2010) 3( 23المجلد مجلة ابن الھیثم للعلوم الصرفة والتطبیقیة لتحام في نظامطاقة اعادة األ فينوع المذیب دراسة نظریة لتأثیر ) "موصله شب -صبغة( محسن عنید حسوني، العكیلي هادي جبار مجبل لتربیة ابن الهیثم ،جامعة بغدادكلیة ا ،قسم الفیزیاء الخالصة Tالسافرانین (الصبغات العضویة ) ₂iOT،ZnO(موصل هااللتحام قد أجریت لنظام شب أعادةالحسابات النظریة لطاقة االلتحام إعادةقیم طاقة أنوتبین .واألیثانول،استونترایل ، فورماماید ، بروبانول ،مثل الماء ولمذیبات مختلفة) ،الكومارین رایل ، 741.0للماء( كبیرة للمذیبات ذات القطبیة العالیة) موصل هشب_صبغة(لنظام ایثانول ، 708.0اسیتونت 669.0 (وقلیلة للمذیبات ذات القطبیة الواطئة )635.0بروبانول-1(. طاقة اعادة االلتحام لنظام) صبغة سافرانین T_635741.0(قیمتها اكبر كانت )شبة الموصل  ( منها لنظام)612.0731.0( )شبة الموصل _صبغة الكومارین ( .الموصل هشب االلكترونياكثر فعالیة لتفاعل االنتقال Tفرانینوهذا یشیر الى أن صبغة السا أنفسها المذیباتو IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 IHJPAS A Theoretical Study of the Effect of The Solvent Type on The Reorganization Energies of Dye - Semiconductor System Interface H.J.M.Al-Agealy, M.A.Hassooni Department of Physics, College of Education Ibn-AL-Haitham, University of Baghdad Abstract A theoretical calculation of the reorganization energies is demonstrated for semiconductor (TiO₂, ZnO) and organic dye (safranine T, and coumarin) with a variety solvent such that (water, 1­propanol, Formamide, Acetonitrile and Ethanol). The reorganization energy values for dye –semiconductor interface system are large in high polar solvent (water 741.0 , Acetonitrile 708.0 , Ethanol 669.0 ) and small in low polar solvent(1­propanol 635.0 . The reorganization energy in safranine T –semiconductor system is larger ( 635741.0  )than in coumarin –semiconductor for with the same solvents ( 612.0731.0  ), this indicates that safranine T dye one more electron transfer reactive towards semiconductor. Introduction Electron transfer (ET) between molecular adsorbaies and semiconductor has been a subject of intense research interests for many years [1]. The understanding of this fundamental process is essential for the application of semiconductor in photography, solar energy comersion, wase degradation, and nano_scale devices [2]. One of these examples is the electron transfer between dyes and semiconductor plays a vital role in silver halide photography, electrophotography, and more recently in solar energy cell [3]. Since the seminal work predicting solvent dynamical control of electron transfer reactions in the early 1980s, a great deal of theoretical effort has gone into clarifying the salvation dynamics electron transfer connection [4]. Consequently, there is a great interest in understanding how the physical properties control the direction and rate of electron transfer. The key factor controlling the rate of electron transfer, is the reorganization energy, which describes the energy necessary to distort the nuclear configuration from its equilibrium donor state to the acceptor state without transfer of an electron. Many theories were used to calculate the reorganization energies one of IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 IHJPAS these is a continuum model that is used in our research to calculate the reorganization energies in dye _semiconductor system for different solvents [5]. In this paper we can use the continuum solvent model to calculate the reorganization energy for safranine T dye_TiO₂, ZnO and coumarin dye _ TiO₂, ZnO. Theory The standard Marcus diagram describes the energy surface of the donor (reactant) and acceptor (product) states as a function of the nuclear configuration coordinate [5]. According to the Marcus cross relation the reorganization energy,  , is defined as the energy necessary to distort the nuclear configuration from its equilibrium donor state to the acceptor [6]. In figure (1) the G is the activation energy, G is the free energy,  is the reorganization energy .This reorganization energy can be broken down further into inner and outer sphere components [7,8]. outin   ……………… (1) The inner sphere reorganization component ( in ) is the intra molecular or inner shell is the energy required to alter bond distances and bond angles with the change in oxidation state. The sphere reorganization out is the energy required for reorientation of the solvent around the changed complexes [9]. The solvent independent term in arises from structural differences between the equilibrium configurations of the reactant and product states; this is the sum of all the molecular vibrational and rotational movements [8].In the harmonic approximation, it can written as [10]. 