1H‐Phenalen‐1‐one: Photophysical Properties and Singlet‐Oxygen Production

Abstract

The efficiency of aromatic ketones as singlet-oxygen ('02('Ag)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near-infrared measurements of the luminescence of singlet oxygen have shown that the quantum yield of singlet-oxygen production (Gd) by 1H-phenalen-I-one (1) is close to unity in both polar ( @, , = 0.97zk0.03 in methanol) and non-polar solvents ( @ A = 0.93+0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant x , A * electronic configurations. The quantum yield of intersystem crossing (cDISc) of 1, determined by laser flash photolysis (partial-saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high GIsc of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The Iff-phenalen-1-one (l), being one of the most efficient singlet-oxygen sensitizers in both polar and non-polar media, could be used as a reference sensitizer, in particular in the area of relatively high energies of excitation.Introduction. -Because of the relatively small energy difference between the ground state (' Z;) and the ('A,) excited state of molecular oxygen (94.2 kJ .mol-'), singlet oxygen ('02('Ag)) should be easily produced by energy transfer from the lowest triplet state of most sensitizers to molecular oxygen (Eqn. I). However, only few sensitizers are of practical use for the generation of singlet oxygen, an activated oxidizing species which plays an important role in photo-oxidation reactions (type-I1 photo-oxidation) [ 1-71.

Triplet state dynamics on isolated conjugated polymer chains

“…Singlet oxygen ( 1 D g ) yields and lifetimes were obtained by direct measurement of the phosphorescence at 1270 nm following irradiation of an aerated solution of the polymers in benzene with a frequency tripled pulse (355 nm) from a Nd:YAG laser, as described in detail elsewhere [23,39]. The quantum yield of singlet oxygen formation was determined by comparison of the initial emission intensity for optically matched solutions at the excitation wavelength (A 355 ¼ 0:5) with 1H-phenalen-1-one taken as standard, using U D ¼ 0:93 in benzene solution [40].…”

Scope and limitations of the TEMPO/EPR method for singlet oxygen detection: the misleading role of electron transfer

“…Neglecting the C term, G was calculated using the following values for the potentials: E ox (TEMP) = 1.0 V and E red = -1.2, -1.3, -2.6 and -1.8 V vs SCE for PN [33], BP [20], NP [34] and CBZ [35], respectively. In the case of PN [36] and BP [20], the lowest triplet excited state energy was considered for E* with values of 220 and 292 kJ mol -1 , respectively, whereas this parameter was associated with the singlet manifold for NP [34] and CBZ [37], using values of 377 and 344 and kJ mol -1 , respectively. Table 1.…”

Singlet molecular oxygen photosensitized by Rhodamine dyes: correlation with photophysical properties of the sensitizers

“…Several techniques have been used to detect 1 O 2 in condensed phase like 1 O 2 → 3 O 2 NIR phosphorescence [25][26][27][28][29][30][31][32][33], time resolved thermal lens spectroscopy [26,34,35], and the analysis of 1 O 2 specific reaction products [21,29,[36][37][38][39][40][41]. Quantum yields of 1 O 2 production have been investigated for a large number of sensitizers.…”