Self-organized organic materials that undergo photoinduced electron transfer

Near-infrared absorbing chromophores were synthesized from perylene-3,4:9,10-bis(dicarboximide) (PDI) in a two-fold Diels-Alder type cycloaddition. The disubstituted product possessed even more accessible redox potentials than the parent chromophore (EOX = 1.1 V vs. SCE, ERED = -0.4 V vs. SCE). Ground-state absorption spectroscopy in methylcyclohexane revealed that it formed H-aggregates in solution, unlike the parent PDI. Small and wide-angle x-ray scattering shows that it forms discrete hexamers in MCH with a 30° twist in the adjacent chromophores to relieve steric repulsion. Spectroelectrochemistry revealed distinct radical anion and dianion optical transitions. Its lower reduction potential relative to PDI makes it an attractive replacement as a long-wavelength photoactive dye.;Ruthenium catalyzed C-H bond activation was used to directly attach phenethyl groups derived from styrene to positions ortho to the imide groups in a variety of rylene imides and diimides including naphthalene-1,8-dicarboximide (NMI), naphthalene-1,4:5,8-bis(dicarboximide) (NI), perylene-3,4-dicarboximide (PMI), perylene-3,4:9,10-bis(dicarboximide) (PDI), and terrylene-3,4:11,12-bis(dicarboximide) (TDI). The monoimides were dialkylated, while the diimides were tetraalkylated, with the exception of NI, which could only be dialkylated due to steric hindrance. A series of symmetric and asymmetric TDI chromophores were synthesized which possess different functional groups (dodecyl and t-butylphenylethyl) to impart greater solubility. The asymmetric TDI's exhibited aggregation behavior dependent on the ortho-substitution. In order to better compare the aggregation behavior of the PDI's a three-fold symmetric trefoil was synthesized and its aggregation behavior was analyzed by x-ray scattering. The absorption, fluorescence, transient absorption spectra, and lowest excited singlet state lifetimes of these chromophores, with the exception of NI, are nearly identical to those of their unsubstituted parent chromophores. The reduction potentials of the dialkylated chromophores are ∼100 mV more negative and oxidation potentials are ∼40 mV less positive than those of the parent compounds, while the corresponding potentials of the tetraalkylated compounds are ∼200 mV more negative and ∼100 mV less positive than those of their parent compounds, respectively. Continuous wave electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) data on the radical anion of PDI reveals spin density on the perylene-core protons as well as on the beta-protons of the phenethyl groups. The asymmetric TDI derivatives even exhibited charge sharing in the aggregated state. The phenethyl groups enhance the otherwise poor solubility of the bis(dicarboximide) chromophores and only weakly perturb the photophysical and redox properties of the parent molecules, rendering these derivatives and related molecules of significant interest to solar energy conversion.;A perylene-3,4:9,10-bis(dicarboximide) (PDI) electron acceptor molecule was covalently attached to a pyrene electron donor chromophore (Py-PDI). Photoinduced electron-transfer (PET) was observed in the picosecond timescale. In a similar fashion four PDI molecules were covalently attached at symmetrical positions around a single pyrene chromophore (Py-PDI4). Aggregation due to Van der Waals interactions led to a monodisperse solution of pentamers in toluene, and PET was observed on a similar timescale as Py-PDI. Femtosecond transient absorption was performed to determine the time constants of charge separation and recombination in toluene. The size of the aggregates was determined by small-angle x-ray scattering.;Photochemical electron donor-acceptor triads having an aminopyrene primary donor (APy) and a p-diaminobenzene secondary donor (DAB) attached to either one or both imide nitrogen atoms of a perylene-3,4:9,10-bis(dicarboximide) (PDI) electron acceptor were prepared to give DAB-APy-PDI and DAB-APy-PDI-APy-DAB. In toluene, both triads are monomeric, but in methylcyclohexane, they self-assemble into ordered helical heptamers and hexamers, respectively, in which the PDI molecules are pi-stacked in a columnar fashion, as evidenced by small- and wide-angle X-ray scattering. Photoexcitation of these supramolecular assemblies results in rapid formation of DAB+•-PDI-• spin-polarized radical ion pairs having spin-spin dipolar interactions, which show that the average distance between the two radical ions is much larger in the assemblies (31 A) than it is in their monomeric building blocks (23 A). This work demonstrates that electron hopping through the pi-stacked PDI molecules is fast enough to compete effectively with charge recombination (40 ns) in these systems, making these materials of interest as photoactive assemblies for artificial photosynthesis and organic photovoltaics.;A photochemical electron donor-acceptor triad with 1,6-diaminopyrene (A2Py) as the secondary donor, aminopyrene (APy) as the primary donor, and perylene-3,4:9,10-bis(dicarboximide) (PDI) as the electron acceptor was prepared to give PDI-APy-A2Py-APy-PDI. This compound was found to self-organize into discrete dimers as evidenced by small- and wide-angle x-ray scattering in such a way as to allow both PDI's as well as the A 2Py to form close pi-stacks in methylcyclohexane (MCH). Photoexcitation of the compound results in rapid formation of A2Py+• -APy-PDI-•. Time-resolve electron paramagnetic resonance (TREPR) indicated the same RP distance in the monomer as in the dimer, which could suggest that both cation and anion are delocalizing through the aggregate.