Tunable Luminescence of Bithiophene-Based Flexible Lewis Pairs

Bithiophene-based flexible Lewis pairs with P(O)R-2 (R = phenyl, isopropyl) and BMes(2) (Mes = 2,4,6-trimethylphenyl) functionalities are able to toggle between closed, Lewis adduct and open, unbound Lewis pair structures. The open structure is favored in strong hydrogen bond donating solvents or at higher temperatures giving rise to an intense charge-transfer (CT) luminescence, while the closed structure without this emission dominates in non-hydrogen bond donating solvents or at lower temperatures. Intermediate solvents result in an equilibrium mixture of both structures, which shows unusual mixed emission that is dependent on excitation wavelength.