Turn-on fluorescence switching and radical formation in a dual-functional negative photochromic dimethyldihydropyrene.

High-contrast fluorescent switchable systems are highly coveted dyes for bioimaging. Here, we report a molecular system that integrates reversible fluorescence modulation and radical formation in a series of covalently linked triphenylamine (TPA)-dimethyldihydropyrene (DHP) photochromic systems. DHP units with different substitutions directly alter the electron density of the photochromic unit, thereby regulating electronic communication with TPA. Photoinduced ring opening of the DHP core activates a charge transfer pathway, resulting in a dramatic enhancement of fluorescence, as reflected in the enhancement of quantum yield from 0.01 to 0.31. The emission can be reversibly turned off by ultraviolet irradiation or heating. Importantly, the bright state is accessed using visible light, making this negative photochromic system particularly attractive for bioimaging applications. Beyond emission control, irradiation of the same molecule at 370 nm in chloroform generates a long-lived radical. The coexistence of controlled fluorescence switching and radical formation highlights the potential of this design strategy to create multifunctional molecular systems. Such bifunctional platforms open new opportunities for accessing optical readout and chemical activity on demand within a single molecular scaffold.