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1.
Phys Chem Chem Phys ; 19(28): 18519-18528, 2017 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-28682368

RESUMO

We present doubly-resonant sum frequency generation (DR-SFG) spectra of fullerene thin films on metallic and dielectric substrates as a way to investigate the interplay between nuclear and electronic coupling at buried interfaces. Modal and substrate selectivity in the electronic enhancement of the C60 vibrational signatures is demonstrated for excitation wavelengths spanning the visible range. While the SFG response of the totally symmetric Ag(2) mode of fullerene is distinctly coupled to the optically allowed electronic transition corresponding to the HOMO-LUMO+1 of C60 (ca. 2.6 eV), the T1u(4) vibrational mode appears to be coupled to a symmetry-forbidden HOMO-LUMO transition at lower energies (ca. 2.0 eV). For dielectric substrates, the DR-SFG intensity of the T1u(4) mode shows lack of enhancement for upconversion wavelengths off-resonance with the optically-dark LUMO. However, the T1u(4) mode shows a unique coupling to an intermediate state (∼2.4 eV) only for the fullerene films on the gold substrate. We attribute this coupling to unique interactions at the buried C60/gold interface. These results demonstrate the occurrence of clear electron-phonon couplings at the C60/substrate interfaces and shed light on the impact of these couplings on the optical response of electronically excited fullerene. This coupling may influence charge and energy transport in organic electronic devices mediated by vibrational motions. We also demonstrate a potential use of this added selectivity in chemical imaging.

2.
J Am Chem Soc ; 136(21): 7571-4, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24820034

RESUMO

Donor-acceptor dyads featuring near-IR sensitizers derived from thieno-pyrrole-fused BODIPY (abbreviated as SBDPiR) and fullerene, C60 have been newly synthesized and characterized. Occurrence of ultrafast photoinduced electron transfer (PET) leading to the formation of charge-separated state in these dyads, capable of harvesting light energy from the near-IR region, is established from femtosecond transient absorption studies.


Assuntos
Fulerenos/química , Processos Fotoquímicos , Luz , Modelos Moleculares , Estrutura Molecular
3.
Chemphyschem ; 15(12): 2462-72, 2014 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-24850373

RESUMO

High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge-separated states. The energy of the charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-energy harvesting and optoelectronic device building applications.


Assuntos
Fulerenos/química , Indóis/química , Ânions/química , Cátions/química , Clorobenzenos/química , Eletroquímica/métodos , Transporte de Elétrons , Isoindóis , Cinética , Ligantes , Luz , Compostos Organometálicos/química , Oxirredução , Fotoquímica/métodos , Piridinas/química , Análise Espectral/métodos , Tolueno/química , Zinco/química , Compostos de Zinco
4.
Chemistry ; 18(36): 11388-98, 2012 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-22807374

RESUMO

Covalent functionalization of diameter sorted SWCNTs with porphyrins (MP), and photochemistry to establish nanotube diameter-dependent charge separation efficiencies are reported. The MP-SWCNT(n,m) [M=2H or Zn, and (n,m)=(7,6) or (6,5)] nanohybrids are characterized by a variety of spectroscopic, thermogravimetric, TEM imaging techniques, and also by DFT MO calculations. The thermogravimetric, Raman and fluorescence studies reveal the presence of a moderate number of porphyrins on the SWCNT surface. The MO results suggest charge separation (CS) via the excited state of MP. Time-resolved fluorescence studies reveal quenching of the singlet excited state of the MP with SWCNT(n,m), giving the rate constants of charge separation (k(CS)) in the range of (4-5)×10(9) s(-1). Nanosecond transient absorption measurements confirm the charge-separated radical cation and the radical anion as [MP(.+)-SWCNT(.-)] with their characteristic absorption bands in the visible and near-IR regions. The charge separated states persist for about 70-100 ns thus giving an opportunity to utilize them to build photoelectrochemical cells, which allowed us to derive the structure-reactivity relationship between the nature of porphyrin and diameter of the employed nanotubes.


