The review covers the knowledge on photoremovable protecting
groups and includes all relevant chromophores studied in the
time period of 2000–2012; the most relevant earlier works are
also discussed.

/pdf/photoremovable-protecting-groups-in-chemistry-and-biology-2n33qs6p7b.pdf

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Photolabile protecting groups enable biochemists to control the release of bioactive compounds in living tissue. ‘Caged compounds’
(photoactivatable bioagents) have become an important tool to study the events that follow chemical signalling in, e.g., cell biology and the neurosciences. The possibilities are by no means exhausted. Progress will depend on the development of photoremovable protecting groups that satisfy the diverse requirements of new applications—a challenging task for photochemists.

https://link.springer.com/content/pdf/10.1039/b200777k.pdf

Photoremovable protecting groups: reaction mechanisms and applications

https://zenodo.org/record/1259719/files/article.pdf

Photolabile protecting groups for nucleosides: Synthesis and photodeprotection rates

The exothermic nonradiative relaxation processes from photoexcited nitrobenzene (NB) are studied by the picosecond time-resolved transient grating method. The decay rate constants and energy of the excited NB are determined. The lifetime of the lowest excited singlet state is found to be very short ( e10 ps) and a surprisingly short lifetime of the lowest excited triplet state (480 ps) is detected. From quantitative measurements of the thermal energies released from the excited states of NB, the lowest excited triplet state is determined to be located at (22-27) 10 3 cm -1 . The triplet formation is very efficient and its quantum yield is found to be grater than 0.80. From the temperature and solvent dependence of the triplet lifetime, it is suggested that motions of the nitro group may cause the surprisingly rapid relaxation from the lowest excited triplet state to the ground state. The photophysical properties and excited states of monosubstituted nitrobenzenes are also discussed.

Nonradiative Relaxation Processes and Electronically Excited States of Nitrobenzene Studied by Picosecond Time-Resolved Transient Grating Method

The simultaneous, concerted transfer of electrons and protons— electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4′-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICTexcited state in which the transferring H þ is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated þ H─B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

/pdf/concerted-electron-proton-transfer-in-the-optical-excitation-4h3enbt567.pdf

Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

Etude de ces composes par spectroscopie transitoire de l'ordre de la picoseconde: les deux bandes observees dans la region 400-650 nm sont attribuees a l'etat triplet excite n, π*. Une conversion intersysteme rapide est mise en evidence par un temps de montee ≤5 ps pour le nitrobenzene et une abstraction d'hydrogene intramoleculaire se produit a partir de l'etat triplet avec une constante de vitesse de 0,9×10 9 s −1

Picosecond excited-state absorption of alkylnitrobenzenes in solution

Several oxygen-substituted o-nitrobenzylic compounds in THF solution were studied by picosecond transient spectroscopy. The o-quinonoid intermediate resulting from intramolecular H abstraction was observed in those compounds which undergo efficient reaction. In the case of phenyl o-nitrobenzyl ether and p-cyanophenyl o-nitrobenzyl ether, both the triplet excited state and the o-quinonoid were observed at early times. For these two compounds, the o-quinonoid intermediate is formed from the singlet excited state at a rate much faster than triplet decay. 18 references, 4 figures.

Photochemistry of the o-nitrobenzyl system in solution: evidence for singlet-state intramolecular hydrogen abstraction

Photochemistry of the o-nitrobenzyl system in solution : identification of the biradical intermediate in the intramolecular rearrangement

Two rigid nitrobenzene derivatives, 5-nitro-1,2,3,4-tetrahydro-1,4-methanonaphthalene (6), and 5-nitro-1,2,3,4-tetra-hydro-1,4-ethanonaphthalene (7), have been synthesized and studied by picosecond...

Photochemistry of the o-nitrobenzyl system in solution: effects of distance and geometrical constraint on the hydrogen transfer mechanism in the excited state

R. Giasson

Papers

Picosecond excited-state absorption of alkylnitrobenzenes in solution

Photochemistry of the o-nitrobenzyl system in solution: evidence for singlet-state intramolecular hydrogen abstraction

Photochemistry of the o-nitrobenzyl system in solution : identification of the biradical intermediate in the intramolecular rearrangement

Photochemistry of the o-nitrobenzyl system in solution: effects of distance and geometrical constraint on the hydrogen transfer mechanism in the excited state

Photochemistry of the o‐Nitrobenzyl System in Solution: Identification of the Biradical Intermediate in the Intramolecular Rearrangement