Karl-Heinz Koch

Band structure of quasi-one-dimensional polycondensed aromatic hydrocarbons I. Poly(periacene)s

Abstract The energy spectrum of a group of poly(periacene)s (PPAcs) is investigated theoretically. The topological ( Δ top ), geometrical ( Δ geom ) and correlation ( Δ corr ) contributions to the energy gap ΔE ∞ are examined, with ΔE ∞ = [Δ corr 2 +(Δ top +Δ geom ) 2 ] 1 2 . If the number of benzene rings n within the elementary unit reaches infinity ( n a ∞ ), the bandgap vanishes, but the ΔE ∞ ( n ) values do not decrease in a monotonic fashion. It appears that PPAc can be classified into the following two series: the (3 n +2) and the (3 n + p ) series with p = 1, 3; in each series ΔE ∞ decreases monotonically. The frontier MOs of the two series, which determine the energy gap, belong to different irreducible representations of the symmetry group D (2 m ) h . The MOs of the (3 n +2) series are symmetric with respect to reflection in the mirror plane σ h , while the MOs of the (3 n + p ) series are symmetric. The connection between the symmetry of the frontier MOs and the energy spectrum of the PPAcs is discussed.

Polynaphthylenes and oligorylenes, soluble electrophores and chromophores

Abstract Soluble oligorylenes ( 1a - 1d ) derived from poly-peri-naphthalene (PPN) 1 [1] together with a soluble, tert-butylated polynaphthylene 2a have been synthesized for the first time and thoroughly investigated. The main features are the extensive redox sequence from a tetracation to a trianion in the case of the quaterrylene 1c and the low energy gap of 1.56 eV for the alkylated pentarylene 1d .

Nonlinear optical properties of tetra-tert.-butyl-oligo (rylene) s

Abstract Third harmonic generation (THG) measurements are described for a series of tetra-tert.-butyl-oligo(rylene)s. The values of the nonlinear susceptibility χ(3)(−3ω;ω,ω,ω) of the smaller rylene molecules (biperylenyle, terrylene, quaterrylene) in the range of 10−12 esu are one order of magnitude lower than that of the pentarylene. Its χ(3) value reaches a magnitude greater than 5 ∗ 10−11 esu which is comparable to the χ(3) of linear conjugated polymers. χ(3) of the oligorylenes increases systematically with χmax. Resonance enhancement is observed for the biperylenyle and especially for the pentarylene.