Comprehensive Investigation of the Photophysical Behavior of Oligopolyfurans

Abstract

The photophysical properties of (oligo)polyfurans (Fn, where n = 1−5 represents the number of rings) are presented for the first time for 2−4 rings and compared to parallel data for the corresponding (oligo)polythiophenes (Tn). The quantum yields of fluorescence of the polyfurans are consistently considerably greater (5−50-fold), and that of the triplet occupation, considerably smaller (2.5−4) than for the polythiophenes. The kF of the Fn set vary from about equal (n = 4) to ≈4-fold greater (n = 2) than for the Tn set. The kISC of the Fn set are from 10−25-fold smaller than for the Tn set. The Fn set shows very little internal conversion (except some for F2) and less than for the Tn set. Triplet lifetimes of the Fn set are ≈3 fold less than for the Tn set. The lowest excited singlet state of the polyfurans is of 1Bu (or 1B1) character and not 1Ag. The magnitude of the intersystem crossing is essentially constant as a function of n for the Fn set whereas there is a large decrease for the Tn set as n increases. This indicates a difference in the mechanism for intersystem crossing as is discussed. The π-delocalization is greater for the Tn set than for the Fn set. It is not possible to clearly distinguish whether cis and trans conformers simultaneously exist (most likely for F2), or the magnitude of inter-ring bond twisting but the latter appears to be no more than 20−30 degrees and the virtual molecules at 77 K are clearly more planar than at room temperature.