Light Energy Harvesting via Supramolecularly Functionalized Semi-Conductive SWCNTs with Sensitizers

Transcription

1 Light Energy Harvesting via Supramolecularly Functionalized Semi-Conductive SWCTs with Sensitizers Francis D Souza a, * Sushanta K. Das, a avaneetha K. Subbaiyan, a Atula S. D. Sandanayaka, b and samu Ito b, * Tohoku University

2 Carbon anotubes S. Iijima - MWCT (1990), SWCT (1993) Rolled graphene sheet with end caps Large aspect ratios Unique properties Finds applications in Conductive plastics and adhesives Energy storage Efficient heat conduits Structural composites Biomedical devices umerous electronic applications Arun Tej M, REACH

3 SWCT Properties Useful for Solar Cells SWCTs Improve mobility SWCTs provide Large interfacial area SWCTs have Suitable energy levels SWCTs have Low energy gaps Low Carrier Mobilities (~10-5 cm 2 V -1 s -1 ) Low Exciton Diffusion Lengths (5-15 nm) Large Exciton Binding Energies (up to 1.5 ev) Large Energy Gaps (2-3 ev) Combine the advantages of rganics and SWCTs

4 SWCT Structure (10,5) (m,n) vector v = ma 1 + na 2 (5,5) (9,0) Zigzag (9,0) Armchair (5,5) dom, T. W. et al. ature. 1998, 391, Dai, H. Acc. Chem. Res. 2002, 35, Iijima, S. et al. ature. 1993, 363, a 2 a 1 Chiral (10,5)

5 Functionalization Covalent functionalization xidation Amidation/Esterification Fluorination Aryl diazonium addition Azomethine ylide 1,3-dipolar cycloaddition Compromises Electronic Structure sp 2 sp 3 oncovalent functionalization

6 Biomimetic Solar Cell e - 1 Donor* Acceptor e - CS.+ Donor Acceptor -. Pt Light IT CR e - Donor Acceptor Redox Mediator e -

7 Specific Aims: Design and synthesis of donor-acceptor supramolecular assemblies using single wall carbon nanotubes, especially diameter sorted tubes without compromising their π-electronic structure and maintaining appropriate donor-acceptor distances Study photoinduced electron transfer to improve charge stabilization and derive structure-reactivity correlations Design heterogeneous assemblies consisting of donor-acceptor as well as semiconductor nanostructures to probe interfacial electron transfer Build organic photovoltaic devices (DSSC type) for harvesting light energy

8 Diameter Sorted SWCTs (6,5)SWCT (7,6)SWCT CoMoCAT, SourthWest ano Technologies E red = V for (6,5) and V for (7,6) E ox = 0.64 V for (6,5) and 0.50 V for (7,6)

9 Energy Level Diagram Showing Photoinduced Processes from Singlet Excited ZnP or Fullerene Sensitizer to Diameter Sorted Ts

10 π-stacked Porphyrin-SWCT Hybrids C C Zn C C

11 k S CS = s -1 for ZnP(pyr) 4 /SWCT(7,6) k S CS = s -1 for ZnP(pyr) 4 /SWCT(6,5) k CR = s -1, τ RIP = 40 ns for SWCT(7,6) k CR = s -1, τ RIP = 50 ns for SWCT(6,5) J. Am. Chem. Soc. 2010, 132, 8158

12 Fullerene-SWCT Hybrids via π π Stacking H G CS = ev for SWCT(6,5)/pyrC 60 G CS = ev for SWCT(7,6)/pyrC 60 C k CS = s -1 for SWCT(6,5)/pyrC 60 k CS = s -1 for SWCT(7,6)/pyrC 60 k CR = s -1 for SWCT(6,5)/pyrC 60 k CR = s -1 for SWCT(7,6)/pyrC 60 SWCT(7,6) k CS /k CR = ~360 Chemical Communications, 2010, 46, 8749

13 Self-assembly Protocols to Build Sensitizer- anotube Assemblies Zn Zn + H 3 H 3 + CH 3 H H H - H 3 C- + H 3 C Zn + -CH CH 3 H + H 3-3 S S 3 - C H Zn - S 3-3 S Journal of Physical Chemistry Letters (Perspective), 2010, 1,

