On the Phosphorescence of 1H-Phenalen-1-one

Abstract

Dedicated to Professor Andre M. Braun, on the occasion of his 60th birthday Combining the effects of heavy atom and low temperature, the phosphorescence spectrum from 1H-phenalen-1-one has been unveiled. The 0-0 band is located at 649 nm in methylcyclohexane and shifted to 646 nm in ethanol, which sets the triplet-energy level to 185 and 186 kJ´mol À1 , respectively. The emission is unambiguously identified as phosphorescence originating from 1H-phenalen-1-one through complementary transient absorption and emission studies. The quantum yield for triplet formation is confirmed to be unity.1. Introduction. ± 1H-Phenalen-1-one (hereafter phenalenone, also called perinaphthenone, PN) is a universal reference for sensitization of singlet oxygen, O 2 (a 1 D g ), owing to its solubility in a large variety of solvents and its high quantum yield for singlet oxygen production, F D , which is close to 0.95 in most solvents investigated so far ranging from H 2 O to cyclohexane [1 ± 5]. Another important property of PN is its high photostability and its low rate constant for O 2 (a 1 D g ) quenching, e.g., 3.2  10 4 m À1 s À1 in perfluorodecalin [6]. The molecular structure and absorption spectrum are shown in Fig. 1.The triplet-energy value of PN, E T , remains a matter of debate in the literature. In 1991, Oliveros et al. proposed a value of 220 kJ mol À1 for the triplet energy, derived from phosphorescence measurements [1]. It was later shown that their emission originated from a PN photoproduct (vide infra). By laser-induced optoacoustic spectroscopy, Schmidt et al. determined a second value of 186 AE 5 kJ mol À1 in toluene [3]. By the same technique, though a different detector arrangement and data-handling procedures, our group obtained a similar value, 178 AE 8 kJ mol À1 [4]. It is important to point out that both works derived the E T value assuming a triplet quantum yield F T of unity, since laser-induced optoacoustic spectroscopy only affords the value of the product F T E T . However, the value reported by Schmidt et al. is probably close to the correct one, since, later, Schmidt and Bodesheim were able to observe a transient emission at 650 nm, which they identified as PN phosphorescence on the basis of its quenching by oxygen [7]. In fact, the authors demonstrated in their paper that PN is able to photosensitise singlet sigma oxygen, O 2 (b 1 S g ), which lies at 157 kJ mol À1 . This value should, therefore, be regarded as a lower limit for phenalenones triplet energy. The lack of spectral information in their work still leaves open the question of where the triplet-energy level lies.Recently, by emission spectroscopy at 77 K, Okutsu et al. showed that the emission reported by Oliveros et al. was due to a photoproduct formed by abstraction of a solvent

Phototoxic Phytoalexins. Processes that Compete with the Photosensitized Production of Singlet Oxygen by 9-Phenylphenalenones†

“…On the other hand, phosphorescence was observed from PN2 in methylcyclohexane at 77 K, from which a triplet energy of 183 kJ · mol ‐1 was calculated. Because this value is almost identical to that reported for PN (185 kJ · mol ‐1 ) (10, 24), we assume it to hold for PN1 as well.…”

Perinaphthenone phototransformation in a model of leaf epicuticular waxes

“…where ∆R is the transient species reflectance change, R 0 and R t correspond to the diffusely 173 reflected light before exposure to the laser pulse and at time t after excitation, respectively.photolysis apparatus has been previously described (29,30) The PN triplet excited state ( 3 PN*) has been previously observed in many solvents (38), its UV-293…”

Photochemistry of Phytoalexins Containing Phenalenone‐like Chromophores: Photophysics and Singlet Oxygen Photosensitizing Properties of the Plant Oxoaporphine Alkaloid Oxoglaucine¶

“…We propose a value of 168 ± 4 kJ mol −1 , which implies a singlet–triplet energy gap of ca 90 kJ mol −1 , which is typical for ππ* states of aromatic compounds (28). For comparison, the triplet energy of PN lies at 185 kJ mol −1 (18, 27).…”

“…Unlike PN, OG is not phosphorescent even in low-temperature glasses containing heavy atoms (27). Nevertheless, a transient species was detected using nanosecond laser flash photolysis, whose spectrum matches that obtained after 40 ps in the ultrafast absorption experiments (Fig.…”