Third-order nonlinear optical manifestations in an intramolecular proton transfer fluorophore due to Tamm-plasmon based broadband optical absorbers

Abstract

The imidazole ring has proven to be a very promising candidate for realizing molecular systems that facilitate efficient generation of broadband optical radiation using an excited-state intramolecular proton-transfer (ESIPT) mechanism. To obtain a targeted RGB-color composition, the conventional route is to create optimum mixtures of dyads and triads of non-interacting ESIPT molecules that cover the entire visible spectral band as well as restrict any energy transfer between wide bandgap donors and narrow bandgap acceptors. However, there is a need for alternate routes that can facilitate dynamic control over color composition during operation. The nonlinear optical (NLO) response of ESIPT fluorophores and configurations derived out of them could be explored from this perspective. In the present work, we design a T i O 2 / S i O 2 based distributed-Bragg-reflector (DBR) configuration with a terminating layer consisting of a film of an ESIPT fluorophore, namely, 2-(4,5-diphenyl-1-(4-(trifluoromethyl)phenyl)-1H-imidazol-2yl)phenol (DTIP). In the presence of thin Ag-film, the DTIP-DBR multilayer geometry supports a Tamm-plasmon-polariton (TPP) mode within the photonic bandgap of DBR, which exhibits an unusual spectral bandwidth greater than 50 nm. The open-aperture and closed-aperture Z-scan measurements reveal the strong TPP based broadband absorption that leads to reversal of third-order NLO characteristics, i.e., the multilayer geometry exhibits saturation absorption behavior at wavelengths where the bare DTIP fluorophore (in solution and film) shows a two-photon absorption signature.