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RISS 인기검색어
- 검색키워드
- 저자 : Reish, Matthew E. (검색결과 2 건)
- 무료
- 기관 내 무료
- 유료
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A Spectroscopic and DFT Study of the Electronic Properties of Carbazole-Based D–A Type Copolymers
Reish, Matthew E.,Nam, Sanghun,Lee, Wonho,Woo, Han Young,Gordon, Keith C. American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.40
<P>The structural and electronic properties of three carbazole containing copolymers used in organic photovoltaic applications, poly[<I>N</I>-1-octylnonyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), poly[<I>N</I>-1-octylnonyl-2,7-carbazole-alt-4,7-(2′,1′,3′-benzothiadiazole)] (PCBT), and poly[<I>N</I>-1-octylnonyl-2,7-carbazole-alt-4,7-(2′,1′,3′-benzoselenadiazole)] (PCBSe) have been studied using resonance Raman (RR) and transient absorption (TA) spectroscopies and density functional theory (DFT) calculations. Enhancement of Raman modes centered on the acceptor unit when a Raman excitation wavelength is coincident with lowest energy electronic excitation suggests that the excitation involves charge transfer from the carbazole donor to the varying benzodiazole acceptors. The pattern of the enhancement when the excitation wavelength is coincident with the higher energy transition indicates that this transition is π to π* in nature; this is consistent with TD-DFT calculations. Nanosecond transient absorption studies show long-lived excited state signals for PCDTBT (126 ± 4 ns and 1.56 ± 0.1 μs) and PCBSe (1.82 ± 0.1 μs), suggesting that population of the triplet state is appreciable. No transient signal could be detected in PCBT. B3LYP TD-DFT calculations of the monomer through to the hexamer indicate a broadly delocalized excited state orbital for PCDTBT as indicated by the linear decrease in excitation energy with an increased number of repeat units, while for PCBSe and PCBT, the reduction in excitation is sublinear. The highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) of PCBSe and PCBT polymers compared to PCDTBT are similarly diffuse, but the population of higher order orbitals is decreased when compared with PCDTBT. CAM-B3LYP calculations reduce the delocalization of the frontier orbitals and show less reduction in excitation energy with additional repeat units for each polymer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-40/jp307552z/production/images/medium/jp-2012-07552z_0012.gif'></P>
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Reish, Matthew E.,Huff, Gregory S.,Lee, Wonho,Uddin, Mohammad Afsar,Barker, Alex J.,Gallaher, Joseph K.,Hodgkiss, Justin M.,Woo, Han Young,Gordon, Keith C. American Chemical Society 2015 Chemistry of materials Vol.27 No.8
<P>The electronic properties of the donor–acceptor (DA) polymer poly{5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[<I>c</I>]-1,2,5-thiadiazole} (PTBT) have been investigated using spectroscopic and computational techniques. Electronic absorption and emission spectra reveal the presence of an ordered and a disordered phase in solution. Franck–Condon modeling of the ordered phase yields Huang–Rhys factors of 0.55 (20 °C) and 0.51 (−180 °C), indicating little structural distortion between ground and excited state. DFT calculations with resonance Raman spectroscopy are consistent with a lowest energy excited state that is electronically delocalized and has little charge-transfer character, unexpected for a copolymer with a low bandgap (∼1.8 eV). Transient absorption spectroscopy of PTBT:fullerene blends reveals near-unity internal charge-transfer yields in both ordered and disordered film morphologies. In the disordered blend, charge transfer is complete within the laser pulse (100 fs), whereas the ordered blend also features a slower phase due to exciton diffusion in the phase separated morphology. In the ordered blend, the spectra and dynamics of charge transfer reveal that excitons and charges promptly occupy delocalized states on extended polymer chains. The pervasive use of donor–acceptor structures in polymer devices makes understanding the interplay of morphology and electronic structure of these polymers essential and here a spectroscopic and computational investigation gives an extensive picture of the electronic properties and their effect on charge dynamics in a DA polymer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-8/cm504655f/production/images/medium/cm-2014-04655f_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm504655f'>ACS Electronic Supporting Info</A></P>
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