Affiliation:
1. Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
Abstract
Oxidative reactions of isomeric amino-, methylamino-, and dimethylamino-pyridines with the 3-vinyl group of methyl pyropheophorbide-[Formula: see text], a chlorophyll-[Formula: see text] derivative, afforded 3-{1-[[Formula: see text]/[Formula: see text]/[Formula: see text]-(non/mono/di-methyl-amino)pyridinio]ethenyl}chlorins bearing the C31–N+ bond. Although all the [Formula: see text]/[Formula: see text]-substituents gave almost the same visible absorption spectra in acetonitrile, the [Formula: see text]-methylation effect on the Qy maxima was observed in the [Formula: see text]-substituted analogs with blue-shifted absorption bands. The substitution with most of the amino moieties suppressed the intramolecular electron transfer from the photoexcited chlorin core to the relatively electron-rich pyridinio periphery to enhance the fluorescence emission in acetonitrile, compared with the unsubstituted pyridinio analog. By contrast, the [Formula: see text]-NH2 substituted pyridine–chlorin conjugate was less fluorescent than any other aminated analogs as well as the unsubstituted counterpart. The electron-donating ability of the [Formula: see text]-NH2 group was recovered by the addition of alcohols to give highly fluorescent species.
Publisher
World Scientific Pub Co Pte Ltd