Photophysical processes in fluorenone

Abstract

Figure 7. Energy levels of excited CT states and the local triplet excited state of 1,1'-binaphthyl.and CT-II states. The fact that racemization was not induced by photoexcitation of the CT-I band can be explained from this diagram. The triplet excited state of l.l'-binaphthyl, which is responsible for the racemization reaction, could not be formed energetically from the CT-I state.Photoexcitation of the CT-II band results in the following three processes: formation of a triplet excited state (racemization reaction), formation of ions, and fluorescence from the excited CT-I state as evidenced by laser photolysis, racemization, and fluorescence experiments. These facts indicate that intersystem crossing and ion formation processes compete with internal conversion from the CT-II to the CT-I state. The unusual intersystem crossing process from the upper excited singlet state is probably due to the large energy difference between the CT-II and CT-I states which consequently gives rise to a small Franck-Condon factor for the internal conversion process.18 The large energy difference slowed the internal CT-II 3BinaphthyI 'CT-I Ground State conversion rate and enabled other processes, such as intersystem crossing or ion formation, to compete with it. The enhancement of intersystem crossing from the CT-II singlet state may arise from a large spin-orbit coupling due to the CT interaction.19 This large spin-orbit coupling in the CT state and the small energy difference between the CT-II state and the local triplet excited state of , -binaphthyl may cause a considerable increase in the rate of intersystem crossing.

Estudo da reatividade do estado excitado triplete de 1,4-diaza-9-fluorenonas frente a doadores de hidrogênio e de elétron

“…Entretanto, para o caso de compostos nos quais haja uma grande similaridade entre as características dos orbitais para padrão e desconhecido, pode-se aceitar como aproximação razoável que ε T 9-fluorenona = ε T 1,4-diaza-9-fluorenona. 32 Empregando-se a técnica de fotólise por pulso de laser, com excitação a 308 nm, o rendimento quântico de cruzamento entre sistemas para as diazafluorenonas 1 e 2 foi calculado utilizando-se filtros de densidade neutra (NDF) com diferentes valores de transmitância, e utilizando como padrão o valor do φ =0,48 para 9-fluorenona (3), 33 em acetonitrila. Assim gráficos de ∆DOo versus %T foram lineares para 1-3 e, a partir da inclinação das retas obtidas, conforme exemplificado na Figura 3 para 1,4-diaza-9-fluorenona (1), e empregando-se a Equação 2, foram obtidos os valores de φ ces para 1 e 2.…”

“…A fotofísica e a reatividade fotoquímica de fluorenona também dependem da polaridade do solvente, [10][11][12][13][14][15][16][17][18][19][20][21] sendo que, neste caso, a característica do solvente vai afetar a posição relativa entre o estado excitado singlete de energia mais baixa (S 1 ) e estados excitados superiores, provavelmente T 3 . Assim, em solventes não polares, o singlete S 1 tem configuração nπ* e energia similar à de T 3 , o que resulta em baixo rendimento quântico de fluorescência e alto rendimento quântico de cruzamento entre sistemas.…”

Intra- and Intermolecular Reactivity of Triplet Sumanenetrione

“…The lifetime was longer than that of the 3 nπ* state of 3 2, i.e., 6.9¯s in benzene, 16 but significantly shorter than the characteristic triplet lifetime of the planar 3 ππ* triplet state, 3 3, whose lifetime is known to be 500¯s in benzene and 100¯s in acetonitrile. 17 The significantly shorter lifetime of the triplet species 3 1 than of the planar 3 3 is rationalized by the curved π-system in mechanism. 12,18 The magnitude of the SOC is in proportion to the value of the sine of the two p orbitals, sin ª.…”

Solvent effects of photoinduced electron transfer reactions of triplet fluorenone with amines

“…The lowest excited singlet and triplet are both identified as (π,π*) [10]. In aprotic solvents, with reducing solvent polarity, the trip-*Corresponding author (email: sqyu@ustc.edu.cn) let yield increases and both fluorescence and internal conversion (IC) decrease [10].…”

“…The lowest excited singlet and triplet are both identified as (π,π*) [10]. In aprotic solvents, with reducing solvent polarity, the trip-*Corresponding author (email: sqyu@ustc.edu.cn) let yield increases and both fluorescence and internal conversion (IC) decrease [10]. In protic solvents, the formation of hydrogen-bonding makes the yields of both triplet and fluorescence decrease and IC becomes the primary quenching process [11].…”