Linear 9,10-distyrylanthracene Derivatives:Design,Synthesis And Optical Property Study

In this paper,we synthesized two series of 9,10-divinylanthracene derivatives,by replacing the end groups and adjusting the length of the terminal alkyl chains,9.10-di(p-alkoxystyryl)-anthracenes(DSA-OCn)and 9,10-bis[(N-alkyl-carbazol-3-yl)vinyl]anthracenes(ACZn).The two series of compounds show similar optical properties.Firstly,they are all having aggregation-induced emission enhancement(AIEE)activity.The fluorescence intensity are very weak,with the fluorescence quantum yield(?)of DSA-OCn less than 2%and ACZn less than 1%,in THF at the concentration of 10-5 M.While in THF/H2O = 1:9,the fluorescence intensity increase greatly with ? rose to about 20%.Secondly,we also found that these compounds exhibit obvious piezofluorochromism(PFC)behaviors:varying degrees of red-shift can be observed by shearing,grinding or compressing,and the subsequent reversion to their original colors through treatment with heating,solvent-vapor fuming or recrystallization.Overall,DSA-OCn derivatives with longer alkoxy chains(n>10)showed blue-shifted emission and are more obviousand easier PFC than that with short ones,but it does not completely depend on the length of the alkyl chains,with large red-shift emission(46-53 nm)for long alkoxy chains(n ? 10)and small that(14-20 nm)for short ones(n:? 9).But the mechanism is complex and require further study.On the contrary,the maximum emission wavelengths(?pristine)of as-prepared powders are gradually red-shift with the increase of the length of N-alkyl chain(511-543 nm),the corresponding maximum emission wavelengths(?pressed)of compressed samples are gradually blue-shift with the increase of the length of N-alkyl chain(600-569 nm),it does completely depend on the length of the alkyl chains.WAXD and DSC experiments reveal that the transformation between crystalline and amorphous states upon external stimuli is responsible for the PFC behavior.Notably,it was found in our laboratory that 9,10-bis(4-styryl)anthracene 9.10-bis(4-tert-butylstyryl)anthracene and 9,10-bis(2-(pyridine-4-yl)vinyl)anthracene all do not exhibit piezofluorochromic behavior although they are all AIEE-active,suggesting that it is necessary to piezofluorochromism in such simple 9,10-diaryl-vinylanthracene derivatives to balance ?-? and aliphatic interactions through the variation of electron density in the central anthracene ring and the length of peripheral aliphatic tails.