An Acid‐Responsive Single Trichromatic Luminescent Dye That Provides Pure White‐Light Emission

A novel acid‐responsive single trichromatic luminescent dye capable of emitting pure white light (WL) is reported. A newly designed p‐phenylene‐bridged bipyrrole bearing N‐alkylimino groups (1 a) specifically provides WL emission upon mixing with trifluoroacetic acid (TFA) in a CH2Cl2 solution. The emission originates from the trichromatic luminescent behavior of 1 a upon protonation of the imino groups. The blue‐light‐emitting 1 a exhibits dramatic color changes in fluorescence to orange and green upon mono‐ and diprotonation, respectively, providing a wide emission band in the range of λ=400–800 nm that provide WL when the compound is in a dynamic equilibrium between the three states. The sample also exhibits low self‐absorption of the emitted light and a high fluorescence quantum yield upon excitation with UV light. The butterfly effect: A p‐phenylene‐bridged bipyrrole bearing N‐alkylimino groups exhibits a trichromatic color change in fluorescence from blue to orange to green upon mono‐ and diprotonation of the imino groups (see figure). The compound demonstrates pure white‐light emission as a result of a dynamic equilibrium between the three states.