Photodimerization of anthracene derivatives

The photodimerization of anthracene derivatives has been advanced as a criterion of photoassociation in these systems it is therefore of interest to examine the extent to which similar behavior exhibited by the pyrimidine constituents of nucleic acids can be described in terms of the same reaction sequence. 

TABLE 21 Inclusion Effects on the Photodimerization of Anthracene Derivatives ... 

The effects of cyclodextrins on [4+4]-photodimerizations of anthracene derivatives have been studied quite extensively. For example, it has been found that such reactions of anthracene-2-sulfonate and -2-carboxylate in water are accelerated by both j8- and 7-cyclodextrin. y-Cyclodextrin has very little effect on the ratio of the four possible cycloadducts but, with each of the anthracene derivatives, j8-cyclodextrin inaeases the proportion of the anft-head-to-tail cycloadduct from less than 45% to more than 85% (Figure 3.9). - The effects observed with the natural cyclodextrins generally arise from the fortuitous way the reagents self-assemble in the cyclodextrin annulus. By comparison, modifled cyclodextrins offer the additional benefit of providing a means to control the... 

T. Tamaki, T. Kokubu, K. Ichimura, Regio- and stereoselective photodimerization of anthracene derivatives included by cyclodextrins. Tetrahedron, 1987, 43, 1485-1494. 

The photodimerization of anthracene has been utilized to produce a number of interesting synthetic derivatives which are essentially photo-isomers of the starting materials,[Pg.28]

The literature of mechanistic aromatic photochemistry has produced a number of examples of [4 + 4]-photocycloadditions. The photodimerization of anthracene and its derivatives is one of the earliest known photochemical reactions of any type97. More recently, naphthalenes98, 2-pyridones" and 2-aminopyridinium salts100 have all been shown to undergo analogous head-to-tail [4 + 4]-photodimerization. Moreover, crossed [4+4]-photocycloaddition products can be obtained in some cases101. Acyclic 1,3-dienes, cyclohexadienes and furan can form [4 + 4]-cycloadducts 211-214 with a variety of aromatic partners (Scheme 48). 

CDx and in particular 7-CDx are known to accommodate two aromatic moieties under certain circumstances. Hence if two appropriate prochiral guest molecules are included in the same CDx cavity, regio- and enantioselective bimolecular photoreactions are expected to occur [108]. Indeed, it is known that the presence of CDx not only accelerates the rate but also modifies the product distribution of photocyclodimerizations of anthracene derivatives [109-111], coumarin derivatives [113-115], stilbene derivatives [116,117], stilbazole [118], and tranilast [119]. For instance, Tamaki and coworkers reported significantly enhanced quantum yields of photodimerization of anthracenesulfonates and anthracenecarboxyl-ates in the presence of 3- and 7-CDx [109-111]. These anthracene derivatives form 2 2 and 2 1 guest-host complexes with (3- and 7-CDx, respectively, and... 

The well-known (4jt -I- 4jt) photodimerization of anthracene and its derivatives can be reversed both thermally and photochemically. The kinetics of the former process have been studied in hexane and carbon tetrachloride in the range 145 to 185°C, °° and the photoprocess in a dianthracene crystal at 2 K has been used to generate properly arranged anthracene pairs for the study of their photodimerization, the results from which are interpreted as dimerization through a tunnelling mechanism. ... 

The cyclization of stilbene occurs through an anti-Hiickel transition state analogous to anti-Hiickel phenanthrene. Photodimerizations of polycyclic aromatic systems are also very common. The dimerization of anthracene derivatives is a classical example ... 

Derivatives of anthracene bearing substituents on the 1 or 2 position can be photodimerized with efficiencies comparable to that for the unsubstituted molecule. However, with substituents at the 9 meso) or 9, 10 dimeso) positions a very interesting photochemical problem results. Since dimerization occurs across the 9, 10 positions, substituents at these positions exert a first-order effect on the photochemical reaction. The mero-substituted anthracenes examined include the following as 19>... 

Azanthracene and its derivatives, the isologs of anthracene, undergo photodimerization on exposure of their solutions in ethanol, ether and/or... 

