Issuu on Google+

Modulation of Intramolecular Charge Transfer via Aryl Substituent for the nonclassical C62 Derivatives KAN, Yu-He*

LI, Qiang

(Department of Chemistry, Huaiyin Teachers College, Jiangsu Province Key Laboratory for Chemistry of Low-Dimensional Materials, Huaian 223300) Abstract In this study, we demonstrate the modulation of intra-molecular charge transfer from aryl substituent to C62, by employing density functional theory (DFT) calculation. C62 and its three Aryl derivatives have been calculated by using density functional theory and time-department density functional theory (TDDFT).The geometries are determined by DFT with TZP basis sets. TDDFT calculated the transition energies and corresponding oscillator strengths by LB and SAOP at TZP level, together with B3LYP/6-31G*. Results show that modulation of energy levels should be achievable by variation or addition of substituents with different characters while electronic accepting ability must be taken into account. Sequentially, intramolecular charge transfer can be modulated by variation or addition of substituents with different characters. This study imply the potencial application of C62 and its derivatives in semiconductor materials and providing a theory guidance on materials-design.

1. Introduction Fullerenes, since its discovering[1], led to a plethora of unprecedented new molecular structures and shapes that are continuously investigated for their fundamental physicochemical properties and their reactivity, as well as for applications in advanced materials[2-4]. All fullerenes characterized so far obey the classical definition: a fullerene is a carbon cage Cn in the form of a trivalent polyhedron with exactly 12 pentagonal and (n/2-10) hexagonal faces[5]. But that is not mean fullerene only contain pentagonal and hexagonal, novel frameworks such as those incorporating four-membered rings also be proved to be stable[6], and structural change can be expected to give rise to unusual physical and chemical properties[7]. Primitively, The energetic cost of introducing square faces to fullerenes with adjacent pentagons is investigated theoretically[5]. Then, various isomers of C62 were studied by six different levels of theory[8]. Recently, synthesis of C62 with one four-membered ring had been reported, and its derivatives (a-c)2-C62 (a=4-Me-C6H4, b=2-Py, and c=3,5-(MeO)2C6H3) also were successfully synthesized[9,10]. Lu et al.[6] studied the electronic properties of (4-Me–C6H4)2-C62, H2-C62, and F2-C62 using density functional theory, and possibility of synthesizing H2-C62 and F2-C62 using frontier orbital theory. Feng et al.[11] studied the stability of C62 isomers at high temperature, and the second-order hyperpolarizabilities of the five most stable isomers of C62 were predicted to be larger than those of C60. Hou et al.[12] devoted to the theoretical understanding of the dimerization of C62, H2-C62 and F2-C62. From the previous investigations on fullerene C60 derivatives, C60 has been revealed as a very attractive electron acceptor with unique photophysical and electrochemical properties[13,14]. As one of the nearest family members of C60, C62 was expected to have richer photophysical and photochemical properities. Thus, a detail of geometry and optical absorption properties of C62 and its derivatives (a-c)2-C62 (a=4-Me-C6H4, b=2-Py, and c=3, 5-(MeO)2C6H3) were taken out. With the ultimate aim of provising a theory guisance for molecular design of novel and special


semiconductor materials, in this paper we investigated the electronic spectra affected by variation of substituents using TDDFT[15,16].

2. Theoretical Methods The geometrical optimizations of C62 and its three derivatives 1-3 carried out at TZP level using DFT method. Local density approximation (LDA) was used with VWN parameterization while Becke-Perdew (BP) no local corrections were used for the exchange and correlation energy. Then, these minimum energy structures were used for TDDFT, where the local density approximation was used the Van Leeuwen-Baerends potential (LB94)[17] and model SAOP[18], using TZP basis set to study the absorption properties. Calculations were performed with ADF2006.01[19,20] suit of program. A confirmaion was also taken out at B3LYP/6-31G* by gaussian 03. AEA[21,22] calculations were applied to examine the electronic accepting ability of C62 and compound 1-3 at B3LYP/6-31G(d) level.

