Our most recent papers...
455. Carbon Nanohoops: Excited Singlet and Triplet Behavior of - and -cycloparaphenylene
Hines, D. A.; Darzi, E. R.; Jasti, R.; Kamat, P. V. J. Phys. Chem. A 2014, ASAP.
Cycloparaphenylene molecules, commonly known as 'carbon nanohoops,' have the potential to serve as building blocks in constructing carbon nanotube architectures. The singlet and triplet excited state characteristics of -cycloparaphenylene (CPP) and -cycloparaphenylene (CPP) have now been elucidated using time resolved transient absorption and emission techniques. The fluorescence quantum yields (Φ) of CPP and CPP were determined to be 0.46 and 0.83 respectively. Rates of non-radiative recombination (knr), radiative recombination (kr) and intersystem crossing (kisc) determined in this study indicate that radiative decay dominates in these nanohoop structures. The triplet quantum yields determined through energy transfer with excited biphenyl triplet were 0.18 and 0.13 for CPP and CPP respectively. The rate of triplet state quenching by oxygen was measured to be 1.7 × 103 s-1 (CPP) and 1.9 × 103 s-1 (CPP). The excited state dynamics established in this study enable us to understand the behavior of a carbon nanotube-like structure on a single subunit level.
454. Charge Transfer Mediation Through CuxS. The Hole Story of CdSe in Polysulfide
Radich, J.G.; Peeples, N. R.; Santra, P. K.; Kamat, P. V. J. Phys. Chem. C 2014, ASAP.
Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar cells is relatively slow when compared to electron transfer from CdSe to TiO2. Controlled exposure of cadmium chalcogenide surfaces to copper ions followed by immersion in sulfide solution promotes development of interfacial CuxS layer, which mediates hole transfer to polysulfide electrolyte by collection of photogenerated holes from CdSe. In addition, CuxS was also found to interact directly with defect states on the CdSe surface and quench emission characteristic of electron traps resulting from selenide vacancies. Together these effects were found to work in tandem to deliver 6.6% power conversion efficiency using Mn-doped CdS and CdSe co-sensitized quantum dot solar cell. Development of n-p interfacial junction at the photoanode-electrolyte interface in quantum dot solar cells unveils new means for designing high efficiency liquid junction solar cells.
453. Recent Advances in Quantum Dot Surface Chemistry
Hines, D. A.; Kamat, P. V. ACS Appl. Mater. Interfaces 2014, ASAP.
Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, the feature article focuses addresses three main issues: (i) How surface chemistry affects the optical properties of QDs, (ii) How it influences the excited state dynamics and (iii) How one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles and in self-assembled QD monolayers.
452. Driving Charge Separation for Hybrid Solar Cells: Photo-induced Hole Transfer in Conjugated Copolymer and Semiconductor Nanoparticle Assemblies
Waldeck, D. H.; Wang, Y.; Kamat, P. V.; Santra, P.; Liu, K.; Hines, D. A.; Mikherjee, P.; Shen, H. Phys. Chem. Chem. Phys. 2014, Advance Article.
This work reports on the use of an internal electrostatic field to facilitate charge separation at inorganic-organic interfaces, analogous to those in hybrid solar cells. Systematic charge transfer studies show that the donor-acceptor charge transfer rate is highly sensitive to the direction of the internal electric field.