Intramolecular 2pπ* → 3dπ charge transfer in the excited state of phenyldisilane studied by picosecond and nanosecond laser spectroscopy

Shizuka, Haruo; Okazaki, Kiyohiko; Tanaka, Masayuki; Ishikawa, Mitsuo; Sumitani, Minoru; Yoshihara, Keitaro

doi:10.1016/0009-2614(85)85016-8

Cited by 43 publications

(29 citation statements)

References 9 publications

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“…A very low quantum yield U fl < 0.01 was also reported for Ph 2 CH-SiMe 3 . 31 High photo-Fries quantum yields (U = 0.86) have been reported for the photolysis of pentamethylphenyldisilane (Ph-SiMe 2 -SiMe 3 ), 38 as well as by the photolysis of the prototype phenyl acetate (U = 0.51). 39 (c) Photolysis of 2 with femptosecond 266 nm laser light in MeCN.…”

Section: Similar Intermediates Have Been Identified Also By Leigh Andmentioning

confidence: 99%

Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

Zarkadis

Georgakilas

Perdikomatis

et al. 2005

Photochem Photobiol Sci

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The photochemistry of three structurally very similar triphenylmethylsilanes 1, 2, 3 [p-X-C(6)H(4)-CPh(2)-SiMe(3): X = PhCO, 1; H, ; Ph(OCH(2)CH(2)O)C, 3] is described by means of 248 and 308 nm nanosecond laser flash photolysis (ns-LFP), femtosecond LFP, EPR spectroscopy, emission spectroscopy (fluorescence, phosphorescence), ns-pulse radiolysis (ns-PR), photoproduct analysis studies in MeCN, and X-ray crystallographic analysis of the two key-compounds 1 and 2. The photochemical behavior of 1, 2 and 3 is discussed and compared with that of a fourth one, 4, bearing on the p-position an amino group (X = Me(2)N) and whose detailed photochemistry we reported earlier (J. Org. Chem., 2000, 65, 4274-4280). Silane 1 undergoes on irradiation with 248 and 308 nm laser light a fast photodissociation of the C-Si bond giving the p-(benzoyl)triphenylmethyl radical (1*) with a rate constant of k(diss)= 3 x 10(7) s(-1). The formation of 1* is a one-quantum process and takes place via the carbonyl triplet excited state with high quantum yield (Phi(rad)= 0.9); the intervention of the triplet state is clearly demonstrated through the phosphorescence spectrum and quenching experiments with ferrocene (k(q)= 9.3 x 10(9) M(-1) s(-1)), Et(3)N (1.1 x 10(9) M(-1) s(-1)), and styrene (3.1 x 10(9) M(-1) s(-1)) giving quenching rate constants very similar to those of benzophenone. For comparative reasons radical 1* was generated independently from p-(benzoyl)triphenylmethyl bromide via pulse radiolysis in THF and its absorption coefficient at lambda(max)= 340 nm was determined ([epsilon]= 27770 M(-1) cm(-1)). We found thus that the p-PhCO-derivative 1 behaves similar to the p-Me(2)N one (the latter giving the p-(dimethylamino)triphenylmethyl radical with Phi(rad)= 0.9), irrespective of their completely different ground state electronic properties. In contrast, compounds 2, 3 that bear only the aromatic chromophore give by laser or lamp irradiation both, (i) radical products [Ph(3)C* and p-Ph(OCH(2)CH(2)O)C-C(6)H(4)-C(*)Ph(2), respectively] after dissociation of the central C-Si bond (Phi(rad)= 0.16), and (ii) persistent photo-Fries rearrangement products (of the type of 5-methylidene-6-trimethylsilyl-1,3-cyclohexadiene) absorbing at 300-450 nm and arising from a 1,3-shift of the SiMe(3) group from the benzylic to the ortho-position of the aromatic ring (Phi approximately 0.85 for 2). Using fs-LFP on 2 we showed that the S(1) state recorded at 100 fs after the pulse decays on a time scale of 500 fs giving Ph(3)C* through C-Si bond dissociation. In a second step and within the next 10 ps trityl radicals either escape from the solvent cage (the quantum yield of Ph(3)C* formation Phi(rad)= 0.16 was measured with ns-LFP), or undergo in-cage recombination to photo-Fries products. Thus, singlet excited states (S(1)) of the aromatic organosilanes (2, 3) prefer photo-Fries rearrangement products, while triplet excited states (1, 4) favor free radicals. Both reactions proceed via a common primary photodissociation step (C-Si bond homolysis) and diffe...

