Owing to their potential application in solar energy conversion, semiconductor nanoparticles have been extensively studied from both experimental and theoretical viewpoints [1-4]. Variety of techniques including spectroscopy, microscopy and X-ray techniques has been used to characterize the properties of nanoparticles. Most of the studies have been focused on their equilibrium properties such as absorption and emission, particle shape, surface structure, inter particle interaction, self assembly, and formation of superlattices [5]. Tindioxide (SnO₂) is a n-type metal oxide semiconductor with the wide bandgap of 3.6 eV. Because of its remarkable electrical, optical and electrochemical properties, SnO₂ serves a wide range of applications in solar cells, catalytic supporting materials, transparent electrodes and solid state chemistry [6]. The higher electron mobility (~100 - 200 cm²·v^–1·s^–1) of SnO₂ NPs proposes a faster diffusion of photo induced electrons in SnO₂ and its larger band gap would be creating fewer oxidation holes in the valence band. Thus low sensitivity of SnO₂ to UV degradation facilitates the long-term stability of dye senstitized solar cells. The low isoelectric point (at pH 4 - 5) of SnO₂ leads to less absorption of the dye with acidic carboxyl groups [7,8]. The ability of organic dyes to sensitize large band gap semiconductor materials has been used for the design of light energy conversion devices [9]. Schiff bases play an important part in the development of co-ordination chemistry. The common structural feature of these compounds is the azomethine group with a general formula RHC=N-R’, where R and R’ are alkyl, aryl, cyclo alkyl or heterocyclic group which may be variously substituted. They are easily prepared in general by the condensation reaction of primary amines with carbonyl compounds [10]. In the field of co-ordination chemistry, Schiff bases from 2-hydroxy 1-napthaldehyde have been used as chelating ligands. N-H…O (keto form) and N…H-O (enol form) are the two types of intra molecular hydrogen bonds in Schiff bases. Both types of hydrogen bonds were found in the aldimine compounds derived from 2-hydroxy 1-Naphthaldehyde [11]. The existence of tautomerism between these two types of bonds created a great interest in 2-hydorxy Schiff base ligands. The ortho hydroxyl naphthalidene anilines show two bands above 400 nm in the visible region which are assigned to the keto form. In naphthaldimines both forms keto/enolimino are possible and O-H…N or N-H…O intra molecular hydrogen bonds can occur [12]. If combined with chelating activities, Schiff base may become a promising dye sensitizer in molecular photovoltaic cells [13].

Semiconducting oxides such as TiO₂ and SnO₂ directly interact with the excited dye molecules thus inducing heterogeneous electron transfer at the semiconductor/dye interface. This interesting property of sensitizing dyes is useful in the design of photochemical solar cells.

A process which decreases the fluorescence intensity of a given substance is known as quenching. It may also result from a photo-induced electron transfer process between the excited dye and the nanoparticles. Our group has studied spectral investigation of NMTHN by silver nanoparticle using fluorescence quenching [14]. Although there are many studies on the photochemical and fluorescence behavior of organic dyes on SnO₂ thin film, there is none for SnO₂ NPs on the fluorescence quenching of Schiff base in methanol medium [15-18]. In the present study, using optical absorption and fluorescence emission techniques the effect of SnO₂ NPs on NMTHN has been investigated.