The UV-Vis absorption spectra of 4CzIPN and pDTCz-DPmS are similar, with both compounds possessing low energy charge transfer (CT) bands (λabs = 448 nm and acceptor in pDTCz-DPmS, which is a result of its more planar conformation, these CT bands are much more intense (Figure ). The onset of absorption is significantly more red-shifted in 4CzIPN in comparison to pDTCz-DPmS. There is a limited degree of negative solvatochromic effect observed for both compounds (Figure ), reflecting a decrease in the transition dipole moment of the compounds in the excited state in these solvents.