分子构型对有机半导体分子TPD,DDB和NPB激射性能的影响

Molecular structure dependence of amplified spontaneous emission in organic semiconductor materials: TPD, DDB and NPB

N,N′-二苯基-N,N′-二(3-甲苯基)-1,1′-联苯-4,4′-二胺(TPD)分子已证明能够在掺杂和非掺杂平面波导结构中产生受激发射,然而对于该分子激射特性的机理却很模糊.为了得到其激射特性的微观解释,我们通过实验和量化理论研究TPD分子的吸收、光致发光、受激发射以及与TPD分子结构类似的两个分子:1,4-二(二苯胺基)联苯(DDB)和N,N′-二苯基-N,N′-二(1-萘基)-1,1′-联苯-4,4′-二胺(NPB).我们发现,DDB分子具有与TPD分子相似的自发辐射放大(ASE)特性,然而NPB分子却没有ASE特性,尽管其斯托克斯位移较大,约0.754eV.量子化学计算分析中,我们利用密度泛函理论(DFT)和弗朗克-康登(Franck-Condon)原理研究分子在电子基态和激发态的分子构型以及电子基态的振动能级.理论分析表明,对于TPD和DDB分子,一些苯环中的较强高频拉伸模式(1199～1664cm-1)对PL谱中的第一振动带(0-1跃迁)有显著贡献,该振动带有利于形成激光的四能级系统.而对于NPB分子,相对大的萘基基团取代了TPD和DDB分子外围的甲基与苯环,会产生一些较强的分子低频振动模式(11～689cm-1),这些低频振动模式则会破坏激光四能级系统.研究结果有助于深刻理解有机分子的激射特性,为新型激射材料的设计和应用提供了理论基础.

N,N＇-diphenyl-N,N＇-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 N,N＇-diphenyl-N,N＇-bis（1- naphthyl）-l,l＇-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.