Collective Excitation Dynamics in Molecular Aggregates

Abstract

The aim of this thesis is to study collective excitation dynamics in molecular aggregates. Half of the work presented here is method development and the remainder is application of these methods to several di.erent molecular aggregates. In the first two papers, the pump-probe signal was derived using the Green function approach of the optical response functions and formulated in the Doorway-Window representation. This method was applied to the B850 aggregate of the purple bacteria, Rhodobacter sphaeroides and compared with recent experimental results. The steady-state absorption as well as the thermalized pump-probe spectra were in good agreement with the experimental data for a given parameter set. Furthermore, the temporal evolution of the transient absorption spectra was also well described for the same parameter set. The concept of exciton delocalization was addressed using this method and several theoretical estimations were discussed and compared with each other. Furthermore, the time evolution and dependency of the initial preparation were studied and compared with different experimental techniques. In the second part, the excitation dynamics in molecular aggregates was studied using the surface hopping technique. This method incorporates coupling to the nuclear coordinates explicitly and treats the nuclear system classically. The third and the forth paper included in this thesis, develops the surface hopping method and the simulations were made for model aggregates. The fifth paper introduces an analytical version of the previously presented surface hopping model. In the last included paper, this method was applied to the B850 antenna complex of Rhodobacter sphaeroides with parameters extracted from a realistic spectral density distribution. A number of explicit harmonic oscillators were used to describe the molecular vibrations. Special attention was directed to the nonlinear dependence of the excitonic potential energy surfaces and the exciton-vibrational feedback term. Polaron formation, migration and self-trapping was shown to occur for certain parameter sets.

Abstract (Swedish)

Popular Abstract in Swedish

Den här avhandlingen är framlagd i ämnet kemisk fysik. Kemisk fysik är ett mycket stort forskningsområde, som innefattar fenomen allt ifrån vibrationer i molekylära bindningar till betydligt större fenomen, som till exempel energi och elektrontransport i den naturliga fotosyntesen. Fotosyntesen är naturens mest betydelsefulla process. Den driver i princip alla växter, som i sin tur är föda för alla jordens djur, inklusive oss människor. Detta är något vi alla känner väl till ifrån skolan och det är säkerligen ingen överraskning för någon att denna process till stora delar är mycket effektiv. Det är dock inte bara gröna växter som utnyttjar fotosyntesen utan även många planktonarter och bakterier nyttjar den. De initiala stegen i fotosyntesen kan i princip beskrivas som en fler-stegs process; (i) infångande av soljus, (ii) transport av den infångade energin och slutligen (iii) den av energin initierade transport av en elektron genom cellmembranet. Vi har studerat egenskaperna hos de grundläggande energipaket som antennsystemen innehåller efter att de har blivit belysta med ljus. Dessa ljusinsamlande antenner består av pigment molekyler. På grund av den starka kopplingen mellan dessa byggstenar så kommer energipaketen att vara ”utsmetade” ¨over en betydande del av antennen. Den här avhandlingen berör de första momenten av energitransporten i den naturliga fotosyntesen och den teoretiska beskrivningen av de grundläggande excitationernas egenskaper och dynamik i antennkomplexen. Avhandlingen innehaller lika delar metod utveckling och applikationer av dessa metoder på fotosyntetiska antenn och modell-system.

• author: Dahlbom, Mats
• supervisor: [unknown] [unknown]
• opponent: Professor Knoester, J., Institute for Theoretical Physics,University of Groningen, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands.
• organization: Chemical Physics
• publishing date: 2002
• type: Thesis
• publication status: published
• subject: Atom and Molecular Physics and Optics
• keywords: Chemistry, Kemi, Fysik, Physics, computational methods, photosynthesis, femtosecond spectroscopy, Exciton, Polaron
• pages: 130 pages
• defense location: Lecture Hall B, Chemisty Center, Getingevägen 60, Lund, Sweden
• defense date: 2002-02-01 14:15:00
• ISBN: 91-7874-174-2
• language: English
• LU publication?: yes
• additional info: Article: Exciton-Wave Packet Dynamics in Molecular Aggregates Studied with Pump-ProbeSpectroscopy, J. Phys. Chem. B 2000, 104, 3976-3983Mats Dahlbom, Tatsuya Minami, Vladimir Chernyak, Tonu Pullerits,Villy Sundström, and Shaul Mukamel Article: Exciton Delocalization in the B850 Light-Harvesting Complex: Comparison of Different Measures,J. Phys. Chem. B 2001, 105, 5515-5524Mats Dahlbom, Tonu Pullerits,Shaul Mukamel, and Villy Sundström Article: Collective Excitation Dynamics in Molecular Aggregates: Exciton Relaxation, Self-trapping and Polaron Formation.In press, Proceedings of BioPhysical Chemistry 2001.Mats Dahlbom, Wichard Beenken, Villy Sundström, Tonu Pullerits Article: Collective Excitation Dynamics and Polaron Formation in Molecular AggregatesSubmitted to Phys. Rev. Lett. 2001.Mats Dahlbom, Wichard Beenken, Villy Sundström, Tonu Pullerits Article: Potential Surfaces and Delocalization of Excitons in Dimers.Manuscript, To be submitted to J. Chem. Phys.Wichard Beenken, Mats Dahlbom, Pär Kjellberg, Villy Sundström, Tonu Pullerits Article: Polaron Transport and Directed Energy Funnelling in Light-Harvesting Pigment-Protein Complexes.Manuscript, To be submitted to J. Phys. Chem. B.Mats Dahlbom, Wichard Beenken, Villy Sundström, Tonu Pullerits The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
• id: 4aeefee1-b3fe-4b80-ab45-adfbc0557174 (old id 464273)
• date added to LUP: 2016-04-04 10:49:49
• date last changed: 2018-11-21 21:01:01