Theoretical study and experimental validation on the optical emission processes in "free" and "locked" pyrazine derivatives

The excited-state properties of the "free" and locked" pyrazine derivatives are investigated in solution. DCFP with "free" phenyls is theoretically calculated to be non-emissive due to the non-radiative energy dissipation through strong Duschinsky rotation effect, in agreement with the available experimental result. Surprisingly, DCBP with "bi-locked" phenyls is also calculated to be nonluminous. The emission of DCAP with "conjoined" architecture is predicted to be weaker than DCPP with "single-locked" phenyls, quite contrary to our intuition but further validated by the experimental measurement. The construction of four-, five- and six-membered ring respectively in DCBP, DCAP and DCPP is found to be the major structural origin for the descending relaxation energy in these "locked" systems, thus giving rise to the ascending luminescence order. Our work not only provides strategy for the molecular design of efficient organic light-emitting materials, but also offers valuable insight into the aggregation-induced emission phenomena. (C) 2019 Elsevier B.V. All rights reserved.