Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• novel material design can overcome typical limitations of organic semiconductors to produce more efficient photocatalysts with an enhanced charge transport. The authors did not discuss the formation of triplet excitons through intersystem crossing, which is facilitated by sulphur spin–orbit coupling, as

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• case (Scheme 1, box 2), the excited photocatalyst can engage in an EnT mechanism. Upon the excitation and intersystem crossing, the triplet state photocatalyst 3PC* can interact directly with a ground state species Sub and transfer the triplet energy to generate an excited state Sub* and the ground

Development of fluorinated benzils and bisbenzils as room-temperature phosphorescent molecules

• Shigeyuki Yamada,
• Takuya Higashida,
• Yizhou Wang,
• Masato Morita,
• Takuya Hosokai,
• Kaveendra Maduwantha,
• Kaveenga Rasika Koswattage and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 1154–1162, doi:10.3762/bjoc.16.102

• photophysical properties of the benzil and bisbenzil derivatives in toluene at 25 °C showed both fluorescence with a photoluminescence (PL) band at a maximum wavelength (λPL) of around 400 nm and phosphorescence with a PL band at a λPL of around 560 nm. Interestingly, intersystem crossing effectively caused

• intersystem crossing (ISC), resulting in the emission of phosphorescence [9]. Phosphorescent molecules generate two excitons (i.e., 25% S1 excitons and 75% T1 excitons) by application of an electric field, which is well known for organic light-emitting diodes. S1 excitons are converted to T1 excitons via an

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• photocatalysts. Under light irradiation, one electron from the ground state (S0) is promoted to the excited singlet state (S1) which has a short lifetime (10−9 s). Therefore, fast intersystem-crossing of one electron gives the excited triplet state (T1) with a relatively longer lifetime (10−6 s). While the

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• a nonbonding electron on the oxygen atom to the first excited singlet state. This singlet state can lead to the corresponding triplet state T1 (n,π*) through intersystem crossing. This triplet state can be quenched through various chemical transformations, like Norrish type I and Norrish type II

• aryl ketones, could participate in HAT processes as hydrogen atom abstractors [20]. More specifically, aldehydes can absorb irradiation at 300 nm and be excited from their ground state S0 to their singlet state S1 (n,π*), Then, through intersystem crossing (ISC), they can transition to a lower energy

• extinction coefficients and charge transfer states as well as relatively long-lived triplet states in solution, making them suitable as photoinitiators [36][37]. The irradiation and excitation of DEABP (27) to the singlet state is followed by intersystem crossing to the triplet state 29, which then leads to

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• emission bands were observed with lowered quantum yields, Φf of 0.25 and 0.16, respectively (Figure 5b and Table 1). The larger Stokes shift and shorter emission lifetime suggest a rapid decay of the excited species after structural relaxation (vide infra, Table 1). Also, intersystem crossing to the

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• matrix molecules to the surrounding (VC) occurring from higher vibrational modes of the ground state formed by IC. Photochemical reactions typically occur from the lowest vibrational level (v’ = 0) of the S1. This figure does not contain an intersystem crossing route resulting in triplet states because

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• studies seem to allow the prediction of the activity of derivatives able to pass intersystem crossing to their triplet energy state and thus create radicals able to damage DNA. With this study, it is shown that oxime carbamate derivatives have the potential to act as novel effective photobase generating

• triplet state energy activators are compounds that have the ability to be efficiently excited to their triplet excited state. TPSs may be used, among others, to transfer their triplet energy to other molecules that have a low yield of intersystem crossing (ISC) and inefficient production of triplet state

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• hand, S1 can also transition to the spin-forbidden T1 through intersystem crossing (ISC), which then decays by (longer) radiative processes to S0 (phosphorescence. Figure 3) [41][42][43]. The triplet excited state is oxygen-sensitive as O2 carries out quenching in solution, thereby leading to the

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

• . This is possible as these compounds possess very small exchange energies between their excited singlet and triplet states (ΔEST), which facilitates reverse intersystem crossing (RISC), in which singlet excitons are generated from triplet excitons. In order to obtain a small ΔEST, the molecular design

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization

• Valentina A. Ol’shevskaya,
• Elena G. Kononova and
• Andrei V. Zaitsev

Beilstein J. Org. Chem. 2019, 15, 2704–2709, doi:10.3762/bjoc.15.263

• the biological efficiency of the photosensitizing agents [21][22]. At the same time fluorinated porphyrins are well known for their photostability and efficiency in generating long-lived triplet excited states through intersystem crossing (ISC) with minimal energy loss from excited states, and are

