Interplay between Charge Carrier Mobility, Exciton Diffusion, Crystal Packing, and Charge Separation in Perylene Diimide-Based Heterojunctions.

Two of the key parameters that characterize the usefulness of organic semiconductors for organic or hybrid organic/inorganic solar cells are the mobility of charges and the diffusion length of excitons. Both parameters are strongly related to the supramolecular organization in the material. In this work we have investigated the relation between the solid-state molecular packing and the exciton diffusion length, charge carrier mobility, and charge carrier separation yield using two perylene diimide (PDI) derivatives which differ in their substitution. We have used the time-resolved microwave photoconductivity technique and measured charge carrier mobilities of 0.32 and 0.02 cm2/(Vs) and determined exciton diffusion lengths of 60 and 18 nm for octyl- and bulky hexylheptyl-imide substituted PDIs, respectively. This diffusion length is independent of substrate type and aggregate domain size. The differences in charge carrier mobility and exciton diffusion length clearly reflect the effect of solid-state packing of PDIs on their optoelectronic properties and show that significant improvements can be obtained by effectively controlling the solid-state packing.

Morphology-Independent Efficient Singlet Exciton Fission in Perylene Diimide Thin Films.

Perylene diimides are conjugated chromophores that are of considerable interest owing to their ability to transform a singlet excited state into two triplets by singlet fission. Although singlet fission has previously been reported for certain perylene diimide derivatives, there is some uncertainty about the rates and yield of the process in these materials. In this report, ultrafast transient absorption spectroscopy is used to demonstrate that singlet fission in perylene diimides can occur on a sub-picosecond timescale with quantum yields approaching the theoretical limit of 200 %.

Synthesis of regioisomerically pure 1,7-dibromoperylene-3,4,9,10-tetracarboxylic acid derivatives.

The perylene derivative 1,7-dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester has been obtained in regioisomerically pure form, by employing a highly efficient, scalable, and robust synthesis starting from commercially available perylene-3,4,9,10-tetracarboxylic bisanhydride. Subsequently, this compound is utilized for the synthesis of extremely valuable and versatile regioisomerically pure intermediates, namely, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic dibutylester monoanhydride, 1,7-dibromoperylene-3,4,9,10-tetracarboxylic bisanhydride, and 1,7-dibromoperylene monoimid monoanhydride. These compounds possess at least one anhydride functionality in addition to the 1,7 bromo substituents and thus allow for a virtually limitless attachment of substituents both at the "peri" and the "bay" positions. The intermediate 1,7-dibromoperylene monoimide monoanhydride is of special interest as it provides access to unsymmetrically imide-substituted 1,7-dibromoperylene derivatives, which are not accessible by previously known procedures. Finally, substitution of the 1,7 bromine atoms in the bay area by phenoxy groups, which is a generally applied reaction for 1,7-dibromoperylene bisimides, was proven to be equally effective for a 1,7-dibromoperylene tetraester and a 1,7-dibromoperylene diester monoimid.

High charge carrier mobility and efficient charge separation in highly soluble perylenetetracarboxyl-diimides.

In this communication we report on the synthesis and charge mobility of highly soluble perylenebisimid derivatives. We show that introduction of alkylester side chains results in compounds combining a high solubility with charge mobilities up to 0.22 cm(2) V(-1) s(-1). These materials are therefore interesting as an electron acceptor for solution-processed organic photovoltaics.

Degenerate molecular shuttles with flexible and rigid spacers.

The preparation and dynamic behavior of degenerate rotaxane molecular shuttles are described in which a benzylic amide macrocycle moves back and forth between two naphthalimide-glycine units along a diphenylethyne spacer or an aliphatic spacer consisting of a C(9), C(12), or C(26) alkyl chain. Subtle differences in the (1)H NMR spectra of the rotaxanes can be related to the presence of conformers in which the macrocycle interacts simultaneously with both glycines, especially in the case of the C(9) spacer. The kinetic data of the shuttling behavior in the C(26) rotaxane were obtained from dynamic NMR spectroscopy. The Eyring activation parameters were found to be ΔH(‡) = 10 ± 1 kcal mol(-1), ΔS(‡) = -6.5 ± 2.0 cal mol(-1) K(-1), ΔG(‡)(298) = 11.9 ± 0.2 kcal mol(-1). For the systems with the shorter spacers, the shuttling rates were higher. Also in the diphenylethyne, rotaxane shuttling is rapid on the NMR time scale, indicating that the rigid unit does not impose a large barrier to the translocation of the macrocycle.