Effects of structural disorder on the optical properties of molecular crystals

Defects Cause Subgap Luminescence from a Crystalline Tetracene Derivative

We use steady-state and ultrafast nonlinear spectroscopies in combination with density functional theory calculations to explain light emission below the optical gap energy (E_o) of crystalline samples of 5,12-diphenyl tetracene (DPT). In particular, the properties of vibrational coherences imprinted on a probe pulse transmitted through a DPT single crystal indicate discrete electronic transitions below E_o of this organic semiconductor. Analysis of coherence spectra leads us to propose structural defect states give rise to these discrete transitions and subgap light emission. We use the polarization dependence of vibrational coherence spectra to tentatively assign these defects in our DPT samples. Our results provide fundamental insights into the properties of midgap states in organic materials important for their application in next-generation photonics and optoelectronics technologies.

Structural, electronic and elastic properties of FeBO3(B = Ti, Sn, Si, Zr) ilmenite: a density functional theory study

A DFT study to investigate the effects of B-cation replacement on the ilmenite structure structural, electronic and elastic properties is reported.

Large electronic bandwidth in solution-processable pyrene crystals: the role of close-packed crystal structure

We examine the interdependence of structural and electronic properties of two substituted pyrene crystals by means of combined spectroscopic probes and density-functional theory calculations. Substituted pyrenes are useful model systems to unravel the interplay of crystal structure and electronic properties in organic semiconductors. To study the effect of steric encumbrance on the crystalline arrangement of two 1,3,6,8-tetraalkynylpyrene derivatives, one features linear n-hexyl side groups while the other contains branched trimethylsilyl groups. Both derivatives form triclinic crystal structures when grown from solution, but the electronic dispersion behavior is significantly different due to differences in π-π overlap along the π-stacking axis. Both systems display dispersion of around 0.45 eV in the valence band, suggesting a high intrinsic hole mobility. However, the direction of the dispersion is different: it is primarily along the π-stacking axis in the trimethylsilyl-substituted derivative, but less aligned with this crystal axis in the hexyl-substituted molecule. This is a direct consequence of the differences in co-facial π electron overlap revealed by the crystallographic studies. We find that photophysical defects, ascribed to excimer-like states, point to the importance of localized trap states.

Effect of static and dynamic disorder on exciton mobility in oligothiophenes

The polarized optical absorption spectra of different quaterthiophene single crystals in the energy region of the exciton bands originating from the first molecular transition are reported as measured in the temperatures ranging from 7 to 140 K. The intrinsic higher mobility of the b-polarized 0-0 a(u) exciton both with respect to its replicas and to the a-polarized structures is demonstrated in high quality crystals at the lowest temperatures. The influence of structural disorder on mobility is discussed considering, for the different samples, the measured lineshape and linewidth of the absorption peaks, and the relative lineshift and intensity ratio between the 0-0 a(u) line and its first replica at the lowest temperature. The influence of dynamic disorder is discussed considering the lineshape and linewidth of the measured peaks as a function of temperature for both polarizations in the framework of the exciton-phonon coupling theory.

REFLECTIONS ON PHYSICAL CHEMISTRY: Science and Scientists

▪ Abstract  This is the story of a young person who grew up in Tel-Aviv during the period of the establishment of the State of Israel and was inspired to become a physical chemist by the cultural environment, by the excellent high-school education, and by having been trained by some outstanding scientists at the Hebrew University of Jerusalem and, subsequently, by the intellectual environment and high-quality scientific endeavor at the University of Chicago. Since serving as the first chairman of the Chemistry Department of the newly formed Tel-Aviv University he has been immersed in research, in the training of young scientists, and in intensive and extensive international scientific collaboration. Together with the members of his “scientific family” he has explored the phenomena of energy acquisition, storage and disposal and structure-dynamics-function relations in large molecules, condensed phase, clusters and biomolecules, and is looking forward to many future adventures in physical chemistry.

“What to leave out and what to put in? That's the problem.” Hugh Lofting, Doctor Dolittle's Zoo, 1925