Photorelaxation Research Articles

Photo Relaxation Change and Emission Quenching in Different Sizes of PbS‐Nanoparticles‐Protein Corona

AbstractIn this study, energy transfer from BSA to different size semiconductor nanoparticles PbS was analyzed by using photo Relaxation change and emission quenching analysis. Structures of thePbS NPs are studied by XRD, TEM, and FT‐IR measurements. The band gap and crystal size of PbS suggest the quantum confinement effect. Photo current of the BSA‐PbS NPs bioconjugate system increased compared to bare PbS nanoparticles from nA to μA. Change in photo relaxation life time of the bare PbS NP and PbS NPs‐BSA bioconjugate system is particle size dependent and interaction dependent. PbS NPs‐BSA bioconjugate were characterized by steady‐state fluorescence spectroscopy to determine the magnitude and mechanism of the energy transfer. It was found that the BSA fluorescence was quenched after the addition of PbS nanoparticles. Quenching of protein is large for larger size PbS nanoparticles. DLS study confirmed that BSA was adsorbed onto the surface of nanoparticles, creating a favourable geometry for quenching. Aggregation of BSA around a single PbS nanoparticle is size dependent. Larger nanoparticles are responsible for hard as well as soft corona due to interaction.Our results, which include photo relaxation times, energy transfer efficiencies showed that energy transferred take place via the Fluorescence Resonance Energy Transfer (FRET) mechanism. These energy transfer processes between protein molecules and PbS nanoparticles, will depend on the size of the particles involved.

The excited state dynamics study of di‐2‐pyridylketone in the A‐band and B‐band absorptions by using resonance Raman spectroscopy, IR and UV–visible spectroscopy

Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S0→S4) photo relaxation dynamics have substantial difference from that of B band (S0→S10) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of hydrogen bond and solvent polarity on the C=O stretching of bis(2-thienyl)ketone in solution

The optimized structural parameters, the absorption and the resonance Raman spectra have been investigated for the bis(2-thienyl)ketone in gas phase, in cyclohexane, methanol, and acetonitrile solvents by means of time dependent density functional theory calculations, the solvent electronic polarization effect on the solvation shift is examined and in well accordance with the calculation. The effect of increasing the polarity of the solvent is well represented by the polarizable continuum model, both for the absorption spectra and resonance Raman intensities. The Raman spectra of the C=O stretching mode, which is sensitive to the intermolecular interaction for bis(2-thienyl)ketone dissolved in solvents, were systematically studied. It was found that the hydrogen bond effect plays an important role in reducing the carbonyl stretching wavenumbers. The results of Raman shifts were interpreted through the dilution effect, solvation effects, and hydrogen bond-forming effects. Furthermore, the excitation profiles of several important Raman bands of bis(2-thienyl)ketone molecule in different solvents have been critically analyzed. The solvent effects on structural and symmetry properties of the molecule in S2 electronic state as well as the short-time photo relaxation dynamics have been discussed.

Photodecay dynamics of octaethylporphine in the condensed phase explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman spectra of free-base octaethylporphine (OEP) were obtained with 368.9 nm, 397.9 nm and 416.0 nm excitation wavelengths, and density functional calculations were done to help the elucidation of Soret ( B x and B y -band) electronic transitions and the corresponding photo relaxation dynamics of OEP. The RRs indicate that the Franck–Condon region photo relaxation dynamics upon S 0 → S 8 eletronic transition is predominantly along the totally symmetric C mC α stretch, the C βC β stretch, and simultaneously along the asymmetric δ(pyr deformation), γ(CH 2) vibrational relaxation processes. The excited state structural dynamics of OEP determined from resonance Raman spectra show that the internal conversion between B y and B x electronic states occurs in tens of femtoseconds and the electronic relaxation dynamics were firstly interpreted with account of the time-dependent wave packet theory and Herzberg–Teller (vibronic coupling) contributions.

