Near-infrared dye-conjugated hyaluronic acid derivative and contrast agent for optical imaging including them

A polymer formed of units each represented by general formula (1):

• wherein:
• R1's are independent of each other from unit to unit in the general formula (1);
• R1 is selected from the group consisting of general formulae (2) to (5), general formula (25), and general formula (29);
• and
• the polymer contains at least one unit in which R1 is selected from the group consisting of the general formula (2) and the general formula (25), and at least one unit in which R1 is the general formula (3):
• provided that:
• in the general formulae (2) to (5), the general formula (25), and the general formula (29), L's represent linkers independent of each other from unit to unit, and * represents a binding site with N in the general formula (1);
• in the general formula (3), R2 represents any one of H, OH, OMe, NH2, and COOH, and k represents an integer of 20 or more and 200 or less;
• and in the general formula (5), R3 represents any one of N3, H, CH3, NH2, SH, and COOH,
• wherein 0.13<x/(x+y+z)≦0.78,
• where:
• x is a number of units in the polymer in which R1 is the general formula (2) or the general formula (25),
• y is a number of units in the polymer in which R1 is the general formula (3), and
• z is a number of units in the polymer in which R1 is the general formula (4) or the general formula (29).