The effect of solvent on exciplex emission from pyrene—tributylamine and anthracene—tributylamine systems

Abstract

The exciplex emissions from the pyrene-tributylamine (TBA) and anthracene-TBA systems have been found to undergo a red shift in solvents of higher dielectric constants. From these shifts it has been estimated that the extent of charge transfer is 66% in the pyrene-TBA system, while it is over 80% in the anthracene-TBA system. In aromatic hydrocarbon solvents the exciplex emission was found to undergo a red shift and an intensification in the order benzene > p-xylene > mesitylene. This has been attributed to triple exciplex formation, for which the equilibrium constants between the exciplex and the aromatic solvents have been found to be 3.2 × 10^-2 (benzene), 2.2 × 10^-2 (p-xylene) and 2.2 × 10^-2 (mesitylene) for the pyrene—TBA system, while for the anthracene—TBA system the equilibrium constants were 8.3 × 10^-3 (benzene) 8.3 × 10^-3 (p-xylene) and 6.6 × 10^-3 (mesitylene). A tentative explanation for the effect of aromatic hydrocarbon solvents on exciplex emission has been suggested. In alcoholic solvents the exciplex emissions were blue shifted owing to the formation of hydrogen bonded complexes between the exciplex and the alcohols. The pyrene—TBA system forms much stronger hydrogen bonds with alcohols than the anthracene—TBA system. This was considered to indicate the participation of the lone pair electrons at the nitrogen of TBA in hydrogen bond formation.