14 Metal-Ligand Axial Coordination and π π Stacking Binding SWCT(6,5) SWCT(7,6) Electron Transfer H Zn ZnP hν Electron Transfer R R H Zn Znc R hν R TEM images of (A) Im-Pyr/SWT(6,5), (B) Im- Pyr/SWCT(7,6), (C) ZnP Im-Pyr/SWCT(6,5) and (D) ZnP Im-Pyr/SWCT(7,6) nanohybrids. Spectral changes in the visible region of (a) ZnP and (b) ZnPc observed during the titration of increasing addition of Im- Pyr/SWT(7,6) in DCB to form the ZnP Im-Pyr/SWCT(7,6) and ZnPc Im-Pyr/SWCT(7,6) nanohybrids. Excitation wavelength λ ex = 550 nm for ZnP and 650 nm for ZnPc. Fluorescence decays collected in the nm range for (a) ZnP and (b) ZnPc in the pristine (i), Im-Pyr/SWCT(6,5) complexed (ii) and Im-Pyr/SWCT(7,6) (iii) complexed nanohybrids in DMF. Excitation wavelength λ ex = 408 nm for time profile.

15 anosecond transient absorption spectra observed by 532 nm (ca. 3 mj/ pulse) laser irradiation in Ar-saturated DMF. Inset: Absorption-time profile. (a) ZnP Im- Pyr/SWCT(n,m) (left (6,5) and right (7,6)) and (b) ZnPc Im-Pyr/SWCT(n,m) (left (6,5) and right (7,6)). Measured rate parameters for charge separation and recombination in DMF. anohybrids k a CS / s -1 k CR / s -1 τ RIP / ns k CS / k CR ZnP Im-Pyr/SWCT(6,5) ZnP Im-Pyr/SWCT(7,6) ZnPc Im-Pyr/SWCT(6,5) ZnPc Im-Pyr/SWCT(7,6)

16 Ion-Ion and π π Stacking Binding + -CH 3 S S M - S 3 H 3 H - 3 S H 3 C- + H 3 C M + -CH Energy and Environmental Chemistry, 2011, 4, 707

17 Photoelectrochemistry

18 Cation-dipole and π π Stacking Binding Structure of the crown ether appended zinc porphyrin and zinc phthalocyanine derivatives, and PyrH 3 + functionalized SWCT(n,m) of different diameter used in the construction of donor-acceptor conjugates anosecond transient absorption spectra of (a) SWCT(6,5)/PyrH 3+ :2, (b) SWCT(7,6)/PyrH 3+ :2, (c) SWCT(6,5)/PyrH 3+ :3, and (d) SWCT(7,6)/PyrH 3+ :3 recorded at different time intervals in DMF using 532 nm laser light. The figure inset shows decay profile of the MP p-cation radical band at 680 nm for 2, and 980 nm for 3.

19 Rate constants of charge separation (k CS ), charge recombination (k CR ) and lifetimes of the radical ion-pair (t RIP ), and ratios (k CS /k CR ) in DMF. anohybrids k CSa / s -1 SWCT(6,5)/PyrH 3+ : SWCT(7,6)/PyrH 3+ : SWCT(6,5)/ PyrH 3+ : SWCT(7,6)/PyrH 3+ : SWCT(6,5)/PyrH 3+ : SWCT(7,6)/ PyrH 3+ : k CR / s -1 τ RIP / ns k CS /k CR ChemPhysChem 2011, in press Incident-photon-to-current conversion efficiencies (IPCE) of (a) SWCT(7,6)/PyrH 3+ :1 (black), SWCT(6,5)/PyrH 3+ :1 (red), SWCT(7,6)/PyrH 3+ :2 (blue) and SWCT(6,5)/PyrH 3+ :2 (green), and (b) SWCT(7,6)/PyrH 3+ :3 (purple) and SWCT(6,5)/PyrH 3+ :3 (orange), drop-coated FT/Sn 2 electrodes in acetonitrile containing I /I 3 mediator.

20 Covalently liked Porphyrin-Semiconductive SWCT Hybrids M M = 2H, Zn HBoC M M = 2H, Zn HBoC ZnP-SWCT(6,5) ZnP-SWCT(7,6)

21 TEM Analysis TGA Analysis H 2 P-SWCT(6,5) 260 C/pyrrolidine H 2 P-SWCT(7,6) 150 C/pyrrolidine Raman Spectra (532 nm) G 1.0 G Raman Intensity pristine SWCT(7,6) ZnP-SWCT(7,6) D Wavenumber, cm -1 Raman Intensity pristine SWCT(6,5) ZnP-SWCT(6,5) D Wavenumber, cm -1

22 (a) (b) Absorption spectrum of (a) (i) H 2 P-SWT(6,5) (black) and (ii) H 2 P-SWT(7,6) (red), and (b) (i) ZnP-SWT(6,5) (black) and (ii) ZnP-SWT(7,6) (red) in DMF.

