Fast Internal Conversion in Nonfluorescent Carbonyl Anthracenes

Abstract

The quantum yield of triplet formation (φT) for two nonfluorescent molecules of 9-acetylanthracene and 9-benzoylanthracene was determined with a time-resolved thermal lensing method (TRTL). The value of φT for 9-benzoylanthracene was 0.19 in cyclohexane, indicating that a fast internal conversion process with a rate constant of 4.0 × 1010 s−1 exists in the deactivation from the first excited singlet state (S1).

Inverse correlation between efficiency of singlet oxygen production and rate constant for oxygen quenching in the S1 state of anthracene derivatives

“…32,33 The quantum yield of triplet state in the absence of oxygen (F 0 T ) was also determined by the same TRTL instrument. 31 A nitrogen laser (NDC JH-1000L) and a He-Ne laser (Spectra-Physics 117A) were used as excitation and probe light sources, respectively. The excitation light (337 nm) was focused at the center of a 1 cm square cell containing a sample solution.…”

“…34 However, these influences are considered to be insignificant in the present measurement for the anthracene compounds with a He-Ne laser (632.8 nm) as the probe light. 31,34 Deaeration of sample solutions was performed by freeze-pump-thaw cycles. Oxygen-saturated solutions were prepared by replacing air in the cell by oxygen gas.…”

Decoding the Curious Tale of Atypical Intersystem Crossing Dynamics in Regioisomeric Acetylanthracenes

“…The excited state dynamics of 1C suggests an ultrafast, proficient ISC (τ ISC ≈ 290 fs) with high triplet yield (ϕ T ≈ 0.8−1.0). 31,33 The fTA spectra of 1C in chloroform reveal an unequivocal evidence of the ultrafast S−T transition, wherein the initial EAS component at 550 nm crosses to the triplet manifold within 290 fs (Figure 2b). The populated hot triplet (*T p ) state relaxes to the lowest triplet manifold (T p ) within 10.27 ps (Figure 3b).…”

“…ISC dynamics in nitro-, − thio-, carbonyl-, , and heavy metal , /atom-appended aromatic chromophores has been previously well documented. Among the carbonylarenes, ,− the photodynamics in carbonylanthracenes is profoundly explored to probe the (de)­population dynamics of the singlet and triplet states. − Concomitantly, solvent polarity − /temperature , /pressure-dependent emission, time-resolved absorption, ,, and photodimerization experiments in solution/supersonic jets have been carried out with carbonylanthracenes. Fascinatingly, the photodynamics in 9-carbonylanthracenes is unique owing to the unique torsional dynamics, , the ultrafast ISC, and the prevalent triplet population. − ,,,, Although ISC dynamics in carbonylanthracenes is well-explored, the influence of the substituent position on the triplet population has hitherto been overlooked. , …”

“…Fascinatingly, the photodynamics in 9-carbonylanthracenes is unique owing to the unique torsional dynamics, 38,42 the ultrafast ISC, and the prevalent triplet population. [31][32][33]37,39,40,43 Although ISC dynamics in carbonylanthracenes is well-explored, the influence of the substituent position on the triplet population has hitherto been overlooked. 44,45 In this Article, we report the origin of the atypical photoinduced relaxation dynamics and the access to the triplet excited state in regioisomeric 1-/2-/9-acetylanthracenes (1A, 1B, and 1C, respectively, Scheme 1).…”