Modulation of Intersystem Crossing by Chemical Composition and Solvent Effects: Benzophenone, Anthrone and Fluorenone

Abstract

Combined density functional theory and multireference configuration interaction methods including spin‐orbit coupling and spin‐vibronic interactions have been used to elucidate the photophysical pathways of benzophenone (BP), anthrone (A) and fluorenone (FL). Our results reveal that the slower S1(1nπ*) T1(3ππ*) passage of FL in the gas phase, as compared to BP and A, originates from the different electronic structures of the T1(3ππ*) states in these compounds and is not related to the planarity of the nuclear arrangement. Temperature effects on the rate constants of intersystem‐crossing (ISC), reverse ISC (rISC) and fluorescence have been investigated for FL in solvents of different polarity. Experimentally observed trends for rate constants are well reproduced. A nearly temperature‐ and solvent‐independent, slower down‐hill ISC component is attributed to the El‐Sayed‐forbidden S1(1ππ*) T1(3ππ*) transition in these environments. The faster El‐Sayed‐allowed S1(1ππ*) T2(3nπ*) ISC requires thermal activation in tetrahydrofuran and acetonitrile solution so that fluorescence may compete against triplet formation. In cyclohexane solution, S1(1ππ*) and T2(3nπ*) are nearly degenerate according to our calculations. Hence S1 T2 ISC and S1 T2 rISC have similar rate constants. If T2 T1 internal conversion could be slowed down by deuteration or perfluorination, for example, FL‐derivatives might show delayed fluorescence.

Tuning the Absorption, Fluorescence, Intramolecular Charge Transfer, and Intersystem Crossing in Spiro[fluorene]acridinone

“…For example, benzophenone has been reported to undergo ISC on the picosecond time scale with near unity efficiency [36–39] . Such a quantitative ISC is observed in thioxanthone, [21,32] acetophenone, [22,40–43] anthrone, etc., [28] as well. Not only the type of aromatic keto but also the environment, such as solvent polarity, [44,45] temperature, [46] and pressure [47] assists in modulating ISC [13] …”

“…Notably, aromatic ketones are well known for their rapid and efficient intersystem crossing (ISC) [11,21,22,28–32] . The lone pair orbital of the carbonyl group contributes to the n‐orbital.…”

Spin-Vibronic Intersystem Crossing and Molecular Packing Effects in Heavy Atom Free Organic Phosphor

“…One of the most widely studied examples of ISC dynamics in heavy metal free organic molecules is benzophenone, which exhibits ISC in the picosecond regime. − Excited state dynamics simulations of benzophenone performed by Favero et al demonstrated that direct (i.e., S 1 → T 1 ) ISC accounted for the majority of the spin-flipping dynamics, with the remaining crossing to the T 2 or higher triplet states, which subsequently undergo ultrafast nonradiative decay into the T 1 state. Their simulations ascribed the fast ISC to two internal coordinates activated after n –π* excitation, namely, the CO stretch and the torsion of phenyl rings.…”

Tuning the Absorption, Fluorescence, Intramolecular Charge Transfer, and Intersystem Crossing in Spiro[fluorene]acridinone

“…[19][20][21][22][23][24][25][26][27] Notably, aromatic ketones are well known for their rapid and efficient intersystem crossing (ISC). [11,21,22,[28][29][30][31][32] The lone pair orbital of the carbonyl group contributes to the norbital. Meanwhile, carbonyl and aromatic rings define the π-orbital.…”

“…Notably, aromatic ketones are well known for their rapid and efficient intersystem crossing (ISC) [11,21,22,28–32] . The lone pair orbital of the carbonyl group contributes to the n‐orbital.…”