3. Results and Discussion 3.1 Geometry Structure The optimization geometry structures of C62 and its derivatives 1-3 are present in Figure 1, some theoretical parameters calculated by DFT method are list in Table 1 correspondingly.

C62

1

2

3

Figure 1: Optimization structure of C62 and compound 1-3 calculated by BP/TZP

C62 was thought to be interesting because of its relationship to the icosahedra C60 cage(1), and there is a obvious bulgy square surrounded by four six-membered ring in C62 comparing with C60. The perfect symmetry of Ih point group of C60 was destroyed by adding the double bond and substituents. The compound 1 was selected as an example because it has been measured experimentally, as mentioned previously, and there are former calculations for the same structure.[6,10] It was found that parameters calculated by using TZP basis set are in good agreement with experiment values provided by X-ray diffraction measurement. So the following discussions about the electronic structures and electronic absorption spectra are based on the geometry obtained at TZP level. As can be seen from Table 1, C1-C2 bond length increase while C3-C4 decrease, and C1-C4, C2-C3 bond length increase correspondingly comparing with C62. The bond angles in the four-membered ring also changed more or less, the rectangle was pulled to be a trapezoid. Pyramidalization angle[23] of C1 in compound 1 25.6째 increase by ~7.7째 comparing with C62, indicated the four-membered ring became more bulgier. There are four isomeric compounds of compound 2, and this trans- form structure (Figure 1) was selected because it had the lowest


energy[24]. Compared compound 2 and 3 with C62, we found similar results. It seems that slightly change be generated by variation of substituents. Table 1: Selected bond lengths、bond angles and Pyramidalization angles of C62 compound 1-3 calculated by BP/TZP

C62 Bond length (Å) C1-C2 C1-C4 C2-C3 C3-C4 C2-C11 C3-C8 Bond angles (°) ∠C1-C2-C3 ∠C4-C1-C2 ∠C3-C4-C1 Pyramidalization angles (°) C1 a

[9]

b

1.429 (0.1436)a;(0.145)b 1.460 (0.1479);(0.148) 1.460(0.1479); (0.148) 1.429 (0.1436);(0.145) 1.379 (0.1388) 1.379

1

2

3

1.645(1.667)c 1.491(1.526) 1.491(1.530) 1.378(1.389) 1.487(1.489) 1.393

1.627 1.490 1.488 1.379 1.484 1.390

1.641 1.490 1.490 1.377 1.485 1.392

84.9(84.8) 84.9(84.8) 95.1(95.3)

85.3 85.2 94.7

84.9 84.9 95.1

25.6

25.2

25.5

90.0 90.0 90.0 17.9(17.9)C [6] c

[10]

B3LYP/6-31G* ; Obtained from BLYP/DNP ; crystal structure reference

3.2 Molecular orbitals and energy levels. Molecular orbitals play a major role in spectrum especially the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The calculated isosurfaces of the HOMO and LUMO for C62 and compound 1-3 are shown in Figure 2. Figure 3 displays energy levels of C62 and compound 1-3. C62

