The present invention provides an imageable member having an imageable layer including a heat-sensitive ionomer characterized by a net positive or negative charge, and a photothermal conversion material. The photothermal conversion material includes carbonaceous particles having thereon both an organic moiety including an ionic substituent having like charge as the ionomer, and a group represented by the formula --X-[NIon].sub.p-R.sub.terminal; wherein X represents an aromatic group or an alkyl group, NIon represents a non-ionic, non-ionizable group, R.sub.terminal represents hydrogen, an aromatic group, an alkoxy group, or an alkyl group, and p is an integer from 1 to about 500. The heat-sensitive ionomer and modified carbonaceous particles can be formulated in water or water-miscible solvents without agglomeration. Imageable members utilizing the modified carbonaceous particles as a photothermal conversion material exhibit acceptable optical density and exposure speed, and imaged members made therefrom exhibit excellent background performance.