Photodimerization of coumarins in solid cyclodextrin inclusion complexes

Multicolor Photoluminescence Including White-Light Emission by a Single Host–Guest Complex

“…As shown in Figure 1a, these ITC experiments clearly demonstrated the occurrence of a strong 1:1 binding interaction between BPC and γ-CD in water with an association constant of Ka (3.3 ± 0.4) × 10 4 M -1 , while under the same conditions BPC did not show any binding affinity for β-CD (Figure 1b). The latter result is quite unexpected because the cavity of β-CD, although being smaller than that of γ-CD, is surely large enough to encapsulate the coumarin unit, 19 a result that is also confirmed by 2D ROESY NMR measurements. As seen in Figure S2 (in SI) BPC shows no interaction with β-CD, while strong rotating-frame nuclear overhauser effect (ROE) signals are found between the protons of the coumarin moiety of the reference compound PC and the internal protons of β-CD.…”

Supramolecular Control of the Template‐Induced Selective Photodimerization of 4‐Methyl‐7‐O‐hexylcoumarin

“…[8] The transition moments can further be influenced by solvent polarity [11] and the use of cyclodextrin or micelles. [12,15,16] With respect to previous reports, [30±34] we set forth the design and subsequent synthesis of a template, which Scheme 1. Schematic representation of the reaction pathway responsible for selective syn photodimer formation within a supramolecular 2:1 species.…”

“…Under typical experimental conditions, however, the two syn (2 A and 2 B) photoproducts are formed predominately, while only trace amounts of the anti dimers 2 C and 2 D are observed. [7] The ratio of coumarin photoproducts can significantly be altered through control of the reaction conditions such as solvent choice, [9,11,12] Lewis acid addition, [13,14] micellar environment, [15,16] solid-state irradiation, [13,14] modification of the coumarin precursor, [17,18] use of inclusion complexes [15] and tethered precursors, [17, 19±21] or recently with pseudo-rotaxanes. [22] Much effort has been focused on crystal engineering and packing within the solid state to influence the product distribution.…”

“…The configuration of the observed photodimers is consistent with previous reports for sensitized dimerization. [15,16,19,20] No appreciable change was observed when performing either direct irradiation in chloroform or sensitized irradiation with acetone. Since the experimental conditions employed are relatively dilute, direct excitation of the precursor undergoes intersystem crossing forming the triplet state before quenching occurs.…”

“…The difference between the two cis and trans isomers is relatively small and the trans cyclobutyl protons give a NMR signal 0.1 ppm upfield from their cis counterparts, due to the shielding effects of the carbonyl and phenyl groups. [15] Through the use of a chiral shift reagent and 2D proton NMR spectroscopy, complete characterization of the isolated photoproducts was possible and led to the assignment of the trans form to both the syn and anti dimers (2 cB and 2 cD). The configuration of the observed photodimers is consistent with previous reports for sensitized dimerization.…”