Photophysics of exciplex emission of crystalline biphenyl doped by pyrene

Fluorescence in crystalline biphenyl powder containing pyrene impurity has been studied at room temperature. The fluorescence spectrum of biphenyl lum inophore containing 10(-3) mole pyrene shows structured monomeric emission of pyrene. The increase in concentration of pyrene quenches the structured monomeric emission due to non radiative transfer of energy Item excited pyr ene to biphenyl. At the higher concentrations, the expected lateral overlap ping of p-molecular orbitals modify the spectrum as broad and structureless . The broad fluorescence band of biphenyl containing 10(-1) mole pyrene is centered at 458 nm. The well known excimer emission of crystalline pyrene i s not observed in the fluorescence spectrum. Hence the red shifted broad, s tructureless emission is attributed to the excited formed in the excited st ate between biphenyl and pyrene.