Four new two-photon polymerization initiators with varying donor and conjugated bridge: Synthesis and two-photon activity

A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the pi-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (sigma) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the a values than extending conjugated chain based on the comparison of small molecules (D-pi-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators. (C) 2013 Elsevier B.V. All rights reserved.