Photo-physical and lasing characterization of neat films of 4-methyl-TPD and of an alternating copolymer of 4-methyl-TPD with MEH–PPV

Abstract

Wave-guided traveling wave lasing, i.e. amplification of spontaneous emission in a waveguide, is studied on neat films of the triphenylamine dimer 4-methyl-TPD (N,N′-bis(4-methylphenyl)-N,N′-diphenyl-benzidine) and an alternating copolymer with MEH–PPV assigned as TPD(4M)–MEH–P–PPV. The solution processable polymer has been prepared via the polycondensation route. Laser action is achieved by transversally pumping neat films on glass substrates with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs around 422 nm for 4-methyl-TPD and around 544 nm for TPD(4M)–MEH–P–PPV. Below laser threshold leaky mode emission into the substrate along the film/surface interface is reported for 4-methyl-TPD. The optical constants (absorption spectra and refractive index spectra), the absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes of the samples are determined for photo-physical characterization. The laser performance and the photo-physical parameters of 4-methyl-TPD are compared with the molecule 3-methyl-TPD and the non-conjugated polymer poly-TPD(4M)–DPX which is built up of 4-methyl-TPD and α,α′-diphenylxylylene units. The parameters of TPD(4M)–MEH–P–PPV are compared with the parameters of TPD(4M)–MEH–PPV another alternating copolymer of 4-methyl-TPD with MEH–PPV. The synthesis details for TPD(4M)–MEH–PPV and TPD(4M)–MEH–P–PPV are given.