[1] 2+ has a hydrophobic core and two charged, hydrophilic N(CH3)3groups at a distance of 2.99 nm from one another based on crystal structure; in the structure optimized with DFT calculation the distance is 3.1 nm, and in the MD-simulations, the distance varies between 2.8-3.1 nm. As the membrane thickness is typically between 3-5 nm, the molecule can span across lipid bilayer as the thickness of the membrane, which is also demonstrated by MDsimulations, see a snapshot in Figure and other trajectories in the SI Section S7. The nature of this preferred orientation is unraveled with molecular dynamics (MD) simulations (see computational setup in Section S7). In those, the photoactive molecule in different ways, such as in a transmembrane fashion, or parallel to the surface of the membrane as we previously found for a different chromophore in a lipid bilayer. However, in our simulations Incidentally, this is exactly the region where both the excitations to S1 and S3 are located. As outlined above, the S1 exhibits a different electronic structure compared to the S0, and because the polar solvent will adjust to the ground state, it will stabilize the S0 more than an excited state of different electronic structure. When this stabilization is removed upon incorporation into the liposomes, the S0 will be more destabilized than the S1, resulting in the excitation redshift evidenced in the absorption spectra. The S3, by contrast, is similar to the S0 in electronic structure and will thus be similarly stabilized, explaining why it is much less affected by the environmental change and thus the excitation is not shifted noticeably.