分子构型对有机半导体分子TPD, DDB和NPB激射性能的影响

Abstract

<italic>N</italic>,<italic>N</italic>′-diphenyl-<italic>N</italic>,<italic>N</italic>′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) demonstrateds to be suitable for stimulated emission in doping and non-doping planar waveguide structure, but the mechanism for its lasing is of ambiguity. In this article, we investigated the absorption, photoluminescence (PL) and stimulated emission of TPD, and the other two similar molecules 1,4-bis (diphenylamino)biphenyl (DDB) and <italic>N</italic>,<italic>N</italic>′-diphenyl-<italic>N</italic>,<italic>N</italic>′-bis(1- naphthyl)-1,1′-biphenyl-4,4″-diamine (NPB) in experiment and theory. It was found that DDB showed the same amplified spontaneous emission (ASE) characteristics as TPD, while NPB didn’t take on ASE behavior although it presented a great Stokes shift of about 0.754 eV. Density functional theory and Frank-Condon principle were used to analyze molecular geometry in the electronic ground state and the optically excited state, and vibronic levels in electronic ground state respectively. It was shown that for TPD and DDB, several strongly elongated high-frequency modes (1199-1664 cm^-1) in the carbon rings contribute to first vibrational sidebands (0-1 transition) obviously in the PL spectra, which form the four-level system for lasing. For NPB, as replacing the peripheral toluene or benzene with naphthyl, the relative large group increases a number of strongly elongated low-frequency modes (11-689 cm^-1) of the molecular, which destroys the four-level system. Our results show an insight into the lasing of organic molecules and benefit the design of new lasing materials and their applications.