1

2

LUMO

HOMO

Figure 2: The HOMO and LUMO of C62 and compound 1-3 calculated by SAOP/TZP

3


From figure 2, we see the HOMO of C62 is delocalized over the C62 molecule, similarly, C62 fragment contribute mostly to the HOMO of compound 1 and 2 while benzyls or pyridines have a little contribution in compound 1 and 2, as well as LUMO. Here, an obvious difference was found comparing with compound 3. The HOMO of compound 3, that has the highest energy (-9.098 eV), is localized on the aryl ligands, and the LUMO is delocalized over the C62 fragment. Thus, a prominent charge-separate state appear clearly. The intermolecular donor-acceptor system gives rise to unusual physical and chemical properties. Furthermore, the deravatives of C62 reveal its potential applications in photovotalic materials. Molecule-design should be possible for frontier orbitals affected evidently by diversities of substituents. Unlike C60[25], the degeneracy energy levels split, result in the energy gap (ΔEHOMO-LUMO) between HOMO and LUMO of C62 obviously decreased, induce C62 not to be energetically favorable. Compound 1-3 show some improvement as theΔEHOMO-LUMO are wider than C62. To investigate the variation of energy levels by dfferent substituented aryl groups and the role that the squre plays, the hybrid systems of 1-3 were separated into three parts: aryls as one, the square as another, and leftovers as the last(C58). The composition of different parts of 20 forntier orbitals are listed in table 2. From table 2, we see the square has a less distinct contribution to the frontier orbitals. Distinct changes of frontier orbitals would be generated by joined substituents comparing with C62 and its derivatives. In higher occupied MOs of compound 1-3, compound 3 reveals its particularity while compound 1 and 2 show some friendliness. Two sets of two quasi degenerate orbitals (HOMO-1 and HOMO-2, HOMO-3 and HOMO-4) are both found in compound 1 and 2. In lower unoccupied MOs of compound 1-3, these three derivatives list some consistency. As shown in Figure 3, with aryls addition, the LUMO levels of the derivatives of C62 are indeed raised with respect to C62. A set of two quasi degenerete orbitals was found in all the three derivatives, followed with a noticeable energy gap between LUMO+1 and LUMO+2. In sum, it can be proposed that both benzyls and pyridines plays a key role for adjusting the level of HOMO-LUMO to improve the efficiency of the photoelectric conversion[22]. Modulation of energy levels should be achievable by variation or addition of substituents with different characters.

-5 -6

Energy (eV)

-7 -8 -9

0.86

1.43

1.46

1.27

1

2

3

-10 -11 -12

C62

Figure 3: Energy levels of C62, compound 1-3 calculated by SAOP/TZP


Table 2: Composition of frontier orbitals of compounds 1-3 (a-c) at Saop/TZP lever MO L+9 L+8 L+7 L+6 L+5 L+4 L+3 L+2 L+1 LUMO HOMO H-1 H-2 H-3 H-4 H-5 H-6 H-7 H-8 H-9

E(eV)

square

a

b

c

-5.89 -5.90 -5.94 -6.45 -6.77 -6.88 -7.05 -7.84 -7.88 -7.97 -9.40 -9.59 -9.62 -9.77 -9.80 -9.99 -10.04 -10.24 -10.41 -10.52

-5.87 -5.92 -6.17 -6.42 -6.74 -6.84 -7.00 -7.80 -7.84 -7.93 -9.39 -9.55 -9.58 -9.74 -9.77 -10.28 -10.37 -10.43 -10.50 -10.68

-5.75 -5.77 -5.80 -6.30 -6.63 -6.74 -6.91 -7.71 -7.75 -7.83 -9.10 -9.30 -9.40 -9.47 -9.49 -9.65 -9.68 -9.91 -9.95 -10.27

a 1.2 6.2 7.2 8.3 0.9 9.4 8.2 2.5 0.3 10.2 2.0 6.1 0.4 3.3 10.5 8.3 2.9 0.1 13.2 1.1

b 1.0 6.9 3.7 7.2 8.5 1.1 8.7 7.9 2.6 0.3 2.5 6.8 0.6 3.5 9.5 12.8 3.3 3.9 2.8 6.4

Aryl c 5.5 1.2 4.7 7.2 8.5 0.9 9.1 8.1 2.5 0.3 0.3 2.0 0.6 5.7 0.5 3.2 10.4 6.7 2.1 14.0

a 1.1 0.3 1.0 1.7 1.8 1.7 0.4 1.3 1.2 0.1 8.6 2.0 0.1 5.4 13.2 69.8 75.6 98.1 12.2 95.1

b 17.4 21.2 90.4 6.3 3.2 2.4 0.6 1.2 1.2 0.1 2.7 2.0 0.2 2.6 2.6 32.4 82.6 37.8 44.5 77.3

