Photophysical properties of a new hyperbranched conjugated copolymer, poly(2-methoxy-5-(2'-ethylhexoxy)-p-phenylene vinylene)-alt- (3,5-bisvinylicbenzene) (MEH-PPV-HS_1), have been investigated. MEH-PPV- HS_1 shows two adjacent absorption bands in UV region, and similar fluorescence emission spectra are obtained when it is excited selectively by these two bands. Effects of pressure on these two absorption bands are quite different and the emission intensity may change with pressure in a different way for excitation at different band. All these results indicate that these two absorption bands are attributed to different effective conjugated structures in MEH-PPV- HS_1 respectively and the selective excitation of MEH-PPV-HS_1 generates different excited states, which transit to the same luminescent excited state by different relaxation pathway.

Key words: BRANCHED POLYMER, FLUOROSPECTROPHOTOMETRY, EXCITED STATE, STYRENE, DIETHENYLBENZENE