Synthetic Metals 139 (2003) 609–612 A detailed study of the photophysics of organic semiconducting nanospheres T. Piok a,b,∗ , L. Romaner a,b , C. Gadermaier a,b , F.P. Wenzl a,b , S. Patil c , R. Montenegro d , K. Landfester d , G. Lanzani e , G. Cerullo e , U. Scherf c , E.J.W. List a,b a Christian Doppler Laboratory Advanced Functional Materials, Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria b Institute of Nanostructured Materials and Photonics, A-8160 Weiz, Austria c Makromolekulare Chemie, Fachbereich Chemie, Bergische Universität Wuppertal, Gauß-Str. 20, D-42097 Wuppertal, Germany d Max Planck Institute of Colloids and Interfaces, Research Campus Golm, D-14424 Potsdam, Germany e Dipartimento di Fisica, Politecnico di Milano, National Laboratory for Ultrafast and Ultraintense Optical Science—INFM, Piazza L. da Vinci 32, I-20133 Milano, Italy Abstract Conjugated polymers are an intriguing class of organic semiconductors which can be utilized as active medium in a wide range of electronic applications. Semiconducting polymer nanospheres fabricated from a conjugated polymer dispersed in aqueous phase have been realized successfully utilizing the miniemulsion process. This class of material combines the properties of conjugated polymers and nanostructured matter and can overcome certain limitations in the film formation of defined multi-layer structures and self assemblies and can, therefore, enable new device design concepts. We present first spectroscopic investigations to characterize nanospheres of methyl-substituted ladder-type poly(para-phenylene) in film and compare them to conventional bulk films of the same polymer. The dynamics of the various photo-excited states is probed via both steady state and transient differential transmission spectroscopy. © 2003 Elsevier B.V. All rights reserved. Keywords: Conjugated polymer; Miniemulsion; Time resolved spectroscopy; Nanostructured materials 1. Introduction The controlled deposition of functional materials on the nano- to mesoscopic scale is one of the key challenges on the way to nano-scale organic electronics. Controlling the material at such a scale one will be able to fabricate im- proved as well as novel devices from organic semiconduc- tors such as conjugated polymers in a cost-effective way. As demonstrated over the last decade, conjugated polymers can be utilized as the active medium in various optoelectronic applications [1–4]. By adopting the so-called miniemulsion principle one can combine the properties of semiconducting polymers with those of nanostructured matter, as recently shown [5]. Miniemulsions are stable emulsions of droplets with a dis- tinct size of 50–500 nm, achieved by shearing a system con- taining water, a solution of a highly water insoluble com- ∗ Corresponding author. E-mail address: t.piok@tugraz.at (T. Piok). pound (the so-called hydrophobe, e.g. a polymer) and a small amount of a surfactant [6]. Semiconducting conjugated poly- mer nanospheres (SPNs) have been produced successfully from such a water-based miniemulsion. This novel approach enables the application of environmentally safe water-based deposition techniques such as ink-jet printing and opens new ways for controlled multilayer formation, simply by using one of the materials as an aqueous SPN dispersion [7,8]. A first basic study of the optoelectronic properties of SPNs fabricated from methyl-substituted ladder-type poly(para-phenylene) (m-LPPP) is given [9]. In the present work, we show a more comprehensive study including a comparison between the regular m-LPPP and m-LPPP SPNs via photomodulation spectroscopy and femtosecond pump-probe spectroscopy. 2. Experimental The preparation of the SPNs is described in detail in [5] while the synthesis of the utilized conjugated polymer 0379-6779/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0379-6779(03)00251-0