title: Confocal ultrafast pump-probe spectroscopy: a new technique to explore nanoscale composites.
abstract: This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state.
authors.affiliation: Istituto di Fotonica e Nanotecnologie (IFN) CNR, Dipartimento di Fisica, Politecnico di Milano, P.zza L. Da Vinci 32, 20133 Milano, Italy. tvirgili@polimi.it
authors.forename: Tersilla
authors.initials: T
authors.lastname: Virgili
authors.forename: Giulia
authors.initials: G
authors.lastname: Grancini
authors.forename: Egle
authors.initials: E
authors.lastname: Molotokaite
authors.forename: Inma
authors.initials: I
authors.lastname: Suarez-Lopez
authors.forename: Sai Kiran
authors.initials: SK
authors.lastname: Rajendran
authors.forename: Andrea
authors.initials: A
authors.lastname: Liscio
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Palermo
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Lanzani
authors.forename: Dario
authors.initials: D
authors.lastname: Polli
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
mesh_terms: D005449:Fluorenes / Q000737:chemistry; D037741:Fullerenes / Q000737:chemistry; D018613:Microscopy, Confocal / Q000295:instrumentation / Q000379:methods; D008954:Models, Biological; D053761:Nanocomposites / Q000737:chemistry* / Q000648:ultrastructure*; D049329:Nanostructures / Q000737:chemistry; D055095:Optics and Photonics; D009930:Organic Chemicals / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods*; D013997:Time Factors
chemical_list: D005449:Fluorenes; D037741:Fullerenes; D009930:Organic Chemicals; C542782:poly(9,9-di-n-octyl-2,7-fluorene); D019904:Polymethyl Methacrylate