Two-photon absorption properties of malononitrile derivatives

Two malononitrile derivatives, 2-[2,5-bis-(4-dimethylamino-benzylidene)-cyclopentylidene]-malononitrile (1) and 2-{2,6-bis-[2-(4-dimethylamino-phenyl)-vinyl]-pyran-4-ylidene}-malononitrile (2), were synthesized and their photophysical characteristics were investigated using UV-vis spectra, fluorescence spectra, nonlinear transmission and two-photon excited spectra. The results showed that both compounds exhibited strong intramolecular charge transfer absorption bands within 400-600 nm, but only compound 2 presented a strong fluorescence emission. By nonlinear transmission method, the two-photon absorption cross-section (σ) values of two compounds were determined as 250 GM and 283 GM, respectively, with 800 nm femtosecond laser pulses. By two-photon excited fluorescence method, the two-photon excited spectra of compound 2 within 720-880 nm was measured and its σmax was obtained as 773 GM at 770 nm.