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

• measurements was limited to 2 ns, it was difficult to determine the time constant of nanosecond time scale exactly. Therefore, the lifetimes of the intersystem crossing (ISC) of benzil and the benzil unit of Benzil-PIC were fixed to a reported value of benzil (2.5 ns) [44]. The lifetime of the T1 state of

Synthesis and properties of sulfur-functionalized triarylmethylium, acridinium and triangulenium dyes

• Marco Santella,
• Eduardo Della Pia,
• Jakob Kryger Sørensen and
• Bo W. Laursen

Beilstein J. Org. Chem. 2019, 15, 2133–2141, doi:10.3762/bjoc.15.210

• enhanced internal conversion or intersystem crossing to the triplet state. Further photophysical work will have to settle this issue and thereby suggest structural improvements and/or the best applications of these dyes. Conclusion The effective introduction of alkylthiol groups into the para-positions of

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

• ground-state complex, with drastic changes in both, band shapes and intensities. The calculated rate constant of PET is faster than that of fluorescence and intersystem crossing, which makes it a more favorable deactivation pathway of the first excited singlet state leading to both fluorescence quenching

• singlet state 1MLCT can undergo ultrafast intersystem crossing leading to the formation of the triplet state 3MLCT which could emit phosphorescence. Ru(dcbpy)3 was employed as a representative candidate in this work to study the photophysical response upon complexation with GC5A. Almost no appreciable

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• by thermal activation. Thus, the excited states can be thermally upconverted to the singlet state by reverse intersystem crossing (RISC), giving rise to a luminescence process arising from the singlet state (fluorescence). The concept of delayed fluorescence is based on the unusual and transient

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

• likely to be involved in PET. A molecule with a low Φf will be unlikely to be found in the S1 state, as this state will be highly susceptible to other decay pathways in the timescale of PET. For a molecule to undergo PET when in the T1 state, the intersystem crossing quantum yield (ΦISC) must be

Recent advances in phosphorescent platinum complexes for organic light-emitting diodes

• Cristina Cebrián and
• Matteo Mauro

Beilstein J. Org. Chem. 2018, 14, 1459–1481, doi:10.3762/bjoc.14.124

• properties, also in terms of electrochemistry. Additionally, the presence of a heavy metal atom induces spin-orbit coupling (SOC) effects to such an extent that intersystem crossing (ISC) processes become thus competitive over other radiationless deactivation pathways owing to relaxation of spin rules. In

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

D–A–D-type orange-light emitting thermally activated delayed fluorescence (TADF) materials based on a fluorenone unit: simulation, photoluminescence and electroluminescence studies

• Lin Gan,
• Xianglong Li,
• Xinyi Cai,
• Kunkun Liu,
• Wei Li and
• Shi-Jian Su

Beilstein J. Org. Chem. 2018, 14, 672–681, doi:10.3762/bjoc.14.55

• increase the cost of the final OLEDs. Alternatively, a thermally activated delayed fluorescence (TADF) material is a kind of noble-metal-free fluorescent material able to transform triplet excitons into singlet excitons through reverse intersystem crossing (RISC) to achieve 100% IQEmax in theory [4]. On the

• property according to the energy gap law [16] as vibrational relaxation and intersystem crossing (IC) processes can consume the energy in S1, leading to increased nonradiative deactivation [17], reduced PL quantum yield, and thus reduced singlet exciton utilization. On the contrary, the geometry of 2 is

• [5][7][16]. where kr, knr, kisc, and krisc represent the rate constant of radiative, nonradiative, intersystem crossing and reverse intersystem crossing, respectively; Φ, ΦPF, ΦTADF, τPF and τTADF represent the photoluminescence quantum yield, quantum yield of the prompt component, quantum yield of

Recent advances on organic blue thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs)

• Thanh-Tuân Bui,
• Fabrice Goubard,
• Malika Ibrahim-Ouali,
• Didier Gigmes and
• Frédéric Dumur

Beilstein J. Org. Chem. 2018, 14, 282–308, doi:10.3762/bjoc.14.18

• singlet excited states by reverse intersystem crossing (RISC). By harvesting both singlet and triplet excitons for light emission, OLEDs competing and sometimes overcoming the performance of phosphorescence-based OLEDs could be fabricated, justifying the interest for this new family of materials massively

• , only singlet excitons can be utilized for light emission, limiting the internal quantum efficiency (IQE) of fluorescent OLEDs to 25%. Conversely, phosphorescent materials can both harvest singlet and triplet excitons for emission by intersystem crossing (ISC), enabling to reach a theoretical IQE of 100

