Ultrafast Intersystem Crossing in Xanthone from Wavepacket Dynamics

Abstract

Most aromatic ketones containing first-row elements undergo unexpectedly fast intersystem crossing in a 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 only ∼1.5 ps. The exact mechanism of this unusually fast transition is still under debate. Here, we perform 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 1 ππ* → 1 nπ* (85 fs), (ii) an intersystem crossing 1 nπ* → 3 ππ* (2.0 ps), and (iii) an internal conversion between triplets 3 ππ* → 3 nπ* (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.

Theoretical study of the absorption and emission spectrum and non‐adiabatic excited state dynamics of gas‐phase xanthone

“…ð 1 nπ Ã Þ; we assume that this mode should be the promoting mode. Using Equation and T fi = 507 cm À1 , we can estimate the lifetime in this case to be about 105 fs (k IC = 9.53 Â 10 13 s À1 ); our calculated results are in agreement with the experimental results by Huix-Rotllant et al [56] T A B L E 3 Assignment of the absorption, fluorescence, and phosphorescence spectra of xanthone, and Huang-Rhys factors of the assignment modes Absorption (S 0 ! S Studying the adiabatic minima of excited states provides insight into the photophysical a species may undergo after being excited by light.…”

Stressing the differences in alizarin and purpurin dyes through UV-visible light absorption and1H-NMR spectroscopies

“…Such an effect cannot be captured by the Herzberg-Teller perturbative treatment of the transition dipole moment. To analyze this mechanism, we have computed approximate interstate couplings from one dimensional potential energy surfaces cuts along the ground-state normal modes that couple the dark and bright states, and we performed quantum dynamics simulations 15,63 for the modes that induce such coupling (see further details in ESI †). It turns out that such linear coupling effects are tiny and, thus, the intensity borrowing mechanism can be excluded.…”

“…4 Some of us studied the efficient singlet-triplet photoconversion in similar aromatic ketones, which could be involved in the degradation. [11][12][13][14][15] The desire to identify and control the possible fading processes requires a better understanding of HAQ physico-chemical properties, especially when HAQ compounds are found in a complex chemical environment, as it is the case in pigments and paintings. This can be achieved using various analytical techniques, among which we herein focus on Nuclear Magnetic Resonance (NMR) spectrometry and UV-visible absorption spectroscopy, as well as those quantum chemical studies aiming at rationalizing the experimental data.…”

Accurate Spin–Orbit Coupling by Relativistic Mixed-Reference Spin-Flip-TDDFT

“…The interest in intersystem crossings (ISC) or spin crossovers has been intensified by the advent of femtosecond time-resolved spectroscopic studies showing that ISC may occur at the picosecond timescale. In the case of xanthone, the 1 n π* → 3 ππ* ISC takes place within ∼ 2.0 ps right after an ultrafast 1 ππ* → 1 n π* internal conversion (IC). Wolf et al have also obtained circumstantial experimental evidence of the population transfer to triplet states on the timescale of 3.5±0.3 ps in the photodynamics of thymine.…”