Photosensitization aspects of pinacyanol H-aggregates. Charge injection from singlet and triplet excited states into SnO{sub 2} nanocrystallites
The singlet and triplet excited-state behavior of a symmetric carbocyanine dye, 1,1{prime}-diethyl-2,2{prime}-carbocyanine (commonly referred as pinacyanol), adsorbed on SiO{sub 2} and SnO{sub 2} nanocrystallites has been investigated using transient absorption spectroscopy. The adsorption of the dye molecules on the negatively charged SiO{sub 2} or SnO{sub 2} colloids results in H-type aggregation. When excited with a 532 nm laser pulse they observe a short-lived ({tau} < 30 ps) singlet excited state of the H-aggregate on the SiO{sub 2} surface. In contrast to this observation, a long-lived cation radical formation is seen on the SnO{sub 2} surface. The dependence of the cation radical yield on the concentration of SnO{sub 2} colloids and the intensity of laser pulse excitation confirms direct electron transfer between the excited aggregate and SnO{sub 2} colloids. Both singlet and triplet excited states of the pinacyanol aggregate participate in the charge injection process on the SnO{sub 2} surface with heterogeneous electron-transfer rate constants of >5 x 10{sup 10} and 7 x 10{sup 9} s{sup {minus}1}, respectively. Such a charge injection process is also confirmed from the photocurrent generation at a dye-modified SnO{sub 2} electrode. The fast reverse electron transfer between the photoinjected electron and the cation radical of the dye aggregate is considered to be a major limiting factor in achieving high photoconversion efficiencies.
- Research Organization:
- Univ. du Quebec, Trois Rivieres, Quebec (CA)
- Sponsoring Organization:
- USDOE; Natural Sciences and Engineering Research Council of Canada (NSERC)
- OSTI ID:
- 20030679
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 15; Other Information: PBD: 20 Apr 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
Similar Records
Dye-capped semiconductor nanoclusters. Excited state and photosensitization aspects of rhodamine 6G H-aggregates bound to SiO{sub 2} and SnO{sub 2} colloids
Dye capped semiconductor nanoclusters. Role of back electron transfer in the photosensitization of SnO{sub 2} nanocrystallites with cresyl violet aggregates