2)()( )( 2 1 Peq i Req iiin rrk   ……………….. (2) Where ik is the reduced force constant for the i –th vibration ri eq(R) and ri eq(p) are the equilibrium bond lengths in the reactant and product states, respectively, and the sum is taken over all active intra molecular. Vibration which are part to the reaction coordinate. The solvent dependent outer term out is called solvent reorganization energy and arises from differences between the orientation and polarization of solvent molecules around D+ A– and D A [11]. It represents the energy necessary to reorient the solvent molecules around the new equilibrium geometry of the product, but neglecting the additional effects due to electron transfer [11]. By treating the solvent as a dielectric continuum the following expression can be derived for out [12]. IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 IHJPAS                         222 22 222 22 2 2 11 2 1111 42 1     sc sc sc sc ou t nnn nn RnD q  ..(3) Where   is the vacuum permittivity ,  is the static dielectric constant of solvent, is the refractive index of the solvent,nsc is the refractive index of the semiconductor,  sc dielectric constant of the semiconductor,D is the radius of the molecular dye, and R is the distance between the complex and the semiconductor , and q is the charge of electron. The radius of the dye molecule can be evaluated from the apparent molar volumes using spherical approach [13].   N M D  3 3 4 …………………………. (4) Where M is the molecular weight, N is Avogadro number, and is the density. Results To calculate the reorganization energies for the systems safranine T­ TiO2, safranine T­ ZnO, coumarin­TiO2, coumarin­ZnO theoretically using the equation (3), one must initially evaluate the values of the radii for both dyes safranine T and coumarin from equation (4),respectively. Inserting of molecular weight saM =350.85, coM =334.35, and density sa =1.5487 mg/m 3 , co = 1.326 mg/m 3 [14,15]. For safranine T and coumarin respectively, the values of radii are saD =4.47820 A°, and coD =4.64227 A°. Inserting the value of dielectric constant  and refractive index n for variety solvent, and the dielectric constant  sc and refractive index nsc for semiconductor in equation (3), with value of radius of dye and the distance between the molecule dye and semiconductor R ,the results have been summarized in Tables(1)and (2). Discussion For both systems (safranine T– semiconductor) and (coumarin– semiconductor), the solvent reorganization energy values, λ are calculated according to the dielectric continuum models for electron transfer reactions. The value of reorganization energy for (safranine T­ZnO) system is larger than that of the (safranine T­TiO2) system with the same solvent. Also the value of reorganization energy for coumarin –ZnO system is larger than that of the coumarin –TiO2 system with the same solvent. Since safranineT­semiconductor and coumarin­ semiconductor system with water solvent possesses is a more reorganization energy than the other solvent. Notably, from Table (1) and Table (2) the dynamic of the reorganization energy is solvent IHJPAS IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 dependent, and the reorganization energy is lower in the less polar solvent compared with higher than polar solvent for the both systems (safranine T­semiconductor) and (coumarin­ semiconductor ) alternatively. Formamide, one of the polar solvent ( =111)gives small reorganization energies for both system compare with other solvents that have less  , this indicates that formamide have large refractive index n =1.4475 in comparison with other solvents .The reorganization energies in safranine T –semiconductor