BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:Delocalization and Electron Transfer in Conjugated Porphyrin Oligo mers DTSTART:20141009T163000 DTEND:20141009T173000 DTSTAMP:20260407T105505Z UID:efebbe645ae0985f586e9a368f24445127d0885d3f1f1b7a481ac048 CATEGORIES:Conferences - Seminars DESCRIPTION:Prof. Bo Albinsson\nDepartment of Chemistry and Biotechnology\ , Chalmers University of Technology\, 412 96 Göteborg\, Sweden\n\nThe ph otophysical properties of a series of butadiyne linked conjugated zinc por phyrin oligomers have been investigated\, specifically on how they are inf luenced by conformations and topologies. Conformational dependence was stu died extensively on the porphyrin dimer\, P2. The butadiyne linker allows almost free rotation of the individual porphyrin moieties and it was shown that a broad distribution of different dihedral conformations was contrib uting to the observed spectral properties of P2. Further\, it was shown th at twisted and planar conformations of P2 could be selectively excited due to their well separated electronic transitions.1 Control of the conformat ional distribution could potentially be utilized in many interesting appli cations\, and this was demonstrated by constructing a molecular based phot onic memory in2 which a pyridine appended DTE photochrome was used to opti cally switch the planarization of P2 on and off. Conformation was also dra matically influenced by aggregation of two porphyrin oligomers (trimers an d larger) upon slowly cooling to around 160 K.3\nThe topological aspects w ere studied by comparing the properties of a linear and a circular porphyr in hexamer. Experiments showed that the fluorescence quantum yield of the circular hexamer was 40 times smaller than the linear counterpart. This wa s explained by the symmetry change associated with bending the linear olig omer\, which makes the S0→ S1 transition symmetry forbidden for circular topologies.4\nThe electron transfer reactions in the fullerene appended p orphyrin oligomers\, Pn-C60\, were studied thoroughly. It was shown how ex citation of different conformations greatly affects the rates and efficien cy of the charge separation. Twisted conformers of P2-C60 showed a 4 times faster charge separation rate compared to planar conformers.5 For longer oligomers excitation of twisted conformers can have the opposite effect si nce it could localize the excitation energy too far away from the fulleren e\nelectron acceptor for efficient charge separation.6\n1. Winters\, M. U. \; Kärnbratt\, J.\; Eng\, M.\; Wilson\, C. J.\; Anderson\, H. L.\; Albin sson\, B.\, Photophysics of a butadiyne- linked porphyrin dimer: Influence of conformational flexibility in the ground and first singlet excited sta te. J. Phys. Chem. C 2007\, 111 (19)\, 7192-7199.\n2. Kärnbratt\, J.\; H ammarson\, M.\; Li\, S.\; Anderson\, Harry L.\; Albinsson\, B.\; Andréas son\, J.\, Photochromic Supramolecular Memory With Nondestructive Readout. Angew. Chem. -Int. Ed. 2010\, 49 (10)\, 1854-1857.\n3. Kärnbratt\, J.\; Gilbert\, M.\; Sprafke\, J. K.\; Anderson\, H. L.\; Albinsson\, B.\, Self -Assembly of Linear Porphyrin Oligomers into Well-Defined Aggregates. The Journal of Physical Chemistry C 2012\, 116 (37)\, 19630-19635.\n4. (a) Hof fmann\, M.\; Karnbratt\, J.\; Chang\, M. H.\; Herz\, L. M.\; Albinsson\, B .\; Anderson\, H. L.\, Enhanced pi conjugation around a porphyrin[6] nanor ing. Angew. Chem.-Int. Ed. 2008\, 47 (27)\, 4993-4996\; (b) Sprafke\, J. K .\; Kondratuk\, D. V.\; Wykes\, M.\; Thompson\, A. L.\; Hoffmann\, M.\; Dr evinskas\, R.\; Chen\, W.-H.\; Yong\, C. K.\; Kärnbratt\, J.\; Bullock\, J. E.\; Malfois\, M.\; Wasielewski\, M. R.\; Albinsson\, B.\; Herz\, L. M .\; Zigmantas\, D.\; Beljonne\, D.\; Anderson\, H. L.\, Belt-Shaped π- Sy stems: Relating Geometry to Electronic Structure in a Six-Porphyrin Nanori ng. Journal of the American Chemical Society 2011\, 133 (43)\, 17262-17273 .\n5. Winters\, M. U.\; Kärnbratt\, J.\; Blades\, H. E.\; Wilson\, C. J. \; Frampton\, M. J.\; Anderson\, H. L.\; Albinsson\, B.\, Control of elect ron transfer in a conjugated porphyrin dimer by selective excitation of pl anar and perpendicular conformers. Chem.- Eur. J. 2007\, 13 (26)\, 7385-73 94.\n6. Kahnt\, A.\; Kärnbratt\, J.\; Esdaile\, L. J.\; Hutin\, M.\; Saw ada\, K.\; Anderson\, H. L.\; Albinsson\, B.\, Temperature Dependence of C harge Separation and Recombination in Porphyrin Oligomer–Fullerene Donor –Acceptor Systems. J. Am. Chem. Soc. 2011\, 133 (25)\, 9863-9871. LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495 STATUS:CONFIRMED END:VEVENT END:VCALENDAR