“…Solutions of (2-5) × 10 -5 M 1-(acyloxy)anthraquinones (Q) I-V in toluene were studied by nanosecond laser photolysis in the temperature range 273-330 K in the presence and absence of oxygen. The results for compounds I-IV are consistent with the occurrence of the processes described in Scheme 1, where 1 Q* represents the excited singlet state, 3 Q* the lowest triplet state of the quinones, a-Q the ground state of the product with a structure of 9-(acyloxy)-1,10-anthraquinone (ana-quinone), and 3 a-Q the lowest triplet state of the product. The arguments which have led to the proposal of this scheme are developed in the following sections.…”
Section: Resultssupporting
confidence: 80%
“…Three types of photochromic processes are currently available to quinone derivatives. They are characterized by light-induced isomerization of the p -quinoid to the anaquinoid structure by photochemical migration of aryl, hydrogen, or acyl groups − …”
Section: Introductionmentioning
confidence: 99%
“…Three types of photochromic processes are currently available to quinone derivatives. They are characterized by light-induced isomerization of the p-quinoid to the anaquinoid structure by photochemical migration of aryl, hydrogen, or acyl groups [1][2][3][4][5][6][7] The thermally reversible photochemical migration of acyl groups was discovered previously for a series of 1-acetoxyanthraquinones with donor substituents in the anthraquinone nucleus [5][6][7] The photochemical products have a structure of substituted 9-acetoxy-1,10-anthraquinones (ana-quinones, a-Q).…”
Nanosecond laser flash photolysis has been used to
study the primary processes in the photochromic reaction
of five O-acylic derivatives of
1-hydroxy-2-methoxyanthraquinone with methyl (I), tolyl (II), phenyl
(III),
ethoxyl (IV), and diethylamino (V) groups in the migrating acyl.
The triplet−triplet absorption spectra of
the reactive triplet states of quinones IV and V were detected, and the
rate constants of the primary
photochemical step were measured. The temperature dependence of
the rate constants of acyl migration in
the triplet states of quinones IV and V was studied, and the Arrhenius
parameters were determined. The rate
constants of thermal acyl migration and their Arrhenius parameters were
measured for compounds I−V. It
was found that migrant nature significantly influences the activation
energy of both thermal and photochemical
reactions of acyl migration. The activation energy of thermal
migration increases from 37.9 ± 0.2 kJ/mol
for compound I up to 66.5 ± 0.7 kJ/mol for compound V. The
photochemical process is characterized by
considerably lower values of the activation energy (15.9 ± 0.8 and
26.0 ± 1.7 kJ/mol for compounds IV and
V, respectively). It was confirmed in the present work that
photochemical migration of acyl groups is an
adiabatic process occurring on the triplet potential energy
surface.
“…Solutions of (2-5) × 10 -5 M 1-(acyloxy)anthraquinones (Q) I-V in toluene were studied by nanosecond laser photolysis in the temperature range 273-330 K in the presence and absence of oxygen. The results for compounds I-IV are consistent with the occurrence of the processes described in Scheme 1, where 1 Q* represents the excited singlet state, 3 Q* the lowest triplet state of the quinones, a-Q the ground state of the product with a structure of 9-(acyloxy)-1,10-anthraquinone (ana-quinone), and 3 a-Q the lowest triplet state of the product. The arguments which have led to the proposal of this scheme are developed in the following sections.…”
Section: Resultssupporting
confidence: 80%
“…Three types of photochromic processes are currently available to quinone derivatives. They are characterized by light-induced isomerization of the p -quinoid to the anaquinoid structure by photochemical migration of aryl, hydrogen, or acyl groups − …”
Section: Introductionmentioning
confidence: 99%
“…Three types of photochromic processes are currently available to quinone derivatives. They are characterized by light-induced isomerization of the p-quinoid to the anaquinoid structure by photochemical migration of aryl, hydrogen, or acyl groups [1][2][3][4][5][6][7] The thermally reversible photochemical migration of acyl groups was discovered previously for a series of 1-acetoxyanthraquinones with donor substituents in the anthraquinone nucleus [5][6][7] The photochemical products have a structure of substituted 9-acetoxy-1,10-anthraquinones (ana-quinones, a-Q).…”
Nanosecond laser flash photolysis has been used to
study the primary processes in the photochromic reaction
of five O-acylic derivatives of
1-hydroxy-2-methoxyanthraquinone with methyl (I), tolyl (II), phenyl
(III),
ethoxyl (IV), and diethylamino (V) groups in the migrating acyl.
The triplet−triplet absorption spectra of
the reactive triplet states of quinones IV and V were detected, and the
rate constants of the primary
photochemical step were measured. The temperature dependence of
the rate constants of acyl migration in
the triplet states of quinones IV and V was studied, and the Arrhenius
parameters were determined. The rate
constants of thermal acyl migration and their Arrhenius parameters were
measured for compounds I−V. It
was found that migrant nature significantly influences the activation
energy of both thermal and photochemical
reactions of acyl migration. The activation energy of thermal
migration increases from 37.9 ± 0.2 kJ/mol
for compound I up to 66.5 ± 0.7 kJ/mol for compound V. The
photochemical process is characterized by
considerably lower values of the activation energy (15.9 ± 0.8 and
26.0 ± 1.7 kJ/mol for compounds IV and
V, respectively). It was confirmed in the present work that
photochemical migration of acyl groups is an
adiabatic process occurring on the triplet potential energy
surface.
“…The quantum yield (φ) of the photorearrangement of 1 at room temperature has been estimated using formation of the 1,10-anthraquinone-1-methide (λ max = 580 nm, ε = 9.25 × 10 3 M –1 cm –1 , φ ac = 0.8 ± 0.2) upon LFP of 1-methyl-9,10-anthraquinone in ethanol as an actinometric reaction …”
Section: Experimental and Computational Detailsmentioning
The photochemistry of tetrasulfur tetranitride (1) was studied in hexane solution by the laser flash photolysis technique (LFP). The experimental findings were interpreted using the results of previous matrix isolation studies (Pritchina, E.A.; Gritsan, N.P.; Bally, T.; Zibarev, A.V. Inorg. Chem. 2009, 48, 4075) and high-level quantum chemical calculations. LFP produces two primary intermediates, one of which is the boat-shaped 8-membered cyclic compound (2) and the other is the 6-membered S(3)N(3) cyclic compound carrying an exocyclic (S)-N═S group (3). The primary products 2 and 3 absorb a second photon and undergo transformation to the 6-membered S(3)N(3) cycle carrying an exocyclic (N)-S≡N group (4), which is very unstable and converts back to intermediate 3. The quantum yield of the primary product formation is close to unity even though the quantum yield of photodegradation of 1 is low (~0.01). Thus, 1 is a photochromic compound undergoing in solution the thermally reversible photochemical isomerization. The mechanism of the photochromic process was established, and the rate constants of the elementary reactions were measured.
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