Abstract
A conjugated-bisimidazolylporphyrin bridged by bis(ethynylfluorene) was synthesized and organized into linear polymer through self-coordination having mean molecular weights, Mw and Mn, of ~2.1 × 105 Da and ~1.6 × 105 Da, respectively. A large two-photon absorption cross section value of 3.4 × 105 GM (per dimer unit) was observed. This value was comparable to that of the previously reported self-assembled linear polymer consisting of butadiyne-bridged imidazolylporphyrins. The two-photon absorption properties could be controlled by tuning the wavelength and absorption intensity of the one-photon absorption.
Highlights
Much attention has been focused on organic dye molecules in view of optical applications such as organic solar cell [1], electronic luminescence [2], photon-mode optical memory using photochromic molecules [3], and nonlinear optics including two-photon absorption (2PA)materials [4,5,6,7,8,9,10,11]
Fluorene is a well-known π-spacer for two-photon absorption materials [26,27,28,29,30,31,32,33] and provides an angle of 160° between two ethynylimidazolylporphyrins when these are connected at the 2- and 7-positions of fluorene (1)
5,15-bis(2-methoxycarbonylethyl)-10(trimethylsilylpropargyl)-20-(1-methyl-2-imidazolyl)porphyrinatozinc 3 [15] and 2,7-diiodo-9,9bis(3,5,5-trimethylhexyl)fluorene 4 [35,36] using a Pd2(dba)3/AsPh3 catalytic system, where deprotection of the TMS group and the coupling reaction were conducted in a one-pot procedure because of the low solubility of the deprotected ethynylimidazolylporphyrin (Scheme 1)
Summary
Much attention has been focused on organic dye molecules in view of optical applications such as organic solar cell [1], electronic luminescence [2], photon-mode optical memory using photochromic molecules [3], and nonlinear optics including two-photon absorption (2PA). An additional expansion of π-conjugation gave rise to a large red-shift of the S0→S1 one-photon absorption (1PA) to the two-photon resonance range (800 nm to 900 nm) [22]. To prevent such an overlap of 2PA and 1PA, it is necessary to control the position of the S0→S1 one-photon absorption by tuning the interaction between chromophores. Similar fluorene-conjugated bisimidazolylporphyrins having two allyl groups at meso-positions have been synthesized to construct large macrocyclic arrays. We report the synthesis of linear polymers self-organized by fluorene-conjugated bisimidazolylporphyrins without allyl groups, and their 2PA properties in the range from 740 to 930 nm
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