Charge Transfer in Single Chains of a Donor-Acceptor Conjugated Tri-Block Copolymer.

The photophysics of a conjugated triblock copolymer comprising poly(9,9-dioctylfluorene-co-bis-N,N'-(4-methylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFM) electron donor and poly(4-(9,9-dioctyl-9H-fluoren-2-yl)benzo[c][1,2,5]-thiadiazole) (F8BT) electron acceptor blocks has been studied in solution, in films, and as single chains. While an additional long-wavelength emission apparent in neat films of the copolymer is attributed to interchain exciplex formation, no such long-wavelength emission is apparent in solution or from single molecules. However, in these cases, time-resolved fluorescence measurements indicate the presence of a delayed fluorescence. The kinetics of the delayed emission can be interpreted in terms of an equilibrium between a locally excited and a charge-transfer state at the interface of the copolymer block components. Rate constants and thermodynamic quantities associated with these processes have been evaluated. The single-molecule results allow the assignment of an intramolecular charge-transfer state in an isolated conjugated block copolymer chain.We thank the Australian Research Council (ARC) for financial support of this research through grants DP0986166, LE100100131 and LE110100161. ENH acknowledges an Australian Postgraduate Award. We acknowledge Sam Ashworth for technical assistance with data collection. NCG is grateful to the School of Chemistry, The University of Melbourne for a Wilsmore Fellowship, and to Queen’s College, Melbourne for a Sugden Fellowship.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/jp510769p

Synthesis, structural studies and photochemistry of cobalt(III) complexes of anthracenylcyclam macrocycles

This work reports the syntheses, structures and some photochemistry in DMF of the cobalt complexes trans-[CoIII( 2)Cl2]Cl·0.5CH3OH and trans-[CoIII( 3)Cl2]Cl·4H2O, where 2 is 6-(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-5,7-dione and 3 is 6-(anthracen-9-ylmethyl)-1,4,8,11-tetraazacyclotetradecane. In the preparation of the macrocyclic ligand, 3, the formation of a polycyclic bis(aminal) intermediate and its subsequent acid hydrolysis to 3 is a cleaner route than the traditional procedure in which the analogous dioxocyclam 2 is reduced with borane reagents. The crystal structure of trans-[CoIII( 3)Cl2]Cl·4H2O shows that the macrocycle adopts the trans-III conformation, in which the anthracene moiety is extended away from the cobalt ion and the anthracene to Co separation is 7.22 . For the related complex trans-[CoIII( 2)Cl2]Cl·0.5CH3OH, however, the anthracene is bent over the highly conjugated tetracycle and significant interactions between the anthracene and the complex occur. A novel new complex, trans-[Co( 12)Cl2](where 12 is 5,7-hydroxy-6-oxo-1,4,8,11-tetraazacyclotetradecane-4,7-diene) which is a degradation product of the complex trans-[CoIII( 2)Cl2]Cl is also reported

Basics of fluorescence

The objective of this chapter is to provide a simple understanding of molecular spectroscopy, with a focus on concepts and techniques relevant to microscopy. The inherently quantum mechanical concepts of phenomena, including energy levels, radiative and nonradiative processes, and quantum yields, will be developed from a nonmathematical framework that is often used by experts in spectroscopy when discussing general principles. This simplified framework is developed into a practical and useful understanding of optical spectroscopy aimed at nonspecialists. This groundwork supports the more detailed discussion of complex techniques in the following chapters. To begin the chapter we will outline basic features and properties of light and energy states of molecules. We then connect the two by exploring the interaction of light with molecules, initially for an isolated molecule. We will consider the key properties of absorption and emission and also those properties that are the bane of microscopy—the so called nonradiative mechanisms. After considering the isolated molecule, we will discuss interactions of molecules with their environment, which develops the concepts underpinning photobleaching and quenching, and also the more recent techniques of FRET and FLIM. En route we will examine the excitation and emission spectra of typical dyes, which can be found in any dye catalogue (see also Jameson et al. [1] for further reading)

Vertical fluctuations of phospholipid acyl chains in bilayers

AbstractThe possibility of vertical displacement of acyl chains in lipid bilayers has been examined by quenching the fluorescence of 2-(9-anthroyloxy)palmitic acid with 5- and 16-doxylstearates in dipalmitoylphosphatidyl-choline unilamellar vesicles. Measurement of lifetime and steady-state quenching showed that the dynamic component of quenching was independent of the transverse position of the quencher indicating that a quencher at the 16-position could interact with a fluorophore at the 2-position with high frequency. The differences in steady-state quenching could be accounted for by the differences in the static component of quenching. The results provide further evidence for rapid vertical displacements of acyl chains in phospholipid bilayers

Miscibility studies in blends of poly(methyl methacrylate) with poly(styren e-co-methacrylonitrile) using solid-state NMR and fluorescence spectroscopy

The miscibility in blends of poly(methyl methacrylate) (PMMA) with poly(styrene-co-methacrylonitrile) (SMAN) was examined by solid-state NMR and fluorescence spectroscopy. The value of the excimer/monomer fluorescence intensity (I(E)/I(M)) in the blends provides a sensitive measure of phase separation. A miscibility window in the blends of PMMA and SMAN containing about 30-65 mol % methacrylonitrile (MAN) monomer has been observed by fluorescence experiments. Measurements of T1pH by solid-state NMR have shown that blends containing 50:50 wt % PMMA blended with each of polystyrene, poly(methacrylonitrile), SMAN (MAN: 18.9 mol %), and SMAN (MAN: 87.6 mol %) are phase-separated. There is an intermolecular penetration between PMMA and copolymers in the blends of PMMA with SMAN (MAN: 43.8 mol %) and SMAN (MAN: 70.9 mol %) at a level of less than about 6 nm. However, the fluorescence data would indicate that intimate mixing does occur below this level. An analysis of the T1pH values for SMAN has indicated that the sequence distribution has an important effect on the interactions in the copolymer system

Observation of back-surface reflected luminescence in GaAs excited by ultrashort pulses

Multiple peaks observed in the temporal evolution of the luminescence of GaAs excited by an ultrashort pulse are attributed to the effect of back-surface reflection. The luminescence components originating from the direct emission and the back-surface reflection are well distinguished using up-conversion luminescence. At an appropriately high excitation energy a sharp peak in the luminescence evolution is observed in a self-assembled InGaAs/GaAs quantum dot sample, which is attributed to stimulated emission excited by the back-surface reflection