C58 c 0.9 0.3 0.5 1.5 1.7 1.5 0.4 1.2 1.3 0.1 89.0 15.7 90.8 9.4 0.1 3.8 5.7 81.3 82.6 8.4

a 94.8 98.5 92.8 91.1 89.9 97.4 90.2 90.5 96.2 99.6 89.4 91.9 99.4 91.3 76.3 21.9 21.4 1.8 74.5 3.9

b 81.6 71.9 5.9 86.5 88.3 96.5 90.8 90.9 96.1 99.6 94.8 91.1 99.2 93.9 87.9 54.8 14.1 58.3 52.7 16.3

c 93.6 98.5 94.8 91.3 89.8 97.6 90.5 90.7 96.2 99.6 10.8 82.3 8.5 85.0 99.4 93.0 83.9 12.0 15.3 77.7

3.3 Adiabatic Electron Affinity As we discussed above, the charge seprate state of compound 3 reveals that C62, the nearest family members of C60, can also act as an electronic acceptor. In addition, the electronic accepting ability can be examined by adiabatic electron affinity (AEA)[21,22]. Sequentially, the first AEA for C62 and its derivatives are determibed by B3LYP/6-31G(d). The results show that C62 (78.45 kcal/mol) has a better electronic accepting ability than C60 (48.28 kcal/mol). The derivatization has an inevitable effect on the electronic accepting ability of C62, espectially the one combined with an electron donor. The calculated first AEA of compound 1-3 is 67.25、66.14 and 64.93 kcal/mol respectively. That remind us that electronic accepting ability must be taken into account when modulate energy levels.

3.4 Electronic absorption spectrum TDDFT[26,27] show a good description of prediction of dipole allowed transitions for fullerene and its derivatives. The calculated transition energies and their oscillator strengths by LB and SAOP at TZP level,together with experimental absorption spectra values of compound 1,are list in Table 3. In comparisons between experimental and theatrical parameters, it is found that calculated parameter are in good agreement with experimental values especially by SAOP. Electronic absorption spectra of C62 and compound 1-3 calculated by SAOP are shown in Figure 4. Mainly molecular orbital diagram related with correlative excitation transition states of compound 1-3 are depicted in Figure 5. C62 reveals richer charicters of absorption bands than C60 above 400 nm. The electronic absorption spectrum of C62 shows absorption peaks at 697nm,554 nm,430 nm and 406 nm respectively. The


transition from S0 to S1 is mainly associated with transition from the HOMO to the LUMO (99﹪),the oscillator strength is zero because the HOMO is not adapted in symmetry to LUMO, and such electronic transition is forbidden. The lowest singlet transition for compound 1-3 are dipole-allowed, compound 1 occurs at 825 nm and compound 2 occurs at 815 nm while compound 3 occurs at 974 nm, this low excitation energy of CT excited state derive from self-interaction error lies in the orbital energies of the DFT calculation[28,29]. The absorption band of compound 1 at 750 nm mainly ascribed to HOMO→LUMO+2, followed at higher energy by an intense HOMO-6→LUMO+2 transition at 550 nm, correspond to the experimental values (705 nm and 535 nm respectively) extremely well, with still a absorption band calculated around 480-400 nm (not given by experiment, and the corresponding transitions are list in Table 3). The most intense absoption band around 370 nm should be out of the question. LUMO+2, delocalized over the C62 fragment, contribute both transitions occurs at 750 nm and 550 nm. Both HOMO and HOMO-10 are mostly contributed by C62 fragment while ligands have very little composition. Whereas, the HOMO-6 orbital is mainly localized on the ligands. Hence, the absorption at 750 nm can be assigned as intermolecular charge transfer (ICT) in C62 fragment while the absorption at 550 nm can be assigned as charge transfer from ligands to parent C62 (L-C62CT) , and the band rang from 426 to 482 nm can be assigned as mixed CT while ICT in C62 in the majority. The friendship between compound 1 and 2 shown in electronic structures has broken up while comparing the electronic spectra of them. The absoption band rang from 637 to 749 nm in compound 2 mostly ascribed to three ICT states-S0→S3, S0→S7 and S0→S11. The peaks at 490 nm and 424 nm are mainly contributed to HOMO-5→LUMO+2, HOMO-9→LUMO+2 respectively (other transitions contribute to these absorption bands are list in Table 2), corresponds to L-C62CT and ICT in C62 fragment. 12000

abs. (1/mol cm)

