Is the LE→TICT process in the S1 excited state of 9,9′-bisanthracenyl influenced by the viscosity or the dipolarity of the solvent?

Experimental evidence is presented which indicates that the intrinsic barrier of the locally excited state (LE)→twisted intramolecular charge-transfer state (TICT) process in the S1 excited state of 9,9′-bisanthracenyl (BA) is enhanced by the viscosity and dramatically diminished by the dipolarity of the solute-surrounding medium. -- Highlights: • The LE→TICT process in the S1 excited state of 9,9′-bisanthracenyl. • The barrier of the process is enhanced by the viscosity of the medium. • The barrier of the process is dramatically diminished by the dipolarity of the solute-surrounding medium