Indexed by:期刊论文

Date of Publication:2018-02-22

Journal:JOURNAL OF PHYSICAL CHEMISTRY C

Included Journals:SCIE、EI

Volume:122

Issue:7

Page Number:3756-3772

ISSN No.:1932-7447

Abstract:Perylenebisimide (PBI)-phenothiazine (PTZ) and PBI diphenylamine (DPA) dyads were prepared, with the PTZ or DPA as the electron donor and the 6-subsituted PBI unit as the electron acceptor. The dyads were designed in such a way that electronic coupling (magnitude is the matrix elements, V-DA and V-DA*) between the electron donor and acceptor is controlled by conformation restriction. The effects of the electronic coupling on UV-Vis absorption and emission were studied. More significant charge-transfer (CT) absorption and CT fluorescence emission bands were observed for dyads with smaller dihedral angles between the electron donor and acceptor, thus stronger electronic coupling (V-DA = 3290 cm(-1) and V-DA* = 4317 cm(-1)) was observed than those with larger dihedral angle, showing weaker coupling effect (V-DA = 1210 cm(-1) and V-DA* = 2770 cm(-1)). Triplet state production was observed only for PBI DPA but not for PBI PTZ dyads. With an intermolecular triplet photosensitizing method, the triplet state of PBI PTZ dyads was observed. The femtosecond transient absorption spectra confirmed the ultrafast charge separation (CS, 0.3 ps similar to 0.6 ps) and slow charge recombination (CR, 130 ps similar to 240 ps) process. These results indicate that the CR does not produce any triplet state in the PBI PTZ dyads, for instance by the expected spin-orbital charge transfer intersystem crossing (SOCT-ISC). We propose that the lack of triplet state production in PBI-PTZ dyads is due to the large separation of the (CT)-C-1 and the (CT)-C-3/(PBI)-P-3 states, and the orthogonal geometry and the CR are not exclusively sufficient criteria for SOCT-ISC. Our results on controlling the absorption, emission, and ISC by tuning the V-DA magnitudes between the donor and acceptor will be useful for molecular design of compact electron donor/acceptor dyads.