| Organic luminescent materials have shown great potential for applications in hot areas such as organic optoelectronic/photonic devices,sensors,photoswitches or bioimaging.In practical applications,most of the materials are in solid state,and their luminescence properties are completely different from those in solution.The properties in the aggregation state will not only be affected by the skeleton of the molecule itself,the conjugated area,the substituents and the stereoscopic structure,but also by intermolecular factors.The study of intermolecular arrangements,interactions,and their relative conformations is of great significance for exploring the relationship between the structure and properties of aggregates.Cyanostilbene compounds has simple synthetize,well self-assembly properties,and strong emission in the aggregation state,which provides favorable conditions for the study of the correlation between the structure of the aggregates and the luminescence properties of the compounds.In this paper,different lengths of alkyl groups are linked to cyanostilbene framework through ester bonds,hoping to change only the stacking mode of molecules without changing the molecular conjugation.First,the fluorescence and[2+2]cycloaddition reactivity of cyanostilbene crystals are selectively activated by the alkyl chain.According to crystallographic analyses and theoretical calculations,the molecular conformation and intermolecular stacking have remarkable effects on the intersystem crossing(ISC)process.Therefore,CSEt crystals with efficient ISC process exhibit poor fluorescence while the[2+2]CA reaction is activated.In contrast,CSPr crystals with blocking ISC processes show intense blue solid-state fluorescence and excellent photostability.Then the effect of alkyl length on photoresponse behavior is discussed.The fluorescence of CSMe and CSBu gradually weakened after UV illumination,the fluorescence of CSEt turned on after UV irradiation,and CSPr showed good photostability. |
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