Optical materials: Studying the role of hetropolyacid to enhance the nonlinear optical responses of porphyrin in their hybrids system

Abstract Nonlinear optical responses are measured to investigate the role of hetropolyacid ( HPA ) in porphyrin-Lindqvist type {∼ P M @ HPA } hybrid systems, {where P M @ HPA  = [(TBA) 8 {(MTPPN 4 )(Mo 6 O 18 ) 4 }]; M = 2H ( 1 ) and Mn ( 2 )}. The well-known Z-scan technique with wavelength (λ) = 532 nm and pulse duration of τ  = 6 ns is used. The results clearly show the significant enhancement in nonlinear self-defocusing effect and reverse saturable absorption under closed and open-aperture configuration for P M @ HPA hybrids. It is also observed that the second hyperpolarizability γ values, { 1 (4.639 × 10 −29  esu)  2 (5.214 × 10 −29  esu)}, are directly proportional to the discrepancy of LUMO level (Δ E ) values { 1 (2.214 eV)  2 (2.339 eV)} while they are inversely proportional to the HOMO−LUMO energy gap E g values { 1 (2.003 eV) >  2 (1.862 eV)} in the P M @ HPA hybrid system where the porphyrin moiety acts as electron donor whilst HPA acts as electron acceptor. Therefore, the emergence of a facile electron transformation from the porphyrin moieties to the low-lying LUMO levels of HPA is mainly responsible for the enhancement in nonlinear optical responses of P M @ HPA hybrids system. As a consequence the hybrid compounds can be fascinating for optical limiting applications.