23 Fluorescence Intensity(au) (a) (pristine SWCT(6,5) ZnP-SWCT(6,5) * 1025 (swcnt(7,6) impurity) Fluorescence Intensity(au) (b) ZnP-SWCT(7,6) 1027 pristine SWCT(7,6) Wavelength(nm) Wavelength(nm) Steady-state fluorescence spectra of (a) (i) pristine SWCT(6,5) (black) and (ii) ZnP- SWCT(6,5) (red), excited at 568 nm, and (b) (i) pristine SWCT(7,6) (black) and (ii) ZnP- SWCT(7,6) (red) excited at 658 nm, in SDBS/H 2.

24 (a) (b) Steady-state fluorescence spectra of (a) (i) H 2 P-SWT(6,5) (black) and (ii) H 2 P-SWT(7,6) (red), and (b) (i) ZnP-SWT(6,5) (black) and (ii) ZnP-SWT(7,6) (red) in DMF (λ ex = 532 nm). Inset: Fluorescence decays (λ ex = 408 nm) k CS = (9 12) 10 9 s -1 and Φ CS = for ZnP- SWCT(n,m) k CS = (3-4) 10 9 s -1 and Φ CS = for H 2 P-SWCT(n,m) Higher quenching for (7,6)SWCTs compared to (6,5)SWCTs

25 anosecond transient absorption spectra of (A) SWT(6,5)-ZnPor and (B) SWT(7,6)-ZnPor observed by 532 nm (ca. 3 mj/ pulse) laser irradiation in DMF. Inset: Absorption-time profile. k CR = ( ) 10 6 s -1 and τ RIP = ns for ZnP-SWCT(n,m) k CR = ( ) 10 6 s -1 and τ RIP = ns for H 2 P-SWCT(n,m) Better k CS / k CR for ZnP-SWCT(n,m) compared to H 2 P-SWCT(n,m)

26 Photoelectrochemistry of Covalently linked Porphyrin-SWCT(m,n) Hybrids DCB:Acetonitrile µ IPCE(%) Zntpp-7,6 Zntpp-6,5 H 2 tpp-7,6 H 2 tpp-6,5 Current Density (A/cm 2 ) -20.0µ -30.0µ -40.0µ -50.0µ Zntpp-7,6 Zntpp-6,5 H 2 tpp-7,6 H 2 tpp-6, Wavelength (nm) -60.0µ Time (sec)

27 Tohoku University Conclusions Efficiency of PET to band gaps of semi-conductive SWCT assembled using self-assembly methods or covalent bonding is investigated. Photochemical studies involving both emission and transient spectral studies revealed charge separation in these hybrids. The rates of charge separation were found to be slightly higher for (7,6)-SWCT derived hybrids compared to the (6,5)-SWCT derived hybrids for a given photosensitizer. The charge recombination revealed an opposite effect indicating that the (7,6)-SWCT are slightly better for charge stabilization compared to the (6,5)-SWCT. Both (7,6)-SWCT and (6,5)-SWCT act as electron acceptor as well as electron donor in the presence of appropriate counterparts. Photoelectrochemical cells built on FTP/Zn 2 surface revealed direct light-to-electricity conversion. A maximum IPCE of 12% is accomplished. $$$$

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29 Donor-Acceptor Hybrids via Metal-Ligand Coordination hν R R ZnP Zn Znc R CH 3 Zn R = C CH 3 CH 3 R Electron Transfer Pyr~Im H SWT J. Phys. Chem. C 2007, 111, 6947

30 Time-resolved emission and Transient absorption spectral studies Znc in THF DMF THF A k = 1.3 x 10 6 s -1 (980 nm) Fluo. Int Absorbance Time / µs Time / ns Fluorescence decays of Znc-ImPyr- SWCTs ( nm) in THF and DMF; λ ex = 400 nm Wavelength / nm 1600 anosecond transient absorption spectra of Znc-ImPyr-SWCTs observed by 532 nm (ca. 3 mj/ pulse) laser irradiation in at 0.1 µs ( ) and 1.0 µs ( ) in DMF. Inset: Absorption-time profile of the 980 nm band.

