Fluorescence Anisotropy of Branched Molecules Containing 1-Aminopyrene Chromophores

Abstract

Fluorescence anisotropy measurements were performed on a set of multichromophoric compounds, which contain a different number of aminopyrenyl moieties linked to a triazine ring, in order to reveal the nature of both the electronic excited states and relaxation pathways of the compounds. Our experimental results complement quantum chemical calculations. We propose that the lowest excited state from which fluorescence proceeds is localized on a single individual aminopyrene moiety. In contrast, excitation to a higher excited state is likely followed by a migration of energy to another nearby aminopyrene chromophore before the internal conversion to the emitting state takes place. We suggest that this migration is responsible for the experimentally measured decrease of fluorescence anisotropy of the studied compounds.

Twist‐Bend Nematic Glasses: The Synthesis and Characterisation of Pyrene‐based Nonsymmetric Dimers

“…It has been shown that the N‐substituent at the 1‐position of pyrene will cause a bathochromic shift in two of the characteristic pyrene emission bands, L b and L a , which correspond to S0→S1 and S0→S2 transitions, respectively. Furthermore, this type of substitution causes a strong increase in both the L b band intensity, and its overlap with the L a band when compared with pyrene's spectrum [51,52] . In the nematic phase, the fluorescence is strongly quenched.…”

“…Furthermore, this type of substitution causes a strong increase in both the L b band intensity, and its overlap with the L a band when compared with pyrene's spectrum. [51,52] In the nematic phase, the fluorescence is strongly quenched. In the solid state (the crystal forms α and β obtained from solution), no fluorescence from isolated pyrene units was observed, only a weak band centred at 575 nm was found, that may be attributed to excimer formation due to πÀ π stacking between pyrene units detected in the crystal structure of the α polymorph.…”