• delayed fluorescence (TADF) emitters. As specificity, these materials can thermally repopulate the singlet state from the triplet state by reverse intersystem crossing (RISC), leading to an increase of the luminescence intensity. From the OLEDs viewpoint, TADF emitters behave by harvesting both singlet

Pyrene–nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies

• Artur Jabłoński,
• Yannic Fritz,
• Hans-Achim Wagenknecht,
• Rafał Czerwieniec,
• Tytus Bernaś,
• Damian Trzybiński,
• Krzysztof Woźniak and
• Konrad Kowalski

Beilstein J. Org. Chem. 2017, 13, 2521–2534, doi:10.3762/bjoc.13.249

• fluorescence intensity and fast decay of fluorescence were rationalized by the presence of low-energy nπ* excited states. In particular, for the lowest excited singlet state 1ππ* efficient intersystem crossing to a triplet state 3nπ* close in energy can be expected according to the El-Sayed rule. Then, this

• pyrene 1ππ* state). Thus, intersystem crossing between these two states can be efficient giving rise to also efficient radiationless depopulation of the emissive singlet state relative to aliphatic analogues, in that quenching 3nπ* states are not present. Interactions with oligonucleotides Compounds 2–5

Cycloheximide congeners produced by Streptomyces sp. SC0581 and photoinduced interconversion between (E)- and (Z)-2,3-dehydroanhydrocycloheximides

• Li Yang,
• Ping Wu,
• Jinghua Xue,
• Huitong Tan,
• Zheng Zhang and
• Xiaoyi Wei

Beilstein J. Org. Chem. 2017, 13, 1039–1049, doi:10.3762/bjoc.13.103

• relaxations via an intersystem crossing (ISC) from the S1 minima 2b and 3b to the T1 maxima 2c and 3c, respectively, are energetically and symmetrically reasonable [14][17] as well as are preferred according to El-Sayed’s rules [18]. Therefore, the isomerization of 2a/3a, after vertical excitation, is

A self-assembled cyclodextrin nanocarrier for photoreactive squaraine

• Ulrike Kauscher and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2016, 12, 2535–2542, doi:10.3762/bjoc.12.248

• appropriate wavelength. Irradiation of the PS causes its transition to the excited singlet state and, via intersystem crossing; the PS reaches its triplet state. Electron transfer occurs upon relaxation to the ground state. This process can take place in two ways distinguished as type I and II mechanisms [5

• class of compounds known as squaraines [13][14][15][16][17][18]. Squaraines are a promising class of fluorescent dyes for PDT. In the past, squaraines showed a very low intersystem-crossing efficiency, leading to the premature conclusion that these dyes cannot be used in PDT [19]. Santos et al. showed

• that the intersystem-crossing efficiency of squaraines can be remarkably increased by incorporation of heavy atoms like selenium or sulfur and the addition of long aliphatic side chains [20][21]. The enhanced intersystem-crossing efficacy due to spin-orbital interactions makes modified squaraines a

Synthesis of 2,1-benzisoxazole-3(1H)-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

• Daria Yu. Dzhons and
• Andrei V. Budruev

Beilstein J. Org. Chem. 2016, 12, 874–881, doi:10.3762/bjoc.12.86

• through a 1,5-electrocyclization reaction [56][57]. Nonreacted singlet nitrenes A may undergo intersystem crossing (ISC) into the less reactive triplet state (Scheme 1, intermediate D). Although a multiplicity change is a spin-forbidden transition, it can be partially allowed in some cases. According to

• intersystem crossing for the initially formed singlet nitrenes (Scheme 1, intermediate A) to the triplet state (Scheme 1, intermediate D), thus resulting in decreased yields of the cyclization products 2c–e. In these cases, the formation of the triplet nitrene D should lead to increased yields of primary

Indenopyrans – synthesis and photoluminescence properties

• Andreea Petronela Diac,
• Ana-Maria Ţepeş,
• Albert Soran,
• Ion Grosu,
• Anamaria Terec,
• Jean Roncali and
• Elena Bogdan

Beilstein J. Org. Chem. 2016, 12, 825–834, doi:10.3762/bjoc.12.81

• the cis isomers 2''b (313 nm, in acetonitrile). All derivatives 2a–d showed an intense emission in acetonitrile in the range 380–393 nm (Figure 4, Table 3), while for the cis isomer 3''b a weaker emission was observed. This may be explained by a less extended conjugation and an intersystem-crossing