31 Fluorescence Lifetimes (τ f collected in nm region), Charge-Separation Rate-Constants (k S CS ) and Quantum Yields (Φ S CS ) via 1 Znc* or 1 ZnP*, Charge-Recombination Rate-Constants (k CR ) and Lifetimes of the Radical Ions (τ RI ) and Yield of HV + ( Φ HV +) for Znc-ImPyr-SWT and ZnP-ImPyr-SWT nanohybrids. Donor Znc Solvent THF DMF τ f / ps (fraction) 450 (38%) 2100 (62%) 415 (41%), 2000 (59%) k S CS s-1 a Φ S CS a 1.8 x x k CR / s -1 τ RIP / ns 1.7 x x ZnP THF 1700 (100%) 0.04 x x DMF 360 (35%), 2900 (65%) 2.8 x x a k S CS = (1/τ f ) sample - (1/τ f ) ref, Φ S CS = ks CS / (1/τ f ) sample. τ f sample for fast component and τ f ref = 1900 and 2400 ps, respectively for Znc and ZnP.

32 Self-assembly via Crown Ether-Ammonium Cation Interactions H 3 H H 3 H hν Zn H 3 H H 3 H Electron Transfer k CS = 3.5 x 10 9 s -1 k CR = 5.1 x 10 6 s -1 Chem. Eur. J. 2007, 13, 8277

33 Photoelectrochemistry Switching H 3 H H 3 H Zn hν H 3 H 3 H H Electron Transfer FF = 0.65 V C = 330 mv I SC = 390 ma η = 0.1 % I-V profile of the FT/Sn 2 electrode coated with ZnP- PyrH 3+ -SWCT. white light (100 mw cm 2 ) illumination (black) and without light illumination (red). Counter electrode, Pt; electrolyte, ai (0.50 M) and I 2 (50 mm) in CH 3 C; the area of the modified working electrode, 0.25 cm 2

34 Self-assembly via Crown Ether-Ammonium Cation Interactions Electron Transf er H 3 H H 3 H Zn hν H H 3 H H 2 k CS = 6.3 x 10 9 s -1 k CR = 1.2 x 10 8 s -1 = 1.1 x 10 7 s -1

35 Porphyrin-SWT via Ion-Pairing SWT Pyr-H 3 H Pyr-C CH 3-3 S M S 3 - H 3 S (TPPS)M; M = 2H, Zn 3 S H 3 C- + H 3 C M + -CH 3 + (TMPyP)M; M=2H, Zn k CS = 2.7 x 10 9 s -1 k CR = 1.0 x 10 7 s -1 k CS = 3.4 x 10 9 s -1 k CR = 1.1 x 10 7 s -1 J. Phys. Chem. C 2009, 113, 13425

36 TEM images of (A) SWT(6,5), (B) SWT(7,6), (C) ZnP(pyr) 4 /SWT(6,5) and (D) ZnP(pyr) 4 /SWT(7,6) at two magnification scales; white bar (left) 100 nm and (right) 5 nm.

37 (a) (b) Steady-state absorption spectra in the Soret region of ZnP(pyr) 4 /SWT(6,5) (dark line) and ZnP(pyr) 4 /SWT(7,6) (red line) and ZnP(pyr) 4 (blue line) in DMF. Raman spectra of (a) (i) ZnP(pyr) 4 /SWT(6,5), and (ii) SWT(6, 5), and (b) (i) ZnP(pyr 44 /SWT(7,6), and (ii) SWT(7, 6) at the laser excitation wavelength of nm.

38 Steady-state fluorescence spectra of ZnP(pyr) 4 /SWT(6,5) (dark line) ZnP(pyr) 4 /SWT(7,6) (red line) and ZnP(Pyr) 4 (blue line) in DMF; λ ex = 428 nm. (ormalized at 614 nm). Fluorescence decays at monitoring region of nm for ZnP(pyr) 4 /SWT(6,5) (dark line), ZnP(pyr) 4 /SWT(7,6) (red line) and ZnP(Pyr) 4 (blue line) in DMF; λ ex = 408 nm. E red = V for (6,5) and V for (7,6) E ox = 0.64 V for (6,5) and 0.50 V for (7,6)

39 (a) (b) anosecond transient absorption spectra of (a) ZnP(pyr) 4 /SWT(7,6) and (b) ZnP(pyr 4 )/SWT(6,5) observed by 532 nm (ca. 3 mj/ pulse) laser irradiation in Ar-saturated DMF. Inset: Absorption-time profile.

