Synthesis and two-photon absorption enhancement of porphyrin macrocycles.

Improving the nonlinear optical properties of organic materials through transition to macromolecular architectures of highly conjugated chromophores has been shown to be a viable strategy for generating materials suitable for TPA applications. In this study we display a simple and elegant method by which to synthesize macrocycles of porphyrin dimers. Two-photon absorption studies show 2 orders of magnitude enhancement of cross-section of the material, giving a maximum delta(2) of 10(6) GM.

Oligothiophene dendrimers as new building blocks for optical applications.

Thiophene branched structures have been proposed as candidates for photon harvesting and electron-hole transporting materials in novel organic light emitting diodes and solar energy conversion devices. To understand the photoinduced processes in a novel thiophene dendrimer system, the excited state dynamics and nonlinear optical properties of 3D oligothiophene dendrimers have been investigated. The key point of this contribution is that we have found that with these thiophene dendrimer systems, the excitation is delocalized over a large number of thiophene units in the dendrimer and there is an ultrafast energy transfer (200-300 fs) to the longest branch of dendrimer, which can be utilized for future optical devices.

Enhancement of two-photon absorption cross-section in macrocyclic thiophenes with cavities in the nanometer regime.

The linear and nonlinear optical properties of two thiophene-based cyclic molecules have been investigated. These molecules represent nanometer sized cavities which may be useful for novel photonic devices. By virtue of long-range interactions, these chromophores serve as novel architectures for enhanced two-photon absorption (TPA) properties.

Building symmetric two-dimensional two-photon materials.

Two-dimensional multi-annulenic carbon networks are important molecules with possible applications in optoelectronic devices and nonlinear optics. Investigations of two-photon absorption (TPA) cross sections have been carried out in a series of annulenes with a basic building block approach and variable symmetries. Enhancement of the TPA cross section has been observed with an increase in number of building blocks and order of symmetry.

Ultrafast excited state relaxation dynamics of branched donor-pi-acceptor chromophore: evidence of a charge-delocalized state.

Excited-state dynamics and complete transient absorption features of the trimer tris-4,4',4' '-(4-nitrophenyleethynyl)triphenylamine and the monomer 4-N,N-(dimethylamino)-4'-nitrotolane have been obtained from femtosecond pump-probe spectroscopy. The measurements are carried out to understand the mechanism behind enhanced two-photon absorption cross-sections of branched systems over their linear counterparts. Absorption and emission transition dipole moments of monomer and trimer in toluene have suggested that the emitting state of trimer is different from the monomer and probably is arising from the charge-delocalized C(3) symmetry state.

Investigation of two-photon absorption properties in branched alkene and alkyne chromophores.

Novel alkene and alkyne branched structures have been synthesized, and their two-photon absorption (2PA) properties are reported. This series of alkene and alkyne trimer systems tests the mechanistic approach for enhancing the 2PA process which is usually dictated by the pi-bridging, delocalization length, and corresponding charge transfer on the 2PA cross sections. The results suggest that alkene branched systems have higher 2PA cross sections.