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Section: Similar Intermediates Have Been Identified Also By Leigh Andmentioning

confidence: 99%

Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

Zarkadis

Georgakilas

Perdikomatis

et al. 2005

Photochem Photobiol Sci

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“…Recently, we reported evidence for the formation of a 1,2-siloxetane derivative ( 3a ) from photolysis of 1,1,1-trimethyl-2,2,2-triphenyldisilane ( 1a ) in cyclohexane solution containing acetone. , Nanosecond laser flash photolysis results, , as well as a substantial amount of prior literature on the photochemistry of aryldisilanes, − provide strong evidence that 3a is derived from the reaction of acetone with the transient 1,3,5-(1-sila)hexatriene ( 2a ) resulting from photoinduced [1,3]-trimethylsilyl migration in 1a (eq 1). The structural assignment for 3a was based on 1 H, 13 C, and 29 Si NMR and infrared spectroscopic data recorded on crude reaction mixtures, since our initial attempts to isolate the compound by chromatographic methods failed owing to its apparently substantial thermal and hydrolytic reactivity.…”

Section: Introductionmentioning

confidence: 96%

Synthesis and Isolation of Stable 1,2-Siloxetanes from Reaction of Transient Silenes with Acetone

Toltl

Leigh

1996

Organometallics

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Direct irradiation of 1,1,1-trialkyl-2,2,2-triphenyldisilanes (R3Si−SiPh3; SiR3 = SiMe3, SiEt3, SiMe2 tBu) in hydrocarbon solution in the presence of acetone leads to the formation of 1,2-siloxetanes and silyl ethers, from reaction of the ketone with the 1,3,5-(1-sila)hexatriene resulting from photochemical [1,3]-trialkylsilyl migration into one of the aromatic rings of the disilane. The two products have been isolated in each case by low-temperature chromatography and identified on the basis of spectroscopic data. The siloxetane is the major product in each case, and its yield relative to silyl ether increases with increasing steric bulk of the −SiR3 group. Photolysis of the three disilanes in the presence of di-tert-butylketone affords the corresponding silyl ether in nearly quantitative yield, to the exclusion of siloxetane. 1,1,1-Triisopropyl-2,2,2-triphenyldisilane yields an intractable mixture upon photolysis in the presence of acetone under the above conditions but shows clear evidence for the formation of the corresponding siloxetane and silyl ether (in addition to chlorotriphenyl- and chlorotriisopropylsilane) when photolyzed in the presence of acetone and chloroform. Nanosecond laser flash photolysis techniques have been employed to determine absolute rate constants for the reaction of acetone, pinacolone, and di-tert-butyl ketone with the silatriene intermediates. These experiments also show that the triisopropyl derivative undergoes Si−Si bond homolysis to yield silyl radicals in competition with rearrangement to silatriene. The yield of silyl radicals is substantially higher in acetonitrile solution than in cyclohexane solution.

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“…[4][5][6][7] Phenyldisilanes are known to exhibit dual emission in solution. [8][9][10][11][12][13][14][15][16][17] Much as in the DMABN system, the occurrence of a 901 twist of a disilanyl group with respect to the phenyl ring in the ICT process has been one of the main issues in this system. 13 In our previous study based on the electronic transition, we determined that the electronic configuration of the CT state of CPDS is a s SiÀSi p*-type configuration.…”

Section: Introductionmentioning

confidence: 99%

Direct observation of the solvent reorientation dynamics in the “twisted” intramolecular charge-transfer process of cyanophenyldisilane–water cluster by transient infrared spectroscopy

Ishikawa¹,

Sugiyama

Setaka

et al. 2007

Phys. Chem. Chem. Phys.

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The solvent reorientation dynamics of the intramolecular charge-transfer (ICT) process of the (p-cyanophenyl)pentamethyldisilane-H(2)O (CPDS-H(2)O) cluster was investigated by transient infrared (IR) absorption spectroscopy. Transient IR bands of two distinct charge-transfer (CT) states appeared in both the OH and the CN-stretching vibration regions. Analyses of the IR spectra and the time profiles of the transient bands revealed that the ICT process of the CPDS-H(2)O cluster proceeds in two steps. The first step is a transition from a photo-prepared locally excited (LE) state to the CT state, which is accompanied by a minor reorientation of the H(2)O moiety. In contrast, the second step is an extensive reorientation process of the H(2)O molecule in the CT state. These two reorientation processes exhibit very distinct pico- and nano-second time scales. In the latter case, a relatively slow time constant of 2 ns was related to a large geometric change in the orientation.

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Intramolecular 2pπ* → 3dπ charge transfer in the excited state of phenyldisilane studied by picosecond and nanosecond laser spectroscopy

Cited by 43 publications

References 9 publications

Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

Synthesis and Isolation of Stable 1,2-Siloxetanes from Reaction of Transient Silenes with Acetone

Direct observation of the solvent reorientation dynamics in the “twisted” intramolecular charge-transfer process of cyanophenyldisilane–water cluster by transient infrared spectroscopy

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