Conformational effects in the absorption spectra and photochemistry of [2, n ](9,10)anthracenophanes ( n = 2,3)

Absorption spectroscopy of sandwich dimers and cyclophanes

“…The absorption spectrum of the APA in the ordered site bears a resemblance to the rotated conformations of the [2.n](9,10)anthracenophanes,131 while the spectrum of the APA in the disordered site is similar to the spectrum of the translated conformation of [2.2]-(9,10)anthracenophane. 95 These results then underline the conclusions reached from an analysis of the absorption spectra of the various anthracenophanes (III.E.) relating to the effect of overlap on the chargetransfer transition intensity.…”

“…The theoretical calculations of Morita et al93 are based on overlapped conformations which are, most certainly, not the most stable conformation in each case. 95,96 which provide an array of conformational geometries particularly useful for the study of the photochemical behavior of the anthracene sandwich dimer as well as its spectroscopy. For the present case we concentrate on the latter aspects.…”

“…A detailed study of the spectroscopy and photochemistry of [2.2] (9,10)AA in crystals has been made which used a method of selective photochemistry to isolate each conformer at liquid helium temperatures. 95 This involved the incorporation of the photoisomer as a guest in single crystals of the photoisomer of 1,3bis(9-anthryl)propane, followed by a few minutes of heating to about 50 °C to decompose some of the It was found that at liquid helium temperatures each conformer is trapped in the crystal, and irradiation with monochromatic light at 417 nm or 399 nm leads to the selective photoisomerization of the translated or rotated conformer, respectively. The photoselection is Figure 17.…”

Unimolecular photochemistry of anthracenes

“…Evidence for biradical intermediates in the photochemical reaction and the thermal cycloreversion has not been obtained. 282,288 Other anthracenophanes undergoing photochemical isomerization by 4x + 4x cycloaddition are [2.3]-(9,10)anthracenophane (150a), [2.4](9,10)anthracenophane (150b), syrc-[2.2](l,4)anthracenophane (151), and [2.2](l,4)(9,10)anthracenophane (152). 285,288,291,292 For anthracenophane 151, excimer fluorescence has been detected in rigid solution, and it has been established, that the cycloaddition reaction involves deactivation of the excimer state.…”

“…282,288 Other anthracenophanes undergoing photochemical isomerization by 4x + 4x cycloaddition are [2.3]-(9,10)anthracenophane (150a), [2.4](9,10)anthracenophane (150b), syrc-[2.2](l,4)anthracenophane (151), and [2.2](l,4)(9,10)anthracenophane (152). 285,288,291,292 For anthracenophane 151, excimer fluorescence has been detected in rigid solution, and it has been established, that the cycloaddition reaction involves deactivation of the excimer state. 285 In a process competing with the intramolecular 4x + 4x cycloaddition, 151 undergoes geometrical isomerization to give anfi-[2.2](l,4)anthracenophane (153) which is characterized by structured fluorescence (4* = 0.27).285 Probably due to steric constraints, [2.5](9,10)anthracenophane (154) does not isomerize photochemicaily by cycloaddition.292 Several [3.3] (l,4)naphthaleno(9,10)anthracenophanes and diaza [3.3]paracyclo (9,10)anthracenophanes such as 155 and 156 have been found to undergo thermally reversible photoisomerization by 4x + 4ir cycloaddition with quantum yields of about 10-30%.…”