40 1 ZnP*(pyr )4 /s-swt k CS ZnP. + ( pyr )4 /s-swt.- hν = k 532 nm CR HS BAH BAH.+ ZnP(pyr )4 /s-swt BA + HV 2+ EM HV. + Steady-state absorption spectra of ZnP(pyr) 4 /SWT(6,5) in Ar-saturated DMF solution measured after five lasershots (6-ns pulse width and 3 mj/pulse) at 532-nm in the presence of HV 2+ (0.5 mm) and BAH (i) 0, (ii) 0.5, (iii) 1.0, (iv) 1.5, (v) 2.0 (vi) 2.5 (vii) 3.0 (viii) 3.5 and (ix) 4.0 mm. Photocurrent action spectra of IPCE; TE/Sn 2 /ZnP(pyr) 4 /SWT(6,5) electrode (blue spectrum) and TE/Sn 2 /ZnP(pyr) 4 /SWT(7,6) electrode (red spectrum). Electrolyte: LiI 0.5 M, I M in acetonitrile.

41 Porphyrin-Semiconducting SWT via Ion-Pairing Pyr-H 3 H Pyr-C CH 3-3 S M S 3 - H 3 S (TPPS)M; M = 2H, Zn 3 S H 3 C- + H 3 C M + -CH 3 + (TMPyP)M; M=2H, Zn

42 (a) (6,5) (a) (6,5) (b) (7,6) (b) (7,6) Steady-state absorption spectrum of (i) SWTpyrH 3+ :(TPPS)H 2 (ii) SWTpyrH 3 + and (iii) (TPPS)H 2 in DMF. Fluorescence spectrum of (i) SWTpyrH 3+ :(TPPS)H 2 (ii) SWTpyrH 3 + and (iii) (TPPS)H 2 in DMF.

43 SWT(6,5)pyrH 3 (TPPS)H 2 SWT(7,6)pyH 3 (TPPS)Zn Fluorescence decays of (i) SWT(7,6)pyrH 3 (TPPS)H 2, (ii) SWT(6,5)pyrH 3 (TPPS)H 2 and (iii) (TPPS)2H λ ex = 408 nm. (TPPS)H ps (100%) SWT(6,5)pyrH 3 (TPPS)H ps (68%), 5200 (32%) SWT(7,6)pyrH 3 (TPPS)H ps (78%), 3100 (22%) (TPPS)Zn 1950 ps (100%) SWT(6,5)pyH 3 (TPPS)Zn 285 ps (80%), 1900 (20%) SWT(7,6)pyH 3 (TPPS)Zn 136 ps (85%), 1200 (15%) anosecond transient absorption spectra in DMF

44 (a) (6,5) (a) (6,5) (b) (7,6) (b) (7,6) Absorption spectra of (i) SWTpyrC - (TMPyP)Zn (ii) SWTpyrC - and (iii) (TMPyP)Zn in DMF. Fluorescence spectra of (i) SWTpyrC - (TMPyP)Zn (ii) SWTpyrC - and (iii) (TMPyP)Zn in DMF.

45 SWT(7,6)pyrC - (TMPyP)Zn Fluorescence decays of (i) SWT(7,6)pyrC - (TMPyP)Zn (ii) SWT(6,5)pyrC - (TMPyP)Zn and (iii) (TMPyP)Zn in DMF. λ ex = 408 nm. anosecond transient absorption spectra in DMF (TMPyP)H ps (100%) SWT(6,5)pyrC - (TMPyP)H ps (88%), 3200 (12%) SWT(7,6)pyrC - (TMPyP)H ps (94%), 2900 (6%) (TMPyP)Zn 2100 ps (100%) SWT(6,5)pyrC - (TMPyP)Zn 230 ps (78%), 1500 (22%) SWT(7,6)pyrC - (TMPyP)Zn 106 ps (85%), 1100 (15%)

46 Donor-Semiconductor SWT Hybrids via Metal-Ligand Coordination ImPyr H ImPyr H ZnP Zn Znc R R CH 3 Zn R = C CH 3 CH 3 R R

47 SWT-Fullerene Donor-Acceptor Conjugates Electron Transfer H 3 hν CH 3 H Pyr~H 3 Crown-C 60 SWT Absorbance ns 1000 ns A Time / µs Wavelength / nm anosecond transient absorption spectra of SWT/Pyr-H 3+ /crown- C 60 nanohybrids (0.1 mm) observed by the 532 nm (ca. 3 mj/ pulse) laser irradiation in DMF. Inset: Absorption-time k CS = 3.46 x 10 9 s -1 profile of the 1020 nm band. k CR = 1.04 x 10 7 s -1 J. Am. Chem. Soc. 2007, 129, 15871

