The increasing energy demand in the near future will force us to seek environmentally clean alternative energy resources. The emergence of nanomaterials as the new building blocks to construct light energy harvesting assemblies has opened up new ways to utilize renewable energy sources. This article discusses three major ways to utilize nanostructures for the design of solar energy conversion devices:  (i) Mimicking photosynthesis with donor−acceptor molecular assemblies or clusters, (ii) semiconductor assisted photocatalysis to produce fuels such as hydrogen, and (iii) nanostructure semiconductor based solar cells. This account further highlights some of the recent developments in these areas and points out the factors that limit the efficiency optimization. Strategies to employ ordered assemblies of semiconductor and metal nanoparticles, inorganic-organic hybrid assemblies, and carbon nanostructures in the energy conversion schemes are also discussed. Directing the future research efforts toward utiliza...

Meeting the Clean Energy Demand: Nanostructure Architectures for Solar Energy Conversion

By using bifunctional surface modifiers (SH−R−COOH), CdSe quantum dots (QDs) have been assembled onto mesoscopic TiO2 films. Upon visible light excitation, CdSe QDs inject electrons into TiO2 nanocrystallites. Femtosecond transient absorption as well as emission quenching experiments confirm the injection from the excited state of CdSe QDs into TiO2 nanoparticles. Electron transfer from the thermally relaxed s-state occurs over a wide range of rate constant values between 7.3 × 109 and 1.95 × 1011 s-1. The injected charge carriers in a CdSe-modified TiO2 film can be collected at a conducting electrode to generate a photocurrent. The TiO2−CdSe composite, when employed as a photoanode in a photoelectrochemical cell, exhibits a photon-to-charge carrier generation efficiency of 12%. Significant loss of electrons occurs due to scattering as well as charge recombination at TiO2/CdSe interfaces and internal TiO2 grain boundaries.

Quantum dot solar cells. harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic TiO2 films.

Noncovalent interactions: a challenge for experiment and theory

Molecular Clusters of π-Systems: Theoretical Studies of Structures, Spectra, and Origin of Interaction Energies

London dispersion, which constitutes the attractive part of the famous van der Waals potential, has long been underappreciated in molecular chemistry as an important element of structural stability, and thus affects chemical reactivity and catalysis. This negligence is due to the common notion that dispersion is weak, which is only true for one pair of interacting atoms. For increasingly larger structures, the overall dispersion contribution grows rapidly and can amount to tens of kcal mol(-1) . This Review collects and emphasizes the importance of inter- and intramolecular dispersion for molecules consisting mostly of first row atoms. The synergy of experiment and theory has now reached a stage where dispersion effects can be examined in fine detail. This forces us to reconsider our perception of steric hindrance and stereoelectronic effects. The quantitation of dispersion energy donors will improve our ability to design sophisticated molecular structures and much better catalysts.

London Dispersion in Molecular Chemistry—Reconsidering Steric Effects

ZEKE Spectroscopy of Complexes and Clusters

Site-specific excitation in molecules at very high energies: changes in ionization patterns of 1,1,1-trifluoroethane (CF3CH3)

ZEKE (zero-kinetic-energy) photoelectron spectra of p-difluorobenzene (p-DFB) were obtained by two-color 1+1' photoionization via the S 1 , 0 0 , 3 1 , 6 1 , 9 2 , 17 1 , 27 1 , and 30 1 vibrational states as intermediate resonances. The ZEKE spectra show substantial activity in transitions to combination bands with totally symmetric modes and a number of transitions which are symmetry forbidden under D 2h symmetry. New fundamentals and combination bands of the electronic ground state of the cation are assigned, and improved vibrational frequencies are derived. Ab initio SCF calculations on the S 0 and S 1 states of p-DFB and the ground ionic state are presented and discussed in comparison to the experimental results

Zero-kinetic-energy (ZEKE) photoelectron spectroscopy of p-difluorobenzene via different intermediate vibrational levels in the S1 state

One-color two-photon ionization of methyl iodide, resulting in the CH3I+ and CD3I+ ions in the 2E3/2 and 2El/z electronic states, is investigated using the zero kinetic energy (ZEKE) photoelectron technique. Unlike the conventional photoelectron spectra, the two-photon spectra are resonantly enhanced via the dissociative A-state continuum and exhibit an extensive vibrational structure. A long progression in the C-I stretching vibration ug+ is observed, and reliable values for all the vibrational frequencies of the ions and for the ionization potentials are obtained. The appearance of the spectra is discussed in terms of consecutive two-photon absorption via a dissociative intermediate state and a time-dependent picture of spectroscopy. Experimental evidence for the influence of the asymmetric V6 vibration on the photodissociation process is presented. It is shown that two-photon ZEKE spectroscopy via a dissociative intermediate state can serve as a powerful probe of the photodissociation dynamics. It also allows one to explore regions of the ground-state potential energy surface of the ion that are far from equilibrium.

Photodissociation Dynamics of CH3I and CD3I Probed by Zero Kinetic Energy Photoelectron Spectroscopy

The hydrogen-bonded phenol-ethanol complex has been studied using both two-color resonant-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) photoelectron spectroscopy. The REMPI spectrum shows vibrational structure which can be assigned to low-frequency intermolecular modes on the S 1 origin and in combination with intramolecular (phenol-localized) vibrations of the S 1 electronic state: a reinterpretation of the low-energy region of the REMPI spectrum gives the frequency of the intermolecular stretch in the S 1 state as 162 cm -1

Vibrational spectroscopy of the phenol-ethanol cation

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