Assuntos
Metaloporfirinas/síntese química , Nanotubos de Carbono/química , Porfirinas/química , Transporte de Elétrons , Hidrogênio/química , Metaloporfirinas/química , Estrutura Molecular , Processos Fotoquímicos , Teoria Quântica , Semicondutores , Zinco/química
5.
Phys Chem Chem Phys ; 14(8): 2940-50, 2012 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-22262196

RESUMO

Photoinduced charge separation processes of three-layer supramolecular hybrids, fullerene-porphyrin-SWCNT, which are constructed from semiconducting (7,6)- and (6,5)-enriched SWCNTs and self-assembled via π-π interacting long alkyl chain substituted porphyrins (tetrakis(4-dodecyloxyphenyl)porphyrins; abbreviated as MP(alkyl)(4)) (M = Zn and H(2)), to which imidazole functionalized fullerene[60] (C(60)Im) is coordinated, have been investigated in organic solvents. The intermolecular alkyl-π and π-π interactions between the MP(alkyl)(4) and SWCNTs, in addition, coordination between C(60)Im and Zn ion in the porphyrin cavity are visualized using DFT calculations at the B3LYP/3-21G(*) level, predicting donor-acceptor interactions between them in the ground and excited states. The donor-acceptor nanohybrids thus formed are characterized by TEM imaging, steady-state absorption and fluorescence spectra. The time-resolved fluorescence studies of MP(alkyl)(4) in two-layered nanohybrids (MP(alkyl)(4)/SWCNT) revealed efficient quenching of the singlet excited states of MP(alkyl)(4) ((1)MP*(alkyl)(4)) with the rate constants of charge separation (k(CS)) in the range of (1-9) × 10(9) s(-1). A nanosecond transient absorption technique confirmed the electron transfer products, MP˙(+)(alkyl)(4)/SWCNT˙(-) and/or MP˙(-)(alkyl)(4)/SWCNT˙(+) for the two-layer nanohybrids. Upon further coordination of C(60)Im to ZnP, acceleration of charge separation via(1)ZnP* in C(60)Im→ZnP(alkyl)(4)/SWCNT is observed to form C(60)˙(-)Im→ZnP˙(+)(alkyl)(4)/SWCNT and C(60)˙(-)Im→ZnP(alkyl)(4)/SWCNT˙(+) charge separated states as supported by the transient absorption spectra. These characteristic absorptions decay with rate constants due to charge recombination (k(CR)) in the range of (6-10) × 10(6) s(-1), corresponding to the lifetimes of the radical ion-pairs of 100-170 ns. The electron transfer in the nanohybrids has further been utilized for light-to-electricity conversion by the construction of proof-of-concept photoelectrochemical solar cells.

6.
J Am Chem Soc ; 133(49): 19922-30, 2011 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-22088093

RESUMO

Photoinduced electron transfer in self-assemblies of porphyrins ion-paired with ssDNA wrapped around single-wall carbon nanotubes (SWCNTs) has been reported. To accomplish the three-component hybrids, two kinds of diameter-sorted semiconducting SWCNT(n,m)s of different diameter ((n,m) = (6,5) and (7,6)) and free-base or zinc porphyrin bearing peripheral positive charges ((TMPyP(+))M (tetrakis(4-N-methylpyridyl)porphyrin); M = Zn and H(2)) serving as light-absorbing photoactive materials are utilized. The donor-acceptor hybrids are held by ion-pairing between the negatively charged phosphate groups of ssDNA on the surface of the SWCNT and the positively charged at the ring periphery porphyrin macrocycle. The newly assembled bionano donor-acceptor hybrids have been characterized by transmission electron microscopy (TEM) and spectroscopic methods. Photoinduced electron transfer from the excited singlet porphyrin to the SWCNTs directly and/or via ssDNA as an electron mediator has been established by performing systematic studies involving the steady-state and time-resolved emission as well as the transient absorption studies. Higher charge-separation efficiency has been successfully demonstrated by the selection of the appropriate semiconductive SWCNTs with the right band gap, in addition to the aid of ssDNA as the electron mediator.


