Third-order optical nonlinearities and femtosecond responses in metallophthalocyanine thin films made by vacuum deposition, molecular beam epitaxy, and spin coating

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Abstract
The molecular design and assembly of metallophthalocyanine systems that have the enhanced macroscopic third-order nonlinear susceptibility (chi) (3)ijkl(-(omega) 4; (omega) 1, (omega) 2, (omega) 3) and show ultrafast responses are described. Enhancement of the third harmonic susceptibility (chi) (3)1111(-3(omega) ; (omega) , (omega) , (omega) ) was observed in vanadyl phthalocyanine vacuum-deposited film with the staggered stacking arrangement induced by thermal treatment. Processable polymeric system based on tert-butyl mono-substituted rich vanadyl phthalocyanine was developed and the favorable staggered stacking arrangement was induced in a polymer matrix to enhance (chi) (3)1111(- 3(omega) ;(omega) ,(omega) ,(omega) ). Femtosecond-time-resolved spectroscopy was performed on vanadyl phthalocyanine thin films with different morphological forms in order to elucidate the exciton dynamics. The exciton decay kinetics consists of three processes: exciton-exciton annihilation, exciton-phonon coupling, and much slower triplet state formation. The decay rate of the exciton population via exciton-exciton annihilation was found to have a time dependence of t-1/2. The vacuum-deposited film and spin-coated film of vanadyl phthalocyanine derivatives showed similar decay behavior, whereas molecular beam epitaxy film showed a faster decay with a time constant of several hundreds of femtoseconds.

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