Spiro-[4,5]-cyclohexadiene-8-one polymers: photoactivated crosslinking and switch-on fluorescence for lithography†

Developing multiple photoresponsive polymers is crucial for creating versatile intelligent materials; however, it poses a significant challenge due to the limited availability of photoactivated moieties. Herein, we present a novel series of dual photoresponsive spiro-[4,5]-cyclohexadiene-8-one polymers exhibiting photoactivated crosslinking and switch-on fluorescence behaviors. These polymers were synthesized through a robust palladium-catalyzed [2+2+1] cycloaddition polymerization reaction of 4-phenol diazonium tetrafluoroborate and diynes. Notably, the single photoreactive spiro-[4,5]-cyclohexadiene-8-one moiety endowed dual photoresponse features to these polymers. Upon UV irradiation, the cyclohexadienone moieties underwent a 2π+2π photocycloaddition reaction to form an insoluble crosslinked polymer network. Concurrently, the photoactivated fluorescence phenomenon of the crosslinked polymers was also observed. To our knowledge, these polymers represent the first examples of merging photocrosslinking and fluorescence turn-on properties into one single functional group. By harnessing the unique photocrosslinking and photoactivated fluorescence properties, we successfully imprinted 2D and 3D photopatterns for lithographic applications. These intriguing results provide an alternative design strategy of multiple photoresponsive polymers for fluorescent labelling and 2D/3D optical security.