The present invention relates to compounds of formula (I) based on DPP moiety being useful as metal-free organic sensitizers or dyes of type D--A in electrochemical or optoelectronic devices, their use as sensitizer or dye and an electrochemical or optoelectronic device comprising a compound of the invention. ##STR00001##

A photoelectric conversion element including a photoconductor layer, wherein the photoconductor layer contains semiconductor fine particles carrying a metal complex dye of Formula (I); a metal complex dye, a dye solution, a dye-adsorbed electrode, a dye-sensitized solar cell, and a method for producing the solar cell:
M(LD)(LA).Math.(CI) Formula (I) wherein M represents a metal ion; LD represents a tridentate ligand of formulas (DL-1) to (DL-4); LA represents a specific tridentate ligand; and CI represents a counter ion: ##STR00001## Y.sup.1 and Y.sup.2 represent an oxygen, sulfur, nitrogen, or phosphorus atom; AD and BD represent a hydrocarbon or hetero ring; L represents a linking group of formulas (L-1) to (L-4); and Ra and Rb represent a substituent, ##STR00002## X represents a nitrogen or carbon atom; CD represents hetero ring; T represents O, S, NR.sup.L2 or PR.sup.L3; R.sup.L1 to R.sup.L3 represent a hydrogen atom or a substituent; and Alk represents an alkylene group.

The present invention provides a novel one-step synthesis method for producing cyanine-based fluorophores with modified polymethine chains to prevent aggregation, enhancing their utility in biomedical research. These fluorophores, such as unsymmetrical heptamethine cyanines like SAT-IR-746, exhibit improved sensitivity, photostability, and brightness, making them ideal for applications such as live-cell imaging, biomolecule labeling, and near-infrared fluorescence microscopy. The synthesis process involves the preparation of a pyridinium benzoxazole (PyBox) intermediate from a substituted pyridine derivative and 2-chlorobenzoxazole, followed by condensation with sulfonated and substituted indolenines to form asymmetrical cyanine dyes, achieving high yields (e.g., 55-82% for SAT-IR series compounds). By addressing the aggregation issue common in traditional cyanine dyes through -position substitution on the polymethine chain, this invention enables more accurate and reliable labeling and tracking of biomolecules without quenching, facilitating advanced imaging techniques and deeper insights into biological processes.