Breakdown of the mirror image symmetry in the optical absorption/emission spectra of oligo(para-phenylene)s

The absorption and emission spectra of most luminescent, pi-conjugated, organic molecules are the mirror image of each other. In some cases, however, this symmetry is severely broken. In the present work, the asymmetry between the absorption and fluorescence spectra in molecular systems consisting of para-linked phenyl rings is studied. The vibronic structure of the emission and absorption bands is calculated from ab-initio quantum chemical methods and a subsequent, rigorous Franck-Condon treatment. Good agreement with experiment is achieved. A clear relation can be established between the strongly anharmonic double-well potential for the phenylene ring librations around the long molecular axis and the observed deviation from the mirror image symmetry. Consequences for related compounds and temperature dependent optical measurements are also discussed.Comment: 12 pages, 13 Figure

Cyclodehydrogenation of di- and tetra(benzimidazol-2- yl)benzenes to give model heteroaromatic discotic systems

Di- and tetra(benzimidazol-2-yl)benzenes upon oxidation undergo cyclodehydrogenation with formation of N-N bonds to form planarized polycyclic compounds which are models for the cores of heteroatom-containing discotic materials, and which can be readily reduced back to the original compounds, thus demonstrating a molecular redox switch

Analyzing the optical properties of a conjugated polymer by the multimode Brownian oscillator model

A multimode Brownian oscillator model has been successfully applied for the first time to model the absorption and emission spectra of a conjugated polymer. Extremely good matches were obtained between the calculated and observed spectra for alkyl- and aryl-substituted indenofluorene-based polymers, revealing the underlying photophysics of the investigated polyindenofluorenes in solution as well as solid thin film. Structure variations, defects, and aggregation effects in polymer are shown to have major impacts on the changes of spectral features according to the MBO analysis. These results confirm that the MBO model is a valid method for analyzing the optical behavior of conjugated systems

Self-assembly of conjugated units using metal-terpyridine coordination

Due to their inherently dynamic natures and fascinating photoluminescent/photoelectronic properties, coordination compounds of metal ions and conjugated terpyridine ligands have attracted considerable attention as functional materials for a variety of potential applications. In this feature article, a summary of recent work toward the development of one- (1D), two- (2D), and three-dimensional (3D) supramolecular polymers, networks, and metallomacrocycles based on zinc metal ion coordination of conjugated units bearing terpyridine ligands is presented, and it is shown how it fits within the overall framework of work in this field. Here, a sequential study from terpyridines as basic building blocks to their zinc-coordinated supramolecular 1D polymers, 2D macrocycles, and 2D and 3D networks is developed. These networks are compared with respect to their thermal stabilities, molecular organization, and linear and nonlinear optical properties. This work opens new prospects for the development of supramolecular chemistry of terpyridines and other transition metal ions, and also their application in future optoelectronic devices

Cyclodehydrogenation of poly(perylene) to poly(quaterrylene): Toward poly(peri-naphthalene)

Cyclodehydrogenation of soluble polyperylenes gives polymers containing predominantly quaterrylene units by spectral analysis. Evidence for larger rylene units is also seen. These polymers represent important intermediates toward a poly(peri- naphthalene) (PPN). Reactions on model compounds suggest that the insolubility of polymers with larger rylene units is predominantly due to the rigidity of the polymer backbone

Synthesis and characterization of biphenyl-based lithium solvated electron solutions

We report on the electric conductivity measurements and FTIR studies carried out on lithium solvated electron solutions (Li-SES) using biphenyl as the electron receptor and tetrahydrofuran (THF) as the solvent. Conductivity measurements carried out on samples with varying compositions of lithium, biphenyl (β), and THF reveal the highest conductivity of 12.0 mS/cm is achieved with the solution composition Li1.0β(THF)8.2 and a metallic behavior. Characteristic fingerprint peaks attributed to the solvated electron solution appear in the FTIR spectra. Also, from the FTIR spectra, we propose a reaction mechanism of lithium reaction with biphenyl in THF in that Li1β(THF)n1 (1 Li atom pairing with 1 biphenyl molecule) is formed first followed by Li2β(THF)n1 (2 Li atoms pairing with 1 biphenyl molecule). A better understanding of the physical properties of the Li-SES is a prerequisite in view of their optimal applications as liquid anodes in lithium batteries