9000

C62

1

2

3

6000 3000 12000 0 9000 6000 3000 0 450

600

750

450

600

750

wavelength (nm) Figure 4: Electronic absorption spectra of C62 and compound 1-3 calculated by SAOP/TZP The absorption spectra of the investigated compound 3 show similar features to compound 1. Both of them maintain the absorption bands around 400-440 nm of C62 that mostly derive from inner electron


transition of C62, 400-480 nm in compound 1 and 400-470 nm in compound 3 respectively. Other from compound 1, the absorption at 738 nm transition in compound 3, which is mainly associated with transition from the HOMO-2 to the LUMO+4 and HOMO-1 to LUMO+2 (67% and 21% respectively), can be assigned as having L-C62CT of mixing with ICT in C62 fragment. It’s noteworthy that the methoxyphenyls have absolute dominant role of HOMO-2 (91%). The participation of substituents lead a larger oscillator strength than the transition occurs at 755 nm in compound 1. Thereafter, absorption wavelength and absorption strength can be modulated by variation or addition of substituents with different characters, e.g. the ability of electron withdrawing. The results imply the potential application in optical materials of derivatives of C62.


Figure 5: Mainly molecular orbital diagram related with correlative excitation transition states of compound 1 (a), 2 (b) and 3 (c) Table 3: Selected TD-DFT Calculated Low-Lying Singlet Excitation Energies (eV) for C62 and its derivatives 1-3

State C62

1

λ/nm

1A'' 1A' 1B' 2B'

1264.1 697.6 554.0 440.2

1B''

430.4

2B'' 2A'

406.5 398.3

1 2

825.4 754.9

3

685.3

Composition (%) 99(47b''→46b') 84(47b''→48b'') 86(47b''→40a'') 36(55a'→47b') 30(46b''→40a'') 12(54a'→46b') 12(43b'→56a') 34(36a''→46b') 23(45b''→56a') 13(47b''→57a') 12(37a''→46b') 67(45b''→56a') 38(53a'→56a') 35(46b''→49b'') 98(H-0→L+0) 76(H-0→L+2) 15(H-0→L+1) 67(H-1→L+1) 19(H-2→L+2)

Transition energy LB 0.95(0.0000) 1.73(0.0127) 2.15(0.0133) 2.73(0.0122)

SAOP 0.98(0.0000) 1.78(0.0141) 2.24(0.0140) 2.82(0.0135)

2.8(0.0207)

2.88(0.0210)

2.97(0.0220) 3.03(0.0190)

3.05(0.0237) 3.11(0.0197)

1.46(0.0013) 1.60(0.0056)

1.50(0.0012) 1.64(0.0081)

1.75(0.0043)

1.81(0.0034)

Exp

ICT ICT ICT ICT ICT

705


4 5 6

553.6 480.3 455.3

7

423.5

8

378.7

9

2

3

369.4

10

367.8

11

366.1

1 2 3

814.9 743.3 636.7

4 5 6

499.4 490.2 467.2

7

454.9

8 9

436.2 424.3

1

973.7 738.3

2 3 4 5 6

542.9 480.4 463.3 424.9

7

374.5

8

367.5

9 10

364.0 350.5

11

349.2

97(H-6→L+2) 79(H-8→L+1) 68(H-0→L+5) 15(H-10→L+2) 30(H-10→L+2) 13(H-15→L+0) 35(H-17→L+0) 21(H-6→L+5) 12(H-15→L+1) 28(H-3→L+6) 13(H-7→L+4) 57(H-17→L+1) 21(H-17→L+0) 42(H-4→L+6)

2.21(0.0224) 2.58(0.0045) 2.78(0.0025)

2.24(0.024) 2.58(0.0082) 2.72(0.010)

2.82(0.0204)

2.93(0.018)

97(H-0→L+0) 80(H-0→L+2) 73(H-4→L+0) 14(H-4→L+0) 90(H-5→L+1) 80(H-5→L+2) 39(H-7→L+2) 24(H-1→L+3) 22(H-8→L+1) 12(H-8→L+2) 10(H-0→L+4) 55(H-2→L+5) 44(H-9→L+2)

