Photoinduced charge transfer is a key step in the mechanism of charge generation in organic solar cells. Charge transfer typically occurs from a photoexcited conjugated polymer donor to an electron acceptor. In an effort to better understand the primary events in solar cells, we have investigated photoinduced charge transfer in model donor-acceptor systems consisting of pi-conjugated oligomer donors that are covalently linked to diimide electron acceptors. These studies utilized oligo(thiophene), oligo(phenylene ethynylene) and oligo(fluorene) pi-conjugated systems with lengths varying from 4 to 12 repeat units linked to naphthalene diimide electron acceptors. Excitation with 100 femtosecond pulses at wavelengths correspoinding to the conjugated oligomer absorption band(s) leads to rapid photoinduced charge transfer to produce a charge separated state, (oligomer+)-(NDI-), which subsequently decays on timescales ranging from 100 ps to 5 ns. The dynamics of the forward and reverse electron transfer reactions depend strongly on the structure and length of the pi-conjugated oligomers, with the fastest rates occurring for oligo(thiophene)s, and considerably slower rates for oligo(phenylene ethynylene)s. The talk will discuss the structure-property relationships and energetic correlations that control the dynamics of charge separation and recombination.
Organometallic complexes comprising of a platinum (II) acetylide core linked with different -conjugated chromophores are promising materials for applications requiring strong nonlinear-optical response. In dual-mode optical power limiting, the chromophore first undergoes ultrafast two-photon absorption (2PA) in singlet manifold, followed by efficient intersystem crossing (ISC) and subsequent T-T absorption. While the heavy atom facilitates efficient T-T absorption, achieving sufficiently high intrinsic 2PA cross-section value has remained an issue. Here we present a series of linear- and cross-conjugated p-phenylene vinylene platinum (II) acetylides (TPV1-Ph, TP01-TPV2, crossTPV1, crossTPV1-DPAF, crossTPV3) with extended π-conjugated chains and discuss their linear- and nonlinear photophysical properties, including comparison to the properties of the constituting ligand chromophores. Remarkably high femtosecond 2PA cross-section values (up to 10,000 GM) were obtained for several of the new complexes by both nonlinear transmission (NLT) and two-photon excited fluorescence (2PEF) method. The large 2PA values, especially in crossTPV1 and crossTPV3, span a broad range of wavelengths, 570 – 810 nm, which overlaps with maximum wavelength of strong T-T excited state absorption measured by nanosecond transient absorption method. This combination of properties renders these compounds efficient dual-mode nonlinear absorbers in the visible to near-IR region. Examination of the photophysical properties allows us to elucidate the structure-property relationships both in the solutions as well as in solid samples where the chromophores are incorporated into a polymer host.
We report results of two ongoing investigations that seek to characterize the photophysics of organometallic complexes
under one- and two-photon excitation. In the first line of investigation we explore the properties of the triplet state in a
complex that contains four individual platinum-acetylide chromophores linked via a tetraphenylmethane unit. Although
the individual platinum-acetylide chromophores are not conjugated in the tetramer, transient absorption studies provide
clear evidence that triplet-triplet annihilation is very efficient when the complex is excited by sequential two-photon
absorption. In a second line of study we have carried out preliminary photophysical studies of an Ir(III) complex that
contains a highly conjugated organic ligand that is designed to exhibit a large two-photon absorption cross section. One
photon excitation of the Ir(III) complex in the visible region produces a long-lived triplet state that absorbs strongly in
the visible and near-infrared regions. Preliminary experiments suggest that the long-lived triplet can be efficiently
produced via two-photon absorption in the near-infrared region.
With the increasing use of night vision goggles and night missions, new methods to display information in the infrared region is of interest. We have developed both inorganic and organic electroluminescent thin films which emit at wavelengths between 700 nm and 1.8 μm. These thin films have been incorporated into simple devices and the feasibility of a NIR flat panel display has been demonstrated. Both inorganic zinc sulfide and organic polymers doped with rare earth lanthanide ions have been demonstrated. The wavelength of emission can be varied by choosing the appropriate lanthanide ion, such as dysprosium, erbium, thulium or neodymium. Power densities of ~30 μW/cm2 have been achieved with these devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.