Synthesis and theoretical and experimental nonlinear optical studies of push–pull benzopyranic derivatives containing an oxo, thioxo or dicyanoethylene group as acceptor site

Abstract

A series of new push–pull molecules, containing 4H-1-benzopyran-4-oxo-2-yl, 4H-1-benzopyran-4-thioxo-2-yl or 4H-1-benzopyran-4-(ylidene malononitrile)-2-yl as acceptor site and 4-dimethylaminophenyl or ferrocenyl as donor site, was synthesized and characterized. The X-ray structures of 2-(4′-dimethylaminophenyl)-4H-1-benzopyran-4-thione and 2-(4′-dimethylaminophenylethenyl)-4H-1-benzopyran-4-thione were established. Experimental dipole moments and first-order hyperpolarizability β data measured in solution by electric-field-induced second-harmonic generation (EFISHG) were compared to computed values obtained by the semiempirical PM3 method for optimized structures. The characteristics of the lowest energy singlet–singlet π→π* transitions were determined through UV/VIS spectral measurements and semiempirical CNDO/S-CIS calculations. All of the experimental and computed results point out the NLO efficiency of the acceptor thioxo group, which was compared to the well-known aldehyde or dicyanomethylene substituents. Synthèse et e′tudes the′oriques et expe′rimentales en optique non-line′aire de compose′s benzopyraniques de type push–pull contenant des groupes accepteurs oxo, thioxo ou dicyanoe′thylène. Une se′rie de nouvelles mole′cules de type donneur–transmetteur–accepteur (D–T–A), comprenant un groupement 4H-1-benzopyrane-4-oxo-2-yle, 4H-1-benzopyrane-4-thioxo-2-yle ou 4H-1-benzopyrane-4-(ylidène malononitrile)-2-yle comme accepteur et un groupement 4-dime′thylaminophe′nyle ou ferrocènyle comme donneur, a e′te′ synthe′tise′e puis caracte′rise′e. Les structures cristallographiques des mole′cules 2-(4′-dime′thylaminophe′nyl)-4H-1-benzopyrane-4-thione et 2-(4′-dime′thylaminophe′nyle′thènyl)-4H-1-benzopyrane-4-thione ont e′te′ e′tablies. Des mesures en solution du moment dipolaire et de l'hyperpolarisabilite′ du premier ordre β (expe′rience EFISHG) ont e′te compare′es aux valeurs calcule′es par la me′thode semi-empirique PM3 à partir de ge′ome′tries optimise′es. Les caracte′ristiques des transitions π→π* singulet–singulet de plus basses e′nergies ont e′te e′value′es à l'aide des spectres UV/VIS et de calculs semi-empiriques CNDO/S-CIS. Tous les re′sultats expe′rimentaux et the′oriques permettent de comparer l'efficacite′ du groupement accepteur thioxo à celle des substituants bien connus alde′hyde et dicyanome′thylène.