Exploration of photophysics and presence of Long singlet exciton diffusion length in dibenz[a,h]anthracene nanoaggregates

Abstract

Disc shape nanoaggregates of dibenz[a,h]anthracene (DBAn) was synthesized following reprecipitation method. This is a nonlinearly attached polyaromatic molecules which upon aggregation shows almost three times stronger absorption, associated with the lowest absorption band. This is governed by the stronger transition dipole, resulted due to correlated interaction of individual transition dipoles of DBAn molecules, present in the aggregate. The stronger transition dipole also results faster radiative decay rate and makes the nanoaggregates 2–3 times highly emissive, as compared to its monomeric form. Time resolved emission studies indicate both excitonic and excimeric contribution in the emission spectrum. The enhanced radiative decay rate, demonstrated in this aggregate, is popularly recognized as the superradiant phenomenon of molecular assembly. Even after the presence of faster radiative decay, these aggregates are found to possess extended singlet exciton lifetime of ∼10.2 ns. The long exciton lifetime consequences elongated singlet exciton diffusion length of ∼50 nm, estimated by analysing the exciton diffusion assisted energy transfer process in tetracene doped DBAn nanoaggregates. The long exciton lifetime is expected to be advantageous for charge separation in photovoltaic devices.