- Email: [email protected]
In honour of Professor Dietmar Möbius
Colloids and Surfaces A: Physicochemical and Engineering Aspects 171 (2000) 1 – 2 www.elsevier.nl/locate/colsurfa
Editorial
In honour of Professor Dietmar Mo¨bius
This issue is dedicated to Dietmar Mo¨bius on the occasion of his 60th birthday in March 1998. He has a large family of friends all over the world. Some of them have expressed their best wishes which are contained in this volume in the form of scientific contributions. As one of the outstanding figures in the fields of interfaces and organised molecular films, Dietmar Mo¨bius has pioneered the modular assembly of molecular films to sophisticated supramolecular structures with brilliant experiments, and motivated his students to perform excellent studies. Professor Mo¨bius received his PhD from the Philipps-Universita¨t Marburg, Germany. He worked a few years at the Institut fu¨r Physikalische Chemie, Marburg, spent several months at the Eastman Kodak Research Laboratories, Rochester, New York, and moved to the MaxPlanck-Institut fu¨r biophysikalische Chemie, Go¨ttingen in 1971. Primarily working in research he educated several graduate students, one of them occupying now a professor position at the University of Seattle. Dietmar Mo¨bius chaired the 3rd International Conference on Langmuir – Blodgett Films and has been on the advisory board of Langmuir. In 1997 he was awarded the TheodorFo¨rster-Geda¨chtnis-Vorlesung by the Gesellschaft Deutscher Chemiker and the Deutsche Bunsengesellschaft fu¨r Physikalische Chemie. Dietmar Mo¨bius is one of the most prominent scientists in the field of organised monolayers and
systems with planned molecular structure. The implications of his work on science and technology of interfaces are extraordinary. He has performed fundamental investigations of complex monolayers incorporating amphiphilic dyes in matrix monolayers of fatty acids, evaluating the lateral distribution of the dye molecules and the position of the dye layers in the assemblies by energy transfer methods. His studies of the mechanism of spectral sensitisation of silver bromide clearly demonstrated the possibility of the energy transfer mechanism by determining the distance dependence of sensitisation. In convincing experiments with competing energy acceptors and electron traps, respectively, positioned at the surface of the silver bromide, he was able to rule out the possibility of defects as cause of the observed effects. Dietmar Mo¨bius was the first to observe very long range photo-induced electron transfer (over distances of 2–3 nm) in monolayer systems. Again he conceived various brilliant experiments to ascertain that the results were not due to defects in the layer systems. Based on the concept of molecular conductor he achieved photo-induced electron transfer across a bilayer (thickness ca. 5 nm). Dietmar Mo¨bius has investigated the energy transfer from an excited donor molecule to other donor molecules in the ground state at the same interface (incoherent exciton hopping) giving rise to energy delocalisation and hence to an increased efficiency of trapping. Energy harvesting due to trapping is most efficient if the donor is
0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 7 7 5 7 ( 9 9 ) 0 0 5 3 8 - 5
2
Editorial
organised in J-aggregates. In these two-dimensional crystalline arrays the excited state is described by the model of coherent exciton in which a number of dipoles representing the transition moments are oscillating in phase. One consequence is the enhanced radiative rate as compared to the dye monomer (this phenomenon is now erroneously termed ‘superradiance’). For the first time, Dietmar Mo¨bius has studied indirectly the unusual temperature dependence of the photophysical behaviour of J-aggregates by energy transfer techniques. Dietmar Mo¨bius has developed the techniques of monolayer manipulation including separation and contacting monolayers and monolayer systems with molecular precision. With the development of reflection spectroscopy, entirely new insights in processes at interfaces such as adsorption, molecular association, chemical and photochemical transformations were gained. Binding of Cytochrome c to phospholipid monolayers may be fast as observed by the optical signal whereas the surface pressure changes at constant area, probably due to protein reorganisation at the interface, are slow. The photochemical (contactfree) generation of surface pressure jumps as well as of longitudinal waves in monolayers at the air–water interface created totally new possibilities of dynamic studies of monolayers. The new dipole compensation technique allowed him to determine the contribution of the terminal dipoles of amphiphilic molecules to the electrical surface potential of monolayers. Professor Mo¨bius and his students developed the Brewster angle microscopy (independently, the group of Jacques Meunier in Paris had constructed such a microscope shortly before). This technique turned out to be extremely well suited for the characterisation and study of monolayer phases, phase transi-
.