Resonance Raman spectroscopy and density functional theory calculation study of photodecay dynamics of tetra(4-carboxyphenyl) porphyrin

The 397.9 nm, 416.0 nm and 435.7 nm resonance Raman spectra were acquired for meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP) in tetrahydrofuran solution, and the Raman effect of relaxation dynamics was analyzed according to Herzberg-Teller (vibronic coupling) contributions. Density functional calculations were done to help the elucidation of the Soret (B(x) and B(y)-band) electronic transitions and the corresponding photo relaxation dynamics of TCPP. The spectra indicate that the Franck-Condon region photo relaxation dynamics upon S(0) → S(4) electronic transition are predominantly along the totally symmetric C(m)-ph stretch and Porphin ring breath stretch, and simultaneously along the asymmetric ν(C(m)-Phenyl) + δ(N-H) and ν(C(α)-C(m)-C(α))(as) + def (pyr) vibrational relaxation processes. The excited state structural dynamics of TCPP determined from the resonance Raman spectra show that the internal conversion between the B(y) and B(x) electronic states occurs in tens of femtoseconds, and the electronic relaxation dynamics were firstly interpreted taking into account the time-dependent wave packet theory and Herzberg-Teller (vibronic coupling) contributions.

Investigation of Excited State Structural Dynamics of Bis(2-thienyl)ketone in the Condensed Phase Using Raman, IR, and UV−visible Spectroscopy Aided by Density Functional Theory Calculation

Detailed investigation on the vibrational and electronic spectra has been carried out in order to study various properties of bis(2-thienyl)ketone molecule in its ground and excited electronic states. To get insight into the structural and symmetry features of the molecule, resonance Raman spectra (RRs) of bis(2-thienyl)ketone have been acquired and the Raman excitation profiles of several normal modes have been analyzed, and density functional calculations were done to help the elucidation of the photo relaxation dynamics of A and B band electronic transitions. The RRs indicate that the photo relaxation dynamics for S(0)→S(2) excited electronic state is predominantly along the nominal the Ring breathing + ν(SynC(1)C(11) C(9)) stretch, ν(CO) + ν(C(2)C(3)) + ν(C(8)C(9)) stretch, and the γ(CH(I, II)) + γ(OC) stretch and simultaneously along the nominal γ(CH(II)) relaxation processes, while that for S(0)→S(5) is predominantly along the ν(CO) + ν(C(2)C(3)) + ν(C(8)C(9)) stretch ν(7) (1616 cm(-1)). The excited state short-time structural dynamics of bis (2-thienyl) ketone determined from RRs were interpreted with account of the Albrecht's theory and Herzberg-Teller contributions.

The photophysics of flavins: What makes the difference between gas phase and aqueous solution?

The ground and low-lying excited electronic states of isoalloxazine, 10-methylisoallox-azine and lumiflavin, three flavin-related compounds, were investigated by means of quantum chemical methods. Minimum structures were determined employing (time-dependent) Kohn–Sham density functional theory. Spectral properties were computed utilizing a combined density functional and multi-reference configuration interaction (DFT/MRCI) method. Solvent effects were mimicked by a conductor like screening model and micro-hydration with four explicit water molecules. At selected points along a linearly interpolated path connecting the Franck–Condon region and the S 1minimum, spin–orbit interaction was computed employing a nonempirical mean-field Hamiltonian. For isoalloxazine, intersystem crossing (ISC) rate constants were computed, taking both direct and vibronic spin–orbit coupling into account. On the basis of these calculations we suggest the following photo relaxation model. In the vacuum, efficient ISC ( k ISC ≈ 1 0 9 s − 1 ) takes place between the primarily excited ( π → π ∗ ) 1 state (S 1) and the lowest ( n → π ∗ ) 3 state (T 2). The energetic proximity of the ( n → π ∗ ) 1 state (S 2) enhances the nonradiative relaxation of S 1 by internal conversion (IC). In aqueous solution these ISC and IC channels are energetically not accessible due to the blue shift of the ( n → π ∗ ) states. The high triplet quantum yield observed in experiment [J.T.M. Kennis, S. Crosson, M. Gauden, I.H.M. van Stokkum, K. Moffat, R. van Grondelle, Biochemistry 42 (2003) 3385–3392] is explained by the intersection between the ( π → π ∗ ) 1 state (S 1) potential energy hypersurface (PEH) and the second ( π → π ∗ ) 3 (T 2) PEH along the relaxation pathway and the strong enhancement of their spin–orbit coupling by vibronic interactions. The calculated ISC rate for this channel ( k ISC ≈ 1 0 8 s − 1 ) is in good agreement with experimental results. According to our model, lack of an efficient IC channel leads to an increased fluorescence quantum yield in aqueous solution.

Endothelium-dependent relaxation, endothelium-derived relaxing factor and photorelaxation of blood vessels.

Endothelium-dependent relaxation, endothelium-derived relaxing factor and photorelaxation of blood vessels.