Assuntos
DNA/química , Nanotubos de Carbono/química , Porfirinas/química , Transporte de Elétrons , Metaloporfirinas/química , Modelos Moleculares , Nanotubos de Carbono/ultraestrutura , Termodinâmica
7.
Chemphyschem ; 12(12): 2266-73, 2011 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-21751336

RESUMO

A non-covalent double-decker binding strategy is employed to construct functional supramolecular single-wall carbon nanotubes (SWCNT)-tetrapyrrole hybrids capable of undergoing photoinduced electron transfer and performing direct conversion of light into electricity. To accomplish this, two semiconducting SWCNTs of different diameters (6,5 and 7,6) were modified via π-π stacking of pyrene functionalized with an alkyl ammonium cation (PyrNH(3)(+)). Such modified nanotubes were subsequently assembled via dipole-cation binding of zinc porphyrin with one (1) or four benzo-18-crown-6 cavities (2) or phthalocyanine with four benzo-18-crown-6 cavities at the ring periphery (3), employed as visible-light photosensitizers. Upon charactering the conjugates using TEM and optical techniques, electron transfer via photoexcited zinc porphyrin and phthalocyanine was investigated using time-resolved emission and transient absorption techniques. Higher charge-separation efficiency is established for SWCNT(7,6) with a narrow band gap than the thin SWCNT(6,5) with a wide band gap. Photoelectrochemical studies using FTO/SnO(2) electrodes modified with these donor-acceptor conjugates unanimously demonstrated the ability of these conjugates to convert light energy into electricity. The photocurrent generation followed the trend observed for charge separation, that is, incident-photon-to-current efficiency (IPCE) of a maximum of 12 % is achieved for photocells with FTO/SnO(2)/SWCNT(7,6)/PyrNH(3)(+):1.


Assuntos
Éteres de Coroa/química , Nanotecnologia/métodos , Nanotubos de Carbono/química , Fármacos Fotossensibilizantes/química , Eletricidade , Eletrodos , Transporte de Elétrons , Indóis/química , Isoindóis , Luz , Metaloporfirinas/química , Nanotecnologia/instrumentação , Processos Fotoquímicos/efeitos da radiação , Pirenos/química , Semicondutores
8.
J Phys Chem Lett ; 7(2): 320-6, 2016 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-26730991

RESUMO

The molecular self-assembly of surfactants on the surface of single-walled carbon nanotubes (SWCNT) is currently a common strategy for the tuning of nanotube properties and the stabilization of carbon nanotube dispersions. Here, we report direct measurements of the degree of interfacial ordering for sodium dodecyl sulfate (SDS) surfactants adsorbed on colloidal, single-chirality enriched, SWCNTs within a solid film and investigate the dependence of surface alkyl chain order on the surfactant concentration in the precursor solution. The degree of order for the SWCNT-bound SDS molecules, is probed by vibrational sum frequency generation (VSFG) spectroscopy. We find concrete evidence for the presence of highly ordered surface structures at sufficiently high SDS concentrations, attributed here to cylindrical-like micelle assemblies with the SWCNT at the core. As the SDS concentration decreases, the interfacial order is found to decrease as well, generating a more disordered or random adsorption of surfactants on the nanotube surfaces.

9.
Chem Asian J ; 10(6): 1335-43, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25779683

RESUMO

We discovered a rare phenomenon wherein a thieno-pyrrole fused BODIPY dye (SBDPiR690) generates singlet oxygen without heavy halogen atom substituents. SBDPiR690 generates both singlet oxygen and fluorescence. To our knowledge, this is the first example of such a finding. To establish a structure-photophysical property relationship, we prepared SBDPiR analogs with electron-withdrawing groups at the para-position of the phenyl groups. The electron-withdrawing groups increased the HOMO-LUMO energy gap and singlet oxygen generation. Among the analogs, SBDPiR688, a CF3 analog, had an excellent dual functionality of brightness (82290 m(-1) cm(-1) ) and phototoxic power (99170 m(-1) cm(-1) ) comparable to those of Pc 4, due to a high extinction coefficient (211 000 m(-1) cm(-1) ) and balanced decay (Φflu =0.39 and ΦΔ =0.47). The dual functionality of the lead compound SBDPiR690 was successfully applied to preclinical optical imaging and for PDT to effectively control a subcutaneous tumor.


