Fluorescence quenching of carmoisine by viologens in neat methanol: Observation of inversion in quenching

► First time observed the inversion in fluorescence quenching of carmoisine by HV in methanol. ► HV shows inversion while MV shows saturation in quenching. Mode of quenching is static. ► HV forms larger aggregates but MV primarily forms smaller aggregates like dimers. ► Larger aggregates of HV are less efficient quenchers. In acetinitrile, no inversion is seen. ► Fluorescence quenching by viologens can be used to monitor their self-aggregation.