Intramolecular heavy-atom effect in the photophysics of organic molecules

Impact of non-symmetric 2,9,10-aryl substitution on charge transport and optical properties of anthracene derivatives

“…While introduction of more bulky substituents reduces the nonradiative decay constant from 7.0 ns to 6.52 ns in solution, for compounds 2a and 5b, respectively. Thus more realistic route of nonradiative deactivation is mechanism of intersystem crossing, which rate is tuned by alignment of S 1 and T n (most likely of T 2 or T 3 ) energy levels[23,24,26,46]. The introduction of 2-phenyl moiety results in proper S 1 and T n level alignment (see Section 2.2) when effective relaxation through triplet states occur what is evidenced reduced τ nr values of compounds 1-6a and 1-6b.…”

Insights into the photochemical transformation pathways of triclosan and 2′-HO-BDE-28

“…The ˚ values of triclosan were found to be higher than those of 2 -HO-BDE-28 at both of the two pH conditions. This might be attributed to the higher internal heavy atom effects of Br atom than Cl atom, since it is widely accepted that the higher internal heavy atom effects may lead to higher intersystem crossing probability of excited aromatic molecules, for instance, from excited singlet state to triplet state and then to ground state, which may lower the life-time of the excited states [40]. Besides, the A r values of triclosan are lower than those of 2 -HO-BDE-28 at the two pH conditions, because of the stronger influence effect of Br atom than Cl atom on the redshift of the UV-vis absorption.…”

“…These results further confirm that no dioxin products are generated in the self-sensitized photo-oxidation reactions and indicate that dioxins formed in the photolysis of triclosan and 2 -HO-BDE-28 are from excited singlet states. As Br atoms have higher internal heavy atom effects than Cl atoms [40], it is easier for 2 -HO-BDE-28 to undergo intersystem crossing from excited singlet state to triplet state, which can lead to the lower dioxin yield of 2,8-DBDD for 2 -HO-BDE-28 than that of 2,8-DCDD for triclosan.…”

Study of intersystem crossing mechanism in organic materials

“…It is known that the spinorbit coupling flips the singlet spin configuration to triplet and vice versa and hence facilitates ISC [6,8,13]. ISC from a singlet excited state to a triplet excited state has been studied theoretically [14][15][16] and as well as experimentally [11,12].…”