Multipulse spectroscopy on the wild-type and YM210W Bacterial Reaction Centre uncovers a new intermediate state in the special pair excited state

The Bacterial Reaction Centre (BRC) has a complex electronic excited state, P∗, that evolves into subsequent charge separated product states P+H− and P+B−. Pump–dump–probe spectroscopy on the wild-type BRC and on YM210W, a mutant with a stabilized, long-lived P∗ excited state, has uncovered a new charge-separated state in both BRC’s. When P∗ is dumped, a fraction of its population is transferred to this state that has a strong Stark shift in the accessory bacteriochlorophyll (BM) region which serves as a signature for P+ and a lifetime highly comparable to the slow phase of P∗ decay. This lead us propose this intermediate to be P+/P−.