Ultrafast spectroscopy of soluble terrylene and quaterrylene

Transient properties of tetra-t-butyl-terrylene and tetra-t-butyl-quaterrylene have been measured by subpicosecond absorption/gain spectroscopy and analysed by a global spectral treatment. A drastic difference in the spectrodynamic behaviour of the lowest excited singlet state is observed. The former shows normal excited singlet absorption and gain, nanosecond fluorescence and a long-lived transient absorption assigned to a triplet. The latter shows a new transient absorption which rises for 30 ps, and no associated gain. These results are interpreted by the ultrafast(much less than 500 fs) formation of a nonradiant intermediate state, precursor of a long-lived reversible photoproduct.