is larger than in the coumarin­ semiconductor system with the same solvent, this indicate that the reorganization energy is depending on the radius of the dye for safranine T ( saD =4.47820 A° , coD =4.64227 A° ). The results of the reorganization energy in Table (1) and Table (2) lead to suggest that electron transfer is most probable in safranineT ­semiconductor system than coumarin­ semiconductor with the same solvents. Notably, the electron transfer in safranineT –ZnO and coumarin –ZnO system are stronger than in safranineT –TiO2 and coumarin –TiO2 system with the same solvent Conclusions In summary, it can be concluded from the present results that the reaction of electron transfer strongly depends on the solvents polarity. For high polar solvents, the values of the reorganization energies are large and small for low polar solvents, this indicates that, the reorganization energies depend on the polarity of the solvent. Consequently, large values of the reorganization energy in coumarin and safranineT dyes with ZnO semiconductor indicate that ZnO is more reactive towards safranineT and coumarin than TiO2 semiconductor. References 1­ Neil, A.A.and Tinuan, L. (2005), Annu. Rev .Phys .Chem , 56:491–519 . 2­ Hirendra,N.G. (2001), Barc.news letter.founders dye special.issue, 94–100. 3­ Tulie, M.R.; George,L. M.; Yutaka. N.; Keitaro, Y.; Jacques, M . and Michal, G., (1996), J. Phys. Chem, 100: 9577–9578. 4­ Horng, M. L.; Dahl, K.; Jones, G. Maroncelli, (1999), Chem. Phys. lett . ,315: 363–370. 5­ Kim, A.S. (1998) , Biophysical Journal, 73: 1241–1250. 6­ Al_Agealy ,H. (2004)″Quantum mechanical model for electron transfer in Q–switched dye used for solid state lasers″ Ph.D Thesis, Baghdad university . 7­ Nalin,L.A. (2001)″ Electron transfer in ruthenium–Manganese complexes for artificial photosynthesis″ Ph. D.thesis, Acta university Uppsala. 8­ Mikael Anderson (2002) ″Tanning electron transfer assemblies″ Ph. D Thesis, Acta university, Uppsala, IHJPAS IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 9­ Miche, J. (2003)″Electron transfer in blue copper proteins″ Ph. D. Thesis, Caltech university. 10­ Marcus, R.A. and Sutin,N.(1985), Biochim. Biophys. Acta, 84,265. 11­ Wachsmanu, Hogeu (2000), ″ Vibronic coupling and ultrafast electron transfer studied by picsecond time resolved resonance Raman and cors spectroscopy″ Ph. D, university at Humboldt, Berlin, 12­ Kuciunskas , and Micheal.S . (2001), J. Phys. Chem. B, 105, No 2. 13­ Renne, M.W. (1996)″ Falorences electron transfer accepting component in super molecular and covalently liked electron transfer system ″ Ph. D. thesis. Amsterdam university, Amsterdam. 14­ Krishna, K.; Velmurgan, D.; Shanmuga, S. ;Sundara Raj.; Fun, H.K.;Sundaram, M.S. Raghunathan, R. (2001), Cryst. Res. Technol , 36: 1289–1294. 15­ Zaghbani,N. ;Hafiane,A. Dhahi,M.( 2008), Desalination, 222:348–356. 16­ Ernst, W. Filck,( 1998), ″Industrial Solvent Handbook ″, Fifth edition, New Jeresy, U.S.A. Table (1): The reorganization energies value for donor safranineT dye and acceptor semiconductor TiO2 and ZnO Solvent Chemical Formula  [16] n [16] λ(eV) for TiO2 λ(eV) for ZnO Water H2O 80 1.333 0.6798942561 0.7410583182 1­propanol C3H8O 20.33 1.3856 0.5795911754 0.6357856215 Formamide HCONH2 111 1.4475 0.5978483206 0.65367811001 Acetonitrile C2H3N 37.5 1.3441 0.6480338344 0.7080101686 Ethanol C2H6O 24.5 1.3614 0.6116580688 o.6697502622 IHJPAS IBN AL- HAITHAM J. FO R PURE & APPL. SC I. VO L.23 (3) 2010 Table (2): The reorganization energies value for donor coumarin dye and acceptor semiconductor TiO2 and ZnO Fig. (1):Energy surface and kinetic parameters for an electron transfer reaction, G is the free energy ,  is the reorganization energy [7] Solvent Chemical Formula  [16] n [16] λ(eV) for TiO2 λ(eV) for ZnO Water H2O 80 1.333 o.6545818996 0.7139673890 1­propanol C3H8O 20.33 1.3856 0.5579871463 0.6125475297 Formamide HCONH2 111 1.4475 0.5757477988 0.6299473232 Acetonitrile C2H3N 37.5 1.3441 0.6238838374 0.6821161364 Ethanol C2H6O 24.5 1.3614 0.5888491116 0.6452520583 D A Reactant Surface D+ A– Energy Product G  Surface G Reaction coordinate IHJPAS IHJPAS