Molecular design of light emitting polymers

Abstract

Fluorene-based alternating and statistical copolymers were synthesized by employing reaction methods of Wittig, Heck; and Suzuki. The copolymers were classified into three groups with the photoluminescence (PL) emission maxima at 420, 475 and 500 nm, respectively. Statistical copolymers with two chromophores having PL emission maxima at 420 and 475 nm Emitted Light with the emission maximum at 475 nm on photoexcitation at 365 nm and improved the quantum efficiency by the energy transfer. However, the intramolecular energy transfer was inefficient compared to the intermolecular energy transfer when the two chromophores were apart from each other in the range of the Forster critical distance. Fluorene-pyridinedivinylene alternating copolymer was synthesized by the Wittig reaction and found to have physical, electronic and electrochemical properties of the individual units intact. The double-layered light emitting diode (LED) with the statistical copolymer as an emitting layer and the pyridine-containing copolymer as an electron transporting-hole blocking layer, which were sandwiched between ITO and Al, displayed a quantum efficiency of 0.1%.