Room temperature phosphorescence of 1-bromo-4-(bromoacetyl)naphthalene induced synergetically by β-cyclodextrin and Brij30 in the presence of oxygen

Strong room temperature phosphorescence (RTP) of 1-bromo-4-(bromoacetyl)naphthalene (BBAN) is induced synergetically by beta-CD and Brij30 without removal of oxygen dissolved in the solution because of the formation of ternary complex of beta-CD, BBAN, and Brij30. Some factors that affect RTP intensity, such as standing time and ethanol etc., are also discussed. Sedimentation phenomena occur in the lactescent ternary system after enough standing time, and strong RTP from the suspended precipitates might indicate that the ternary complex exists as microcrystals in the measurement system. The proton nuclear magnetic resonance (H-1 NMR) experimental results are consistent with the inclusion behavior of BBAN molecules. Chemical shift changes in H-5 of beta-CD are larger than those in H-3, which indicates that the phosphor is included in the hydrophobic cavity at the narrower end. H-6 also witnesses relatively large changes in its chemical shifts, so the outside-exposed part of BBAN may be locked by the seven groups of methylol in the short section of the truncated cone molecule. NMR spectra also indicate that the alkyl chain of Brij30 is partially inserted into the beta-CD cavity so as to enhance the rigidity of the cavity that BBAN dwells in, whereas the polar moiety lies outside of the cyclodextrin molecule at the narrower end. Additionally, ROESY spectra validate the reciprocity between Brij30 and beta-CD. To further elucidate the so-called synergetic effect, fluorescence measurements of solvatochromic probe 4-(dicyanomethylene)-2-methyl-6-[4-(dimethylamino)stryryl]-4H-pyran (DCM) are also conducted in the same microenvironment as that of BBAN, and the evident shifts to shorter wavelength of emission spectra imply that the BBAN resides in a more rigid environment with lower dielectric constant in the presence of both beta-CD and Brij30 than exists when beta-CD and Brij30 are present individually.