SPECTROSCOPIC STUDIES ON BROOKERS MEROCYANINE

The origin of the multiple absorption bands of Brooker's merocyanine, 1- 4-aza-4-methylphenyl)-2-trans-(4-oxyphenyl)ethene, found in the vis ible region of the spectrum in solvents such as chloroform and tetrahy drofuran, has been explored experimentally using H-1 and C-13 NMR spec troscopy and theoretically using molecular orbital methods. While NMR analysis rules out the presence of a cis conformer, AM1/COSMO calculat ions in various solvents strongly suggest that there are a number of s table nonplanar conformations of the merocyanine as well as a dimer wh ich are predicted to absorb at longer and shorter wavelengths, respect ively, than the favored planar conformer. Spectroscopic analysis at va riable temperature is supportive with the intensity of the longer wave length absorption initially reducing with decreasing temperature, foll owed by an increase in the concentration of dimers and possibly aggreg ates. Further support is provided by synthesis of the corresponding no nplanar merocyanine containing methyl groups at the double bond and at the ortho positions of the oxyphenyl ring, which absorbs at longer wa velength than its related planar analogue.