Intersystem Crossing in the ¹nπ* and ¹ππ* States

Abstract

Fast intersystem crossing is observed in the S(1)(1)nπ* state of N-heterocyclic aromatic hydrocarbons and carbonyl compounds. It is attributed to spin-orbit coupling with the (3)ππ* state in the same energy region. The strong singlet-triplet mixing was confirmed by large Zeeman splitting of rotational lines in a high-resolution spectrum. For the S(1)(1)ππ* state of aromatic hydrocarbons, the observed Zeeman splitting was found to be considerably small, and intersystem crossing was considered to be minor. These facts are in accordance with El-Sayed's rule, which states spin-orbit coupling is forbidden between the (1)ππ* and (3)ππ* states. The Zeeman splitting of several derivatives was also observed and the substitution effect on the intersystem crossing rate is discussed.

Jet spectroscopy of buckybowl: Electronic and vibrational structures in the S and S1 states of triphenylene and sumanene

“…23,24 Intersystem crossing (ISC) to the triplet state is considered to be very slow for planar aromatic hydrocarbons. 25,26 The mechanism of the deuterium effect in channel three has not yet been identified. Radiationless transitions are generally suppressed by deuterium substitution because of the shrinkage of the vibrational wave function.…”

Aggregation Induced Phosphorescence in the Main Group

“…[10] Phosphorescent materials are coveted for OLED applications due to their potential to attain a theoretical maximum of 100 % electroluminescence effi-ciency [vs. 25 % from fluorescent materials] due to the ability to harness light emission from triplet excitons. [14] This principle has been used to obtain phosphorescence from purely organic compounds such as pyrazines [15] and carbonyl-containing molecules (e. g. benzophenone). [12] In photoinduced phosphorescence, initial excitation to an excited singlet state (or states) (S n ) transpires and is followed by spin-forbidden intersystem crossing (ISC) to an excited triplet state (T n ).…”

“…[13] There are several strategies that can be used to achieve efficient intersystem crossing to triplet excited states: 1) El-Sayed's rule states that the rate of intersystem crossing from a singlet to a triplet excited state is increased if the transition occurs between molecular orbitals of different symmetry (e. g. 1 pp* to 3 np* or 1 np* to 3 pp*). [14] This principle has been used to obtain phosphorescence from purely organic compounds such as pyrazines [15] and carbonyl-containing molecules (e. g. benzophenone). [16] 2) Spin exchange of a radical-ion pair can also lead to population of excited triplet states, as is observed in solid isophthalic acid.…”

Mimicking Heme Enzymes in the Solid State

“…[89][90][91][92] In the case of intersystem crossing (ISC) the rate of conversion from the singlet to triplet state is dependent on the spin-orbit coupling between the states according to: 〈ψ S (π,π*) |H so |ψ T (π,π) 〉 〈υ S |υ T 〉, where H so is the spin-orbit coupling element, υ s is the lowest energy vibrational mode in the S 1 state and υ T is the vibrational mode of the T state that overlaps with the υ s mode. 89,90 The spin-orbit coupling integral will only be non-zero for transitions between states with different configurations. The fact that the symmetry of the close lying T 2 and the S 1 state are equivalent makes the 〈ψ S1 (π,π*) |H so |ψ T2 (π,π*) 〉 = 0.…”