Luminescence, Singlet Oxygen Production, and Optical Power Limiting of Some Diacetylide Platinum(II) Diphosphine Complexes

Abstract

A series of four new trans-diphosphine Pt(II) diacetylide complexes, with a thiophene and two benzenoid rings in each acetylide ligand, have been synthesized and characterized with respect to optical absorption, spectrally and time-resolved luminescence, and optically nonlinear properties such as two-photon absorption cross section and optical power limiting. Density functional theory (DFT) calculations of a few ground state conformations of three Pt(II) diacetylide structures showed similar total energy for each geometry-optimized rotamer but some differences in the vertical excitation energies and in the ligand-to-metal charge-transfer character. The wavelengths of the calculated excitations were found to be red-shifted compared with peaks in the optical absorption spectra, but the general trends and shifts of wavelengths between the different structures are well reproduced. Static emission spectra for degassed samples in THF solution of the larger compounds showed small Stokes shifts and low fluorescence quantum yields, indicating fast intersystem crossing to the triplet manifold. More pronounced differences between the compounds were displayed in the phosphorescence data, in terms of spectral emission wavelengths and decay times. For instance, the phosphorescence decay of the compound with the thiophene ring close to the Pt center was found to be significantly faster than for the other compounds. A possible relationship between triplet lifetime and conformation of the compounds is discussed. It was also demonstrated that the quenching of the excited triplet states in air-saturated samples involves energy transfer to the oxygen triplet state, and subsequent generation of singlet oxygen showing the typical emission at approximately 1275 nm. The amount of produced singlet oxygen followed the phosphorescence yields of the solute molecules. Two-photon absorption cross sections (sigma(2)) were measured and showed values on the order of 10 GM at 780 nm for all compounds. Optical power limiting measurements of the new complexes in THF using 5 ns pulses, showed only slightly better performance at the wavelength of 532 nm compared to that of similar platinum compounds with only two aryl rings in each ligand. At 600 nm the complexes with three aryl rings were significantly better optical limiters than the smaller compounds with two aryl rings in the ligands.

Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor–bridge-acceptor assembly

“…[16][17][18][19][20][21] Here we investigate light-induced processes in a linear, asymmetric trans acetylide donor-acceptor Pt(II) triad 1, Fig. 22 Our design employs a neutral co-ligand phosphine, [23][24][25][26][27][28][29][30][31][32] which lacks low lying π* orbitals hence does not engage in the chargetransfer processes between the trans configured donor and acceptor ligands, ensuring that the light-harvesting system has a pre-conditioned charge transfer directionality. 22 Our design employs a neutral co-ligand phosphine, [23][24][25][26][27][28][29][30][31][32] which lacks low lying π* orbitals hence does not engage in the chargetransfer processes between the trans configured donor and acceptor ligands, ensuring that the light-harvesting system has a pre-conditioned charge transfer directionality.…”

A simple and efficient synthesis of 1,3,5-tris[2-(3,5-diethynylphenyl)ethynyl]benzene from 1,3,5-triethynylbenzene

“…Although the 2-hydroxypropyl groups were attractive in consideration of separation, the deprotection reaction always required harsh conditions (e.g., strong base, high temperature, and a long reaction time) [21][22][23]. Furthermore, for molecules bearing more than one 2-hydroxypropyl group, the deprotection yields were often low or long reaction time was required [24][25][26].…”

How to assess good candidate molecules for self-activated optical power limiting

“…The pulse-picker is necessary to reduce the pulse repetition frequency (PRF) of the laser if longer lifetimes are to be investigated. 68,69 By scanning the monochromators, the spectral properties for a given excitation wavelength and pulse configuration can be systematically studied. A representative fluorescence lifetime decay of C110 and phosphorescence decay of Pt-OEP are shown in Fig.…”