TY  - JOUR
A1  - Yang, C.
A1  - Vardeny, Z. V.
A1  - Köhler, Anna
A1  - Wohlgenannt, M.
A1  - Al-Suti, Mohammed K.
A1  - Khan, Muhammad S.
T1  - Spectroscopic study of spin-dependent exciton formation rates in pi-conjugated semiconductors : Comparison with electroluminescence techniques
N2  - It has been found in recent measurements that the singlet-to-triplet exciton ratio in organic light-emitting diodes (OLEDs) is larger than expected from spin degeneracy, and that singlet excitons form at a larger rate than triplets. We employed the technique of optically detected magnetic resonance to measure the spin-dependent exciton formation rates in films of a polymer and corresponding monomer, and explore the relation between the formation rates and the actual singlet-to-triplet ratio measured previously in OLEDs. We found that the spin-dependent exciton formation rates can indeed quantitatively explain the observed exciton yields, and that singlet formation rates and yields are significantly enhanced only in polymer OLEDs, but not in OLEDs made from the corresponding monomer
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Devi, Lekshmi Sudha
A1  - Al-Suti, Mohammed K.
A1  - Dosche, Carsten
A1  - Khan, Muhammad S.
A1  - Friend, Richard H.
A1  - Köhler, Anna
T1  - Triplet energy transfer in conjugated polymers : I. Experimental investigation of a weakly disordered compound
N2  - Efficient triplet exciton emission has allowed improved operation of organic light-emitting diodes (LEDs). To enhance the device performance, it is necessary to understand what governs the motion of triplet excitons through the organic semiconductor. Here, we have investigated triplet diffusion using a model compound that has weak energetic disorder. The Dexter-type triplet energy transfer is found to be thermally activated down to a transition temperature T- T, below which the transfer rate is only weakly temperature dependent. We show that above the transition temperature, Dexter energy transfer can be described within the framework of Marcus theory. We suggest that below T-T, the nature of the transfer changes from phonon-assisted hopping to quantum-mechanical tunneling. The lower electron-phonon coupling and higher electronic coupling in the polymer compared to the monomer results in an enhanced triplet diffusion rate.
Y1  - 2008
ER  - 
TY  - JOUR
A1  - Khalil, Mahmoud
A1  - Raila, Jens
A1  - Ali, Mostafa
A1  - Islam, Khan M. S.
A1  - Schenk, Regina
A1  - Krause, Jens-Peter
A1  - Schweigert, Florian J.
A1  - Rawel, Harshadrai Manilal
T1  - Stability and bioavailability of lutein ester supplements from Tagetes flower prepared under food processing conditions
JF  - Journal of functional food
N2  - Tagetes spp. belongs to the Asteraceae family. It is recognized as a major source of lutein ester (lutein esterified with fatty acids such as lauric, myristic and palmitic acids), a natural colorant belonging to the xanthophylls or oxygenated carotenoids. Four species of Tagetes flower (Tagetes tenuifolia, Tagetes erecta, Tagetes patula, and Tagetes lucida) were used to extract lutein and lutein esters with three different methods. The results showed that T. erecta, type "orangeprinz", is the richest source of lutein esters (14.4 +/- 0.234 mg/g) in comparison to other Tagetes spp. No significant differences between extractions of lutein esters with medium-chain triacylglycerols (MCT) oil, orange oil or solvent (hexane/isopropanol) could be observed. MCT oil also improved stability of lutein esters at 100 degrees C for 40 min. Emulsification of MCT oil improved the stability of lutein ester extract against UV light at 365 nm for 72 h. Finally, an emulsion was prepared under food processing conditions, spray dried and its bioavailability investigated in a preliminary human intervention study. The results show a lower resorption, but further data suggest improvements in implementation of such supplements. (c) 2012 Elsevier Ltd. All rights reserved.
KW  - Tagetes
KW  - Lutein ester
KW  - Emulsion
KW  - Stability
KW  - Whey protein
KW  - Bioavailability
Y1  - 2012
U6  - https://doi.org/10.1016/j.jff.2012.03.006
SN  - 1756-4646
VL  - 4
IS  - 3
SP  - 602
EP  - 610
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - CHAP
A1  - Machumi, F.
A1  - Yenesew, Abiy
A1  - Midiwo, J. O.
A1  - Heydenreich, Matthias
A1  - Kleinpeter, Erich
A1  - Khan, S.
A1  - Tekwani, B. L.
A1  - Walker, L. A.
A1  - Muhammad, I
T1  - Antiparasitic and anticancer carvotacetone derivatives from Sphaeranthus bullatus
T2  - Planta medica : journal of medicinal plant and natural product research
Y1  - 2012
SN  - 0032-0943
VL  - 78
IS  - 11
SP  - 1201
EP  - 1202
PB  - Thieme
CY  - Stuttgart
ER  -