Effect of Conjugation of Chromophores
electrons are considered to be further delocalized by conjugation; the orbitals involve four (or more) atomic centers. The effect of this delocalization is to lower the energy level of the * orbital and give it less antibonding character. Absorption maxima are shifted to longer wavelengths as a consequence. Conjugation of chromophores, has a profound effect on spectral properties. 1,3-butadiene, CH2=CHCH=CH2, has a strong absorption band that is displaced to a longer wavelength by 20 nm compared with the corresponding peak for an unconjugated diene.