Direct observation of the Twisted Intramolecular Charge-Transfer (TICT) state in Polycyclic Purinium Salts

Based on femtosecond transient absorption spectroscopy (fs-TAS) of 3-methyl-7,8-diphenyl-3H-purino[6,1-a] isoquinolin-6-ium trifluoromethanesulfonate in dimethyl sulfoxide (DMSO), the stimulated emission (SE) signal redshifts from 400 to 500 nm in 4.8 ps. In a glycerol/DMSO mixed solution, when the glycerol content is 25% and 50%, the delay is extended to 6.9 and 68 ps, respectively. The theoretical emission spectrum in the scanning of potential energy curves demonstrates that the rotation of the φ