Fig. 3
Absorption properties of MEH-PBI aggregates. a Molecular structure of monomeric MEH-PBI compound (inset), actual absorbance spectrum of MEH-PBI aggregates in MCH (with a molecular concentration of 1.5 × 10−4 M) as used for EEI2D experiments and laser spectrum of pump pulse (red). b Concentration-dependent absorption spectra of MEH-PBI in MCH at 20 °C in the concentration range from 6 × 10−6 to 1.7 × 10−4 M. Arrows indicate spectral changes with increasing concentration
