Sequential energy and electron transfer in aggregates of tetrakis[oligo(p-phenylene vinylene)] porphyrins and C60 in water

Chiral aggregation of oligo(p-phenylene vinylene)-functionalized Zn and free-base porphyrins is observed in water. The formation of mixed assemblies containing both porphyrins results in sequential energy transfer from OPV via zinc porphyrin to free-base porphyrin. Furthermore, the incorporation of C60 as electron acceptor yields a charge separated state by ultimate electron transfer

Charge transfer kinetics in fullerene-oligomer-fullerene triads containing alkylpyrrole units

A photoinduced electron-transfer reaction has been observed in three fullerene-donor-fullerene triads containing an electron-rich pyrrole ring in the donor moiety. The kinetics of charge separation in solution has been investigated by photoluminescence and transient absorption spectroscopy. The polarity of solvent and the distance between donor and acceptor affect the forward electron-transfer reaction, in qualitative agreement with a semiempirical model for the Gibbs free energy for charge separation. Depending on the conditions, charge separation occurs at a rate of 10(9)-10(10) s(-1). The charge recombination rate is estimated to be faster than 2 x 10(10) s(-1). The relatively large contribution of the singlet-excited-state S-

Orientational effect on the photophysical properties of quaterthiophene-C60 dyads

Two quaterthiophene-[60]fullerene dyads in which C60 is singly (4TsC) or doubly (4TdC) connected to the inner b-position of the terminal thiophene rings have been synthesized. The electronic properties of these donor-acceptor compds. were analyzed by UV/Vis spectroscopy and cyclic voltammetry, and their photophys. properties in soln. and in the solid state by (time-resolved) photoluminescence (PL) and photoinduced absorption (PIA) spectroscopy. Both the flexible and geometrically constrained 4TsC and 4TdC dyads exhibit photoinduced charge transfer from the quaterthiophene to the fullerene in toluene and o-dichlorobenzene (ODCB). In toluene, charge transfer occurs in both dyads by an indirect mechanism, the first step of which is a singlet-energy transfer from the 4T(S1) state to the C60(S1) state. In the more polar ODCB, direct electron transfer from 4T(S1) competes with energy transfer, and both direct and indirect charge transfers are obsd. The geometrical fixation of the donor and acceptor chromophores in 4TdC results in rate consts. for energy and electron transfer that are more than an order of magnitude larger than those of the flexible 4TsC system. For both dyads, charge recombination is extremely fast, as inferred from picosecond-resolved temporal evolution of the excited state absorption of the 4T.+ radical cation both in toluene and ODCB. [on SciFinder (R)

Supramolecular Fullerene Architectures By Quadruple Hydrogen Bonding

The synthesis and full characterization of a quadruple bonded fullerene dimer using self-complementary 2-ureido-4[1H]-pyrimidinone units with high dimerization constants is described. The chemical integrity of the monomeric moiety in either compound is fully preserved, also with respect to its redox and UV-Vis behavior. Two novel supramolecular dyads consisting of an oligo(p-phenylene vinylene) (OPV) donor and fullerene (C60) acceptor are created via quadruple hydrogen bonding upon mixing the fullerene dimer and an OPV dimer. In these supramolecular dyads, singlet-energy transfer from the excited OPV unit to the fullerene causes a strong quenching of the OPV fluorescence. The high association constant of the 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonding unit results in high quenching factors (Qmax ≥ 90). The lower limit obtained for the rate constant for energy transfer (kEN ≥ 6 × 10e10 s-1) is rationalized in terms of the Förster mechanism.

Supramolecular fullerene architectures by quadruple hydrogen bonding

The synthesis and full characterization of a quadruple bonded fullerene dimer using self-complementary 2-ureido-4[1H]-pyrimidinone units with high dimerization constants is described. The chemical integrity of the monomeric moiety in either compound is fully preserved, also with respect to its redox and UV-Vis behavior. Two novel supramolecular dyads consisting of an oligo(p-phenylene vinylene) (OPV) donor and fullerene (C60) acceptor are created via quadruple hydrogen bonding upon mixing the fullerene dimer and an OPV dimer. In these supramolecular dyads, singlet-energy transfer from the excited OPV unit to the fullerene causes a strong quenching of the OPV fluorescence. The high association constant of the 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonding unit results in high quenching factors (Qmax ≥ 90). The lower limit obtained for the rate constant for energy transfer (kEN ≥ 6 × 10e10 s-1) is rationalized in terms of the Förster mechanism.

The importance of nanoscopic ordering on the kinetics of photoinduced charge transfer in aggregated pi-conjugated hydrogen-bonded donor-acceptor systems

Aggregated complexes of diaminotriazine oligo(p-phenylene vinylene) (OPV) units hydrogen bonded to different complementary perylene bisimide (PERY) compds. have been investigated by means of absorption, CD, photoluminescence, and photoinduced absorption spectroscopy. These studies reveal that in the aggregated state an ultrafast photoinduced charge sepn. occurs via an intermol. pathway in the J-type stack of hydrogen-bonded OPV-PERY arrays. The subsequent charge recombination reaction strongly depends on small structural differences within the J-type geometry as revealed by comparison of stacked supramol. dimers, trimers, and covalently OPV-PERY linked systems. A coupled oscillator model is used to analyze absorption and CD spectra and to identify intermol. arrangements that are consistent with the exptl. spectra and the charge-transfer kinetics. [on SciFinder (R)