Oxidation reduces spin-orbital coupling to achieve robust fluorescence emission in halogen-substituted dithieno[3,2-b:2′,3′-d]thiophene

Abstract

The development of a reliable and feasible strategy for constructing organosulfur luminogens bearing good performance is highly desirable. Traditional organosulfur luminogens with large spin–orbit coupling (SOC) always possess weak emission both in solution and the solid state. Reducing SOC through an oxidation approach to obtain robust fluorescent luminogens has been rarely explored. In this study, we present dithieno[3,2-b:2′,3′-d]thiophene 4,4-dioxide (DTTO) and its halogen-substituted derivatives possessing robust deep blue fluorescence emission in THF and greenish emission in the solid state. Furthermore, the developed DTTO and its derivatives present aggregation-enhanced emission (AEE) behavior. Single-crystal analyses reveal that upon oxidation, multiple supramolecular interactions inhibit intramolecular motions of DTTOs in the solid state and enhance the fluorescence intensity. Additionally, density functional theory (DFT) calculations demonstrate that negligible SOC of DTTOs suppresses rapid intersystem crossing in the excited state and improves the radiative transition rate. For this initial discovery, oxidation reduces SOC to boost molecular fluorescence and provides a novel approach for developing luminescent organosulfur materials.