1.49(0.0001) 1.63(0.0020) 1.85(0.0025)

1.52(0.001) 1.67(0.0021) 1.95(0.0022)

2.28(0.0045) 2.33(0.0158) 2.60(0.0048)

2.48(0.0064) 2.53(0.0065) 2.65(0.0061)

ICT/L-C62CT ICT/L-C62CT ICT/L-C62CT

2.74(0.0047)

2.73(0.0064)

ICT/L-C62CT ICT/L-C62CT

2.78(0.0067) 2.91(0.0045)

2.84(0.0073) 2.92(0.0209)

99(H-0→L+0) 52(H-1→L+2) 26(H-2→L+1) 97(H-8→L+2) 82(H-9→L+1) 76(H-2→L+4) 21(H-10→L+2) 15(H-15→L+0) 11(H-5→L+3) 31(H-17→L+0) 26(H-0→L+17) 17(H-5→L+6) 14(H-17→L+2) 40(H-6→L+6) 28(H-6→L+6) 20(H-1→L+9) 19(H-1→L+7)

1.27(0.0001) 1.67(0.0170)

1.27(0.0001) 1.68(0.011)

3.27(0.024)

L-C62CT

ICT ICT ICT ICT ICT ICT L-C62CT

3.36(0.033)

ICT ICT L-C62CT

3.37(0.013) 3.39(0.016)

ICT ICT ICT ICT ICT ICT ICT

ICT

2.28(0.0318) 2.58(0.0080) 2.68(0.0144) 2.70(0.0081)

2.28(0.028) 2.56(0.0095) 2.68(0.014) 2.92(0.022)

3.31(0.019) 3.37(0.027) 3.41(0.023) 3.54(0.039) 3.55(0.050)

ICT ICT L-C62CT L-C62CT

ICT L-C62CT L-C62CT

ICT L-C62CT

ICT ICT ICT ICT ICT ICT ICT ICT ICT ICT ICT

535


Additionally, to constrast with methods and to make further efforts to investigate the process of charge transfer of the D-A system, we applied Becke’s hybrid-functional B3-LYP and the 6-31G* basis set for TDDFT calculation of compound 1 and 3 at the BP/TZP geometry. The calculated transition energies and their oscillator strengths of compound 1 and 3 are list in Table 4, together with corresponding electronic spectra shown in Figure 6. The results indicate similar characteristic absoption bands and corresponding transitional states in spite of some unavoidable differeneces. In order to indentify charge tranfer states of compound 3, we plot the charge difference density (CDD)[30,31] which is illustrative and detailed of the excited states. The CDD of S1, S8, S20 are shown in Figure 6, as well as main molecular orbital diagram related with correlative excitation transition states. Consistent with SAOP/TZP, the first singlet excited state, the electron delocalized over the whole molecule while the hole localized on C62 fragment. It interpret the S1 can be assigned as having L-C62CT of mixing with ICT. Simulaniously, S8 and S20 are assigned as ICT and L-C62CT respectively. What’s more, the CDD of compound 3 confirms that the charge tranfer from the substituents to C62 do exist, and show evident electronic coupling between the substituents and the C62 core.

abs. (1 / mol cm)

12000

9000

a

c

6000

3000

0 400

500

600

700

400

500

600

700

wavelength (nm) Figure 6: Optical absorption spectra compound 1(a) and 3(c) calculated by B3LYP/6-31G* Table 4: Selected TD-DFT Calculated Low-Lying Singlet Excitation Energies (eV) for Compound 1 and 3 by B3LYP/6-31G*

λ/nm 661.5 598.5 560.7 520.0 414.7 403.8

1 Composition (%) H-0→L+0 (93) H-0→L+2 (61) H-1→L+0 (25) H-1→L+1 (58) H-2→L+2 (22) H-4→L+0 (60) H-4→L+1 (29) H-5→L+1 (55) H-0→L+3 (13) H-6→L+2 (56) H-5→L+1 (19)

