Internal conversion of the anionic GFP chromophore: in and out of the I-twisted S1/S0 conical intersection seam

The Z–E photoisomerization quantum yield of the HBDI− chromophore is a result of early, non-statistical dynamics around a less reactive I-twisted intersection and later, statistical behavior around the more reactive, near-enantiomeric counterpart.

Ultrafast intersystem crossing in xanthone from wavepacket dynamics

Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in few tens of picoseconds and a quantum yield close to unity. Among them, xanthone (9H-xanthen-9-one) possesses one of the fastest singlet-triplet rates of ~1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform the wavepacket dynamics of the photochemistry of xanthone in the gas phase and in polar solvents. We show that xanthone follows El-Sayed's rule for intersystem crossing. From the second singlet excited state, the mechanism is sequential: (i) an internal conversion between singlets 1pipi*-1npi* (85 fs), (ii) an intersystem crossing 1npi*-3pipi* (2.0 ps), and (iii) an internal conversion between triplets 3pipi*-3npi* (602 fs). Each transfer finds its origin in a barrierless access to electronic state intersections. These intersections are close to minimum energy structures, allowing for efficient transitions from the initial singlet state to the triplets.