Photo-induced charge transfer and nonlinear absorption in dyads composed of a two-photon-absorbing donor and a perylene diimide acceptor

This paper reports the synthesis and electrochemical and optical properties of two molecular dyads (Dyad 1 and Dyad 2) consisting of a 2,7-bis(4-(diarylamino)styryl)carbazole two-photon-absorbing donor chromophore, connected by different linkers to a perylene diimide (PDI) acceptor. The photo-induced charge transfer in these compounds is characterised using transient absorption measurements. The use of the compounds for optical limiting is discussed; because of spectral overlap between the donor two-photon absorption band and the one-photon absorption band of the PDI radical anion, the dyads exhibit enhanced nonlinear absorption at wavelengths between 700 and 800 nm relative to that seen for the two-photon absorbing donor chromophore. The stronger nonlinear absorption observed for Dyad 1vs.Dyad 2 is attributed to a higher yield of photo-generated radical ions and a longer lived charge-separated state, resulting from differences in the linker between the donor and acceptor.