Surendra B. Anantharaman
Swiss Federal Laboratories for Materials Science and Technology (Empa), Switzerland
Title: Strongly red-shifted photoluminescence band induced by molecular twisting in cyanine (cy3) dye films
Biography
Biography: Surendra B. Anantharaman
Abstract
Cyanine dye molecules, used as monomers or in aggregate form, find interesting applications in opto-electronic devices. Among the various aggregate species incorporating organic dyes, centrosymmetric dimers are known as non-luminescent. They can act as exciton quenchers due to a low energy optically forbidden excited state. In this study, however, we show that a dimer species in thin films exhibits efficient and strongly red-shifted photoluminescence [1]. When the films were excited, a monomer emission at 590 nm along with a second emission peak at 680 nm was observed. Temperature dependent fluorescence were studied for cyanine films. The dimer emission increases with decreasing temperature due to reduced non-radiative process becoming less effective. A close relation between the dye concentration and the emission showed that a new emission at 680 nm corresponds to the dimer emission. Circular dichroism (CD) spectroscopy reveals that a fraction of the dimers exists in a twisted dimer configuration. Stable, long-lived and quenchable fluorescence with high quantum yield are attributed to this dimer emission. Organic light emitting electrochemical cells (OLECs) fabricated with this dye showed a higher luminance owing to the dimer emission [2].
