Electronic Relaxation Dynamics in 2-Quinolinones with Extended Conjugation.

The 2-quinolinone family of molecules, also known as carbostyrils, have been proposed as light absorbing donor molecules in energy transfer based sensing schemes and as possible photocatalysts. Both of these applications make use of electronic excited states, but the photophysics of 2-quinolinones have not yet been examined closely. This study applies static and dynamic spectroscopy, with supporting density functional theory calculations, to reveal the electronic relaxation dynamics of a family of five 2-quinolinones with extended conjugated rings.

Elucidating the Solution-Phase Structure and Behavior of 8-Hydroxyquinoline Zinc in DMSO.

The solution-phase structure and electronic relaxation dynamics of zinc bis-8-hydroxyquinoline [Zn(8HQ)] in dimethyl sulfoxide (DMSO) were examined using a broad array of spectroscopic techniques, complimented by ab initio calculations of molecular structure. The ground-state structure was determined using extended X-ray absorption fine structure (EXAFS) data collected on the Zn K-edge and diffusion ordered spectroscopy (DOSY) NMR. The complex was found to be monomeric and octahedral, with two bidentate 8-hydroxyquinolate ligands and two DMSO molecules coordinated to the zinc through oxygen atoms.

Controlling quantum-beating signals in 2D electronic spectra by packing synthetic heterodimers on single-walled carbon nanotubes.

In multidimensional spectroscopy, dynamics of coherences between excited states report on the interactions between electronic states and their environment. The prolonged coherence lifetimes revealed through beating signals in the spectra of some systems may result from vibronic coupling between nearly degenerate excited states, and recent observations confirm the existence of such coupling in both model systems and photosynthetic complexes. Understanding the origin of beating signals in the spectra of photosynthetic complexes has been given considerable attention; however, strategies to generate them in artificial systems that would allow us to test the hypotheses in detail are still lacking.

Ultrafast energy transfer from rigid, branched side-chains into a conjugated, alternating copolymer.

We present the synthesis and characterization of a benzodithiophene/thiophene alternating copolymer decorated with rigid, singly branched pendant side chains. We characterize exciton migration and recombination dynamics in these molecules in tetrahydrofuran solution, using a combination of static and time-resolved spectroscopies. As control experiments, we also measure electronic relaxation dynamics in isolated molecular analogues of both the side chain and polymer moieties.

Response to Comment on "Engineering coherence among excited states in synthetic heterodimer systems".

Halpin, Johnson, and Miller contest our assignment of quantum beating signals observed in the two-dimensional electronic spectra of a series of fluorescein heterodimers to electronic coherences. Here, we present resonance Raman spectra, statistical analysis on multiple data sets, and an explanation of differences between the family of molecules described in our Report and the homodimer examined by the commenters. We contend that these results all support our assignment of the beating signals to electronic coherences.

Persistent Inter-Excitonic Quantum Coherence in CdSe Quantum Dots.

The creation and manipulation of quantum superpositions is a fundamental goal for the development of materials with novel optoelectronic properties. In this letter, we report persistent (~80 fs lifetime) quantum coherence between the 1S and 1P excitonic states in zinc-blende colloidal CdSe quantum dots at room temperature, measured using Two-Dimensional Electronic Spectroscopy. We demonstrate that this quantum coherence manifests as an intradot phenomenon, the frequency of which depends on the size of the dot excited within the ensemble of QDs.

Exploring size and state dynamics in CdSe quantum dots using two-dimensional electronic spectroscopy.

Development of optoelectronic technologies based on quantum dots depends on measuring, optimizing, and ultimately predicting charge carrier dynamics in the nanocrystal. In such systems, size inhomogeneity and the photoexcited population distribution among various excitonic states have distinct effects on electron and hole relaxation, which are difficult to distinguish spectroscopically. Two-dimensional electronic spectroscopy can help to untangle these effects by resolving excitation energy and subsequent nonlinear response in a single experiment.

Engineering coherence among excited states in synthetic heterodimer systems.

The design principles that support persistent electronic coherence in biological light-harvesting systems are obscured by the complexity of such systems. Some electronic coherences in these systems survive for hundreds of femtoseconds at physiological temperatures, suggesting that coherent dynamics may play a role in photosynthetic energy transfer. Coherent effects may increase energy transfer efficiency relative to strictly incoherent transfer mechanisms.

Two-dimensional electronic spectroscopy of CdSe nanoparticles at very low pulse power.

