RESUMEN
Blebbistatin was demonstrated as a promising two-photon near-infrared activated photoremovable protecting group of hydroxyl radicals with various potential applications. However, the photocleavage mechanism of the blebbistatin derivatives remains ambiguous. Herein, blebbistatin derivatives with various electronic characteristic leaving groups were synthesized and studied, and the photocleavage mechanism(s) and the tunable effect of the leaving groups were unveiled by combining photoproduct analysis, reactive oxygen radical species detection, femtosecond transient absorption spectroscopy, and density functional theory calculation. More substantial electron-withdrawing leaving groups facilitate heterolysis of the C-O bond, which results in a cationic intermediate and a corresponding remnant. Weaker electron-withdrawing groups lead to a higher proportion of homolysis of the C-O bond, accompanied by the generation of the reactive oxygen radical species. With this structure-property relationship, the protected groups of the molecules of interest can be rationally chosen to satisfy the different requirements needed for specific applications.
RESUMEN
Photolysis of pyridazine N-oxide (PNO) results in the detection of a complex series of transient phenomena. On the ultrafast (fs) timescale, we could detect the decay of the first singlet excited state of PNO and the formation of a short-lived transient species, which, based on its time-resolved resonance Raman (TR3) spectrum, we assign to oxaziridine 1,2-diaza-7-oxa-bicyclo[4.1.0]hepta-2,4-diene. On a longer (hundreds of ns) timescale, this species rearranges to a ring-opened diazo compound, which we have also detected by time-resolved infrared and TR3 spectroscopy. In addition, we identify 1-oxa-3,4-diazepine as a long-lived species formed in the photochemistry of PNO. This species is formed via its oxirane isomer, which in turn is likely formed directly from the S1 state of PNO via a conical intersection. The barrier determined experimentally for the decay of 1,2-diaza-7-oxa-bicyclo[4.1.0]hepta-2,4-diene (Ea = (7.1 ± 0.5) kcal mol-1) is far larger than any barrier calculated by any method that includes dynamic electron correlation but very close to the barriers calculated at the RHF or CASSCF levels of theory. Many methods (B3LYP, MP2, and MP4) fail to give a minimum structure for 1,2-diaza-7-oxa-bicyclo[4.1.0]hepta-2,4-diene, while M06, M06-2X, MP3, CCSD, or CCSD(T) yield activation energies for its electrocyclic ring opening that are far too small. In addition, we note that several important geometric parameters, both of 1,2-diaza-7-oxa-bicyclo[4.1.0]hepta-2,4-diene and of the transition state of its ring opening reaction, clearly have reached no convergence, even at the fully optimized CCSD(T)/cc-pVTZ level of theory. We therefore suggest that the transient species described in this contribution might be excellent test molecules for further development of highly correlated and density functional theory methods.
RESUMEN
Aggregation-induced emission (AIE) is a photophysical phenomenon correlated closely with the excited-state intramolecular motions. Although AIE has attracted increasing attention due to the significant applications in biomedical and optoelectronics, an in-depth understanding of the excited-state intramolecular motion has yet to be fully developed. Here we found the non-aromatic annulene derivative of cyclooctatetrathiophene shows typical AIE phenomenon in spite of its rotor-free structure. The underlying mechanism is investigated through photoluminescence spectra, time-resolved absorption spectra, theoretical calculations, circular dichroism as well as by pressure-dependent fluorescent spectra etc., which indicate that the aromaticity reversal from ground state to the excited state serves as a driving force for inducing the excited-state intramolecular vibration, leading to the AIE phenomenon. Therefore, aromaticity reversal is demonstrated as a reliable strategy to develop vibrational AIE systems. This work also provides a new viewpoint to understand the excited-state intramolecular motion behavior of lumiongens.
RESUMEN
A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII(ttp)(IMe)2]+ (2a), [IrIII(oep)(BIMe)2]+ (2d), [IrIII(oep)(I i Pr)2]+ (2e) and [IrIII(F20tpp)(IMe)2]+ (2f) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 Å and long Ir-CNHC bonds of 2.100-2.152 Å. Variable-temperature 1H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol-1. The UV-vis absorption spectra of IrIII(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the 1MLCT dπ(Ir) â π*(por) transition. The near-infrared phosphorescence of IrIII(por)-NHC complexes from the porphyrin-based 3(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (Φ em < 0.01; τ < 4 µs). [IrIII(por)(IMe)2]+ complexes (por = ttp and oep) are efficient photosensitizers for 1O2 generation (Φ so = 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC50 values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC50 values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of [IrIII(oep)(IMe)2]+ (2c) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. [IrIII(oep)(IMe)2]+ catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.
RESUMEN
Aggregation-induced emission (AIE) is the long-sought solution to the problem of aggregation-caused quenching that has hampered efficient application of fluorescent organic materials. An important goal on the way to fully understand the working mechanism of the AIE process was, for more than a decade, and still remains obtaining more comprehensive insights into the correlation between the ultrafast excited-state dynamics in tetraphenylethylene (TPE)-based molecules and the AIE effect in them. Here we report a number of TPE-based derivatives with varying structural rigidities and AIE properties. Using a combination of ultrafast time-resolved spectroscopy and computational studies, we observe a direct correlation between the state-dependent coupling motions and inhibited fluorescence, and prove the existence of photocyclized intermediates in them. We demonstrate that the dominant non-radiative relaxation dynamics, i.e. formation of intermediate or rotation around the elongated C[double bond, length as m-dash]C bond, is responsible for the AIE effect, which is strongly structure-dependent but not related to structural rigidity.
RESUMEN
Resonance Raman spectra were obtained for 2-nitrophenol in cyclohexane solution with excitation wavelengths in resonance with the charge-transfer (CT) proton transfer band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion along more than 15 normal modes: the nominal CCH bend+CC stretch nu(12) (1326 cm(-1)), the nominal CCC bend nu(23) (564 cm(-1)), the nominal CO stretch+NO stretch+CC stretch nu(14) (1250 cm(-1)), the nominal CCH bend+CC stretch+COH bend nu(15) (1190 cm(-1)); the nominal CCH bend+CC stretch nu(17) (1134 cm(-1)), the nominal CCC bend+CC stretch nu(22) (669 cm(-1)), the nominal CCN bend nu(27) (290 cm(-1)), the nominal NO(2) bend+CC stretch nu(21) (820 cm(-1)), the nominal CCO bend+CNO bend nu(25) (428 cm(-1)), the nominal CC stretch nu(7) (1590 cm(-1)), the nominal NO stretch nu(8) (1538 cm(-1)), the nominal CCC bend+NO(2) bend nu(20) (870 cm(-1)), the nominal CC stretch nu(6) (1617 cm(-1)), the nominal COH bend+CC stretch nu(11) (1382 cm(-1)), nominal CCH bend+CC stretch nu(9) (1472 cm(-1)). A preliminary resonance Raman intensity analysis was done and the results for 2-nitrophenol were compared to previously reported results for nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone. The authors briefly discuss the differences and similarities in the CT-band absorption excitation of 2-nitrophenol relative to those of nitrobenzene, p-nitroaniline, and 2-hydroxyacetophenone.