Spectrochimica Acta Part A 53 (1997) 1485–1493 Deactivation of excitation energy in bacterial photosynthetic reaction centres in Langmuir–Blodgett films J. Miyake a , M. Hara a , J. Goc b , A. Planner b , D. Wro ´bel b, * a National Institute for Adanced Interdisciplinary R esearch, AIST /MITI , 1 -1 -4 H igashi, Tsukuba, Ibaraki 305, Japan b M olecular Physics L aboratory , Institute of Physics, Poznan ´ Uniersity of T echnology , Piotrowo 3, 60 -965 Poznan ´ , Poland Received 31 October 1996; accepted 25 February 1997 Abstract Absorption, photoacoustic and time-resolved in s time range delayed luminescence spectra have been measured in order to follow the interaction among chromophores when R hodobacter sphaeroides and R hodopseudomonas iridis reaction centres are closely packed in a form of Langmuir–Blodgett multilayers. Two types of Langmuir–Blodgett samples have been prepared and investigated: multilayers consist of one type of reaction centre (R hodobacter sphaeroides or R hodopseudomonas iridis ) and multilayers composed of mixed reaction centres (R hodobacter sphaeroides mixed with R hodopseudomonas iridis ). Using the Langmuir–Blodgett multilayers composed of two types of bacteria reaction centres mixture, we were able to extend the spectral region of the light /solar energy absorbed by the system. It was shown that each form of pigment participates in thermal dissipation but to a different degree. A special pair (bacteriochlorophyll dimer) does not contribute to delayed luminescence. Delayed luminescence in R hodopseudomonas iridis and R hodobacter sphaeroides differs very significantly from each other. Bacteriopheophytin as well as dihydromesochlorophyll contribute to delayed luminescence but the degree of their participation in this radiative process depends strongly on the type of reaction centre. Delayed luminescence and thermal processes have been indicated as important processes of deactivation of the photoexcited chromophores in reaction centres. © 1997 Elsevier Science B.V. Keywords: Bacterial reaction centre; Bacteriochlorophyll; Bacteriopheophytin; Delayed luminescence; Langmuir– Blodgett films; Photoacoustic spectra; R hodopseudomonas iridis ; R hodobacter sphaeroides A bbreiations: BChl, bacteriochlorophyll; BPhe, bacterio- pheophytin; RC, reaction centre; DL, delayed luminescence; DHP, dihydromesochlorophyll; LB, Langmuir–Blodgett; PAS, photoacoustic spectra; Rb. sphaeroides, R hodobacter sphaeroides ; Rp. iridis, R hodopseudomonas iridis. *Corresponding author. Tel.: +48 61 782 344; fax: +48 61 782 324; e-mail: wrobel@phys.put.poznan.pl 1. Introduction In photosynthetic organisms, the reaction cen- tre (RC) is able to convert absorbed light energy into electrical energy. The trapped energy quickly migrates to a special bacteriochlorophyll (BChl) 1386-1425/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S1386-1425(97)00060-7