Transition energy

λ/nm

1.87(0.0017) 2.07(0.0036)

664.4 600.1

2.21(0.0055) 562.2 2.38(0.0036) 518.4 2.99(0.0031) 478.7 3.07(0.0260) 396.8

3 Composition (%) H-0→L+0 (79) H-1→L+0 (14) H-2→L+0 (48) H-0→L+2 (37) H-2→L+1 (58) H-3→L+2 (20) H-6→L+0 (53) H-6→L+1 (23) H-4→L+1 (84) H-6→L+1 (12) H-9→L+0 (28)

Transition energy 1.87(0.0017) 2.07(0.0029) 2.21(0.0055) 2.39(0.0030) 2.59(0.0101) 3.12(0.0074)


395.5

385.5

H-6→L+2 (26) H-7→L+1 (26) H-2→L+3 (21) H-7→L+2 (49) H-5→L+2 (11)

3.14(0.0250) 396.4 3.22(0.0159)

H-7→L+0 (26) H-3→L+3 (24) H-8→L+2 (26) H-9→L+0 (23) H-7→L+1 (20)

3.13(0.0128)

1.87 eV (0.0017)

HOMO

LUMO

CDD (S1)

LUMO+1

CDD (S8)

LUMO+1

CDD (S20)

2.21 eV (0.0055)

HOMO-2

2.59 eV (0.0101)

HOMO-4

Figure2-7: CDD (red = hole; blue = electron) of the 1, 8, 20 singlet-excited states and main molecular orbital diagram related with correlative excitation transition states for compound 3

4. Conclusion In conclusion, the geometries of C62 and its derivates compound 1-3 have been determined and the geometrical parameters calculated at BP/TZP level have been show in good agreements with the observed ones. The slightly variation of the geometry of compound 1-3 seems insignificant and neglectable. The small energy gap indicated that C62 has higher reactivity than C60, but compound 1-3 show stable chemical characteristic. The electronic structure has changed a lot of compound 1 espectially unoccupied orbitals cpmparing with C62, similar with compound 2. It’s noteworthy that the benzyl and pyridine as a functional group plays an important role for raising the LUMO level of C62 for an excellent photovoltaic performance.


A prominent charge separate state was found in compound 3, that demonstrate that C62 can be a favorable electron acceptor and its potencial application in photovalic materils which confirmed by AEA calculations. The results indicate modulation of energy levels should be achievable by variation or addition of substituents with different characters while electronic accepting ability must be taken into account. TDDFT calculations suggest that optical absorption spectra of C62 show richer feature than C60 because of absorption in the visible region with considerable oscillator strength. The calculated parameters of compound 1 are in good agreement with experimental values especially by SAOP at TZP level. The absorption bands around 750 nm and 740 nm which ascribed to ICT of compound 1 and 2 are weaker while compound 3 has an intense one around 740 nm, which can be assigned as ICT mixing with L-C62CT. L-C62CT atate that contribute to the bands around 550 nm were found both in compound 1 and 3. Simultaneously, tranistions at higer energy mostly derive from inner electron transition of C62. the results of B3LYP/6-31G* confirms the precision and credibility of SAOP/TZP, as well as a further investigation of process of charge transfer of compound 3. Intramolecular Charge Transfer can be modulated by variation or addition of substituents with different characters, thus imply the potencial application in semiconductor materials and providing a theory guidance on materials-design.

