Change of photoluminescence properties of cyano-substituted poly p-phenylene vinylene controlled by photoirradiation

Photoluminescence (PL) changes in cyano-substituted poly p-phenylene vinylene (PPV) derivatives caused by photooxidation are discussed. PL blue shift of ordinary PPVs due to photooxidation is usually known to involve a significant quenching of PL intensity. In the case of cyano-substituted poly p-phenylene vinylene (CN-PPVs), we found that photooxidation at higher temperature results in blue shift without a significant PL quenching, and that photooxidation at lower temperature results in quenching with little blue shift. Our results indicated that photooxidation of CN-PPVs at an appropriate temperature can attach PL blue shift without a quenching of PL intensity, from the PL peak wavelength of solid film state to the PL peak wavelength of solution state. The appropriate temperature is different for each of the CN-PPVs. It is demonstrated that the PL peak wavelength of MEH-CN-PPV solid film can be changed with little significant PL quenching, from the 594 nm, which is the PL peak wavelength of bulk MEH-CN-PPV, to the blue limit of the PL peak wavelength of 547 nm, which is the PL peak wavelength of a well-dispersed state of MEH-CN-PPV. The changed PL properties can be preserved under a reduced pressure atmosphere, even if samples are irradiated by a light source. The dominant factor of the blue shift to the PL peak wavelength of solution state is considered to be expanding of distance between planes (cl-space) of the CN-PPV-layered structure, which determines the intermolecular interaction. Controlling d-space of cyano-PPV derivatives by photoirradiation is suggested to be a useful method of creating various PL or EL color patterns of CN-PPVs. (C) 2008 Elsevier B.V. All rights reserved.