J-type aggregation of a simple merocyanine skeleton: Spectral features and structure of 4-amino-6-oxopyrimidine

The absorption and fluorescence spectral properties of 4-amino-6-oxopyrimidine (1), which has a simple streptopolymethine merocyanine skeleton, clearly showed that the molecule 1 formed the aggregate 1n, and showed an exciton band, appearing at an absorption of 350 nm due to the red-shifted HOMO–LUMO transition. Upon light irradiation of the exciton band, a fluorescence band at 398 nm (ΦFL = 0.10) was observed, and its decay lifetimes were determined. Based on these spectral features, the aggregated 1n was found to be formed by J-type aggregation. The molecular orientation 1 in the crystal was revealed as being both parallel π–π stacking and hydrogen bonding chains.