2-Arylvinylpyrimidines versus 4-arylvinylpyrimidines: synthesis and comparison of the optical properties

Condensation of donor-substituted aldehydes on methylpyrimidine led to two series of fluorescent molecules depending on the position of the methyl group. Whereas highly emissive 4-arylvinylpyrimidine derivatives are well-known, this is the first example of fluorescent 2-arylvinylpyrimidine compounds. The optical properties of the two families have been thoroughly compared. Whereas the series derived from 2-methylpyrimidine exhibit a blue shift in absorption and emission in comparison with 4-arylvinylpyrimidine, the influence of the position is less predictable on the fluorescence quantum yield. These compounds also exhibit halochromism: when adding acid, a bathotromic shift is observed in absorption whereas an increase of the fluorescence intensity which is red-shifted except for amino derivatives (a progressive quench of emission is observed in these cases). An emission solvatochromism study has shown that a higher intramolecular charge transfer seems to occur in 2-arylvinylpyrimidines than in 4-arylvinylpyrimidines.