No abstract

Nanoparticle organic hybrid materials (NOHMs) have been recently developed that comprise an oligomeric or polymeric canopy tethered to surface-modified nanoparticles via ionic or covalent bonds. It has already been shown that the tunable nature of the grafted polymeric canopy allows for enhanced CO(2) capture capacity and selectivity via the enthalpic intermolecular interactions between CO(2) and the task-specific functional groups, such as amines. Interestingly, for the same amount of CO(2) loading NOHMs have also exhibited significantly different swelling behavior compared to that of the corresponding polymers, indicating a potential structural effect during CO(2) capture. If the frustrated canopy species favor spontaneous ordering due to steric and/or entropic effects, the inorganic cores of NOHMs could be organized into unusual structural arrangements. Likewise, the introduction of small gaseous molecules such as CO(2) could reduce the free energy of the frustrated canopy. This entropic effect, the result of unique structural nature, could allow NOHMs to capture CO(2) more effectively. In order to isolate the entropic effect, NOHMs were synthesized without the task-specific functional groups. The relationship between their structural conformation and the underlying mechanisms for the CO(2) absorption behavior were investigated by employing NMR and ATR FT-IR spectroscopies. The results provide fundamental information needed for evaluating and developing novel liquid-like CO(2) capture materials and give useful insights for designing and synthesizing NOHMs for more effective CO(2) capture.

Here, we compare analogous cyclic and acyclic π-conjugated molecules as n-type electronic materials and find that the cyclic molecules have numerous benefits in organic photovoltaics. This is the first report of such a direct comparison. We designed two conjugated cycles for this study. Each comprises four subunits: one combines four electron-accepting, redox-active, diphenyl-perylenediimide subunits, and the other alternates two electron-donating bithiophene units with two diphenyl-perylenediimide units. We compare the macrocycles to acyclic versions of these molecules and find that, relative to the acyclic analogs, the conjugated macrocycles have bathochromically shifted UV-vis absorbances and are more easily reduced. In blended films, macrocycle-based devices show higher electron mobility and good morphology. All of these factors contribute to the more than doubling of the power conversion efficiency observed in organic photovoltaic devices with these macrocycles as the n-type, electron transporting material. This study highlights the importance of geometric design in creating new molecular semiconductors. The ease with which we can design and tune the electronic properties of these cyclic structures charts a clear path to creating a new family of cyclic, conjugated molecules as electron transporting materials in optoelectronic and electronic devices.

We report an investigation of the nuclear spin-lattice relaxation of H 2 and H 2 @C 60 1 as a function of solvent and temperature. These studies explore and compare the nature of the interactions of a guest H 2 molecule confined transiently within the walls of a solvent cavity and a guest H 2 molecule encapsulated within the walls of the C 60 cavity.The relaxation time (T 1 ) of H 2 has been extensively studied in the gas phase and in liquid hydrogen at low temperatures. 6 The values of T 1 are 10-20 times smaller for H 2 @C 60 than for H 2 even though the ratios of T 1 for H 2 and H 2 @C 60 are similar in all the solvents.The temperature dependences of T 1 for H 2 and H 2 @C 60 were investigated in detail for toluene-d 8 ( Figure 1) and for benzene-d 6 , 1,1,2,2-tetrachloroethane-d 2 , 1,2-dichlorobenzene-d 4 , and chloroformd 1 . Striking features of the data are the occurrence of a maximum for T 1 at ∼240 K for both the H 2 and H 2 @C 60 in toluene-d 8 and a ratio of T 1 values which is nearly independent of temperature. A maximum of the value of T 1 with temperature is also found in 1,1,2,2-tetrachloroethane-d 2 and chloroform-d 1 . For benzene-d 6 and 1,2-dichlorobenzene-d 4 in the available range of temperatures, only a decrease of T 1 with increasing temperature was observed.This kind of dependence of T 1 on temperature is uncommon, although a maximum of T 1 has previously been observed for small molecules such as H 2 O, 7 HCl, and HBr in solution, 8,9 and it is consistent with two relaxation mechanisms with different temperature dependences dominating in turn below and above 240 K for both H 2 and H 2 @C 60 . Since the value of T 1 for both H 2 and H 2 @C 60 does not significantly change in going from benzene-h 6 to benzened 6 (Table 1), the dominating interactions determining H 2 and H 2 @C 60 nuclear relaxation must be intramolecular. Furthermore, the intramolecular dipole-dipole interaction and spin-rotation interaction are known 2 to be responsible for the relaxation of gaseous H 2 and their magnitude has been measured for H 2 in molecular beams. 10 Therefore it is likely that the relaxation of H 2 in solution also depends on the competition between intramolecular dipole-dipole interaction and spin-rotation interaction.The contribution to 1/T 1 (in extreme narrowing conditions) from intramolecular dipolar and spin-rotation interaction may be estimated by eq 1 2 and eq 2, 11,12 respectively:where γ H is the magnetogyric ratio for the proton, r is the equilibrium internuclear distance of H 2 (0.74 Å), C is the spinrotation coupling constant (7.16 × 10 5 rad s -1 ), 10 I is the moment of inertia of H 2 (4.6 × 10 -48 kg m 2 ), and k B is the Boltzmann constant. The correlation times τ dip and τ sr are measures of the timedependent fluctuations in the orientation and angular velocity of H 2 , respectively. Both correlation times are expected to be functions of viscosity and temperature which depend on the details of the motion of H 2 molecules and the surrounding medium. 11 Qualitatively, the dipole-...