The resulting work of Artyukov and co-workers , using a semi-empirical partial neglect of differential overlapping method , found that S 1 internal conversion was comparable with intersystem crossing across three acridine chromophores. The calculated interexcited state rate constants (Table ) are several orders of magnitude faster compared to the excitedground transition, however as per Kasha's exciton model , this is common behaviour. Similarly fast rates for the laurdan fluorescent probe chromophore were shown by Zharkova and coworkers . Their earlier work on bi-polyacene systems suggested energy transfer between a donor naphthalene fragment to an acceptor anthracene fragment as equivalent to internal conversion; with very fast internal conversion pathways (∼10 8 -10 13 s -1 ). Valiev and co-workers examined the case of internal conversion in free-base porphyrin, and found a rate of 1.12×10 8 s -1 . They also examined tetrabenzoporphyrin and tetraphenylporphyrin, and found corresponding rates of 8.3 × 10 7 s -1 and 1.91 × 10 8 s -1 , respectively. Artyukhov and co-workers performed a comprehensive study of internal conversion in the polyacenes for the three lowest singlet excited states, and yielded rate constants in reasonable agreement with experimental observations. Baryshnikov and co-workers calculated internal conversion for a myriad of different compounds also correlating well with experiment. Samsonova and co-workers performed an extended analysis on some acridine compounds, and found that the S 1 → S 0 was generally slower than fluorescence, with ultra-fast interexcited state transitions at least 10 10 s -1 .