Assuntos
Compostos de Boro/química , Compostos Heterocíclicos de 4 ou mais Anéis/química , Pirróis/química , Oxigênio Singlete/metabolismo , Animais , Apoptose/efeitos dos fármacos , Compostos de Boro/toxicidade , Linhagem Celular Tumoral , Cristalografia por Raios X , Desenho de Fármacos , Corantes Fluorescentes/química , Halogênios/química , Compostos Heterocíclicos de 4 ou mais Anéis/toxicidade , Humanos , Lasers , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Nus , Conformação Molecular , Neoplasias/tratamento farmacológico , Fotoquimioterapia , Fármacos Fotossensibilizantes/química , Fármacos Fotossensibilizantes/uso terapêutico , Fármacos Fotossensibilizantes/toxicidade , Teoria Quântica , Oxigênio Singlete/química , Espectroscopia de Luz Próxima ao Infravermelho , Relação Estrutura-Atividade , Transplante Heterólogo
10.
Chem Asian J ; 8(12): 3123-32, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24038940

RESUMO

We report the synthesis, photophysical and electrochemical properties, and in vivo fluorescence imaging of a series of new thieno-pyrrole-fused near-infrared (NIR) BODIPY agents by using a versatile intermediate as a building block. The versatile thieno-pyrrole-fused BODIPY intermediate was rationally designed to bear bromo-substituents and absorb in the mid-red region (635 nm) to act as an organic electrophile for the development of NIR multifunctional agents. The use of subsequent palladium-catalyzed and nucleophilic substitution reactions afforded highly conjugated NIR BODIPYs. The novel BODIPYs exhibit long-wavelength absorptions in the NIR region (650-840 nm). The agents produce sharp fluorescence bands, and most of them display respectable quantum yields of fluorescence (0.05-0.87) useful for biomedical imaging, as demonstrated by in vivo imaging with SBDPiR740. Interestingly, a number of agents in the series that are non-halogenated were reactive to O2 at the triplet photo-excited state coupled with a favorable redox potential and decent fluorescence, and hence could be potential candidates for use as photosensitizers in fluorescence-guided photodynamic therapy. Furthermore, the synthetic approach allows further functionalization of the highly conjugated NIR BODIPYs to tune the excited states (PET, ICT) and to conjugate targeting moieties for enhanced biological applications.


Assuntos
Compostos de Boro/síntese química , Corantes Fluorescentes/síntese química , Fármacos Fotossensibilizantes/síntese química , Pirróis/química , Compostos de Boro/química , Fluorescência , Corantes Fluorescentes/química , Raios Infravermelhos , Fotoquimioterapia , Fármacos Fotossensibilizantes/química
11.
Chem Commun (Camb) ; 49(20): 2013-5, 2013 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-23380812

RESUMO

Graphene oxide decorated with an electron donor, zinc(II) phthalocyanine, and an electron acceptor, fullerene, has been synthesized, and photoinduced electron transfer leading to charge-separation is reported.


Assuntos
Grafite/química , Óxidos/química , Transporte de Elétrons , Elétrons , Fulerenos/química , Indóis/química , Isoindóis , Lasers , Oxirredução , Temperatura , Zinco/química
12.
Chem Commun (Camb) ; 48(97): 11859-61, 2012 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-23125975

RESUMO

Supramolecular donor-acceptor hybrids composed of few-layer graphene as an electron acceptor and phthalocyanine or porphyrin bearing four pyrene entities as photosensitizer donors have been synthesized, and occurrence of ultrafast charge separation in the order of 10(11)-10(12) s(-1) due to close proximity of the donor and acceptor entities is demonstrated.


Assuntos
Grafite/química , Tetrapirróis/química , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Estrutura Molecular , Tamanho da Partícula , Propriedades de Superfície
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