Optimizing Simultaneous Two-Photon Absorption and Transient Triplet−Triplet Absorption in Platinum Acetylide Chromophores

Abstract

A series of platinum-containing organometallic dimer complexes has been synthesized and the photophysical properties have been investigated under one- and two-photon (2PA) absorption conditions. The complexes have the general structure [DPAF-C[triple bond]C-Pt(PBu(3))(2)-C[triple bond]C-Ar-C[triple bond]C-Pt(PBu(3))(2)-C[triple bond]C-DPAF], where Ar is a pi-conjugated unit, Bu = n-butyl, and DPAF = diphenylamino-2,7-fluorenylene. The core Ar units include 1,4-phenylene, 2,5-thienylene, 5,5'-(2,2'-bithienylene), 2,5-(3,4-ethylenedioxythiophene, 2,1,3-benzothiadiazole, and 4,7-dithien-2-yl-2,1,3-benzothiadiazole. Absorption and photoluminescence spectroscopy indicates that the complexes feature low-lying excited states based on both the core [-Pt(PBu(3))(2)-C[triple bond]C-Ar-C[triple bond]C-Pt(PBu(3))(2)-] chromophore as well as the DPAF units. Photoexcitation of the complexes produces a singlet state excited state, which rapidly undergoes intersystem crossing to afford a triplet state that has a lifetime in the microsecond time domain. In most cases, the lowest energy triplet state is localized on the core chromophore. Femtosecond 2PA spectra are measured along with triplet-triplet absorption spectra and nanosecond intensity-dependent transmission for solutions of the complexes. Each of the complexes features a 2PA absorption band in the near-infrared region (lambda approximately 700-750 nm) with a cross section 50-200 GM that is ascribed to the DPAF chromophore. The complexes also feature broad triplet-triplet absorption throughout the visible and near-infrared regions (lambda approximately 500-800 nm, (TT) approximately 5-10 x 10(4) M(-1) cm(-1)). Each of the complexes exhibits efficient nonlinear absorption of nanosecond pulses in the near-infrared region (600-800 nm), and we demonstrate that effect is most efficient in the chromophores where the 2PA cross section maxima coincides spectrally with the excited triplet state absorption.

Synthesis, characterization, luminescence and nonlinear optical (NLO) properties of truxene-containing platinum(II) alkynyl complexes

“…The positive bands that occurred at 400e700 nm for these complexes could be assigned as derived from the 3 p,p * absorption of the triplet excited state. The transient absorption decay lifetimes in each case are found to be comparable to that of their emission decay lifetimes, which supported the assignment of a transient absorption due to the tripletetriplet transition from the lowest energy triplet excited state [109]. The transient absorption spectrum of 3 showed a broad excited state absorption at l max w550 nm with a lifetime of 62 ms.…”

“…370 nm for complexes 1e3 are characteristic of the p,p * (S 0 /S 1 ) absorption [44,103,106,109]. The bands of the ground-state bleaching represented the ground-state absorption of the central triethynylhexabutyltruxene and the peripheral alkynyl moieties.…”

Expanding iClick to group 9 metals

“…Preparing metallopolymers requires either appending metal ions to an already existing polymer backbone or incorporating them into the repeating unit directly . Conjugated platinum(II) acetylide oligomers/polymers, studied extensively by Schanze and co-workers [33][34][35][36][37][38][39][40], are hallmark examples of incorporating metal ions into the propagating repeat unit. The platinum ions engender photophysical properties that are challenging or impossible to replicate by organic polymers alone.…”

Symmetry Breaking in Platinum Acetylide Chromophores Studied by Femtosecond Two-Photon Absorption Spectroscopy

“…Furthermore, if the chromophores also possess a large one-photon absorption (1PA) cross section from excited singlet and/or triplet states, then a combined 2PA + ESA nonlinear absorption mechanism is observed. 14,23,24,29,31 Recently, we have reported on the synthesis and photophysical characterization of a series of platinum(II) trans-bis(tributylphosphine)-bis(4-((9,9-diethyl-7-ethynyl-9H-fluoren-2-yl)-ethynyl)-R)-complexes, where R represents one of the different end groups N(phenyl) 2 (NPh 2 ), NH 2 , OCH 3 , t-butyl, CH 3 , H, F, CF 3 , CN, benzothiazole (BT), or NO 2 . 34 The previous study showed that the series exhibits broad spectral bandwidth femtosecond ESA as well as efficient nanosecond ESA, where the latter is attributed to long triplet lifetime and rapid singlet-to-triplet intersystem crossing that is characteristic of Pt complexes.…”