Photodimerization of 1-substituted anthracene usually give four photodimers. Ueno et al. prepared y-CD derivatives bearing two 1-carbonylan-... 

The opposite behaviour, namely photodimerization, can take place when local concentrations of substrate are high, as for anthracene in Langmuir-Blodgett monolayers." In fact, this is a common reaction pathway for anthracene derivatives and occurs by both bimolecular and intramolecular routes. The efficiency of intramolecular photocyclization depends on the length and flexibility of the connecting chain. 

Quantum yields of the photodimerization of some anthracene derivates A in ionic surfactant solutions are given in Table 3 as functions of the micelle concen-... 

Tamaki et al. reported that water-soluble anthracene derivatives, snch as 2-anthrace-nesulfonate and 2-anthracenecarboxylate, form 2 1 complexes with y-CD in aqueous solution. The [4+4] photodimerization of 2-anthracenecarboxylate (AC) accommodated in y-CD and its derivatives was investigated in detail. Inoue and co-workers have recently reinvestigated the photodimerization of AC from the chiral point of view by using a variety of chiral hosts. y-CD forms very stable 1 2 host-guest complex with AC in aqueous buffer solution with association constants of Ki = 160M and K2 = 38500... 

Inoue and co-workers also examined the [4+4] photocyclodimerization of a-CD appended anthracene derivative 58 mediated by CB[8] (Scheme 1.11). Photodimerization... 

Photodimerization of 1-substituted anthracene derivatives 97a and 97b (Scheme 1.19) templated by a full-match DNA 98 selectively afforded only two isomeric dimers among the eight dimers that are possibly formed from the dimerization of 97a and 97b. Photoreaction with the full-match template was found to be much more efficient than those with mismatch templates. ... 

Ueno, A. Moriwaki, F. Osa. T. Hamada. F. Murai, K. Association photodimerization, and induced-fit types of host-guest complexation of anthracene-appended y-cyclo-dextrin derivatives. J. Am. Chem. Soc. 1988. 110 (13), 4323-4328. 

Kobayashi investigated a self-assembled boronic ester cavitand capsule for photochemical reaction of 2,6-diacetoxyanthracene. Tsuda found a self-assembled helical anthracene nanofiber in a vortex. Chou examined rotational behaviors and fluorescence energy transfer of N-l- and N-2-anthryl succinimide derivatives. " Reversible photoinduced twisting of molecular crystal microribbons via [4 - - 4] photocycloaddition of 9-anthra-cenecarboxylic acid. Reversible single walled carbon nanotubes of 1,3-bis(9-anthracenylmethyl)imidazolium chloride was examined as a functionalized anthracene salts.Karatsu reported the intramolecular photodimerization of 9-substituted anthracene derivatives (253) tethered by oligosilanes giving [4 + 4] and [2 - - 4]cycloadducts (254), (255), and (256). ... 

Recently, we have found that the photodimerization of water-soluble anthracenes is greatly accelerated in the presence of y-CyD in water (16). It has been explained as the result of the formation of a sandwich dimer in the host cavity. This report describes the detail s of the photodimerization and of the inclusion behavior of the anthracene derivatives/CyDs systems in water. 

As in the former cases, k2 was calculated from the integrated extinction coefficients,149 k3 + kt was derived from fluorescence quantum yields,149 while k3 and k4 were separately estimated from the maximum quantum yields of photooxygenations at high oxygen concentrations.150 Flash spectroscopy techniques were used in order to determine k5 and k7, while kB was obtained from the Stern-Volmer quenching constant of oxygen.149 The ratio ke/kg was determined from the variation of AOz with the concentration of the anthracene.71 When photodimerization occurred, k13l(kia + k13) was calculated from the maximum yield of... 

A simultaneous increase in photodimerization yield and reduction in molecular fluorescence yield with increasing solute concentration provides convincing evidence that photodimerization involves the molecular singlet state,90,93 and in certain systems, notably derivatives of naphthalene48 and anthracene,41 excimer fluorescence is exhibited simultaneously. 

---