIPT is a fast process even comparable to the internal conversion [15][16]. This is

• these two moieties. As it is expected, the stable structure of the ESIPT is found computationally only in the excited state. (Hereafter, we denote 1o-NH (1c-NH) as the ESIPT state of 1o (1c) and 1o-OH (1c-OH) as the original structure shown in Figure 2 to emphasize the structural difference

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• solubilities. The electron-donating diaminoalkyl substituents together with the electron-deficient aromatic core of the naphthalene diimides increase the charge-transfer character of their photoexcited states and thus shift their absorption into the visible light (500–650 nm). The excited state reduction

• CH2Cl2, only the extinction is slightly reduced. The charge transfer character of the excited state of cNDI 6 should yield an absorbance in the visible range for photoredox catalysis. In fact, the absorbance of the new cNDI 6 in CH2Cl2 shows considerably red-shifted bands in the range between 500 nm and

• quantum yield of 48%. The Stokes’ shift is rather large (715 cm−1). The excitation energy E00 of cNDI 6 in the singlet state is approximately 1.98 eV and is significantly smaller than that of NDI 1 due to the visible light excitation which delivers less energy to the excited state. The redox potentials of

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• exchange was especially developed to describe main-group thermochemistry and noncovalent interactions. It shows very good results in predicting the position of the tautomeric equilibria for compounds with intramolecular hydrogen bonds as well as describing the ground and excited state proton transfer

Synthesis, photophysical and electrochemical properties of pyridine, pyrazine and triazine-based (D–π–)₂A fluorescent dyes

• Keiichi Imato,
• Toshiaki Enoki,
• Koji Uenaka and
• Yousuke Ooyama

Beilstein J. Org. Chem. 2019, 15, 1712–1721, doi:10.3762/bjoc.15.167

• transfer (TICT) excited state due to the twisting between the pyrazyl or triazyl group and the (diphenylamino)carbazole thiophene moiety, leading to non-radiative deactivation [1]. On the other hand, it is worth mentioning here that the brightness values (ε × Φf) for OUY-2, OUK-2 and OUJ-2 in various

• with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots revealed that the difference in the dipole moment of the dye between the excited state and the ground state increases in the order of OUY-2 < OUK-2 < OUJ-2. Thus, the fact explains our findings that

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• less than 50% water to an inhibited rotation of the 9,10-phenyl groups in the DPA units, which reduced the inactivation of the excited state through non-radiative transition [53]. However, when increasing the amount of water, the fluorescence starts to decrease due to the π–π stacking of DPA, which led

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

• , TPPS and AlPcS4 are four commonly used PSs in photodynamic therapy with ACQ features. Upon light excitation, PSs are excited from the singlet ground state to the singlet excited state and then to a triplet excited state via intersystem crossing. PSs at their excited triplet states are able to react

• ). We studied the photophysical response upon complexation in detail taking AlPcS4 as an example. The emission peak of AlPcS4 remains unshifted when the overall fluorescence intensity is reduced by addition of GC5A, indicating that the singlet excited state of AlPcS4 returns to the ground state through

• -accepting structures. An increase in charge separation within ICT probes would occur upon excitation which results in a larger dipole moment in the excited state. The energy of the excited state with a larger dipole moment could be reduced by interaction with a high polarity environment and could be

Selenophene-containing heterotriacenes by a C–Se coupling/cyclization reaction

• Pierre-Olivier Schwartz,
• Sebastian Förtsch,
• Astrid Vogt,
• Elena Mena-Osteritz and
• Peter Bäuerle

Beilstein J. Org. Chem. 2019, 15, 1379–1393, doi:10.3762/bjoc.15.138

• heterotriacenes 1 and 3 rationalize their unexpected higher melting point compared to 2 and 4. Quantum chemical calculations Quantum chemical DFT and TDDFT calculations (CAMB3LYP and B3LYP with the functional 6-31G++ (d,p)) were performed for the ground and excited state of heterotriacenes 1–4 in order to

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

• yields in DMSO of 5a and 5b were determined to be 16.1 and 8.6%, respectively, although no emission was observed from these compounds in non-polar benzene, indicating that the excited state has zwitterionic character. The charge transfer transition was supported by time-dependent density functional

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• -deazapurine class, which could be explained by a better stabilization of the ICT excited state by the solvatic shell. A decrease of QY accompanied by a high red shift of the emission maxima with increasing polarity of the surrounding media is a typical characteristic for the enhanced ICT of the excited states

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• dioxygen for this purpose is frequently exploited to effect synthetically useful copper-catalyzed aerobic oxidation reactions [27][28]. However, the use of molecular oxygen as a terminal oxidant presents unique challenges in photoredox chemistry. Triplet dioxygen rapidly quenches the excited state of most

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

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

• absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to

• ]. The photochemical reactivity can be tuned by the absorption and excited state characteristics of the photocatalyst. In this context, organic dyes represent a perfectly suited class of photocatalysts as they can easily be modified by the introduction of functional groups that allow fine-tuning the

• excited states. Normally, this is the reason why photochemical processes can hardly compete with photophysical decay processes. However, a pre-coordination of the substrate may facilitate electron transfer under non-diffusional controlled conditions. Very recently, the fast (picosecond) excited state

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• having a high molecular weight with a narrow molecular weight distribution. It was proposed that the polymerization is initiated by single-electron reduction of xanthate 4 by the highly reducing photo-excited state of fac-Ir(ppy)3 (6) [46], although the details were not elucidated (Scheme 2) [39][40

• agreement with the lower process efficiency (Table 1, entry 1) observed in the reaction with fac-Ir(ppy)3 (6) that possesses a lower triplet energy (ET = 55.2 kcal/mol [50]). The optimal photocatalyst 8 [47] has a longer excited state lifetime than 7 does [46], suggesting that the lifetime of the excited

• state of the photocatalyst is a key factor for the energy transfer mechanism. To obtain a detailed mechanistic insight, steady-state photoluminescence (PL) quenching of photocatalyst 8 was examined using xanthate 1a and 1-octene (2a) as potential quenchers (Figure 1). The intensity of the PL peak of