Electronic spectroscopy and photophysics of calix[4]azulene

Prospects for useful fission from singlet states higher than S1 in aggregated organic chromophores

“…55 However, no ultrafast transient absorption evidence of a T 1 product was found in this species on excitation to S 2 so direct SF to 2T 1 appears to be improbable. However, a unique SF process involving direct S 2 to 2S 1 followed by internal conversion to 2S 0 was proposed 55 following elimination of all other S 2 decay routes. Singlet fission from S 2 producing a pair of correlated S 1 excited states, 1 [S 1 S 1 ], i.e., the reverse of bimolecular S 1 electronic energy pooling, 43 is possible (vide infra).…”

“…Scheme 1), consisting of four azulene species interconnected at the 1 and 3 positions by methylene groups, exhibits spectroscopic evidence of significant chromophore interaction and yields no measurable S 2 fluorescence. 55 However, no ultrafast transient absorption evidence of a T 1 product was found in this species on excitation to S 2 so direct SF to 2T 1 appears to be improbable. However, a unique SF process involving direct S 2 to 2S 1 followed by internal conversion to 2S 0 was proposed 55 following elimination of all other S 2 decay routes.…”