Ligand exchange leads to efficient triplet energy transfer to CdSe/ZnS Q-dots in a poly(N-vinylcarbazole) matrix nanocomposite

Abstract

Upon exchanging long chain alkylamine ligands with a carbazole terminated fatty acid as 6-(N-carbazolyl)-hexanoic acid (C6) and 11-(N-carbazolyl) undecanoic acid (C11), efficient photoluminescence (PL) of CdSe/ZnS colloidal quantum dots (QDs) was observed upon excitation in the absorption band of the carbazole moiety at 330 nm. This effect, which occurred both in solution and in a poly(N-vinylcarbazole) (PVK) matrix doped with the QDs, is attributed to sensitization of the QDs by PVK and the ligands. More efficient energy transfer was observed in solution for the shorter ligand (C6) capped QDs, due to a shorter average distance between the donor (carbazole) and the acceptor (QD). The binding of C6 and C11 to the QDs was confirmed by 1H solution nuclear magnetic resonance, which showed line broadening of the carbazole signal due to a decrease of the mobility of the carbazoles upon binding to the QDs compared with the sharp lines observed for the free molecules in solution. In doped PVK films, the significant enhancement of the energy transfer to the QD core could also be related to a better miscibility between the QDs and the PVK as confirmed by optical transmission and confocal microscopy images. In contrast to the experiment in solution, the overall energy transfer in the doped films was found more efficient for QDs capped with C11. To study in more detail the energy transfer between the carbazole moieties and the QDs, time-resolved fluorescence measurements were performed for solutions of C6 and C11, capped QDs and PVK films doped with the QDs. In contrast to the large enhancement of the QD emission indicated by steady-state PL spectra, the latter experiments suggested only a relatively low efficiency (19.6% and 10.8%) for singlet transfer from the carbazole ligands to the QDs. This suggests that the enhancement of the QD emission must be largely due to triplet transfer.

Ultrafast exciton decay in PbS quantum dots through simultaneous electron and hole recombination with a surface-localized ion pair

“…This proposed charge transfer mechanism is a Dexter-type energy transfer, [2] the typical mechanism for triplet-triplet energy transfer, [3,4] where the excitonic electron and hole are recombining with a charge-separated state spread over two distinct sites, rather than to a single redox or chromophoric center. A similar concerted mechanism was observed for the ultrafast transfer of both an electron and hole from the charge-transfer-type excited state of a molecular chromophore, 4-aminonaphthalene-1,8-imide, to separate covalently linked redox partners.…”

Особенности Фотопроцессов В Пленках Поли(9,9-Ди-Н-Октилфлуоренил-2,7-Диил), Допированных Солью KI

“…С развитием органической электроники и фотоволь-таики вырос интерес к композитным материалам на основе полупроводниковых полимеров, что связано с возможностью регулирования оптических и электри-ческих свойств полимерных композитов (ПК) [1][2][3]. В качестве примесей часто используют наночастицы металлов [4,5], красители [3], органические соединения, выступающие по отношению к полимерному матери-алу в качестве донора или акцептора электронов [6].…”

Triplet harvesting in poly(9‐vinylcarbazole) and poly(9‐(2,3‐epoxypropyl)carbazole) doped with CdSe/ZnS quantum dots encapsulated with 16‐(N‐carbazolyl) hexadecanoic acid ligands

“…Therefore, it remains a challenge to develop alternatives to these organo‐transition metal compounds, compatible with the matrix material of the emitting layer and especially so for blue emission or a matrix consisting of a conductive polymer. For solution processed devices, semiconductor quantum dots (QDs) can be an alternative for the organo‐transition metal complexes as these QDs can in principle act as a suitable energy acceptor for singlet and triplet excitons of such emitting matrices by, respectively, Förster and Dexter transfer and are furthermore excellent emitters after singlet or triplet excitation …”

“…Earlier work indicated that the limited miscibility between CdSe/ZnS QDs and the poly(9‐vinylcarbazole) (PVK) matrix, leading to clustering of the QDs, was a factor limiting the efficiency of the energy transfer to the QDs . By encapsulating the QDs with an organic ligand terminated by a carbazole moiety (ω‐( N ‐carbazolyl)‐ω‐alkanoic acids), the miscibility of the QDs with the PVK matrix and, hence, the energy transfer through both singlet and triplet manifolds were significantly enhanced compared to the situation where more common organic ligands such as a long‐chain amine or oleic acid (OA), present on commercially available QDs, were used . The improved triplet energy transfer was attributed to the presence of ligands terminated by a carbazole moiety which is a key factor for improving the miscibility between the QDs and PVK.…”