tions and long range ordering. This field has rapidly developed by the use of this new instrument. Biological materials have very often attracted the attention of Professor Mo¨bius. He has contributed with beautiful experiments to the understanding of the structure and function of the thin layer of Meibomian gland secretion. New types of experiments were done with the human lung surfactant layers, and his investigations of the behaviour of gangliosides provided new insights in their function. More recently, Dietmar Mo¨bius has turned his attention to lateral ordering of mixed monolayers. He has been able to organise surfaces carrying a molecular footprint and consequently binding the target molecule much more strongly than a surface with unorganised binding sites. He has constructed a large variety of designed materials with particular properties like non-linear optical properties, optical bistability (for molecular information storage and processing), photochemically controlled binding and release of ions, vectorial electron transfer, efficient light emission after charge injection. His ability for creating new ideas and finding efficient ways for their realisation made Dietmar Mo¨bius a much sought-after partner by diverse groups around the world. For his long-term collaboration with scientists in the former East, many colleagues are very grateful to him. I express my best wishes to Dietmar Mo¨bius on his 60th birthday, also on behalf of all the authors who contributed to this issue. May he have the same joy in his scientific work in the years ahead. We wish Dietmar many years of health and happiness. DIETER VOLLHARDT
Editorial
In honour of Professor Dietmar Mo¨bius
This issue is dedicated to Dietmar Mo¨bius on the occasion of his 60th birthday in March 1998. He has a large family of friends all over the world. Some of them have expressed their best wishes which are contained in this volume in the form of scientific contributions. As one of the outstanding figures in the fields of interfaces and organised molecular films, Dietmar Mo¨bius has pioneered the modular assembly of molecular films to sophisticated supramolecular structures with brilliant experiments, and motivated his students to perform excellent studies. Professor Mo¨bius received his PhD from the Philipps-Universita¨t Marburg, Germany. He worked a few years at the Institut fu¨r Physikalische Chemie, Marburg, spent several months at the Eastman Kodak Research Laboratories, Rochester, New York, and moved to the MaxPlanck-Institut fu¨r biophysikalische Chemie, Go¨ttingen in 1971. Primarily working in research he educated several graduate students, one of them occupying now a professor position at the University of Seattle. Dietmar Mo¨bius chaired the 3rd International Conference on Langmuir – Blodgett Films and has been on the advisory board of Langmuir. In 1997 he was awarded the TheodorFo¨rster-Geda¨chtnis-Vorlesung by the Gesellschaft Deutscher Chemiker and the Deutsche Bunsengesellschaft fu¨r Physikalische Chemie. Dietmar Mo¨bius is one of the most prominent scientists in the field of organised monolayers and
systems with planned molecular structure. The implications of his work on science and technology of interfaces are extraordinary. He has performed fundamental investigations of complex monolayers incorporating amphiphilic dyes in matrix monolayers of fatty acids, evaluating the lateral distribution of the dye molecules and the position of the dye layers in the assemblies by energy transfer methods. His studies of the mechanism of spectral sensitisation of silver bromide clearly demonstrated the possibility of the energy transfer mechanism by determining the distance dependence of sensitisation. In convincing experiments with competing energy acceptors and electron traps, respectively, positioned at the surface of the silver bromide, he was able to rule out the possibility of defects as cause of the observed effects. Dietmar Mo¨bius was the first to observe very long range photo-induced electron transfer (over distances of 2–3 nm) in monolayer systems. Again he conceived various brilliant experiments to ascertain that the results were not due to defects in the layer systems. Based on the concept of molecular conductor he achieved photo-induced electron transfer across a bilayer (thickness ca. 5 nm). Dietmar Mo¨bius has investigated the energy transfer from an excited donor molecule to other donor molecules in the ground state at the same interface (incoherent exciton hopping) giving rise to energy delocalisation and hence to an increased efficiency of trapping. Energy harvesting due to trapping is most efficient if the donor is
0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 7 7 5 7 ( 9 9 ) 0 0 5 3 8 - 5
2
Editorial
organised in J-aggregates. In these two-dimensional crystalline arrays the excited state is described by the model of coherent exciton in which a number of dipoles representing the transition moments are oscillating in phase. One consequence is the enhanced radiative rate as compared to the dye monomer (this phenomenon is now erroneously termed ‘superradiance’). For the first time, Dietmar Mo¨bius has studied indirectly the unusual temperature dependence of the photophysical behaviour of J-aggregates by energy transfer techniques. Dietmar Mo¨bius has developed the techniques of monolayer manipulation including separation and contacting monolayers and monolayer systems with molecular precision. With the development of reflection spectroscopy, entirely new insights in processes at interfaces such as adsorption, molecular association, chemical and photochemical transformations were gained. Binding of Cytochrome c to phospholipid monolayers may be fast as observed by the optical signal whereas the surface pressure changes at constant area, probably due to protein reorganisation at the interface, are slow. The photochemical (contactfree) generation of surface pressure jumps as well as of longitudinal waves in monolayers at the air–water interface created totally new possibilities of dynamic studies of monolayers. The new dipole compensation technique allowed him to determine the contribution of the terminal dipoles of amphiphilic molecules to the electrical surface potential of monolayers. Professor Mo¨bius and his students developed the Brewster angle microscopy (independently, the group of Jacques Meunier in Paris had constructed such a microscope shortly before). This technique turned out to be extremely well suited for the characterisation and study of monolayer phases, phase transi-
.
tions and long range ordering. This field has rapidly developed by the use of this new instrument. Biological materials have very often attracted the attention of Professor Mo¨bius. He has contributed with beautiful experiments to the understanding of the structure and function of the thin layer of Meibomian gland secretion. New types of experiments were done with the human lung surfactant layers, and his investigations of the behaviour of gangliosides provided new insights in their function. More recently, Dietmar Mo¨bius has turned his attention to lateral ordering of mixed monolayers. He has been able to organise surfaces carrying a molecular footprint and consequently binding the target molecule much more strongly than a surface with unorganised binding sites. He has constructed a large variety of designed materials with particular properties like non-linear optical properties, optical bistability (for molecular information storage and processing), photochemically controlled binding and release of ions, vectorial electron transfer, efficient light emission after charge injection. His ability for creating new ideas and finding efficient ways for their realisation made Dietmar Mo¨bius a much sought-after partner by diverse groups around the world. For his long-term collaboration with scientists in the former East, many colleagues are very grateful to him. I express my best wishes to Dietmar Mo¨bius on his 60th birthday, also on behalf of all the authors who contributed to this issue. May he have the same joy in his scientific work in the years ahead. We wish Dietmar many years of health and happiness. DIETER VOLLHARDT