References and Notes [1] H.W. Kroto, J.R. Heath, S.C. Obrien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162-63. [2] F. Giacalone, N. Martin, Chemical Reviews 106 (2006) 5136-90. [3] Z.F. Chen, R.B. King, Chemical Reviews 105 (2005) 3613-42. [4] X. Lu, Z.F. Chen, Chemical Reviews 105 (2005) 3643-96. [5] P.W. Fowler, T. Heine, D.E. Manolopoulos, D. Mitchell, G. Orlandi, R. Schmidt, G. Seifert, F. Zerbetto, Journal of Physical Chemistry 100 (1996) 6984-91. [6] G. Lu, Y. Yuan, K. Deng, H. Wu, J. Yang, X. Wang, Chemical Physics Letters 424 (2006) 142-45. [7] W.Y. Qian, Y. Rubin, Journal of the American Chemical Society 122 (2000) 9564-65. [8] A. Ayuela, P.W. Fowler, D. Mitchell, R. Schmidt, G. Seifert, F. Zerbetto, Journal of Physical Chemistry 100 (1996) 15634-36. [9] W.Y. Qian, M.D. Bartberger, S.J. Pastor, K.N. Houk, C.L. Wilkins, Y. Rubin, Journal of the American Chemical Society 122 (2000) 8333-34. [10] W.Y. Qian, S.C. Chuang, R.B. Amador, T. Jarrosson, M. Sander, S. Pieniazek, S.I. Khan, Y. Rubin, Journal of the American Chemical Society 125 (2003) 2066-67. [11] Y.H. Cui, D.L. Chen, W.Q. Tian, J.K. Feng, Journal of Physical Chemistry A 111 (2007) 7933-39. [12] J.Q. Hou, H.S. Kang, Journal of Computational Chemistry 28 (2007) 1417-26. [13] A.A. Popov, I.E. Kareev, N.B. Shustova, E.B. Stukalin, S.F. Lebedkin, K. Seppelt, S.H. Strauss, O.V. Boltalina, L. Dunsch, J.Am.Chem.Soc. 129 (2007) 11551-68. [14] A.S. Sandanayaka, K. Ikeshita, G.A. Rajkumar, Y. Furusho, Y. Araki, T. Takata, O. Ito, J.Phys.Chem.A 109 (2005) 8088-95. [15] T.L. Toivonen, T.I. Hukka, J.Phys.Chem.A 111 (2007) 4821-28. [16] R. Bauernschmitt, R. Ahlrichs, F.H. Hennrich, M.M. Kappes, Journal of the American Chemical Society 120 (1998) 5052-59. [17] R. Vanleeuwen, E.J. Baerends, Physical Review A 49 (1994) 2421-31. [18] P.R.T. Schipper, O.V. Gritsenko, S.J.A. van Gisbergen, E.J. Baerends, Journal of Chemical Physics 112 (2000) 1344-52. [19] F.M. Bickelhaupt, E.J. Baerends, Reviews in Computational Chemistry, Vol 15 15 (2000) 1-86.


[20] G.T. Velde, F.M. Bickelhaupt, E.J. Baerends, C.F. Guerra, S.J.A. Van Gisbergen, J.G. Snijders, T. Ziegler, Journal of Computational Chemistry 22 (2001) 931-67. [21] N.A. Richardson, S.S. Wesolowski, H.F. Schaefer, Journal of Physical Chemistry B 107 (2003) 848-53. [22] Z.X. Zhang, P.D. Han, X.G. Liu, J.F. Zhao, H.S. Jia, F.G. Zeng, B.S. Xu, Journal of Physical Chemistry C 112 (2008) 19158-61. [23] R.C. Haddon, Journal of the American Chemical Society 119 (1997) 1797-98. [24] Y.H. Kan, Q. Li, Chemical Journal of Chinese Universities-Chinese 30 (2009) 174-77. [25] X.D. Li, W.D. Cheng, D.S. Wu, H. Zhang, Y.J. Gong, Y.Z. Lan, Chemical Physics Letters 380 (2003) 480-85. [26] J. Modin, H. Johansson, H. Greenberg, Organic Letters 7 (2005) 3977-79. [27] Y. Zhu, S. Zhou, Y. Kan, L. Yan, Z. Su, J.Chem.Phys. 126 (2007) 245106. [28] M.F. Charlot, A. Aukauloo, Journal of Physical Chemistry A 111 (2007) 11661-72. [29] A. Dreuw, M. Head-Gordon, Journal of the American Chemical Society 126 (2004) 4007-16. [30] W.J.D. Beenken, Chemical Physics 357 (2009) 144-50. [31] M.T. Sun, Journal of Chemical Physics 124 (2006).


sample 2