Aggregation-caused quenching versus crystallization induced emission in thiazolo[5,4-b]thieno[3,2-e]pyridine (TTP) derivatives: theoretical insightsElectronic supplementary information (ESI) available: Choice of the XC functional, selected molecular orbitals; frequencies and HR factors; packing structures in single crystals. See DOI: 10.1039/c8cp04730h

We report a QM (TD-DFT) and QM/QM′ (ONIOM) study of the modulation of emission in a series of thiazolo[5,4, b ]thieno[3,2- e ]pyridine (TTP) derivatives [Huang et al. , J. Mater. Chem. C , 2017, 14 , 3456]. By computing the excitation energy transfer couplings and the Huang-Rhys (HR) factors, we rationalize the aggregation-caused quenching (ACQ) observed for the parent molecule and the crystallization-induced emission (CIE) observed for the derivatives presenting intra-molecular H-bonding. We also show that the CIE strategy relying on the rigidification of the arch-bridge-like stator should be considered with caution since it can promote the energy dissipation through vibrational motions. Combining adequate theoretical strategies enables rationalization of the different photophysical processes at the origin of the ACQ/CIE effects.