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 ایثانول ، 708.0اسیتونترایل ، 741.0للماء( كبیرة للمذیبات ذات القطبیة العالیة) موصل هشب_صبغة(لنظام 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 o n The Reorganization Energies of Dye - Semiconductor System Interface H.J.M.Al-Agealy, M.A.Hassooni Departme nt of Physics, College of Education Ibn-AL-Haitham, Unive rsity of Baghdad Abstract A theoretical calculation of the reorganization energies is demonst rated for semiconductor (TiO₂, ZnO) and organic dy e (safranine T, and coumarin) with a variety solvent such that (water, 1­p rop anol, Formamide, Acetonitrile and Ethanol). The reorganization energy values for dy e –semiconductor interface sy st em are large in high p olar solvent (water 741.0 , Acetonitrile 708.0 , Ethanol 669.0 ) and small in low p olar solvent(1­p rop anol 635.0 . The reorganization energy in safranine T –semiconductor sy st em is larger ( 635741.0  )than in coumarin –semiconductor for with the same solvents ( 612.0731.0  ), this indicates that safranine T dy e one more electron transfer reactive towards semiconductor. Introduction Electron transfer ( ET) between molecular adsorbaies and semiconductor h as been a subject of intense resear ch interests for many y ears [1]. The understanding of this fundamental p rocess is essential for the app lication of semiconductor in p hotography , solar energy comersion, wase degr adation, and nano_scale d evices [2]. One of these examples is the electron transfer between dy es and semiconductor p lay s a vital role in silver h alide p hotography , electrop hotography , and more recently in solar ener gy cell [3]. Since the seminal work p redictin g solvent dy namical control of electron transfer reactions in the early 1980s, a great deal of theoretical effort has gone into clarify ing the salvation dy namics electron transfer connection [4]. Consequently , there is a great interest in understanding how the p hy sical p rop erties control the direction and rate of electron transfer. The key factor controlling the rate of electron transfer, is the reorganization ener gy , which describes the ener gy necessary to distort the nuclear configur ation from its equilibrium donor st ate to the acceptor state without transfer of an electron. M any theories were used to calculate the reor ganization 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 r esearch to calculate the reor ganization ener gies in dy e _semiconductor sy stem for different solvents [5]. In this p aper we can use the continuum solvent model to calculate the reorganization ener gy for safranine T dy e_TiO₂, ZnO and coumarin dy e _ TiO₂, ZnO. Theory The standard M arcus diagr am describ es the energy surface of the donor (reactant) and accep tor (p roduct) states as a function of the nuclear configuration coordinate [5]. Accordin g to the M arcus cross relation the reorganization ener gy ,  , is defined as the ener gy necessary to distort the nuclear configur ation from its equilibrium donor st ate to the acceptor [6]. In figur e (1) the G is the activation ener gy , G is the free energy ,  is the reorganization ener gy .This reorganization ener gy can be broken down further into inner and outer sp here comp onents [7,8]. outin   ……………… (1) The inner sp here reorganization component ( in ) is the intra molecular or inner she ll is the ener gy required to alter bond distances and bond angles with the change in o xidation st ate. The sp here reorganization out is the energy required for reorientation of the solvent around the chan ged co mplexes [9]. The solvent indep endent term in arises from st ructural differences between the equilibrium configurations of the reactant and product states; this is the sum of all the molecular v ibrational and rotational movements [8].In t he harmonic ap p roximation, it can writt en 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 equilibr ium bond lengths in the reactant and p roduct st ates, resp ectively, and the sum is taken over all active intra molecular. Vibration which are p art to the reaction coordinate. The solvent dependent outer term out is called solvent reorganization ener gy and arises from differences between the orientation and p olarization 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 p roduct, but neglectin g the additional effects due to electron transfer [11]. By treating the solvent as a dielectric continuum the following exp ression 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 p ermittivity ,  is the st atic dielectric constant of solvent, is the refractive index of the solvent, nsc is the refractive index of the semiconductor,  sc dielectric constant of t he semiconductor,D is the radius of the molecular dy e, and R is the dist ance between the comp lex and the se miconductor , and q is the char ge of electron. T he radius of the dye molecu le can be evalu ated from the app arent molar volumes using sp herical app roach [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 ener gies for the sy st ems safranine T­ TiO2, safranine T­ ZnO, coumarin­TiO2, coumarin­ZnO theoretically using the equation (3), one must initially evaluate the v alues of the radii