Photoinduced charge separation in self-assembled cofacial pentamers of zinc-5,10,15,20-tetrakis(perylenediimide)porphyrin

Citations Over TimeTop 10% of 2007 papers

Abstract

A bichromophoric electron donor-acceptor molecule composed of a zinc tetraphenylporphyrin (ZnTPP) surrounded by four perylene-3,4:9,10-bis(dicarboximide)(PDI) chromophores (ZnTPP-PDI(4)) was synthesized. The properties of this molecule were compared to a reference molecule having ZnTPP covalently bound to a single PDI (ZnTPP-PDI). In toluene, ZnTPP-PDI(4) self-assembles into monodisperse aggregates of five molecules arranged in a columnar stack, (ZnTPP-PDI(4))(5). The monodisperse nature of this assembly contrasts sharply with previously reported ZnTPP-PDI(4) derivatives having 1,7-bis(3,5-di-t-butylphenoxy) groups (ZnTPP-PPDI(4)). The size and structure of this assembly in solution was determined by small angle X-ray scattering (SAXS) using a high flux synchrotron X-ray source. The ZnTPP-PDI reference molecule does not aggregate. Femtosecond transient absorption spectroscopy shows that laser excitation of both ZnTPP-PDI and (ZnTPP-PDI(4))(5) results in quantitative formation of ZnTPP(+*)-PDI(-*) radical ion pairs in a few picoseconds. The transient absorption spectra of (ZnTPP-PDI(4))(5) suggest that the PDI(-*) radicals interact strongly with adjacent PDI molecules within the columnar stack. Charge recombination occurs more slowly within (ZnTPP-PDI(4))(5)(tau= 4.8 ns) than it does in ZnTPP-PDI (tau= 3.0 ns) producing mostly ground state as well as a modest yield of the lowest triplet state of PDI ((3*)PDI). Formation of (3*)PDI occurs by rapid spin-orbit induced intersystem crossing (SO-ISC) directly from the singlet radical ion pair as evidenced by the electron spin polarization pattern exhibited by its time-resolved electron paramagnetic resonance spectrum.

Related Papers

• → Ultrafast Charge-Transfer Dynamics: Studies of p-Nitroaniline in Water and Dioxane(1998)94 cited
• → Intersystem crossing in transition metal complexes(2006)67 cited
• → Ultrafast Excited-State Dynamics of 6-Azauracil Studied by Femtosecond Transient Absorption Spectroscopy(2015)15 cited
• → Conjugated Porphyrin Polymers: Control of Chromophore Separation by Oligophenylenevinylene Bridges(1997)60 cited
• → Concerning apparent intersystem crossing efficiencies in molecules with small S1T1 energy gaps(1991)15 cited