Synthesis and photophysical properties of donor- and acceptor-substituted 1,7-bis(arylalkynyl)perylene-3,4:9,10-bis(dicarboximide)s

A series of 1,7-bis(arylethynyl)-N,N′-bis[2,6-diisopropylphenyl] perylene-3,4:9,10-bis(dicarboximide)s has been obtained from Sonogashira coupling of the 1,7-dibromoperylene-3,4:9,10-bis(dicarboximide) with p-substituted phenylacetylenes in which the p-substituents include π-donors (dialkylamino, diarylamino, p-(diarylami-no)phenyl, alkoxy) and π-acceptors (diarylboryl, p-(diarylboryl)phenyl). The bis(arylethynyl)-substituted chromophores all show two reversible molecular reductions and are all slightly more readily reduced than unsubstituted perylene-3,4:9,10-bis(dicarboximide)s with the electrochemical potentials being rather insensitive to the π-donor or acceptor nature of the aryl group. The amine derivatives also show reversible molecular oxidations. The UV-vis spectra of the chromophores with alkoxy and boryl substituents show red-shifted absorptions relative to unsubstituted perylene diimides with discernible vibronic structure. In contrast, the lowest energy absorptions of the amino derivatives are broad and structureless, suggesting donor-to-acceptor charge-transfer character. Transient absorption spectra for the amine derivatives were interpreted in terms of ultrafast charge separation, followed by charge recombination on a time scale of ca. 80-2000 ps. Two compounds were also synthesized in which an additional stronger, but more weakly coupled, donor group is linked by a nonconjugated bridge to the p-amine donor, to investigate the effect on the charge recombination lifetimes; however, the lifetimes of the charge-separated states, ca. 150 and 1000 ps, were within the range observed for the simple amine systems. Finally, the two-photon absorption properties of three bis(arylethynyl)-substituted derivatives were investigated, along with those of 1,7-di(pyrrolidin-l-y1)-N,N′-bis[2,6- diisopro-pylphenyl]perylene-3,4:9,10-bis(dicarboximide). As with other perylene-3,4:9,10-bis(dicarboximide)s and related species, strong two-photon absorption (>1000 GM) was observed for three of these species close to the one-photon absorption edge; however, an additional feature (100-500 GM) was also observed at longer wavelength. An example with (p-aminophenyl)ethylnyl substituents showed a qualitatively different two-photon spectrum with a cross-section >500 GM being observed over a broad wavelength range.