for both dy es safranine T and coumarin fro m equation (4),resp ectively. Inserting of molecular we ight 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 resp ectively, the values of radii are saD =4.47820 A°, and coD =4.64227 A°. Inserting the value of dielectric constant  and refractive ind ex n for variety solvent, and the dielectric constant  sc and refractive index nsc for semiconductor in equation (3), with value of radius of dy e and the distance between the molecule dy e and semiconductor R ,the results have been summar ized in Tables(1)and (2). Discussion For both sy stems (safranine T– semiconductor) and (coumarin– se miconductor), the solvent reorganization ener gy values, λ are calcu lated according to the dielectric continuum models for electron transfer reactions. The value of reorganization ener gy for (safranine T­ZnO) system is lar ger than that of the (safran ine T ­TiO2) sy stem with the same solvent. Also the value of reorganization ener gy for coumarin –ZnO sy stem is lar ger than that of the coumarin –TiO2 system with the same solvent. Since safranin eT­semiconductor and coumarin­ semiconductor system with water solvent p ossesses is a more r eorganization ener gy than the other solvent. Not ably , from Table (1) and Table (2) the dy namic of the reor ganization 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 p olar solvent compared with higher than p olar solvent for the both sy stems (safranine T­semiconductor) and (coumarin­ semiconductor ) alternatively. Formamide, one of the p olar solvent ( =111)gives sm all reorganization ener gies for both sy stem comp are with other solvents that have less  , this indicates that formamid e have lar ge refractive index n =1.4475 in comparison with other solvents .The reorganization energies in safranin e T –semiconductor is lar ger than in the coumarin­ semiconductor system with the same solvent, this indicate that the reorganization ener gy is dep ending on the radius of the dy e 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 p robable in safranin eT ­semiconductor sy stem than coumarin­ semiconductor with the same solvents. Notably , the electron transfer in safranineT –ZnO and coumarin –ZnO sy stem are st ronger than in safranin eT –TiO2 and coumarin –TiO2 sy stem with the same solvent Conclusions In summary , it can be concluded fro m the p resent results that the reaction of electron transfer st rongly depends on the solvents p olarity . For high p olar solvents, the values of the reorganization ener gies are lar ge and small for low p olar solv ents, this indicates that, the reorganization energies depend on the p olarity of the solvent. Consequently , large values of the reorganization energy in coumarin and safranineT dy es with ZnO semiconductor indicate that ZnO is more reactive towards safranineT and coumarin than TiO2 semiconductor. Re ferences 1­ Neil, A.A.and Tinuan, L. (2005), Annu. Rev .Phy s .Chem , 56:491–519 . 2­ Hirendra,N.G. (2001), Barc.news lett er.founders dy e sp ecial.issue, 94–100. 3­ Tulie, M .R.; George,L. M .; Yutaka. N.; Keitaro, Y.; Jacques, M . and M ichal, G., (1996), J. Phys. Chem, 100: 9577–9578. 4­ Horng, M . L.; Dahl, K.; Jones, G. M aroncelli, (1999), Ch em. Phy s. lett . ,315: 363–370. 5­ Kim, A.S. (1998) , Biophy sical Journal, 73: 1241–1250. 6­ Al_Agealy ,H. (2004)″Quantum mechanical model for electron transfer in Q–switched dy e used for solid state lasers″ Ph.D Thesis, Baghdad univ ersity . 7­ Nalin,L.A. (2001)″ Electron transfer in ruthenium–M anganese comp lexes for artificial p hotosy nthesis″ Ph. D.thesis, Acta university Upp sala. 8­ M ikael 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 M iche, J. (2003)″Electron transfer in b lue copp er p roteins″ Ph. D. Thesis, Caltech university . 10­ M arcus, R.A. and Sutin,N.(1985), Biochim. Biophys. Acta, 84,265. 11­ Wachsmanu, Ho geu (2000), ″ Vibronic couplin g and ultrafast electron transfer st udied by p icsecond time resolved resonance Raman and cors sp ectroscopy ″ Ph. D, university at Humboldt, Berlin, 12­ Kuciunskas , and M icheal.S . (2001), J. Phy s. Chem. B, 105, No 2. 13­ Renne, M .W. (1996)″ Falorences electron transfer accepting component in sup er molecular and covalently liked electron transfer sy stem ″ Ph. D. thesis. Amst erdam university , Amsterdam. 14­ Krishna, K.; Velmur gan, D.; Sh anmu ga, S. ;Sund ara R aj.; Fun, H.K.;Sundaram, M .S. Raghun athan, R. (2001), Cry st. Res. Technol , 36: 1289–1294. 15­ Zaghbani,N. ;Haf iane,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 safrani neT dye and acceptor se miconductor TiO 2 and ZnO S olvent Chemical Formul a  [16] n [16] λ(eV) for TiO 2 λ(eV) for ZnO Water H2O 80 1.333 0.6798942561 0.7410583182 1­p rop anol 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 TiO 2 and ZnO Fig. (1):Ene rgy surface and kine tic paramete rs for an electron transfer reaction, G is the free ene rgy ,  is the reorganizati on ene rgy [7] S olvent Chemical Formul a  [16] n [16] λ(eV) for TiO 2 λ(eV) for ZnO Water H2O 80 1.333 o.6545818996 0.7139673890 1­p rop anol 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 – En ergy Produ ct G  Surface G Reaction coor dinat e IHJPAS IHJPAS