Mikkel Jørgensen

Chemistry of TTF. Easy synthesis of TTF and selective synthesis of unsymmetrically substituted TTFs

Abstract A low cost, easy to perform synthesis of TTF has been developed together with a new Wittig type reaction for preparation of unsymmetrical TTFs.

Donor-acceptor interfaces in langmuir-blodgett films. Structural and optical features related to nonlinear optical properties

Abstract The linear optical properties of Langmuir-Blodgett films of alternating layers of the electron acceptor, octadecylthiobenzoquinone, and the electron donor 7-( N -octadodecylaminomethyl)-8-16-dioxadibenzo [f,g]perylene indicate that only a weak intermolecular contact is formed at the interface between donors and acceptors. Structural data based on linear dichroism and X-ray diffraction show that the intermolecular contact between donor and acceptor layers is possible due to the carbonyl lonepairs in the acceptor, which are directed towards the interface. The prospects for donor-acceptor interfaces in nonlinear optical materials are discussed.

Nonlinear optical phenomena due to donor–acceptor interfaces created in Langmuir–Blodgett films

Langmuir–Blodgett films consisting of two-dimensional interfaces between corbiene donor and quinone acceptor molecules show a significant nonlinear optical property (second-harmonic generation) that can be attributed to the intermolecular contact across the interface between the donor and acceptor molecules in the film.

New π-Electron Donors

Abstract The synthesis of a series of new donor molecules, 1,6-dioxa-pyrenes, is reported. Also reported is a series of dimeric TTF systems. For the dimeric TTF structures the implications for the Fermi surface in 1:1 donor-acceptor salts are discussed. Preliminary results for a few new conducting salts derived from the dimeric TTFs are given.

Low Band Gap Polymers for Roll-to-Roll Coated Organic Photovoltaics – Design, Synthesis and Characterization

Abstract In this paper we present the design and synthesis of 25 new low band gap polymers. The polymers were characterized by UV-vis spectroscopy which showed optical band gaps of 2.0–0.9 eV. The polymers which were soluble enough were applied in organic photovoltaics, both small area devices with a spin coated active layer and in large area modules where all layers including the active layer were either roll-to-roll coated or printed. These experiments showed that the design of polymers compatible with roll-toroll coating is not straightforward and that there are various issues such as donor/acceptor fitting within the polymer, side chains to ensure solubility and HOMO/LUMO level alignment with the acceptor (e.g. [60]PCBM) to take into consideration.

A Molecular Switch Involving Large Conformational Changes. A Theoretical Study

Abstract Ab initio and semi-empirical calculations on a supramolecular structure consisting of the electron acceptor molecule bianthrone covalently linked to the electron donor molecule 2,3-dimethyl-6-alkyl-l,4-dithiafulven are prensented. The molecule may act as a molecular switch and calculations show that a charge transfer state is involved in the initial stage of the switch process. The charge recombination process is calculated to occur early in the switching process. Experimental data supports this interpretation and calculations are used as a guideline for synthetic strategies leading to molecules with improved switching properties.

Excited state transient spectroscopy of anthracene based photochromic systems

Abstract In this study, picosecond time resolved excited state absorption spectroscopy is employed to determine the evolution and lifetime of the photochromic states in anthracene based molecular systems and the contribution of conformational changes. The unsubstituted bianthrone shows a broad transient absorption which peaks in the region of 600 nm. Equivalent measurements on anthracene give similar results indicating that this transition originates from a locally excited state on the anthrone ring system. Upon substitution of the bianthrone, an additional transient absorption at 700 nm evolves within 10 ps after excitation. This is assigned to a twisted state in which the excited state is stabilised by a strong conformational change. The metastable nature of the state is confirmed by time delay measurements.

Time resolved excited state spectroscopy of anthracene based photochromic systems

In this study, picosecond rime resolved excited state absorption spectroscopy is employed to determine the evolution and lifetime of the photochromic states in anthracene based molecular systems and the contribution of conformational changes. The unsubstituted bianthrone shows a broad transient absorption which peaks in the region of 600 nm. Equivalent measurements on anthracene give similar results indicating that this transition originates from a locally excited state on the anthrone ring system. Upon substitution of the bianthrone, an additional transient absorption at 700 nm evolves within 10 ps after excitation. This is assigned to a twisted state in which the excited state is stabilised by a sarong conformational change. The metastable nature of the state is confirmed by rime delay measurements

2-dialkylamino-5-alkyl-1,3-dithiolium-4-thiolate mesoions as versatile intermediates in the synthesis of TTF derivatives

Abstract Several new monoalkyl-thioalkyl substituted TTF donors have been prepared via the mesoionic 2-dialkylamino-5-alkyl-1,3-dithiolium-4-thiolate 1 . By S-alkylation 1 was transformed into a number of mono- and bis-1,3-dithiolium salts 6 , which were coupled with the anion of 4., 5-dimethyl-2H-1,3-dithiole-2-phosphonate ester 7 to yield series of bis-TTFs 2 and alkylthio substituted TTFs 3 . By conventional methods 6 was also coupled to “symmetrically” substituted dialkylthio-TTFs 4 . An improved synthesis of 1 is also reported.

Computer modelling of dimer geometries in simple radical ion salts

Abstract A simple dimer calculation can be calibrated to reproduce dimer geometries in a number of hydrocarbon- and TTF-based charge-transfer solids. The calculations make it possible to discriminate between a number of donors which form complicated or simple crystal structures. For this reason, dimer calculations are proposed to be the first step in a rational design of donors likely to form stoichiometric radical ion salts.