9 June 2000 Ž . Chemical Physics Letters 323 2000 117–124 www.elsevier.nlrlocatercplett Time-resolved analysis of intramolecular electronic energy transfer in methylenes-linked naphthalene–anthracene compounds Yoshinobu Nishimura a, ) , Akira Yasuda a , Shammai Speiser b , Iwao Yamazaki a a Department of Molecular Chemistry, Graduate School of Engineering, Hokkaido UniÕersity, Sapporo 060-8628, Japan b Department of Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel Received 10 December 1999; in final form 11 April 2000 Abstract Ž . The mechanism of intramolecular electronic energy transfer EET in methylene-linked naphthalene and anthracene Ž . referred to as A nN, n s1, 3 and 6 was examined by time-correlated single-photon counting technique. The chain length dependence of measured EET rate constants is explained in terms of through-bond interaction via the connecting bridge, besides direct Coulombic interaction. In addition, intramolecular energy transfer in A1N and A3N may compete with vibrational relaxation of the corresponding vibrational level of the excited anthracene moiety by comparing the time-resolved spectra of A1N, A3N and A6N. q 2000 Elsevier Science B.V. All rights reserved. 1. Introduction Significant investigations of electronic energy Ž . transfer EET have been performed to elucidate the mechanisms of light harvesting, the photosynthetic process and polymer photophysics, and other funda- wx mental processes 1 . For instance, energy transfer between antenna pigments was investigated by using the single-photon counting technique in comparison Ž . with multilayer Langmuir–Blodgett LB films, serv- wx ing as an artificial antenna assembly 2 . Approaches to fabricate artificial photosynthetic systems includ- ing photon antenna and charge separation pigments have also been developed using to a great extent Ž wx. porphyrin derivatives see, e.g., Ref. 3 . Investiga- ) Corresponding author. Fax: q 81-11-709-2037; e-mail: ny@eng.hokudai.ac.jp tions for elucidating these mechanisms have recently attracted much interest and were applied even for wx apparatus development 4 . The pioneering formulations of EET by Forster ¨ and Dexter involved Coulombic and exchange inter- action, respectively. The former acts over large dis- tances and is expressed in terms of the transition dipoles of the excited donor and ground state accep- wx tor 5 . Exchange interaction is effective within the range of interchromophore orbital overlap, which decays exponentially with the interchromophore dis- wx tance 6 . Speiser et al. approached the mechanism of Ž X X intramolecular energy transfer in 1,8 6 ,7 -dioxodo- . decamethylene phenanthrene and in other aromatic- wx diketone bichromophoric compounds 1, using a wx modified Dexter model 1 . The basic system to examine energy transfer between antenna pigments has a well-oriented structure containing two chro- mophores. For example, Oevering et al. investigated 0009-2614r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0009-2614 00 00485-1