where ε 0 is the permittivity of free space, and kr is positively related to f value. Benefiting from a much larger f value, the kr of CCO-1 calculated in solid state is 1.2 × 10 6 s -1 , being about ten-fold larger than that of CBP-1 (1.1 × 10 5 s -1 ), indicative of faster radiative transition. Therefore, the SSA process can be better alleviated in CCO-1. decay curves of 20 wt% doped films, measured under nitrogen. Transient absorption spectra of e CCO-1 and f CBP-1 on nanosecond timescales in oxygen-free toluene solutions (10 -5 M). Excitation wavelength: 355 nm. g Transient absorption spectra of CCO-1 (top line) and CBP-1 (bottom line) on microsecond timescales in oxygen-free toluene solution (10 -5 M). Transient absorption contour maps of h CCO-1 and I CBP-1 in toluene solutions under air (top line) and nitrogen (bottom line) atmosphere (10 -5 M).