Pentacyano-N,N-Dimethylaniline in the Excited State. Only Locally Excited State Emission, in Spite of the Large Electron Affinity of the Pentacyanobenzene Subgroup

2010 ◽  
Vol 114 (50) ◽  
pp. 13031-13039 ◽  
Author(s):  
Klaas A. Zachariasse ◽  
Sergey I. Druzhinin ◽  
Victor A. Galievsky ◽  
Attila Demeter ◽  
Xavier Allonas ◽  
...  
Keyword(s):  
Excited State ◽  
Electron Affinity ◽  
Locally Excited ◽  
Locally Excited State

scholarly journals Role of active site conformational changes in photocycle activation of the AppA BLUF photoreceptor

2017 ◽  
Vol 114 (7) ◽  
pp. 1480-1485 ◽  
Author(s):  
Puja Goyal ◽  
Sharon Hammes-Schiffer
Keyword(s):  
Electron Transfer ◽  
Free Energy ◽  
Excited State ◽  
Charge Transfer ◽  
Conformational Changes ◽  
Ground State ◽  
Active Site ◽  
Locally Excited ◽  
Proton Relay ◽  
Locally Excited State

Blue light using flavin adenine dinucleotide (BLUF) proteins are essential for the light regulation of a variety of physiologically important processes and serve as a prototype for photoinduced proton-coupled electron transfer (PCET). Free-energy simulations elucidate the active site conformations in the AppA (activation of photopigment and puc expression) BLUF domain before and following photoexcitation. The free-energy profile for interconversion between conformations with either Trp104 or Met106 closer to the flavin, denoted Trpin/Metout and Trpout/Metin, reveals that both conformations are sampled on the ground state, with the former thermodynamically favorable by ∼3 kcal/mol. These results are consistent with the experimental observation of both conformations. To analyze the proton relay from Tyr21 to the flavin via Gln63, the free-energy profiles for Gln63 rotation were calculated on the ground state, the locally excited state of the flavin, and the charge-transfer state associated with electron transfer from Tyr21 to the flavin. For the Trpin/Metout conformation, the hydrogen-bonding pattern conducive to the proton relay is not thermodynamically favorable on the ground state but becomes more favorable, corresponding to approximately half of the configurations sampled, on the locally excited state. The calculated energy gaps between the locally excited and charge-transfer states suggest that electron transfer from Tyr21 to the flavin is more facile for configurations conducive to proton transfer. When the active site conformation is not conducive to PCET from Tyr21, Trp104 can directly compete with Tyr21 for electron transfer to the flavin through a nonproductive pathway, impeding the signaling efficiency.

scholarly journals Locally Excited State-Charge Transfer State Coupled Dyes as Optically Responsive Neuron Firing Probes

2017 ◽  
Vol 23 (58) ◽  
pp. 14639-14649 ◽  
Author(s):  
Dumitru Sirbu ◽  
John B. Butcher ◽  
Paul G. Waddell ◽  
Peter Andras ◽  
Andrew C. Benniston
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Charge Transfer State ◽  
Neuron Firing ◽  
Locally Excited ◽  
Locally Excited State ◽  
State Charge ◽  
Transfer State

Target-assembled exciplexes based on Scorpion oligonucleotides

2008 ◽  
Vol 28 (1) ◽  
pp. 1-5 ◽  
Author(s):  
Abdul Gbaj ◽  
Lindsey Walsh ◽  
Maria Candelaria Rogert ◽  
Alireza Sardarian ◽  
Elena V. Bichenkova ◽  
...  
Keyword(s):  
Excited State ◽  
Dna Probe ◽  
Hairpin Loop ◽  
Specific Detection ◽  
Locally Excited ◽  
Fluorescence Change ◽  
Exciplex Emission ◽  
Locally Excited State ◽  
Phosphate Groups

Scorpion probes, specific DNA probe sequences maintained in a hairpin–loop, can be modified to carry the components of an exciplex for use as a novel fluorescence-based method for specific detection of DNA. The exciplex partners (5′-pyrenyl and 3′-naphthalenyl) were attached to oligonucleotides via phosphoramidate links to terminal phosphate groups. Hybridization of the probe to a complementary target in a buffer containing trifluoroethanol produced an obvious fluorescence change from blue (pyrene locally excited state emission) to green (exciplex emission).

scholarly journals Solvent-dependent photochemical dynamics of a phenoxazine-based photoredox catalyst

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1475-1494 ◽  
Author(s):  
Mahima Sneha ◽  
Luke Lewis-Borrell ◽  
Darya Shchepanovska ◽  
Aditi Bhattacherjee ◽  
Jasper Tyler ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Radiative Decay ◽  
Radiative Lifetime ◽  
Dimethyl Formamide ◽  
Iridium Complexes ◽  
Locally Excited ◽  
State Recovery ◽  
Quantum Chemistry Calculations ◽  
Excited State Lifetimes

AbstractOrganic substitutes for ruthenium and iridium complexes are increasingly finding applications in chemical syntheses involving photoredox catalysis. However, the performance of these organic compounds as electron-transfer photocatalysts depends on their accessible photochemical pathways and excited state lifetimes. Here, the UV-induced dynamics of N-phenyl phenoxazine, chosen as a prototypical N-aryl phenoxazine organic photoredox catalyst, are explored in three solvents, N,N-dimethyl formamide, dichloromethane and toluene, using ultrafast transient absorption spectroscopy. Quantum chemistry calculations reveal the locally excited or charge-transfer electronic character of the excited states, and are used to assign the transient electronic and vibrational bands observed. In toluene-d8, complete ground-state recovery is (31 ± 3) % by internal conversion (IC) from the photo-excited state (or from S1 after IC but before complete vibrational relaxation), (13 ± 2) % via direct decay from vibrationally relaxed S1 (most likely radiative decay, with an estimated radiative lifetime of 13 ns) and (56 ± 3) % via the T1 state (with intersystem crossing (ISC) rate coefficient kISC = (3.3 ± 0.2) × 108 s−1). In dichloromethane, we find evidence for excited state N-phenyl phenoxazine reaction with the solvent. Excited state lifetimes, ISC rates, and ground-state recovery show only modest variation with changes to the solvent environment because of the locally excited character of the S1 and T1 states.

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