Studies have revealed that the photoacidity of phenol derivatives have been enhanced manifolds by the substitution of electron withdrawing groups on the aromatic ring1. It has been recently investigated that the UV-Vis absorption and fluorescence emission properties such as absorption/emission maxima, fluorescence quantum yield, fluorescence life time of the aromatic compounds have been dramatically changed on substitution of electron withdrawing cyano (-CN) groups2. The photophysical properties of 2,3,5,6-tetracyanohydroquinone (TCHQ) have shown proton transfer from solute to solvent molecules when studied in basic and/or polar solvents3. In present studies, the solvatochromic and proton transfer properties of different cyano-substituted derivatives of p-hydroquinone (dicyano-p-hydroquinone, DCHQ) have been investigated in aqueous as well as in non-aqueous solvents. The absorption spectra in various binary solvent mixtures have also been investigated to discuss the preferential solvation of the solute molecule in the ground state. The solvents have been chosen based on their acidity, basicity and polarity characteristics. Different solvent parametric scales such as developed independently by Kamlet-Taft, Javier Catal�n and Reichardt have been used to evaluate the quantitative share of the specific and non-specific interaction during the solvation process. Linear Solvation Energy Relation (LSER) has been applied to evaluate the solvent-solute interaction using multi-parameter approach4. LSER analyses of cyano-substituted hydroquinones show higher values for the LSER co-efficient of the basicity terms.  Both TCHQ and DCHQ have tendency to release their proton in protic and polar aprotic solvents.  The substitutions of aromatic ring with cyano group (-CN) make the hydroquinone (HQ) from basic to acidic (DCHQ) and even super photo-acidic (TCHQ).References: 1.            (a) Kaneko, S.; Yotoriyama, S.; Koda, H.; Tobita, S., J. Phys. Chem. A 2009,  113 (13), 3021-3028; (b) Malval, J. P.; Diemer, V.; Savary, F. M.; Jacques, P.; Allonas, X.; Chaumeil, H.; Defoin, A.; Carr�, C., Chem. Phys. Lett. 2008,  455 (4-6), 238-241.2.            (a) Angulo, G.; Grampp, G.; Grilj, J.; Jacques, P.; Landgraf, S.; Rosspeintner, A., Journal of Photochemistry and Photobiology A: Chemistry 2008,  199 (2-3), 204-210; (b) Zahid, M.; Rosspeintner, A.; Angulo, G.; Grampp, G.; Jacques, P.; Mansha, A., Journal of Photochemistry and Photobiology A: Chemistry 2011,  220 (1), 54-63.3.            Zahid, M.; Grampp, G.; Mansha, A.; Bhatti, I.; Asim, S., Journal of Fluorescence 2013 , 1-9.4.            Reichardt, C., Solvents and Solvent Effects in Organic Chemistry (WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 2003,  3rd edition.

Proton transfer studies of cyano-substituted hydroquinones

248th National Meeting (2014)

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