A push-pull aromatic chromophore with a touch of merocyanine

The solvatochromic behavior of N-(2,5-di-tert-butylphenyl)-9-pyrrolidinoperylene-3,4-dicarboximide ( 5PI) was investigated by measuring the excitation and emission spectra over a wide range of temperature in 2-methyltetrahydrofuran (MTHF). The temperature induced spectral changes can be compared with the changes caused by changing solvent polarity using different solvents at room temperature. In both cases a strong positive solvatochromism is observed both in absorption/excitation and in emission. The difference between excitation and emission energies decreases with increasing solvent polarity. The behavior of 5PI can be rationalized in terms of a change in electronic structure with solvent polarity. Although 5PI has the typical molecular structure of a push-pull substituted aromatic system, in which the solvatochromic shift in emission is normally larger than that in absorption, in its solvent-induced electronic structure change it resembles a merocyanine.