48 hν Electron Transfer ET hν H 3 CH 3 H Pyr~H 3 Crown-C 60 SWT(6,5) SWT (7,6)

49 SWT (7,6) SWT(6,5)

50 TEM images (A) SWT (6,5) 100 nm 5 nm (C) SWT (6,5)pyC nm 5 nm (A) SWT (6,5) chirality with C60pyrene in DMF (B) SWT (7,6) chirality with C60pyrene in DMF (C) Pristine SWT (6,5) (D) Pristine SWT (7,6) (B) SWT (7,6) 100 nm 5 nm (D) SWT (7,6) pyc nm 5 nm

51 Steady-state absorption spectrum of SWT (6,5)pyrC 60 and SWT (7,6) pyrc 60 in DMF. Steady-state fluorescence spectra of SWT (6,5) pyrc 60 and SWT (7,6) pyrc 60 in DMF (λ ex = 532 nm)

52 Fluorescence decays of SWT (6,5) pyrc 60 and SWT (7,6) pyrc 60 λ ex = 408 nm. pyrc ps (100%) SWT(6,5)pyrC ps (75%), 1800 (25%) SWT(7,6)pyrC ps (80%), 2500 (10%) anosecond transient absorption spectra of SWT (6,5) pyrc 60 and SWT (7,6) pyrc 60 observed by 532 nm (ca. 3 mj/ pulse) laser irradiation in DMF. Inset: Absorption-time profile.

53 (A) (B) Wavelength / nm Steady-state absorption spectra of (A) SWT (6,5)pyrC 60 ZnP and (B) SWT (7,6)pyrC 60 in Arsaturated DMF solution measured after 5 laser-shots with laser light (6-ns pulse width) at 532-nm in the presence of HV 2+ (0.5 mm) and BAH (i) 0, (ii) 0.5, (iii) 1.0, (iv) 1.5, (v) 2.0 (vi) 2.5 (vii) 3.0 (viii) 3.5 and (ix) 4.0 mm.

54 SWT(6,5) and (7,6) chiralit y dependent charge transfer study H 3 CH 2 CH 2 C CH 2 CH 2 CH 3 CCH 3 CH 2 CH 2 CH 3 CH CH H 1eq 3eq 4eq Propionic Acid, reflux for 8hr H 3 CH 2 CH 2 C H H CCH 3 Chemical Formula: C 55 H Molecular Weight: KH,THF,reflux 20hrs H 3 CH 2 CH 2 C CH 2 CH 2 CH 3 H 3 CH 2 CH 2 C SCl2, Pyridine in toluene reflux 3hr, solvent evaporated, H added toluene, pyridine, Added hydroxybenzaldehyde H H 3 CH 2 CH 2 C C Chemical Formula: C 61 H Molecular Weight: CH H 3 CH 2 CH 2 C H H CH 2 CH 2 CH 3 CH Chemical Formula: C 54 H Molecular Weight: H H HBoc SWCT(7,6)/(6,5)/DMF, Chemical Formula: C 13 H Molecular Weight: R 2 R' where R 1 = Porphyrin and R 2 = H 2 C HBoc

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56 R k CS = 2.0 x 10 9 s -1 k CR = 1.4 x 10 7 s -1 R hν Zn R H R Electron Transfer k CS = 3.5 x 10 9 s -1 k CR = 5.1 x 10 6 s -1 CS H 3 H H 3 H hν Zn H 3 H H 3 H J. Phys. Chem. C 2007, 111, 6947 hν Chem. Eur. J. 2007, 13, 8277 Electron Transfer CH 3 H 3 H P yr-h 3 crown-c 60 k CS = 3.46 x 10 9 s -1 k CR = 1.04 x 10 7 s -1 SWT J. Am. Chem. Soc. 2007, 129, 15871

57 S S S S S S S S Zn S S S S S S S S

58 anotube Properties Useful for Solar Cells High carrier mobilities (~1,20,000 cm 2 V -1 s -1 ) Large surface areas (~1600 m 2 g -1 ) Absorption in the IR range (E g : 0.48 to 1.37 ev) Conductance - Independent of the tube length Enormous current carrying capability 10 9 A cm -2 Semiconducting CTs Ideal solar cells Mechanical strength & Chemical stability