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Amplified Spontaneous Emission of Poly(ladder‐type phenylene)s – The Influence of Photophysical Properties on ASE Thresholds
Author(s) -
Laquai Frédéric,
Mishra Ashok K.,
Müllen Klaus,
Friend Richard H.
Publication year - 2008
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200800299
Subject(s) - materials science , carbazole , polyfluorene , phenylene , photoluminescence , polymer , amplified spontaneous emission , photochemistry , absorption (acoustics) , ultrafast laser spectroscopy , excited state , quantum yield , fluorescence , polaron , spectroscopy , optoelectronics , optics , chemistry , copolymer , atomic physics , laser , electron , quantum mechanics , physics , composite material
Amplified spontaneous emission (ASE) of a series of blue‐emitting poly(ladder‐type phenylene)s (LPPP)s has been studied in thin film polymer waveguide structures. The chemically well‐defined step‐ladder polymers consist of an increasing number of bridged phenylene rings per monomer unit starting from fully arylated poly(ladder‐type indenofluorene) up to poly(ladder‐type pentaphenylene). The ASE characteristics of the polymers including the onset threshold values for ASE, the gain and loss coefficients as well as the photoluminescence (PL) properties, i.e., the solid state fluorescence lifetimes, decay kinetics and solid state quantum efficiencies have been studied by time‐resolved PL spectroscopy. A fully arylated polyfluorene has been synthesized and its photophysical properties were compared to the step‐ladder polymers. Steady‐state photoinduced absorption and ultrafast transient absorption spectroscopy have been used to study excited state absorption of singlet and triplet states and polarons present in the solid state. The results demonstrate a minimum regarding the onset threshold value of ASE for a fully arylated poly(ladder‐type indenofluorene) and a successive increase of the ASE threshold for the step‐ladder polymers with more bridged phenylene rings. In particular, carbazole‐containing step‐ladder LPPPs exhibit significantly increased ASE threshold values as compared to their carbazole‐free analogues due to a pronounced overlap of stimulated emission (SE) and photoinduced absorption (PA).