Search

The dynamics of charge carrier generation in poly(spirobifluorene-co-benzothiadiazole) was investigated by electric field-induced fluorescence quenching and differential absorption measurements. Three different time domains of carrier generation have been identified: an ultrafast phase, a subnanosecond phase, and an entire lifetime phase. The charge generation efficiencies during the first and second phases were found to be almost independent of temperature, being about 25% and 10%, respectively, at an applied electric field of 1.3×106 V/cm, while the generation efficiency during the third phase increases from 2% at 80 K to 10% at room temperature. The results of transient spectroscopy measurements and quantum chemical calculations suggest an intramolecular charge transfer for about 1 ps from the alkoxy-substituted fluorene side group to the benzothiadiazole subunit of the main chain. The formation and evolution of the resulting charge transfer states determine the way of charge carrier generation. [ABSTRACT FROM AUTHOR]

Four novel nanocomposite films based on poly(di-n-hexylsilane) (PDHS) incorporated into an inorganic matrix having different structure are fabricated. Polymer chains are localized into the nanopores of SiO2 and TiO2 films, between globules of photonic crystals, as well as in the matrix of nano-sized SiO2 particles. Photoelectronic properties of the composites have been studied using fluorescence (FL) and FL decay measurements in a wide temperature range (5-330) K. The temperature dependence of FL intensities enabled us to establish the nature of a conformational structure of polymer chains, as well as to obtain information about the thermochromic transition of confined PDHS and the excitation energy transfer pathways. [ABSTRACT FROM AUTHOR]

Highlights: [•] Silicon polymer PDHS has been embedded into nanoporous SiO2 and TiO2 films. [•] PDHS fluorescence is quenched several times in TiO2 film. [•] Fluorescence intensity of the composite films weekly depends on temperature. [Copyright &y& Elsevier]

Abstract: Absorption and fluorescence spectroscopy including ultrafast transient absorption spectroscopy together with quantum chemistry calculations were applied to reveal properties of multicomponential carbazole–fluorene–benzothiadiazole compounds in the ground and excited states. Despite different structures of compounds possessing benzothiadiazole units, all of them display very similar spectroscopic properties. This feature is caused by similar HOMO levels of all the constituents resulting in delocalization of HOMO levels and by electron localization on benzothiadiazole units in the excited states. Excited state solvation is suggested to be an additional important factor causing unification of the fluorescence properties. [Copyright &y& Elsevier]

Abstract: Excited-state relaxation of dendrimers functionalized with terminal cyanoazobenzene-type groups was studied by means of fluorescence and femtosecond transient absorption spectroscopy. We compare the relaxation dynamics with that of azobenzene molecules in solutions and conclude that the excited-state relaxation is determined by the excited state twisting of terminal groups, which takes place on a time scale of several picoseconds. The twisting dynamics only slightly differs in solutions and in solid film, which indicates that conformational motions during the twisting reaction are only weakly coupled to the environment. [Copyright &y& Elsevier]