Nanoparticles have been proposed as a promising material for creating devices that harvest, transport, and manipulate energy and electrons. Ultrafast charge carrier dynamics represent a critical design aspect and are dependent on both size and shape of the nanoparticle. Spectroscopic investigation of the electronic structure and dynamics of these systems is complicated by sample inhomogeneity, which broadens peaks and leads to ambiguity in interpretation of both spectra and dynamics.

Inhomogeneous dephasing masks coherence lifetimes in ensemble measurements.

An open question at the forefront of modern physical sciences is what role, if any, quantum effects may play in biological sensing and energy transport mechanisms. One area of such research concerns the possibility of coherent energy transport in photosynthetic systems. Spectroscopic evidence of long-lived quantum coherence in photosynthetic light-harvesting pigment protein complexes (PPCs), along with theoretical modeling of PPCs, has indicated that coherent energy transport might boost efficiency of energy transport in photosynthesis.

Electronic relaxation dynamics in large anionic water clusters: (H2O)n(-) and (D2O)n(-) (n = 25-200).

Electronic relaxation dynamics subsequent to s --> p excitation of the excess electron in large anionic water clusters, (H(2)O)(n)(-) and (D(2)O)(n)(-) with 25 < or = n < or = 200, were investigated using time-resolved photoelectron imaging. Experimental improvements have enabled considerably larger clusters to be probed than in previous work, and the temporal resolution of the instrument has been improved. New trends are seen in the size-dependent p-state lifetimes for clusters with n > or = 70, suggesting a significant change in the electron-water interaction for clusters in this size range.

Auger recombination and excited state relaxation dynamics in Hg(n)(-) (n=9-20) anion clusters.

Using femtosecond time-resolved photoelectron imaging, electron-hole pairs are created in size-selected Hg(n)(-) anion clusters (n=9-20), and the subsequent decay dynamics are measured. These clusters eject electrons via Auger decay on time scales of 100-600 fs. There is an abrupt increase in the Auger decay time for clusters larger than Hg(12)(-), coinciding with the onset of the transition from van der Waals to covalent bonding in mercury clusters.

Photoinduced electron transfer and solvation in iodide-doped acetonitrile clusters.

We have used ultrafast time-resolved photoelectron imaging to measure charge transfer dynamics in iodide-doped acetonitrile clusters I(-)(CH(3)CN)(n) with n = 5-10. Strong modulations of vertical detachment energies were observed following charge transfer from the halide, allowing interpretation of the ongoing dynamics. We observe a sharp drop in the vertical detachment energy (VDE) within 300-400 fs, followed by a biexponential increase that is complete by approximately 10 ps.

Time-resolved photoelectron imaging of large anionic methanol clusters: (methanol)n-(n approximately 145-535).

The dynamics of an excess electron in size-selected methanol clusters is studied via pump-probe spectroscopy with resolution of approximately 120 fs. Following excitation, the excess electron undergoes internal conversion back to the ground state with lifetimes of 260-175 fs in (CH3OH)n- (n=145-535) and 280-230 fs in (CD3OD)n- (n=210-390), decreasing with increasing cluster size. The clusters then undergo vibrational relaxation on the ground state on a time scale of 760+/-250 fs.

Photoelectron imaging of large anionic methanol clusters: (MeOH)n - (n approximately 70-460).

Electron solvation in methanol anion clusters, (MeOH)(n) (-) (n approximately 70-460), is studied by photoelectron imaging. Two isomers are observed: methanol I, with vertical binding energies (VBE) ranging from 2-2.5 eV, and methanol II, with much lower VBE's between 0.

Electron solvation in water clusters following charge transfer from iodide.

The dynamics following charge transfer to solvent from iodide to a water cluster are studied using time-resolved photoelectron imaging of I-(H2O)n and I-(D2O)n clusters with n< or =28. The results show spontaneous conversion, on a time scale of approximately 1 ps, from water cluster anions with surface-bound electrons to structures in which the excess electron is more strongly bound and possibly more internalized within the solvent network. The resulting dynamics provide valuable insight into the electron solvation dynamics in water clusters and the relative stabilities between recently observed isomers of water cluster anions.

Dynamics of charge-transfer-to-solvent precursor states in I- (water)n (n = 3-10) clusters studied with photoelectron imaging.

The dynamics of charge-transfer-to-solvent states are studied in I- (H2O)(n=3-10) clusters and their deuterated counterparts using time-resolved photoelectron imaging. The photoelectron spectra for clusters with n > or = 5 reveal multiple time scales for dynamics after their electronic excitation. An increase in the vertical detachment energy (VDE) by several hundred millielectronvolts on a time scale of approximately 1 ps is attributed to stabilization of the excess electron, primarily through rearrangement of the solvent molecules, but a contribution to this stabilization from motion of the I atom cannot be ruled out.