Lennard-Jones potential coefficients A ij and B ij . For the latter, OPLS mixing rules are used to determine Lennard-Jones coefficients for pairs of atoms i and j. All QM calculations in this study were performed with the Gaussian09 package. Geometry optimisations were performed in vacuum using DFT for S 0 states and TD-DFT for S 1 states with the M06-2X functional and def2-SVP basis set. In contrast to literature suggestions, the Tamm-Dancoff approximation (TDA) was not used here for the S 1 state of PTZ-DBTO2 because it failed to produce an optimised structure with no imaginary frequencies. Bond and angle parameters were calculated from the Hessian matrix of the optimised structures using the modified Seminario method. Single point calculations were subsequently performed using the optimised structures in an implicit solvent. The Guassian09 default PCM using the integral equation formalism was employed with the static dielectric constant, , set to 4 to account for induction in an effective manner. Atomic partial charges were computed using density derived electrostatic and chemical (DDEC) atoms-in-molecule partitioning of the total electron density, using the DDEC3 method in the Chargemol program. Lennard-Jones parameters were derived from the resulting atomic electron densities using the Tkatchenko-Scheffler method, as previously described. Dihedral scans were performed for all freely rotatable torsion angles in the three molecules.