Ultrafast responses of dipolar and octupolar compounds with dipicolinate as an electron acceptor

Two dipolar compounds with dipicolinate as electron acceptor group named trans-dimethy1-4-[4'-(N,N-dimethylamino)-styry11-pyridin-2,6-dicarboxylate (M-1), trans-dimethy1-4-[4'-(N,N-diphenylamino)styry1]-pyridin-2,6-dicarboxylate (P-1) as well as a P-1 based multi-branched octupolar compound (4[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl) vinyln-N,N-bis[4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4yl)vinylphenylllaniline (P-3) with intense two-photon fluorescence emission properties are systematically investigated by using steady-state absorption and fluorescence spectroscopy, Z-scan, and two photon excited fluorescence (TPF) method. The two-photon absorption cross section of octupolar compound P-3 in THF solution is determined to be 376 GM, which is approximately 12 times greater than that of dipolar counterpart P-1 (32 GM). Transient absorption spectroscopy is employed to investigate the excited state dynamics of the dipolar and octupolar compounds. The formation and relaxation lifetimes of the intra-molecular charge transfer (ICT) state are determined to be in the ranges of several picoseconds and several-hundreds of picoseconds, respectively, for all the three compounds in THF solutions. An extended pi-conjugated system and increased intra-molecular cooperative effect are responsible for the observed large two-photon absorption character. (C) 2016 Elsevier B.V. All rights reserved.